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Jim Caudill
02-07-2010, 04:14 PM
I have been trying, on and off, for several years to determine the heat loss of my home. I tried to simply “measure” the heat loss characteristics by timing the cycling of my natural gas furnace (when the temperature was at 5 degrees F outside) and timing the cycling of the heat pump (when the temperature was at 35 degrees F). Using the efficiency of the furnace and the documentation for the heat pump, I was able to calculate that the heat loss per hour when the outside temperature was 5 degrees at about 950Btu per degree of temperature differential as compared with the inside temperature; however, when I used the data from the heat pump, I came up with a heat loss of 460Btu per hour for each degree of temperature difference. The inside temperature for the 2 measurements was close (69 degrees for the 5 degree outside temp and 70 degrees when the outside was 35 degrees).

Is temperature loss a linear function, or does the rate increase as the temperature difference increases? Do my numbers of 950Btu per degree @ 5 degrees and 460Btu per degree @ 35 degrees make sense?

I paid around $50 for a limited-time access to a software program to try and calculate the thermal properties of the house – I was unsuccessful in utilizing the software due to the complexity of my house. Our house is a “tri-level”, with ½ of the "footprint" about 4 feet below ground. You basically enter the front half of the house on ground level and can go either up or down to access the 2-story back half. The ground level portion has a cathedral ceiling that limits the airspace between the outside roof and interior ceiling (think very little room for insulation here) and would make it difficult to provide for proper venting of the roof and allow any type of insulation. I could probably blow it full, but then the roof would get too hot in the summer and trying to shove those foam vent sections down the long roof and into the overhang would be extremely difficult. Several years ago, I removed all the siding and installed a layer of insulated foam board with foil backing before installing new vinyl siding. While the house was stripped, I installed new, high-efficiency windows and doors; since the front is brick veneer, I left it alone. All this detail is necessary to explain that there are all kinds of different wall materials with differing insulation properties. Total square footage of the house is about 1700 with about 575 sq ft below ground, 550 sq ft @ ground level, and 575 sq ft above ground. The shadow cast in the second picture, does a pretty good job of depicting the portion of the house that is actually 2-stories (partially submerged in the ground).

http://i72.photobucket.com/albums/i183/Ferrofab/Housewest.jpg http://i72.photobucket.com/albums/i183/Ferrofab/Houseeast.jpg

J Tiers
02-07-2010, 04:20 PM
You have more variables......

Wind speed affects rate of heat loss, just as with a "heatsink" in power electronics.

And air infiltration leaks hot air out, and brings in cold air, adding another loss path.

Then also, the running of uninsulated ducts (or hot water pipes) through cold basements loses heat that may or may not be still effective in heating.

A decent formula should have inputs for those..... Somewhere I have a couple HVAC books, I will see what they say, since I am supposed to do some similar calculations.

dp
02-07-2010, 05:07 PM
If you don't care about units of measure one good way to understand heat transfer is to calculate your annual bill for gas and electricity. That will give you your energy consumption rate in dollars/day. Once you know what your dollars/day average is you can break it down seasonally, monthly, and even get a rough estimate on day vs night.

All energy that enters your home leaves as heat. That includes burners, light bulbs, motors, sunlight, etc. It's all heating your house or removing heat from your house. Even the occupants contribute to heat. Your house is 100% inefficient which means all heat that enters your house will leave your house. Using nothing but your power bill you can come up with a rough idea of what the rate of heat loss is in dollars/hour and that converts to watts/hour. This also has the advantage of calculating energy consumption rate for cooling as well as heating.

oldtiffie
02-07-2010, 05:36 PM
Dennis.

I think you are nearest the mark as regards simplicity as I guess the OP needs a reliable "ball park" figure to start with.

There are some excellent tables, guides etc. that various manufacturers put out for use by Contractors and HVAC engineers etc. to estimate/"size" HVAC components for optimum capital and recurrent costs. This includes multiple zones. They have taken most or all variables for a particular locality, size/s, insulation, construction materials, etc. etc, into account.

Hiring in a specialist may well be a very good proposition as the longer it takes for a non-skilled person to work it out the more it costs and so the "break even" point for paying to have the assessment done can be very short.

A "DIY" method assumes that the occupant gets the capital costs (equipment plus installation etc.) and recurrent costs (power, gas etc.) right. If he gets it wrong and it is inadequate - it may be either or both very unsatisfactory or very expensive or both. And if the funds are borrowed it makes it even worse if it is wrong.

While a good professional may seem expensive in raw $ terms, it should be very good value at the end of the job as it is more likely than not that he will save the client a lot more that his fees were - and while the fees are are a "one off" cost the benefits are on-going.

The Artful Bodger
02-07-2010, 06:09 PM
Not all energy that enters the house leaves as lost heat through the walls and roof, a goodly proportion leaves as hot water down the drains too.

Carld
02-07-2010, 06:11 PM
Some power companies will come out and do a heat loss study. I don't know if they charge for it or not. You might call your power company and see what they can do.

hoof
02-07-2010, 06:17 PM
I would also think if a motot is turning, like washing clothes, or making a mudslide in a blender :D then that mechanical effort would not leave as heat as some work was accomplished. a drill press might do some effort as well. FWIW.

hoof

J Tiers
02-07-2010, 06:18 PM
I actually had a full house efficiency survey done this past December. I frankly was disappointed.

I hired the best rated firm in the area.

They were competent at operating their equipment, but quantitative data was lacking, and the report was not what I would call a complete report of the type I would give to a client. I could not use teh data they gave to prioritize actions, and I am not at all sure that they actually GOT data that would allow it.

Perhaps that disappointment is the effect of being in the consulting business, but I don't see it as a great and helpful thing to have done.

As for ways heat leaves, or inputs of heat, they tend to mostly pale in comparison to the furnace and ordinary heat loss thru walls and windows, unless the house is very tight and well insulated. Few are.

DFMiller
02-07-2010, 06:21 PM
Jim,
I think you are talking about HVAC calc.
It is to my understanding a very good piece of software. With some work you will be able to get your data. BTW the person who wrote it is very knowledgeable and very helpful. Or at least that was my impression when I asked him a few questions. Another associate also have been very pleased with the software.

Dave

Carld
02-07-2010, 06:43 PM
The power company here does an infrared study to determine where the heat loss is and somehow they convert that into how much is lost at those spots. It's mostly to show where you need to insulate from what I understand and it's not exact.

Jim Caudill
02-07-2010, 06:50 PM
I found the information required to be too daunting to collect. I have different roof structures with varying insulation, flooring that is below grade, walls that are partially below grade and partially above (but insulated on the outside), a front wall with very different properties from the side walls, etc.

It is not the software's fault, it is my ability to asess, characterize and quantify all the elements that are needed.

I would gladly pay to have an "expert" figure all this out. I don't know where to find one. All the HVAC folks I know, size units on some "rules of thumb" and recommendations from the distributors. Just like the settings for the heat pump, the distributor will tell them where to set the "crossover" switch (or whatever you call it). Replacement units are sized based on whatever was installed and the anticipated improvement in efficiency - no calculations whatsoever.

Years ago I received a free energy audit from my power company - I don't think they do that anymore, since the gas and electric were "split up". Since I have a "dual fuel" system with heat pump and natural gas, some of my heat comes from the gas folks and some of it comes from the electric folks - neither get all my money. Neither can tell me how much energy I use to heat my home. Since I have resistance heat for the shop, and use a fair amount of electricty for heat, lights, and machinery - even the amount of electricity used for the heat pump is hard to determine.

The energy audit didn't tell me very much, other than the payback for new windows would be something like 17 years. They said the single best thing I could do, was to dig down and insulate the concrete block walls that are below grade. But even that wouldn't make sense unless I was already going to dig them out for some other reason. It seems like if that were the case, they would recommend adding insulation to the interior walls that are simply wood panelling over firring strips.

ckelloug
02-07-2010, 07:22 PM
Jim,

Your idea to compute the loss by energy balance was a great idea but comparing the furnace and the heat pump is apples and oranges. If you measure the gas or electricity usage vs. the temperature drop, you have account for the fact that the efficiencies of the heat pump and the furnace are different.

Given your circumstance, the numbers for the furnace are much closer to the actual heat loss of your house than those from the heat pump. I say this because the furnace efficiency is likely between 70% and 90%. The heat pump efficiency is likely between 100% and 200%. The efficiency of the heat pump varies dramatically with temperature. (I'll leave the explanation of heat pump physics to the pedants.) As a result of the efficiency differences, the heat pump used significantly less energy than the furnace to deliver the same amount of heat.

Simplistically, the heat exchange in a system is proportional to the temperature difference between the inside and the outside times a constant. See http://en.wikipedia.org/wiki/R-value_(insulation) for an explanation of how its computed in practice.

If you are really interested in a number that professionals in the industry would believe, the correct way to do it is an ASHRAE Manual J calculation or the software automation of it. I've never actually seen manual J or done the calculation so I can't help beyond that. All I can say is the book is bloody expensive.

I think in principal it might be possible to calculate the loss coefficient with newton's law of cooling but it is difficult to recover the loss coefficient without knowing the specific heat of the house and the area.

Conclusion:
The code word to ask for what you want is "What would it cost for you to do a manual J calculation on my house?"

--Cameron

Sparky_NY
02-07-2010, 08:14 PM
Manual J heat loss methods/calculations are what the quality heat loss programs are based on. Still, I heat loss calculation has the potential for a fair amount of error due to the many variables that cannot be accurately measured and inputted. For example, the color of the roof, shading on the house etc. Also, calculations are based on a "worst case outdoor temperature" for the region during the heating season.

The desired result in obtaining a accurate heat loss is so that heating equipment can be sized for the house and be equal (actually a little larger) than the calculated loss. When loss equals the furnace output we have equalibrium.

With equalibrium in mind........ Your method of timing the furnace was not a bad idea all together. First you need to know the real BTU input to the furnace, you get that by reading the gas meter for a timed peroid when the furnace is running. Exact details of how this common procedure is done is available on the net. A adjustment for the quality of natural gas can also be made (therms).

Next, you need to apply a efficiency factor to account for the efficiency of the furnace. Furnaces 90% and over use PVC for their venting. A 80% furnace is the most common by far. Depending on the age, there might be a sticker on the doors with the efficiency.

Next you can do your measurments/calculations. Don't forget that the only furnace time to be used is when the burner is on, not just the fan running! A neat method is to put a 24V AC hobbs (time) meter across the gas valve wires. This then gives operating hours for the burner only.

ALTERNATELY, you could simply turn the furnace off and measure the time it takes for the house to drop say 10 degrees. That may be more accurate with less potential errors. If you think about it, that would be a TRUE heat loss number. (varies according to outside temp, sunshine etc. of course) Don't open a door either! LOL Personally, I believe this to be the best method of all.

Remember though, manual J calculations and good software programs are based on the worst case temperature for your region. Your measurements will be for the given day.

Sparky_NY
02-07-2010, 08:21 PM
Oh yea........ I forgot to ask........
Why do you want a heat loss? What do you plan to do with the "number" once you have it?

Let say the number is 55,000 btu/hr (a reasonable guess for your house).
Now what? I suppose that provided you get a detailed output you could look at how that loss is divided up among various line items. You could then change a line item parameters and see how much differerence in makes in btu's for that item. Having someone do a one time loss calculation for your house wouldn't provide that information however.

aboard_epsilon
02-07-2010, 08:33 PM
Something i cant work out

wouldn't it be more efficient to have a boiler that turned the flame down lower and not out ..infinatly variable flame ..than have some thermostat turning it on and off at full blast every ten Min's or so.

i mean its like using full aceleration in your car to reach the top speed every time .we all know that uses more fuel

why is this sort of system not made ..a system that cruises

i can also see such a system lasting a lot longer, if it were done this way ..because you're not getting all the expansion contraction and cooling down of the boiler.

the flames would be mostly quite small most of the time ..so this will not eat the metal like huge flames

such a system would not heat the crap out of the water and lead to calcium deposits either

you could put a smaller more electrically efficient pump in the system ..that runs twenty four seven

so all someones got to invent is a robust infinitely controllable valve. and a 1500000 hour pump

I'm sure the above would improve efficiency a lot over the conventional systems.

all the best.markj

Your Old Dog
02-07-2010, 09:11 PM
If you want to get your heating system to work more efficiently put in two furnaces. The object in winter months is to have one smaller furnace run 24-7 and the second one to kick in when the first one can't keep up. This of course saves you the heat up, cool down cycles on the first furnace.

When it gets real windy around here and the wind starts to suck the warm air out of the house I always run the wood burning stove with a damper in circuit. It seems to replace what is being sucked out of the house.

If you have blinds close them to add a degree of insulation. If you have venetian blinds keep in mind that if you close them so that you can see down but not up, the coldness from the window tends to stay put. The warm air from the registers goes up past the venetian blinds without be routed to the windows. It makes a huge difference and you can tell by simply opening the blinds and feeling th cold air near them.

I purchased a infrared thermometer to work on our home. Turns out it wasn't all that necessary. Any windy day will tell you everything you want to know. My basement was full of air leaks, particularly around the cheap old wooden windows and the house sill plate. Of course doors that don't seal right are also a big loss but in the main, if the wind ain't blowing you won't be loosing all that much heat through a door unless you leave it open.

Iwouldn't bother with a formal energy survey unless you are prepared financially to do something about it such as repair all the defeciancys and my guess is you won't want to do that. It would be ch4eaper to build a new house !

I know Tiff! He wants to know how to calculate and not winterize. This is my way of saying if you can't figure out how to calculate how to the heat loss, then try to figure out first if its worth all the effort :D I did not answer his question.

aboard_epsilon
02-07-2010, 09:16 PM
. It would be ch4eaper to build a new house !

CH4....was that deliberate ..tis methane

all the best.markj

MTNGUN
02-07-2010, 09:17 PM
I would gladly pay to have an "expert" figure all this out. I don't know where to find one.
Any Mechanical Engineering consulting firm that has an HVAC guy could do the calculations, but they will charge you several thousand, and I fail to see how the final result is going to help you in any tangible way.

I am, or more accurately, I was an HVAC engineer once upon a time, before I graduated to machining. :) I took the HVAC class in college and did all of one HVAC design on the job. The calculations are not complicated, but they are tedious. At the end of the day, the result may not be terribly accurate because a lot of the heat loss will depend on stuff like air infiltration that you can only take a wild guess at.


All the HVAC folks I know, size units on some "rules of thumb" and recommendations from the distributors. Yep, in the real world, almost no one does the detailed calculations, they just use quick and dirty rules of thumb. The only time the detailed calculations are actually done is on government jobs, i.e., schools and other public buildings, due to liability and code requirements.

Residential HVAC just goes by the rules of thumb, and realistically, it works fine, since at the end of the day you are going to be conservative and make the heating unit plenty big. You don't want it running 100% of the time trying to keep up with the load.


The energy audit didn't tell me very much, other than the payback for new windows would be something like 17 years.Weeeell........... it depends. If the wind is whistling through or around your old windows, then the payback may only be one year. Air infiltration is a wildcard and that's one reason it is almost a waste of time to do fancy engineering calculations.


They said the single best thing I could do, was to dig down and insulate the concrete block walls that are below grade. But even that wouldn't make sense unless I was already going to dig them out for some other reason. It seems like if that were the case, they would recommend adding insulation to the interior walls that are simply wood panelling over firring strips.
It might be cheaper to insulate the outside of the walls rather that demolish and reconstruct the interior finish. Plus, you'd gain the thermal inertia of the insulated concrete. Plus, there typically isn't a lot of room for insulation in a firred wall. Plus, if you used foam insulation between the firring strips, the foam would be a fire hazard.

RancherBill
02-07-2010, 09:21 PM
Your OP does not say why you are doing the calculation. I can guess there are at least two reasons.

First you are contemplating a furnace replacement. You need the same size furnace as you currently have. BTU ratings are the 'output' values. The new high efficiency furnaces just use less energy to produce the same 'BTU output' value. Resizing may be an option if your furnace has a low duty cycle, eg 5 min on 20 minutes off. A furnace guy can tell you the features on the new furnaces to solve the problem. We have a new Lennox furnace that has variable heat output etc.

The second reason might be to address insulation issues. I have found out a great deal with an infra-red thermometer. I got mine on sale at Princess Auto, it is like this one. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93984

I had great fun one checking out a house. I was amazed to see temperature differences in the ceiling. I poked my head into the attic and could see where insulation had settled over time. I taped a piece of paper onto a window and was able to see the big differences in temperature of double glass versus a sealed unit. This combined with a toilet paper test on a windy day will give a place to start.

To try to prioritize projects you probably just have to go by the 'local mantras' for houses your age which might be air infiltration, attic insulation, windows, and finally wall upgrades.

mechanicalmagic
02-07-2010, 09:25 PM
Is temperature loss a linear function, or does the rate increase as the temperature difference increases?

Yes, Jim it's a linear function at the temperatures you are talking about.

You probably have a Junior College close by, classes in Thermodynamics typically (used to) run calculations of this type. Thermo was req'd for many disciplines. An instructor there might lead you to a star student that might be willing to run the full calculation, by hand.

DJ

Jim Caudill
02-07-2010, 09:54 PM
This kind of makes me sad. I took Heat & Thermodynamics back in college (around 1975). I was a Physics major (got a degree in Physical Science so I could take ROTC stuff). Now I'm 59 and my eyes glaze over when I read some of the math stuff. Oh how the mighty have fallen.....

mechanicalmagic
02-07-2010, 10:07 PM
Now I'm 59 and my eyes glaze over when I read some of the math stuff. Oh how the mighty have fallen.....
Jim,
I took Thermo in ~1967, I look for things to calculate. Keeps the mind sharpp and helps me to avroid mistrakes.
DJ

lorenrs
02-07-2010, 10:11 PM
Jim

You are on the right track. What do you need the heat loss calculation for?

This is what I do at my day job I am a mechanical engineer (PE) and I do this often.

I am out here often learning from this site. This would be a way that I could share knoledge I have.

If you are interested let me know and we could talk.

Sparky_NY
02-07-2010, 10:49 PM
Something i cant work out

wouldn't it be more efficient to have a boiler that turned the flame down lower and not out ..infinatly variable flame ..than have some thermostat turning it on and off at full blast every ten Min's or so.

i mean its like using full aceleration in your car to reach the top speed every time .we all know that uses more fuel

why is this sort of system not made ..a system that cruises

i can also see such a system lasting a lot longer, if it were done this way ..because you're not getting all the expansion contraction and cooling down of the boiler.

the flames would be mostly quite small most of the time ..so this will not eat the metal like huge flames

such a system would not heat the crap out of the water and lead to calcium deposits either

you could put a smaller more electrically efficient pump in the system ..that runs twenty four seven

so all someones got to invent is a robust infinitely controllable valve. and a 1500000 hour pump

I'm sure the above would improve efficiency a lot over the conventional systems.

all the best.markj

To reply to this and Your Old Dogs similar post:

Two stage furnaces are extremely common, 3 stage less common but out there. A 2 stage runs at 100% output on high flame and 60% on low flame. The blower automatically slows for low flame. The "decision" to switch to high flame is mostly based on the amount of time the thermostat has been calling for heat and the last few heating cycles statistics. The 2 stage concept works fantastic. (although I am speaking of hot air gas furnaces, the same types exist for boilers, even fancier, they vary the water temp along with the btu)

I put at a couple of these in a week. With the $1500 federal tax credit and the utilities in NY state rebating another $600, the end cost is usually under $1000 !

Sparky_NY
02-07-2010, 10:57 PM
I have seen IR thermometers mentioned in this thread but there is also such a thing as a infared camera that shows temperature variations on the outside of the house. It is sort of like the FLIR in our fighter planes only color. You might also have seen them on the various "ghostbuster" shows on tv looking for temperature variations in a room. Larger insulating contractors used to have them and show before and after pictures to the customer. You might attempt to find someone with this capability, it would disclose a lot. You can actually "see" each stud in the wall outside because of the higher heat loss through the wood stud than the adjoining insulation.

Jim Caudill
02-07-2010, 11:10 PM
Since several of you have asked, I basically want to know 2 things: What kind of mileage is my car getting and is my mileage better than most, about avergae, or worse than most?

When I drive a vehicle, I want to know how efficient it is and how much can I improve that efficiency by things that are within my control. I also like to know how does it compare with the other vehicles that are out there driving down the highway.

I have no idea whether my house is like driving a motorhome (7mpg), a pickup truck (say 15mpg), or a sedan (22-25mpg). I know for sure it's not a subcompact getting 35mpg. Also, if I am more or less than average in heating/cooling energy use, I want to understand how much I might reasonably be able improve on fuel consumption.

I had a neighbor that lived across the street and had basically the same house as I. He moved to a new plat and purchased a house that has 3 times the sq ft of the old one. He did specify and pay for a number of energy saving options; bottom line is that he heats and cools his much larger (5700sq ft) house for the same or less than his old house. This tells me that I'm very much towards the 'ol motorhome in terms of energy use than a Honda Civic.

I need to understand how much money I'm throwing away, by not making certain improvements. For example: if the poor insulation in the cathedral ceiling is costing me $150 per year, it will never be modified - the payback won't occur in my lifetime. If it is costing me $500 per year, we'll take a look at it.

J Tiers
02-08-2010, 12:03 AM
Those things are very difficult to quantify, except on average..... but don't forget to throw in the expected sharp rise in the cost of gas for heating, as electric generation and many other coal usages are forced to compete for the scarce natural gas to reduce carbon emissions.

About all you can do is to take each section of the house separately, look at the construction, and determine a probable loss per degree difference for it.

Looks like you have brick, or brick face on the front, and possibly frame on sides etc. Roof is another issue. Each wall has a different "thermal resistance" depending on type, insulation , etc and will lose a different amount per degree difference. Wind exposure is different also for each area.

So you figure the area of each, and the loss, then add them up to get a net number. take the expected time and degree differences and you may get to a total 'seasonal cost" in fuel usage. The dollar cost is then the fuel cost x usage. You can compare your calculated number to your actual to see if you need to 'recalibrate". I would apply any calibration to all areas equally, in the absence of better data.

You can also break it down and get a fuel usage per each area. Then it is fairly simple to calculate a different fuel usage for a different material, or a specific addition of material, etc.

What you DO need is at least a general figure for each of the construction types used in your house, expressed in average loss per degree difference, or similar usable unit. This may be available on-line, or in books available at the library, etc.

deltap
02-08-2010, 12:14 AM
I have been trying, on and off, for several years to determine the heat loss of my home. I tried to simply “measure” the heat loss characteristics by timing the cycling of my natural gas furnace (when the temperature was at 5 degrees F outside) and timing the cycling of the heat pump (when the temperature was at 35 degrees F). Using the efficiency of the furnace and the documentation for the heat pump, I was able to calculate that the heat loss per hour when the outside temperature was 5 degrees at about 950Btu per degree of temperature differential as compared with the inside temperature; however, when I used the data from the heat pump, I came up with a heat loss of 460Btu per hour for each degree of temperature difference. The inside temperature for the 2 measurements was close (69 degrees for the 5 degree outside temp and 70 degrees when the outside was 35 degrees).

Is temperature loss a linear function, or does the rate increase as the temperature difference increases? Do my numbers of 950Btu per degree @ 5 degrees and 460Btu per degree @ 35 degrees make sense?

I paid around $50 for a limited-time access to a software program to try and calculate the thermal properties of the house – I was unsuccessful in utilizing the software due to the complexity of my house. Our house is a “tri-level”, with ½ of the "footprint" about 4 feet below ground. You basically enter the front half of the house on ground level and can go either up or down to access the 2-story back half. The ground level portion has a cathedral ceiling that limits the airspace between the outside roof and interior ceiling (think very little room for insulation here) and would make it difficult to provide for proper venting of the roof and allow any type of insulation. I could probably blow it full, but then the roof would get too hot in the summer and trying to shove those foam vent sections down the long roof and into the overhang would be extremely difficult. Several years ago, I removed all the siding and installed a layer of insulated foam board with foil backing before installing new vinyl siding. While the house was stripped, I installed new, high-efficiency windows and doors; since the front is brick veneer, I left it alone. All this detail is necessary to explain that there are all kinds of different wall materials with differing insulation properties. Total square footage of the house is about 1700 with about 575 sq ft below ground, 550 sq ft @ ground level, and 575 sq ft above ground. The shadow cast in the second picture, does a pretty good job of depicting the portion of the house that is actually 2-stories (partially submerged in the ground).

http://i72.photobucket.com/albums/i183/Ferrofab/Housewest.jpg http://i72.photobucket.com/albums/i183/Ferrofab/Houseeast.jpg
Shut off your heat pump for a month or two and use your gas bill to calculate the heat loss of your home. This actual usage is more accurate than a calculation. The gas company can help with this. The total heat loss will not help to determine where to make improvements but may help you decide if you need to lower your bill. Adding insulation will get you diminishing returns. The first few inches return a great deal of money. Adding more not so much. Like your truck example rising fuel cost will make improvements more attractive. Consider a blower door test on your home to quantify the infiltration. Weatherstripping is very cost effective. Cold air infiltration happens because a negative pressure is created by exhaust fans, clothes driers, fire places, furnaces, and water heaters. A heat recovery ventilator will keep a slightly positive pressure in the home to reduce infiltration while recovering heat from exhaust fans. Horizontal foam insulation from the basement wall outward to about 4' will be nearly as effective as vertical insulation on the basement wall below grade without the cost of excavation. Make sure the above grade portion and the box sill are insulated. Keep in mind when making improvements not to trap moisture in insulation making it inefective. Vapor barriers always go on the warm side of the wall/ceiling. Energy efficiency and comfort do not always go hand in hand especially where heating equipment is concerned. Your heat pump delivers air at about 100F whereas the gas furnace output even in a high eff. unit wil be 20F warmer.

mechanicalmagic
02-08-2010, 12:34 AM
I need to understand how much money I'm throwing away, by not making certain improvements. For example: if the poor insulation in the cathedral ceiling is costing me $150 per year, it will never be modified - the payback won't occur in my lifetime. If it is costing me $500 per year, we'll take a look at it.
Jim,
OK, how about a plan. Start with one thing first, let's say windows. First, you need to know the inside and outside temp over a long time. For this, something like a weather station with inside and outside temp monitors, and a computer to collect the data. I have a Davis:
http://www.davisnet.com/weather/
With the proper software you can record the data as often as you like.

After you have a known delta T over time, you can easily calculate the approximate loss thru the windows. (You need to know the area of the wondows, and the approx. heat loss per sq. ft.) If you have single pane windows, this is a good place to start.

DJ

Jim Caudill
02-08-2010, 12:45 AM
Thanks guys, much to absorb and contemplate.

Evan
02-08-2010, 01:44 AM
Is temperature loss a linear function, or does the rate increase as the temperature difference increases?


It obviously cannot be linear since if the temperature on each side is the same the rate is zero. The actual rate depends on a combination of mechanisms. If we consider just the rate of emission by radiated energy from the outside of the house the rate goes up with increasing temperature dramatically. By Stefan's law the total power radiated by an ideal black body increases as the fourth power of absolute temperature. That is a very steep curve even though it is referenced to zero kelvin.

However, that assumes the radiation is not reflected back to the source. Anything other than a clear view of the night sky will act to reflect back some heat. Also, unless your house is painted flat black it won't be approximating a black body. Unfortunately there is no easy way to discover the actual radiating characteristics of your exterior walls. The colour in the visible spectrum is not an indication of the emissivity in the IR spectrum. Snow for instance is an almost perfect black body in the IR range.

It is for this reason than even a little insulation makes a huge difference since it allows the outside to cool by slowing the transmission of heat through the structure. Even a single layer of aluminum foil hung free in the airspace of a stud wall will act as R3 insulation by reflecting back heat to the interior and by reducing convection between the inner and outer walls.

The first thing to do always is to check the ceiling insulation. Because of the 4th power law the warmest areas lose the greatest amount of heat and the rate is much higher than cooler areas. I strongly recommend buying an infrared thermometer. They are extremely useful and quite accurate. You can check for heat loss both inside and outside. Inside you are looking for colder ceiling areas and walls. Outside you are looking for warmer areas. If you crank up the inside temperature for a few hours the differences will be much more obvious on a cold day.

Windows are a total loss. It's like have a hole in the wall. Even with special coatings and argon fill etc the thermal characteristics are about a good as a wall with zero insulation. The best bet is to reduce window area. Failing that adding a layer of glazing helps, especially if it is of a material that is a poor heat conductor. I have one of the sliding glass doors in my dining room covered with a sheet of .040" PET-G plastic sheet. This is a plastic that is crystal clear, even better than glass but a much better thermal insulator. It also reduces convection as long as the air gap is kept small, no more than 1/2".

Another area is the roof itself. Lighter materials radiate less heat than dark material. Conversely, because emissivity is the inverse of absorption a light roof stays cooler in summer. The difference is large. I recently reroofed my house and while doing so I took some pictures to try to quantify the difference in radiative characteristics between the old dark red roof and the new almost white roof.

Here is what I found. I took a picture while part of the roof was finished and part was still the old shingles, all in full sun. By comparing the normalized spectral distribution in the image it is possible to estimate the difference in heat gain and loss.

http://metalshopborealis.ca/pics4/roofcolor.jpg

Note the difference in the mean lightness values. That is a direct indication of the reflectance of the roof. Reflectance actually works in both directions since emissivity and absorption are two sides of the same coin. A light roof reflects energy back into the house in the winter just as it reflects energy back into the sky in the summer.

aboard_epsilon
02-08-2010, 06:09 AM
Since several of you have asked, I basically want to know 2 things: What kind of mileage is my car getting and is my mileage better than most, about avergae, or worse than most?

When I drive a vehicle, I want to know how efficient it is and how much can I improve that efficiency by things that are within my control. I also like to know how does it compare with the other vehicles that are out there driving down the highway.

I have no idea whether my house is like driving a motorhome (7mpg), a pickup truck (say 15mpg), or a sedan (22-25mpg). I know for sure it's not a subcompact getting 35mpg. Also, if I am more or less than average in heating/cooling energy use, I want to understand how much I might reasonably be able improve on fuel consumption.

I had a neighbor that lived across the street and had basically the same house as I. He moved to a new plat and purchased a house that has 3 times the sq ft of the old one. He did specify and pay for a number of energy saving options; bottom line is that he heats and cools his much larger (5700sq ft) house for the same or less than his old house. This tells me that I'm very much towards the 'ol motorhome in terms of energy use than a Honda Civic.

I need to understand how much money I'm throwing away, by not making certain improvements. For example: if the poor insulation in the cathedral ceiling is costing me $150 per year, it will never be modified - the payback won't occur in my lifetime. If it is costing me $500 per year, we'll take a look at it.

if you lived in the uk and had a brick house ..all those answers are known commonly

here's just one typical website that shows you how and where the heat is going .

http://www.peterborough.gov.uk/environment/climate_change/heat_loss_and_insulation.aspx

first a diagram of the house

then scroll for chart ob the savings you can make with insulation

all the best.markj

ptjw7uk
02-08-2010, 06:43 AM
I always have to take exception to all those heat saving diagrams as they always leave the most important thing out!
Insulate the roof space as much as you like and not save a penny as all you get is warmer bedrooms!!

You have to put some form of temperature control in the bedrooms before you will save any money but never seen that stated just the fact you will save money by doing the insulation bit.

Peter

Circlip
02-08-2010, 08:16 AM
Did a bit of design/specifying on the ducted warm air/A/C many years ago using the heat loss tables and calcs put out by the American and Canadian component suppliers we used, Seemed logical as they have COLD weather most years, so you expect them to have some grasp on the problem. One thing that has become apparent is the fact that the heat requirement figures used over here are in excess of what I used 40 years ago as it seems that the system thermostat is sited in the coldest place in the house and temperature figures are based on being able to sit in shorts and tee-shirt WHATEVER the external temperature.

One thing I learned from my Grandparents, if it's cold, put a flamin cardy on, and it's easy to get warm, but more difficult to stay cool.

Regards Ian.

Evan
02-08-2010, 09:48 AM
That isn't how it works in our house. The bedrooms are unheated except for whatever wafts in through open doors. The main sources of heat are located in the basement being a natural gas furnace and a wood burning stove. We don't have forced air ducting at all. The natural gas furnace is a free standing convection unit that requires no electricity to operate. The thermostat is self powered and is located in the center of the house on the main floor above.

The wood stove is located next to the furnace and both distribute the heat via a grill directly above that has a circulating fan to pull air from the floor in the basement and mix it with the hot air as it blows it up through the grill. Cold air return to the basement is via a ceiling fan at the top of the stairwell that leads directly down to where the furnace is located.

We also have a fireplace in the living room. It is in the massive brick three flue chimney which measures eight feet by four feet all the way to the roof. The fireplace is a heat recovery design with a steel air circulating jacket. Set into that is a cast iron fireplace insert with additional heat recovery ducts. It has cast iron doors with draft controls and is meant to be operated with the doors closed. We almost never need to use the fireplace although it is capable of heating the house alone.

We also have auxillary heat in the form of baseboard electric heaters in each room. We rarely use these but they are a reliable system to prevent freezing if we leave the house for any lengthy amount of time (days or more) in winter.

Our house is very comfortable with good heat distribution thanks to several ceiling fans that prevent heat pooling near the ceiling.

Your Old Dog
02-08-2010, 10:10 AM
CH4....was that deliberate ..tis methane

all the best.markj

That was a typo but just for the record, I retired 3 years ago from Channel 4, WIVB-TV in Buffalo New York :D

J Tiers
02-08-2010, 10:15 AM
It obviously cannot be linear since if the temperature on each side is the same the rate is zero. The actual rate depends on a combination of mechanisms. If we consider just the rate of emission by radiated energy from the outside of the house the rate goes up with increasing temperature dramatically. By Stefan's law the total power radiated by an ideal black body increases as the fourth power of absolute temperature. That is a very steep curve even though it is referenced to zero kelvin.



Much the simplest technique is to assume the outside surface of the house is essentially at external ambient, and the inside wall surface at interior ambient.

This is often pretty much the case.

Now, the heat flow is moderated by the 'thermal resistance" or thermal conductivity (the inverse) of the walls.

THAT is pretty much linear.

There is no reason to invoke extraneous physics, since the primary heat removal means is likely to be straight convection with "forced flow" due to wind.

It does not involve any contradictions or issues with no transfer if no temp difference, because the flow is simply isolated to the wall. If you want to assume some warmer temp of the wall exterior, and/or lower temp of interior, fine. It may or may not be of any significance.

The better your wall insulation, the better the outside surface will approximate exterior ambient.

Evan
02-08-2010, 10:33 AM
Much the simplest technique is to assume the outside surface of the house is essentially at external ambient, and the inside wall surface at interior ambient.

Bad assumption Jerry. The exterior is always warmer than ambient when the house is heated. If it weren't there would be no heat loss. :rolleyes:

Examples:

http://ixian.ca/pics7/heatloss.jpg


There is no reason to invoke extraneous physics, since the primary heat removal means is likely to be straight convection with "forced flow" due to wind.


This is obviously not your area of expertise. The primary heat loss from a house is air exchange followed by radiation cooling at night with the windows being the main avenue of radiative loss followed closely by loss through the roof.

Your Old Dog
02-08-2010, 10:37 AM
..................................
I need to understand how much money I'm throwing away, by not making certain improvements. For example: if the poor insulation in the cathedral ceiling is costing me $150 per year, it will never be modified - the payback won't occur in my lifetime. If it is costing me $500 per year, we'll take a look at it.

I disagree with you Jim. If you are facing retirement, I think your financial well being will be determined in large part by energy cost. And, it's looking politically like we are heading for huge increases in cost as energy suppliers make less and less due to coservation efforts. Thier corporat static cost stay the same although income is less. Therefore, if you have a cathedral ceiling I think you would see the return. According to my wife's cousin, an energy consultant for Penn Electric, you won't get your money back necessarily on thermopayne windows unless you are 20 years old now.

Keep in mind also, a large part of the cost of brand new homes is in the energy sealing they do. Many have insulated basements, windows on only one side of the house ( :rolleyes: ) and specialized heating systems. When we bought this old house, we had the 275,000 btu steam heat (not a typo) taken out and replaced with a 75,000 btu high efficancy forced air gas furnace and a 3 ton AC unit. It works to perfection for an antique house.

MtnGun, as I understand it, the most efficiant furnace is one that runs 24-7 and does not have to endure heat up and cool down periods. This of course does not mean that excess heat gets vented to waste. The second furnace only kicks on when the higher effiancy 1st unit can't keep up with demand. Therefore, you have have don't have the 20 or so heating and cooling periods per day that are waste as the house derives next to no benefit to the living quarters.

sorry for the spelling guys, can't get my checker to work right and I never could spell, I won't be learning anytime soon at 63 :D Just try to make your way through it as best you can.

Evan
02-08-2010, 11:02 AM
I think your financial well being will be determined in large part by energy cost.

Absolutely. Energy costs are going to dominate all other living costs in the future. That includes the cost of food if you take into account the energy value in food. In fact, it all comes down to energy which is what makes life possible and we are starting to realize that.

RancherBill
02-08-2010, 12:26 PM
I need to understand how much money I'm throwing away, by not making certain improvements. For example: if the poor insulation in the cathedral ceiling is costing me $150 per year, it will never be modified - the payback won't occur in my lifetime. If it is costing me $500 per year, we'll take a look at it.

Jim you are an empirical guy trying to solve a theoretical problem. It is theoretical, because, there are so many variables that you don't know such as exact material used 3½ fiberglass. for example, insulation comes in different R values, the quality of installation etc. In addition specs change over time, for example, attic insulation settles. The 'as built' never comes close to the 'spec' on jobs like this.

You have to measure actual values! Get an infrared thermometer or do IR photography as Evan suggested. Do it at 6:00 in the morning so the effect of solar warming are minimized. Find the bad spots and see what it costs to upgrade specific items.

I haven't looked, but, I am sure there is some govt. program that will tell you what building code was for the year your house was built. I am also sure they could tell you the priorities in what should be upgraded in buildings this age. There might even be some grant money or incentive.

My guess is that you will get biggest bang for the buck in air penetration sealing, new furnace, new AC, attic insulation, windows, and finally exterior wall upgrades. For $50-100 you can get a big change with weather stripping and foam.

aboard_epsilon
02-08-2010, 02:14 PM
i know exactly what kWh it needs to heat my house .

from using kerosene heaters to heat my house for the last couple of years .

my largest heater is 2 kw left on 24/7 with supplementary heater of 700 watts left on in my bedroom overnight when temp outside is below 5

and this will keep my whole house at 17.5 - 20 degrees c at outside temps of 0 -10 degrees c

if its windy.........i then, I am at 17 degrees..........it never seems to be windy when the temperature is below 5c

if it drops below 0 c outside.......not that often .i just put up with the temp being about 15 degrees c in the house and wear more clothes :)

so looking at that .then realistically i can heat my house probably with a constant 2.7 k-watts at outside temps of 0-10 degrees C

i have double glazing.....cavity wall insulation and loft insulation

BTW ........a good 98 percent efficient kero heater will burn roughly 0.1 litre every hour to make 1000 kWh...so its easy to work out the kwh of your heater.

All the best.markj

Evan
02-08-2010, 02:22 PM
I recently discovered something very interesting that I didn't anticipate. Last year I upgraded the drain system for the foundation of this house (it didn't have one) by digging a trench about 100 feet long an up to 9 feet deep to a deep gully that runs along the front of our property. In the trench I put 4 inch PVC pipe which leads inside to where the sum pump is located and connects to the bottom of the sump from the side. This should permanently eliminate the threat of flooding each year when the ice comes out of the ground and the ground suddenly becomes supersaturated with water.

What I discovered is that even in -40 weather the drain system was acting a a source for warm makeup air for the house. The furnace has it's own 3 inch makeup air pipe that bring outside air in to the furnace burner gallery. That of course reduces the efficiency and also acts as a source of very cold makeup air for the house when the furnace is off.

Air is coming in the 4" drain with enough volume to act as the primary makeup air for the entire house and is being warmed by the heat in the ground on the way in. The average temperature in December of 2008 was -5 C and we used 12 gigajoules of gas energy. This year the average temp in Dec was -8.5 and we used 13 gigajoules. Based on my historical billing records we should have used about 15 gigajoules for that period so we are looking at around a 15% reduction in gas usage.

MTNGUN
02-08-2010, 04:51 PM
I haven't read the whole thread, but it sounds like the OP wants to quantify the heat loss so he can quantify the payback, if any, for improvements.

I hate that. I had a couple of jobs where that was basically all I did, calculating the payback period and return on investment for every little purchase. The CEOs were "into" that sort of thing. What a crazy way to run a company ! ! !

I don't run my company like that, and I bet you don't run your shop like that. When you buy an endmill, do you ask yourself "what is the payback on this endmill ?" Heck, no.

There is nothing wrong with quantifying things for the sake of learning. That's what science is all about, and I'm all for it.

But PLEASE don't worry about payback. Who knows what the price of fuel will be in the future ? How do you put a price on your comfort ?

When I remodeled my previous house, I installed new windows because the wind was whistling through the old windows. I added 1/2" of foam sheathing on the outside and taped it and calked it to reduce the air infiltration to nil. I put new weatherstripping on the doors. As it turned out, my heating bill was cut in half, so the pay back was very quick. That was nice, but it didn't matter to me. What mattered was that the wind was no longer whistling in, and I was much more comfortable.

When I built my current house, I insulated it as best my budget allowed. I didn't worry about payback, I just wanted it to be comfortable to live in.

BTW, my current house is heated strictly by wood. If the power goes out, as it often does, the wood stoves still keep me warm. If the price of heating oil goes up, I could care less. Since the wood stove normally puts out an excess of heat, temperature regulation consists of opening a window or two. The temperature in my shop right now is 70 degrees, thanks to free wood heat. Wood is renewable, carbon neutral, and in my case, it's nearly free. I highly recommend wood heat if your local regulations allow it.

bsmith
02-08-2010, 06:24 PM
To reduce home heating and cooling costs, you need a two prong attack. First, is to improve the building structure as much as possible and second is to improve the efficiency of your hvac equipment. The structure can be made more energy efficient in many ways, but there is not much you can do to improve the equipment other than to replace it with a new more efficient unit.

Concerning hvac load calculation software, the main point of that is to size hvac equipment for the worst case summer and winter cooling and heating loads. Hvac loads are expressed in btu per hour rates or watts in the metric system. Running a load calculation program on an existing structure would only tell you whether your existing equipment is properly sized for the home. In most cases, the existing equipment is usually oversized 20-50% more than what a load calculation program suggests. As was noted in earlier posts, a great number of hvac installers still use “rules of thumb” to size equipment and these simplistic rules are often very conservative which results in numerous oversized equipment.

It is very likely that Jim’s current hvac equipment has sufficient capacity for his home. If on the coldest day of the winter the furnace can still keep the house sufficiently warm, then its capacity is sufficient.

Using standard load calculation software, one can model possible changes to the structure (more insulation, better sealing against air infiltration, etc.) and see the reduction in the “peak” heating and cooling loads on the home. A reduction in the peak loads will also result in a reduction of hvac operating costs, but a basic load calculation program does nothing to predict reduction in operating costs. For that, you need an energy analysis program.

Before leaving the subject of load calculation programs, note that concerning residential load calculations, ACCA’s Manual J 8th edition methodology is the standard for this calculation procedure in the U.S. You can buy the Manual J book here http://www.acca.org/store/category.php?cid=2 Manual J 8th edition is an ANSI standard and is included in the 2009 International Residential Code (IRC). Chapter 14 of the IRC, Heating and Cooling Equipment: M1401.3 Sizing. Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated with ACCA Manual J 8th edition or other approved heating and cooling methodologies.

Note that I keep pointing out the 8th edition of Manual J often referred to as MJ8. This is because there are other computer programs out there, such as the one Jim rented for $49, that are based on the outdated 7th edition of Manual J. Presently there are only four computer programs approved by ACCA for MJ8 calculations as seen here http://www.acca.org/software/ In the interest of full disclosure, I am the owner and founder of Elite Software which makes the RHVAC MJ8 load calculation software.

ACCA (Air Conditioning Contractors Association) is very different from ASHRAE (American Society of Heating Refrigeration and Air Conditioning Engineers). ASHRAE is an engineering society while ACCA is a contractor association. ACCA procedures and guidelines tend to dominate the residential world while ASHRAE procedures dominate the commercial world even though both organizations have residential and commercial calculation procedures and manuals. I am a mechanical engineer and thus Elite Software offers software that automates both ACCA and ASHRAE procedures.

But as noted before, a basic hvac load calculation program cannot calculate hvac operating costs. For those willing to really dig in, there are several free high level energy analysis programs that can calculate hour by hour for an entire year (8760 hours) for both residential and commercial structures. They use hourly weather data for the city of your choice and they calculate the net hourly hvac loads and hvac operating costs. The most popular free program is called eQuest and it can be downloaded from here www.doe2.com The other program, considered the most technically correct, is called Energy Plus (E-Plus) and it can be downloaded from here http://apps1.eere.energy.gov/buildings/energyplus/

I must warn you though, that these programs are very complex and difficult to use, particularly E-Plus. There is very little support available on these programs. You just send email and pray for a response. Please do not email or PM me about using those programs either. I can barely run eQuest and can’t do much with E-Plus other than to run its test suite.

There are consultants around the U.S. that will run these programs for you and even offer training on them. Check the web sites out above for that info. Again, eQuest is the much easier one to use and is very capable with full LEED (Leadership in Energy and Environmental Design) capability. Not sure on the appropriateness of giving a recommendation here, but Dennis Koop of GeoExchange Design in the Dallas area can do a good eQuest analysis for you on residential structures starting from $150 up which is way, way less than what a typical consulting engineering firm charges. Dennis did authorize me to post his business phone number of 214-289-1260.

What you basically want to do with these programs is investigate the possible operating cost savings of various improvements. Concentrate on improving the structure first by sealing all air leaks as well as possible. To test your air leaks, contract out a blower door test as described here http://www.energysavers.gov/your_home/energy_audits/index.cfm/mytopic=11190

Blower doors are expensive as seen here http://www.google.com/products?q=blower+door&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&ei=noRwS_vnNYu1tge38_GFBg&sa=X&oi=product_result_group&ct=title&resnum=3&ved=0CCYQrQQwAg

Since all of us on this forum can make things, you could consider making your own simple temporary blower door. The main benefit of a blower door is not so much that it can measure precise air flows and pressures, but that you can use it to trace where your air leaks are. All that needs to be done is to rig a shop fan such that it is well sealed to a door frame with canvas or heavy tarp material so that the fan is able to put the interior building space into a bit of a vacuum.

Then using a smoke pencil or puffer device, walk around the inside of the building and watch where the smoke source is affected by air leaking into the building. Use caulk, foam, and any other way you can think of to seal all the air leaks as best as possible. See this link for various sources of smoke puffer devices http://hvac-talk.com/vbb/showthread.php?t=98517 The hvac-talk forum is a great forum to learn from, but it is very hard on DIY people like most of us here. Be very careful posting there or you will be sharply rebuked.

Another corollary of building air leaks is duct air leakage. Use mastic to seal any duct leaks you can find and consider contracting a duct blaster test to see how well your duct system is sealed. See info on a duct blaster here http://www.energyconservatory.com/products/products2.htm Again, resourceful people can often duplicate a duct blaster test to some degree on their own.

After you have sealed the building and duct system for air leaks, then consider adding insulation and other improvements. Use software like eQuest to decide if the money needed for those improvements will reduce operating costs to your satisfaction. After all building improvements are considered, again use software to see if there is economic justification to upgrade your hvac equipment. In many cases, especially where the hvac equipment is old and breaking frequently, it makes sense to replace equipment before doing all the possible building improvements.

As I mentioned earlier, structure improvements are the best thing to consider first. For more on efficient structure information see these sites http://www.buildingscience.com/index_html and http://www.joelstiburek.com/topten/index.html Another great book on creating energy efficient structures soon to be released is by Galveston City inspector, Berry Smith. It is called Structure as a System. Contact Berry here http://www.rescom-consulting.com/about_us for more info on his new book.

I hope this helps everyone in making their home, shop, or business more energy efficient. But again, please don’t PM or email me about whether this or that idea might be cost effective for your situation. The answer is always, “it depends”. Learn to use the free software mentioned or find a guy like Dennis Koop who loves to talk this stuff and is in business just for that.

Your Old Dog
02-08-2010, 08:32 PM
BSmith, thanks for taking the time topost that. I found it an informative read. As for the smoke device you mentioned when checking for air currents and leaks I find a common $8.00 pack of cigarettes works great. The blue smoke is easy to show and will show you theslightest air currents. MAKE SURE AND READ THE SAFETY WARNING ON THE PACKAGE :D

J Tiers
02-09-2010, 12:48 AM
We had that sort of procedure done in our efficiency check.

Since this is a brick house (with hollow tile insulation), we were not overly surprised to find that we had a net of less than one square foot of leakage, and were down around 0.3 or so air changes per hour. This with ordinary wood sash original 80 year old windows, plus triple track storms.

The house is so tight that we actually got some backdrafting with every exhaust fan and flue going at once (two bathroom fans, one kitchen fan, furnace, water heater, and dryer all on full at once). We basically need to make MORE leakage!

That may be one reason I was disappointed, there was so little leakage that the inspectors could only tout piddly improvements, most of which would have made the lack of leakage worse. They admitted that new windows would never pay back their cost, due to the house already being so tight, and walls being brick.

However, the audit made NO effort to assess basic heat loss issues, which I was surprised about. They accepted the structure as-is.

There are some rooms with multi-wall exterior exposures. I have considered stripping the interior plaster from the bricks in the worst areas, and adding a layer of insulating foam board, then a plaster or (perish the thought) wallboard interior finish.

That's one reason I want to do the heat loss calcs for this place..... The leakage is nil, but the straight wall losses are significant. Adding the insulation in strategic places would likely make those cold areas more habitable, but some quantification is required..

J Tiers
02-09-2010, 01:16 AM
Bad assumption Jerry. The exterior is always warmer than ambient when the house is heated. If it weren't there would be no heat loss. :rolleyes:

This is obviously not your area of expertise. The primary heat loss from a house is air exchange followed by radiation cooling at night with the windows being the main avenue of radiative loss followed closely by loss through the roof.

EVAN, MUST we go through this tiresome pedantic crap every DAMN thread?

I did NOT say it was TRUE, I specifically said it was an ASSUMPTION for purposes of assessing the RELATIVE HEAT CONDUCTIVITY losses for the different portions of the house. The ONLY reason that ANY part of the outside of the house is hotter than ambient is that heat is conducted through the wall (or roof).

The assumption merely puts the entire 'temperature drop" across the wall material. And, yes, there IS STILL a temperature difference that drives heat flow.

Areas of expertise? Go soak your head.... I deal with heat conductivity all the time with power electronics.....

When assessing the heat conductivity of a material, you can maintain ONE side of it at temp "A", and the other at temp "B". Then you measure the heat flow. From that data, you can assess the heat flow possible per unit area with any other difference of temp between the surfaces.

Your %$#@ pedantic crap neglects to handle the basic issue..... obscuring it with more 'fuzzy issues" that cannot be easily measured, such as the amount of heat carried away from the outside of the house.... which affects the actual temp difference between the surface and the air.... which actually does not make one bit of real difference.

I KNOW you are likely to come back with another load of crap taking this point by point and picking at selected details.... Feh....

* In fact, ALL the heat you input to the inside of the house leaves the house. it leaves through walls, (including windows and roofs), and it leaves through leakages, either hot air out, or cold makeup air entering and requiring to be warmed. if your house is as tight as ours, walls are a huge part of the losses, leakage is down the list.

* In fact, the better your insulation, the closer the outside of the house is to ambient temp, and the closer the inside surface is to interior ambient. The "thermal resistance" of the walls is larger than the thermal resistance 'air to wall" and "wall to ambient"

* In fact, there is a temp difference ACROSS THE THICKNESS OF THE WALLS (including windows, etc) which is the driver for heat flow.

* In fact, once the heat has flowed through the wall, you really don't care what happens to it as far as radiation or convection, etc, it is already lost. So fussing and fuming about whether the outside of the wall is at ambient, or is a couple degrees warmer is not relevant when the total difference through the wall is 60+ degrees F.

Assuming the outside is at ambient and inside likewise at interior ambient is not a "physics error", it is a simplifying assumption which makes no practical difference. What it DOES do is to isolate the issue, which is heat flow through the wall system, driven by the temp difference between inside and outside. if you are trying to decide whether insulation will pay, you are trying to compare the heatflows with and without the added insulation, and attaching a reasonably accurate cost reduction figure to the insulation, relative to doing nothing.

The loss off the wall surface to the air doesn't come into it, it will be the same either way, insulation inside the wall does not affect the ability of heat to leave the surface, it only affects how much DOES leave. And assuming that the outside is simply at air temp removes variables which account for only a small part of the issue.

I'd recommend you go and measure the actual temp of the surface of your house some day..... inside and out. I did that, and found that the difference from interior and exterior ambient, respectively, was low. if it is NOT low, on the inside you will have severe drafts from cold air passing down the wall, and you will right away know what to do, no energy audit required......

Evan
02-09-2010, 03:41 AM
Your %$#@ pedantic crap neglects to handle the basic issue..... obscuring it with more 'fuzzy issues" that cannot be easily measured, such as the amount of heat carried away from the outside of the house.... which affects the actual temp difference between the surface and the air.... which actually does not make one bit of real difference.


You may not like dealing with the "fuzzy issues" but they are the ones that present the greatest opportunity for improvement. There is nothing pedantic about my objections to your statements. In particular, the emissivity of the outer wall covering on the house makes a large difference to the heat loss. The difference between a white wall and a black wall will create a steeper gradient with a the black wall and that increases the transfer of heat through the insulation. It is far from negligible as anybody that has owned a black car can attest. Remember, heat loss and heat gain operate on the same mechanism.


I'd recommend you go and measure the actual temp of the surface of your house some day.....

I did, this evening. It was only a very cursory inspection because I am working on an IR imaging system that doesn't cost 10,000 dollars. There are very significant differences depending on which side of the house you measure and between the windows and the walls. I did this after the sun had set so it wasn't confounding the results. I found differences of as much as 12 degrees F between the ambient and the walls with the greatest difference being on the north side where the local ambient surface temperature of the ground was much colder. Air temperature is far from the entire story because of the IR reflection factor.

Radiant heat loss is the largest contributor to heat loss in a house. It operates all the time, not just when the wind is blowing and it is by far the greatest loss mechanism through windows. Just painting your house a light colour will make a big difference. This also brings up a very counterintuitive fact. If you reduce radiation losses you increase the contact temperature of the outer walls given no change in insulation. This reduces the temperature gradient in the wall and that reduces the heat transfer.

beanbag
02-09-2010, 05:55 AM
This also brings up a very counterintuitive fact. If you reduce radiation losses you increase the contact temperature of the outer walls given no change in insulation. This reduces the temperature gradient in the wall and that reduces the heat transfer.

I had to think about this for a minute, but it does make sense after all

Weston Bye
02-09-2010, 09:07 AM
Somewhat related, will the position of venetian blinds affect heat flow? My wife perfers to close them slanting down toward the inside of the house, year round. That is, the inside edge of each slat lower than the outside. I perfer the opposite, and maintain it is more energy efficient.

The reason being that there will always be gaps between the slats and any rising warm air or falling cold air will be deflected by the slats. I perfer that the warm air be deflected inward and cold air be deflected outward.

In addition to the convective theory, there is also radiation that may be accounted for. The cracks, looking up at a clear night sky, will loose heat through direct radiation.

In the summer I turn them the opposite to take advantage of cooling.

Certainly very minor savings or loss. Any comments?

SmoggyTurnip
02-09-2010, 09:12 AM
It is far from negligible as anybody that has owned a black car can attest. Remember, heat loss and heat gain operate on the same mechanism.


Very interesting thread. I do own a black car. Last week we had a sunny day with the outside air temp at -18 degrees C with no wind. I put my hand on the surface of my car and it was hot to the touch. Obviously the black color was working in my favour at the time. So I am thinking there are times when having a house that is completely black would be an advantage for heating. It is surprising to me that overall the lighter color house would be better. I am not arguing against because I don't know enough about it and suspect you are right. But what you are saying is that the heat gained by absorbtion of energy by the sun during the day is all lost after sunset and then much more on top of that because the house is black. Hmmmm -- tell me more to convince me.

Evan
02-09-2010, 09:56 AM
In the winter here the sun is so low in the sky and the daylight is so short that radiation losses far outweigh any possible gains. In particular, the effective temperature of a clear night sky is around -70C regardless of the air temperature. Radiation loss depends on the temperature difference of the black body and it's surroundings. The usual black body calculation makes the assumption that the surrounding are at absolute zero. If the surroundings were at the same radiation temperature as the black body the absorption and emission would be in balance and no loss would occur.

While it is true that heat may be gained through the side walls of a house illuminated by the sun in winter the loss incurred by attempting to enhance that gain far outweighs the gain. The sun cannot shine on all sides of the house at once and of course not at all during the up to 16 hours of darkness here. It does make sense to increase the gain through windows. Our back entry door faces south and doors are also poorly insulated at best because of the limited depth of insulation. We have a glass storm door that acts as a solar collector on that door and the door itself is painted dark brown. It can become positively hot on a cold but sunny winter day because of the greenhouse effect of the glass door.

We also have very heavy opaque drapes on the south facing windows. When drawn closed at night they act to block radiation losses through the windows. We also leave some of them closed during sunless days and open them only when it is sunny to capture some solar radiation.

There is work being done on "one way" coatings that either selectively absorb or selectively reflect differently in the IR wavelengths compared to visible light. A group at the Lawrence National Lab in Berkeley has developed roof shingles that appear black, dark green or dark red in visible light but are effectively white at IR wavelengths to reduce heat gain in summer. Similar but opposite effects may be possible to increase heat gain in winter. A very simple method is to build a green house on the south wall of your house with shades or awnings that may be drawn in summer.

aboard_epsilon
02-09-2010, 10:03 AM
my double glazing units are filled with argon ..one of of each pain is a special glass called pilkington K glass ..
this has a special coating on the inside that reflects heat back inside .

to look at, they look tinted ...you have to go right up to the house to be able to look in ........with the lights on you can see in though .

most of the glass units fitted in the UK over the last ten years are this spec or higher.

all the best.markj

J Tiers
02-09-2010, 10:06 AM
For a house to have such a high outside temp, the insulation must be relatively ineffective..... perhaps you should be working on that.......

I find no more than a 5 or so degree difference at temperatures of interest, amounting to an error of between 5% and 10%, depending on outside temp. Neglecting that produces errors on the same order as the probable accuracy of the measurements and the average values for the heat loss through walls of that type.

Since you will NOT be measuring the wall system's losses, you will need to make assumptions, and use the average losses for that type construction... Those tables probably apply only within 10% or so at best, to your particular house.

So being tiresomely pedantic about it does very little to increase the accuracy of the process.

I will point out that the SLIGHTEST wind begins to produce turbulence that scours off the boundary layer of warmed air, and increases heat loss drastically with wind speed.

In fact, even in totally still air, the warmed air at the surface rises, which produces a scouring effect, with a large influence on the losses. A heatsink is much more effective as the surface temp rises, specifically because of the convection air currents. There is no particular reason why a house does not behave the same.

As for radiation, a house, modeled most simply as a cube, has most surface area unobstructed, so it does radiate...

There are modifying effects....

A house with a courtyard or similar feature has walls facing, which lose radiation effectiveness.

A house with trees, particularly evergreens, near it loses radiation effectiveness in those directions.

an attic cuts radiation in that direction, re-radiating some energy back to the ceiling below it, as well as radiating heat outwards

And, the more effective the radiation is, the lower the outside surface temp, because the "thermal resistance of house to ambient" is lower compared to the "thermal resistance of wall system".

In any case, ALL the heat is lost, and the assumption make very little or no difference on a RELATIVE basis for comparing the same wall in same conditions but different thermal resistance (or conductivity, if you prefer ).

It is possible to see the problem as very complicated with many inter-related factors. And indeed it IS that way, if you consider every possible effect.

In such a case, anyone who has actual experience in solving practical engineering problems will instantly, as a normal reaction, look for simplifying assumptions which have a minimal effect on the results. Assuming the entire temperature drop is across the wall is one such.

AND, the better the insulation of the wall system, the better the assumption is. So the assumption is self-correcting.

Don't put complications in when they are not required. It won't help solve practical problems, no matter how nice it is in an academic paper, where absolute rigor is the gold standard.

digger_doug
02-09-2010, 10:14 AM
a little brevity:
1. Had my parents 109 year old farms house checked.
For $150 I got a complete report using a thermal
imaging camera, all outside walls, with a normal
photo next to it for reference.
The operator also walked around inside, and highlited
all the problem spots as well.

2. Yes it's relative, no numbers involved. But it shows
where the greatest loss is.

3. The guy is experienced, been doing it for years, and
has seen allot of houses. His experience told me
what to do and where.

4. A home show I listen to has been extoling the virtues
of an air-to-air heat exchanger to allow ventilation
(you mentioned your house needed more leakage)
this unit solves that problem, but unlike plain leakage,
conditions the incoming air, using the outgoing air.

J Tiers
02-09-2010, 10:18 AM
4. A home show I listen to has been extoling the virtues
of an air-to-air heat exchanger to allow ventilation
(you mentioned your house needed more leakage)
this unit solves that problem, but unlike plain leakage,
conditions the incoming air, using the outgoing air.

Counter-flow heat exchangers are very effective....... but most require power to operate. Yet another way to pry you out of your house during a power failure.......:rolleyes:

makes more sense to use outside air for combustion, and use the flue gas to warm it up on its way in...... just like a power plant does. Definite increase of efficiency right there. Not one unit on the market that I am aware of.

Evan
02-09-2010, 10:21 AM
Don't put complications in when they are not required. It won't help solve practical problems, no matter how nice it is in an academic paper, where absolute rigor is the gold standard.

The effect of radiation losses because of surface coatings is not an "unnecessary complication". Preventing radiation loss with an external coating is effectively adding insulation on the outside wall and thereby reducing the heat transfer in the wall. The difference between a good radiator and a poor radiator is huge, not some easily ignored technicality.

J Tiers
02-10-2010, 12:57 AM
The effect of radiation losses because of surface coatings is not an "unnecessary complication". Preventing radiation loss with an external coating is effectively adding insulation on the outside wall and thereby reducing the heat transfer in the wall. The difference between a good radiator and a poor radiator is huge, not some easily ignored technicality.

oif course it has an effect..... but how much in your case, or more to the point, in Jim's case? The problem is getting better information, isn't it?

And now that you have brought it up, what do you propose to DO about it?

generally, this is not an exactly quantifiable area of work.... You must accept probable errors of anywhere from 5% to 25% with existing construction estimates. If you don't like that, well, feel free to do better yourself..... i.e., if you don't like mackerel, help yourself to the mustard.

The tables of typical loss values for different types of construction and/or surfaces, already HAVE that information buried in them. The tables often give you values for the wall system including all loss paths which allow you to treat the wall essentially as if it has the given loss with inside at interior temp and outside at exterior. As I said.

The tables bury the details because you are generally not going to be able to obtain better information about your particular individual wall system with it's local variations from "standard'.

You may either use it, or indignantly ignore it as "inferior", but if you DO ignore the tables, you must then find a way to derive better ones.

if you expect to get something done, you use the data and go, otherwise you get pretty much nowhere unless you are prepared to instrument each different type of wall you are interested in and get your own values.

Mr Caudill wants to estimate the existing losses and get some guidance on improvements.....

IR imaging can help see the worst areas, but may not do much for a "yearly cost" estimate. And it may not do anything at all for estimating the effect of a change to a different wall system, or added insulation etc, as far as future bills. It is not a predictor, and is often not a quantitative measurement in the first place. While it tells you "put more here", it does not tell you how much you will save. You need other data for that.

To get the improvement numbers, you need to estimate the heat flow through that wall area, and then estimate the heatflow for a different and presumably better setup on that same wall area.

This can be done using the figures for the type of construction you have, and then for the type you are considering a change to.

Nitpicking about surface finish and radiation, no matter how academically true, is of no help unless you can actually give a useful quantitative figure for the improvements if the surface finish is changed in a specific way.

I certainly haven't seen that yet, so if you have it , give. Mr Caudill is waiting.

Evan
02-10-2010, 04:35 AM
Here is one example:


Reducing heating costs is an important concern for householders, but many conventional methods of cutting down heating costs, such as insulating lofts and cavity walls and fitting double glazing, involve considerable capital outlay. An effective way of reducing heat losses with a minimum of capital outlay is to fit reflecting metal foil behind the central heating radiators, but little has been done to measure the amount of energy saved in this way. Similarly, a foil layer can be used to reduce heat losses from beneath suspended floors, but little data are available on its effectiveness. Work is reported here on experiments carried out in an environmental chamber to measure the effect on heat losses of metal foils behind radiators and beneath suspended floors. Reductions in the overall energy consumption of the room of up to 6% were recorded by installing foil behind a radiator, while the heat loss through the area of wall immediately behind the radiator fell to less than 30% of the original value. The heat loss from a suspended timber floor was reduced by up to 48% when foil was applied to its under surface.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V1T-3YXC0K0-2&_user=10&_coverDate=12%2F31%2F1995&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1201163203&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7e73bc2a98a1b884a8e71ec247787423

speedy
02-10-2010, 05:42 AM
So once we have closed up the home so that it is somewhat like a chilly bin, or an esky to you Tiff.
What do we do about the internal moisture that can no longer make its way out?, before it causes rotting building syndrome from the inside?
Now, is that the next biggy for the homeowner?
I am lucky in that our climate is such that all we use is the dehumidifier and a small fan heater in the Winter months...and open doors n windows along with a big pedestal fan or two in the Summer.
This is an interesting and relevant thread to me all the same as the Carbon credit Nazi Stormtroopers are on there way here soon.
I understand that Aussie households are in for energy efficiency inspections soon too....at a substantial cost of course.

Circlip
02-10-2010, 07:35 AM
Strange how the green incentive becomes SO obvious when the cash register is brought into play and the hitherto undiscovered technological breakthroughs occurr.

Regards Ian.

Evan
02-10-2010, 08:00 AM
I have been using so called "green" methods and systems since I was young, and that was far too long ago. My father installed solar water heat on his house in the 1960's and they are still there and they still work. I notice from the satellite images that he has also installed a couple of sq meters of photovoltaics in the last few years. We use a variety of small items here that all together add up to a 50% reduction in our energy use over the last 20 years and there is room yet to reduce further without compromising our lifestyle. I am right now working on a unit to capture flue gas heat from my natural gas furnace. I will probably post something on it today or tommorrow.

J Tiers
02-10-2010, 10:07 AM
Here is one example:


That is less than nothing.

The fact of differing radiation is not in dispute, or perhaps you did NOT notice.

But exterior radiation can be made to be a non-issue, even with a very effective radiator as the surface.... it may be irrelevant. see below.

And a "30% reduction" or any other percent reduction in radiation over a very small area of wall is not a helpful number to begin with. And particularly not unless you know the original numbers for radiation and convection so that you can turn that into a dollar figure.

Foil is in fact used in some insulation systems, but is rather uncommon on the exterior of houses. And such application probably violates every 'covenant" in existence if you happen to live in one of those obnoxious communities that have covenants.

Mr Caudill wants, not surprisingly, a way of determining the dollar value of larger scale improvements, which he can apply whatever inflation factors to, and compare against the construction costs.

In the case of radiation losses, information on specific brands and types of surface treatment, with numeric figures, is the sort of thing he needs.

But that is merely one small part of the picture,

The radiation losses are minuscule if the wall system has a very low thermal conductivity to begin with. In that case, there is not very much TO radiate, and teh radiation or lack of it becomes a non-issue.

Evan
02-10-2010, 12:33 PM
I am going to be buying some of the NASA developed paint additive that creates an insulating IR reflective layer in the top surface of the paint. It consists of microscopic ceramic spheres that are hollow and evacuated. These may be mixed with any paint and reflect up to 90 percent of incident radiation. I will be doing a few tests and it will probably be used to help insulate the north wall of this house.

All you are managing to do Jerry is to possibly dissuade people from taking steps that can both make their house more comfortable and save money at the same time.


The radiation losses are minuscule if the wall system has a very low thermal conductivity to begin with. In that case, there is not very much TO radiate, and the radiation or lack of it becomes a non-issue.

Which is rarely the case in North America, unless the walls are a foot thick.

RancherBill
02-10-2010, 12:43 PM
This page categorizes heat loss through walls and ceilings into three categories Radiant, Conductive and Convective.

http://www.radiantbarrier.com/what-is-radiant-barrier.htm (http://www.radiantbarrier.com/what-is-radiant-barrier.htm)

It is interesting, it is from a company peddling a product, but, there is a good explanation that might be useful in the radiator tinfoil discussion.

J Tiers
02-11-2010, 01:05 AM
All you are managing to do Jerry is to possibly dissuade people from taking steps that can both make their house more comfortable and save money at the same time.




Not at all. it isn't difficult. But there are different ways to do it.

if you want to make improvements, there are three ways to do it. maybe four.

1) do the "home remedy", or "folklore solutions" stuff..... tinfoil behind radiators, etc... This is usually well-meaning and somewhat effective for what it does, but doesn't form part of a real plan, and often is just diverting attention from the real issues that cause the most loss.

2) Do the "obvious well-known solution" stuff..... Typically what is "sold" to people as 'good to do", one size fits all.
not everything is good in all cases. Most people, for instance, have been 'sold" the idea that "energy saving windows are the thing to do". But that may not be the case.
An energy saving window doesn't do bupkis if the rest of the wall is lossy. Better you should fix the wall and leave the window alone. Or move.

3) Do the things that can be done, regardless if they are the most effective.... put attic insulation in, etc. Can be effective if you hit the needs, won't do much if you do not.

4) develop a plan, identifying and addressing the major actual losses first, and proceeding to the lesser ones, prioritizing in order of savings and according to payback.
This plan can be done by a homeowner, or by a competent energy audit firm.

Evan
02-11-2010, 01:45 AM
An energy saving window doesn't do bupkis if the rest of the wall is lossy. Better you should fix the wall and leave the window alone. Or move.


[shakes head] A window easily loses more energy than all the entire outside wall in a room even if that wall isn't insulated. The only thing worse would be to open the window. Windows are nearly as bad as a hole in the wall and the colder it is outside the greater the difference between the walls and the window becomes. The window is entirely transparent to IR.

bsmith
02-11-2010, 02:03 AM
The discussion between Jerry and Evan remind me of some of the ASHRAE technical committee meetings I have attended. ASHRAE has two strong factions consisting of the Phd university academics and the practicing consulting engineers who are also well educated with advanced degrees. The academics are always pressing that the ASHRAE hvac load calculation procedures should progress towards using the most correct and true physics solution as possible. The consultants don't disagree with that perspective, but they have to keep reminding the academics that the calculation process must remain practical and manageable so that buildings can be analyzed at reasonable cost in reasonable time frames.

Balancing the two perspectives has always resulted in compromises that greatly simplify what is really going on so that the procedures are more manageable. Before the era of personal computers, the simplifications were huge and even with personal computers, significant simplifications are still made because our PC's would need to be super computers to calculate everything perfectly correct. As PC's progress towards current super computer status there may come a day when the ASHRAE hvac calculation methods will perfectly factor in the complete physics that is involved.

The ACCA Manual J 8th edition residential calculation methods are still so simplified that there are not even hourly load factors for roofs and walls, weighted average load factors are used. Only glass is given hourly load factors in the ACCA procedures.

In the ASHRAE world, there are two current approved calculation methods, something ASHRAE has never done before. These methods are the Heat Balance method and the Radiant Time Series (RTS) method. The heat balance method was promoted by the academics and is the most technically correct even though it still does not consider all the nuances Evan mentions. The engineers do not prefer the heat balance method because it blends loads from the roof, wall, and glass together in such a way that these component contributions are lost when the net heat gain/loss results are achieved.

The engineers want to know the different load component amounts even as they evaluate the total loads. The RTS method is a simplification of the Heat Balance method that preserves the component load amounts. For the engineers, the small loss of accuracy the RTS approach causes is well worth the ability to more quickly evaluate the effects of different building materials.

The only software I know right now that uses the more theoretically correct Heat Balance approach is the public domain Energy Plus program which was created with government funding. All the current best selling ASHRAE based hvac load calculation programs use the RTS method or one of the earlier methods called TFM (transfer function method) or even the much older and still very popular but super simple method called CLTD (cooling load temperature difference).

dp
02-11-2010, 02:06 AM
[shakes head] A window easily loses more energy than all the entire outside wall in a room even if that wall isn't insulated. The only thing worse would be to open the window. Windows are nearly as bad as a hole in the wall and the colder it is outside the greater the difference between the walls and the window becomes. The window is entirely transparent to IR.

You can sense the difference when sitting next to a glass window. I have a sliding glass door just 3' from where I'm sitting, and because I'm radiating heat from my body out into the back yard, that side of me feels quite chilled at times. The other side is radiating into the house which is much warmer so the amount of heat I radiate in that direction is far less and I feel warmer. If I draw the drapes there is no chill. It is simple thermodynamics.

A more dramatic example for entropy deniers :)

Face the night sky on a calm, clear cold night. Close your eyes and have somebody hold a large sheet of paper between your face and the sky. You will sense the temperature difference when your face is screened from the sky. The night sky is frequently much colder than the air around you, reaching temperatures far below 0º F on very clear nights.

That same cold outdoor temperature is what allows your room to radiate so much heat out the window. Skylights can easily allow 50-80 watts/meter square to radiate out into space.

Evan
02-11-2010, 06:28 AM
More about windows:


Radiation, Conduction and Convection

Absorbed by the inside pane of a double-glazed window, heat moves to the cooler outside pane and is released to the outdoors. This heat loss through windows takes place through the glazing (by radiation); across the spacer material which separates the two glazing layers at their edges and through the frame of the window (by conduction); through the movement of air in the space between the two glazings (by convection); and between the moveable or operable frame components (by air leakage).

Radiation losses through the window glass represent about two thirds of the total heat loss in a standard window. Because ordinary glass readily emits heat to colder surfaces (ie., has a high emissivity), radiation losses can be reduced by lowering the emissivity of the glass (hence the term low emissivity or low-E glass).

Conduction losses in windows occur primarily through the edges and frames of the units. Advances in materials and designs that more effectively use insulating materials have dramatically reduced these losses.

Convection losses occur due to air movement between the spaces of multi-glazed windows. If the space is too small, conduction through the air is significant. If the air space is too large, the still air will begin to rise as it is heated on the warm interior side, and fall as it is cooled on the cold exterior side of the window. This convection movement of the air passes heat to the exterior. The best spacing to minimize convection losses is 12 to 16 mm (one half to two thirds of an inch) between the glazings. Other gases (argon, krypton) are often used to reduce convection heat loss. Optimum spacing for these gases can be different.
http://hometechwindow.com/blog/?cat=1


And, the main bone of contention, walls and surface treatments. Note the differences quoted for just the surface colour and the "average temperature" adjustment to be made to account for night sky radiation which is a factor equal to a -4 degree colder night for walls and 10 degrees colder for roofs.



A simple and equally realistic approach is to use approximate surface temperatures. Table 3
is a compilation of the most useful approximate surface temperatures based on calculation
(using refined surface heat transfer coefficients) and supported by several years of field
measurements.
emitted radiation

roof exposed to night-sky t - 10 ?
walls exposed to night sky t - 4 ?

Notes: t refers to the ambient air temperature, ? is the surface emmittance
The emmittance is about 0.90 for most materials. The absorptance varies with colour from about 0.3 for white/beige objects to 0.65 for forest green to 0.95 for flat black.
http://www.civil.uwaterloo.ca/BEG/Arch264/Arch264%20Heat%20Flow%20Basics.pdf


The emittance will vary directly with the absorption according to the values posted above.

BWS
02-11-2010, 07:20 AM
Jim,go take a ride.........you're looking for early 1800's farm/estate houses in,and this is REAL important.......in YOUR area.Look at the overall shape and design,try to take BS embellishments out of this picture...........See how these designs differ from your post WWII subdivision,one size fits all,house.Not trying to be over critical,but I find it a tad humorous that your house looks exactly like houses in quite a few other areas of U.S,which are drastically different in the climates.

Think trying to force a 2 story Williamsburg colonial into Az.,N.M.,ect.It don't work to well.Just look at what your area was sporting around 1810,throw a little insulation and a new efficient furnace in and its gonna be pretty close to ideal.

As has been said by a cpl posters.........you can have all the calculations you want,when the wind is howling @50+ mph,all bets are off.BW


PS.sitting in front of our SW 'erly facing windows here in the mnts of Va.is more often than not the warmest spot in the house this time of year.So kitchen/daytime living area goes here.Bdrms on the other hand go twds N.Est'erly end.Considering which way Hurricanes hit houses in this area determine where closets and service areas reside.

J Tiers
02-11-2010, 10:03 AM
The entire issue among people NOT in the trade is really an issue of understanding.

Bsmith has the right idea, Evan doesn't.

Its all about practicality. And local conditions.

Evan is apparently claiming that the IR loss through one 2 x 2 foot window is larger that that through ANY wall, even 50 x 50 feet. At least his comments did not exclude that, so we can assume he means that (I am sure on reflection he will decide he does not)

Has Evan never heard of curtains?

1000 years ago people who lived in stone buildings understood radiant loss to the walls. Those tapestries you hear about were not primarily decorative, they were to hang on the cold stone walls to cut teh radiant losses from people to the walls. And they worked, if yu were among the rich who had a few.

The whole point is NOT to argue about the effects of this or that detailed technique....

That's the "home remedy" approach, "how to insulate your house cheaply with egg crates and tinfoil" and the like.

Without ACTUAL KNOWLEDGE about the house, it is IMPOSSIBLE to make a flat statement that the window loses more heat than the wall.

The window may be a 2 x 2 window in a large blank poorly insulated wall, OR it may be a sliding glass "win-door" that goes floor to ceiling.... In the former case, the window could almost be OPEN in some situations, and lose less than the wall, in the latter case the window IS the wall, and installing a better one may make a HUGE difference. Getting RID of the stupid thing is the best, of course.....

We have 17 1934 era wooden sash single pane windows. our energy audit folks agreed that (despite their desire to sell us windows) new windows were not a potential big benefit to us. The house is generally very tight, and snug, and the windows lose very little heat. We do NOT feel a chill near the windows.... but we have evergreen vegetation outside a number of them, and the windows have triple-track storms outside.

Without NUMBERS, even if they are pre-defined loss figures multiplied by the area of the various walls, windows, roof etc, there is NO way to effectively prioritize action, nor to estimate the effects of improvements..

One can take the pre-defined total loss prediction, and the degree-days/average temp with the heat bill, and "calibrate" the loss numbers to your situation. Then you have some basis for estimation of future bill reduction.

Sorry folks, but this area really IS "engineering". You don't have to BE an engineer, but to get decent results predictably, you need to take an "engineering approach".

or, you can try the egg crates and tinfoil (behind radiators, or on your head;) )..... or replace all the windows and see if you get any better performance after you write the check.

If the house is bad enough, you will get results no matter what your improvements are, but in the case of a house with reasonable losses, you can easily waste more money than you will ever save.

There is no point to replacing windows or adding wall insulation if the real issue is the attic/roof.

Evan
02-11-2010, 01:38 PM
Evan is apparently claiming that the IR loss through one 2 x 2 foot window is larger that that through ANY wall, even 50 x 50 feet. At least his comments did not exclude that, so we can assume he means that (I am sure on reflection he will decide he does not)

Has Evan never heard of curtains?


Still lacking reading comprehension Jerry. Either that or you aren't really replying to anything but just running off at the mouth. Your comment is ridiculous and in no way illuminates the topic.

I posted:

"We also have very heavy opaque drapes on the south facing windows. When drawn closed at night they act to block radiation losses through the windows. We also leave some of them closed during sunless days and open them only when it is sunny to capture some solar radiation. "

Most curtains have very little impact and are transparent at IR wavelengths. To be of any use they must be opaque, both in visible AND IR.

Also, I have never seen a house with a 50 foot long exterior wall with no windows or just one 2x2 window. Trying to counter valid information with meaningless and ridiculous examples serves no purpose for anyone.


Bsmith has the right idea, Evan doesn't.


I hate to point out the obvious but there is no way that you can tell how well a house is insulated, weatherstripped and heated just by looking at it from the street. There isn't much to be learned by looking at house designs other than how to deal with the effects of bad weather specific to the area. That isn't going to tell you very much about energy efficiency.


Without ACTUAL KNOWLEDGE about the house, it is IMPOSSIBLE to make a flat statement that the window loses more heat than the wall.


Oh? Read this:



"U" Factors: The number of BTUs that will pass through a square foot section of a building in one hour for each one degree Fahrenheit of temperature difference is known as the "U" Factor. Both the Air Conditioning Contractors of America (ACCA and the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) overprinted tables to determine the "U" Factor. A partial list of typical "U" Factors is given below.


Building Section "U" Factors
Standard Frame Wall (Uninsulated) 0.23
Standard Frame Wall (Insulated) 0.07
Glass Window, Single 1.10
Glass Window, Double 1/4" Air Space 0.63
Glass Window, Single Width Storm 0.55

http://www.propane.ca/Resources/heatloss.asp


Each square foot of single pane glass loses as much heat as FIVE square feet of uninsulated wall. Each square foot of single glazed window loses as much heat as SIXTEEN sq feet of insulated wall and even if the window is double glazed it loses NINE times as much heat per sq ft.


There is no point to replacing windows or adding wall insulation if the real issue is the attic/roof.

Sorry Charlie. If the windows are not up to standard then that is the second greatest heat loss in a house after air exchange. Even when everything is insulated as well as possible the windows are still the greatest loss area. The only way to really stop that loss is to reduce the area of the windows or shutter them (same thing).

J Tiers
02-12-2010, 10:35 AM
Evan...

This is getting very tiresome..... You can stick your asinine comments about "reading comprehension". they are just basic 'ad hominem abusive" or the like. yes, the very stuff you have been vocal in complaining about, you are using on a daily basis.

Curtains of many types are not at all "transparent" to IR........ if the IR heats the curtain, it obviously isn't "transparent", although it may be poorly transmissive, or may in turn re-radiate. But a thick (not 'scrim") curtain is very effective. A curtain which thoroughly blocks visible light is probably going to be of use for blocking IR losses, although it may not be perfect.

A "one solution fits all" "one answer fits all" approach does not work with curtains either.

And unless you want to block all windows and live in a cave, well........... you will be putting up with SOME window losses.

Your own table appears to show that double pane (thermal type) windows are not hugely better than ordinary windows, particularly versus single "with" storm (I assume the "width" is a misprint for 'with".) No factors of ten here.

Any window made of glass will act to lose heat. the question isn't really whether a window is or is not a loss, it is whether a "better" window is really better and reduces losses sufficiently to justify replacing it at relatively large cost.

In many houses, the ratio of window area to wall area is considerably greater than the ratio of the losses per your own example table. In that case, the window is NOT the largest loss.

Assuming the 0.07 figure and the 0.55 single with storm figure, the wall will lose an equal or greater amount of heat if it is at least 7.8 x the area of the window, which is not unusual at all for older houses, which commonly have smaller window areas, particularly if constructed of brick.

Newer houses with "picture windows" are another matter altogether. They often ARE a single thick pane, and commonly have no storm window, so they would be like leaving the barn door open. Almost anything done to improve them would be the best plan for that room.

Again, that is a "engineering" question, and cannot be addressed universally with a "one-size fits all' approach.

Evan
02-12-2010, 11:55 PM
This is getting very tiresome..... You can stick your asinine comments about "reading comprehension". they are just basic 'ad hominem abusive" or the like. yes, the very stuff you have been vocal in complaining about, you are using on a daily basis.



You are complaining about ME!!???

I am guessing that you don't realize that in just about every post you make you engage in ad hominem commentary. I don't think you know what the term means. Directly translated it means "To the Man" rather than "to the question". This for example is an ad hominem comment: "Has Evan never heard of curtains?". My reply was justified in that I had already clearly pointed out that I use such in our home.



Curtains of many types are not at all "transparent" to IR........ if the IR heats the curtain, it obviously isn't "transparent", although it may be poorly transmissive, or may in turn re-radiate. But a thick (not 'scrim") curtain is very effective. A curtain which thoroughly blocks visible light is probably going to be of use for blocking IR losses, although it may not be perfect.


Look up Sony Nite Shot. Most curtains are not only ineffective but they can actually increase heat loss. If the curtains don't reach the floor they may create a chimney effect causing much greater air circulation along the surface of the windows and in turn pumping heat out by radiation from the glass. For best results you need curtains that are properly made with a light fabric on the window side and a dark fabric on the inside.



Your own table appears to show that double pane (thermal type) windows are not hugely better than ordinary windows, particularly versus single "with" storm (I assume the "width" is a misprint for 'with".) No factors of ten here.


That isn't my table. It is from national standards used to compute heat loss.

You were expecting orders of magnitude? Sorry, no can do. You have to be content with improvements of 100 to 200 percent. Triple pane windows are popular here and they make a really big difference in the comfort level since with three panes the inside pane always stays above freezing. Not so with ordinary double glazed windows.

Feel free to ignore what I have to say but you will have a hard time disputing the principles. On a cost per sq ft basis upgrading windows will pay back faster than anything else you can do after weather stripping.

dp
02-13-2010, 12:05 AM
On a cost per sq ft basis upgrading windows will pay back faster than anything else you can do after weather stripping.

This is an immediate payback even if you don't change anything but the windows. Taping foam poster board over the windows will probably pay for itself in 90 days. We put up polyethylene screens outside over our Okanogan home's windows each winter and it makes an immediate difference in comfort and reduces heat loss by convection. Those windows are all single pane so anything is going to help as it gets bitter cold in that area.

J Tiers
02-13-2010, 12:41 AM
Say what you will... windows are NOT the "no brainer answer" in every case.

We got, from reputable folks who would LIKE to sell us windows, the information that they did not expect that their windows, or anyone else's, would pay back their cost.

And they are correct.... We already HAVE double windows, although not the newest plastic-framed "thermal" ones. Ours are the old style sash with outer storm, and the "energy audit" folks could find no leaks of any significance in them.

We would not experience the slightest usable improvement from replacing them, as the new ones would lose essentially the same heat as the ones presently installed. How would THAT ever pay back? The new ones would probably fail in a similar time period to the old ones which are still in good shape.

Basement windows were a different story... we had them replaced with glass block years ago, purely because the old ones were rusting out. That has made a 5 to 10 degree difference in basement temperature. The prior ones were very leaky old-style steel-frame windows.

Now, our neighbors also had a different story..... They have a newer post-war house, built on the old neighborhood tennis court. They had aluminum-frame single-pane windows, of a type common in newer houses of that era. The windows had ho thermal break in teh metal frames and settings.

The frames would get ICE forming on the inside of the FIXED part as well as the movable parts. Their large picture window was basically an open freezer door in the living room. Whoever designed those windows had simply no clue, or must have gotten the windows at a huge discount.

Our neighbors have now replaced every window, and the house is HUGELY improved. I don't think even Evan could have imagined how bad windows CAN be, if designed with absolutely no concern for insulation value.

In their case, it WAS an obvious no-brainer. But clearly they had an extreme, almost ludicrous problem.

My point is, AND IT CONTINUES TO BE, that it is IMPOSSIBLE to make a blanket statement as to what will definitely improve heat loss and heating efficiency without actually studying the house in question.

Anyone who pops up with "this solution is what you need to do", without examining the house, is either fooling themselves, or trying to fool you.

The study means a thorough examination, and preferably making quantitative measurements of leakage rate, air changes, etc.

If you LIVE in the house, you will already know much of what is needed, since you will know where the drafts are, where the cold walls are, etc. And that is very likely to be good info, almost as good as what a professional auditor would get. The real causes may be not what you think, but old houses are quiet commonly an interesting surprise.

if you have already added insulation etc, you may benefit from a calculation of the improvement from any proposed further changes. The tables, similar to Evan's, but more detailed, will give good guidance, and may even allow figuring the gas or oil savings from any given improvement.

Evan
02-13-2010, 02:39 AM
Anyone who pops up with "this solution is what you need to do", without examining the house, is either fooling themselves, or trying to fool you.


I haven't made any assumptions about the house in question. If you read back you will find I also have not made specific recommendations of what needs to be upgraded. What I have said it to examine particular areas that are often ignored. I presented options that are rarely considered concerning heat loss and you proceeded to dismiss them because you aren't familiar with the ideas the same as most people.

Radiation gains and losses are largely ignored, not because they don't exist but because they are not understood by even many well educated people. The moment you mention "black body radiation" eyes begin to glaze over. Mention "inverse 4th power" and bad memories of reports cards flash through people's heads.


My point is, AND IT CONTINUES TO BE, that it is IMPOSSIBLE to make a blanket statement as to what will definitely improve heat loss and heating efficiency without actually studying the house in question.



That is simply not true. Radiation gains and losses must be considered as part of a solution to insulating a house. Why do you think thermal scans are used so much? They work solely by imaging the heat that escapes by radiation from the outer envelope of the house. They don't measure convection or conduction. If radiation were not important then the FLIR images would be meaningless. There are very few houses that cannot benefit from additional radiation control measures. It is usually easy to do and often has the shortest pay back time.

The colder the climate the more important it becomes to properly manage radiation losses. The easiest and cheapest way to do that is to use radiative barriers, both inside and out. The space shuttle has large radiators on the inside of the bay doors. If for some reason they aren't able to open the bay doors it is an immediate mission abort. They only have about 3 orbits before it becomes so hot inside that systems begin to fail. This is because the shuttle is so well insulated by the reentry thermal management system.

If you could build a house that well insulated you wouldn't need a furnace. The heat from ordinary activites would be sufficient to heat your house.

dp
02-13-2010, 03:00 AM
Here's a great page that shows the greatest rate of heat loss per square unit is the windows. Obviously the windows are small relative to other surfaces, but they are clearly (bad pun) the highest offender. Not likely they'll give off as much heat as the roof which is cooler, but also much larger. But Windows are sooo cheap to insulate.

http://www.scotland.gov.uk/Publications/2009/03/20155542/4

And who better to ask than a tight fisted Scot? :)

J Tiers
02-13-2010, 11:44 AM
The best way to prevent window losses is to take out all the windows and fill them in with wall. Not very practical.

Windows are a big offender per unit area, of course. but, as DP admits, they are not necessarily the biggest NET loss on a section of the house.

I looked around as I went to work.... Many ,many houses had large wall expanses with only one or two smallish windows. Obviously the window was not the largest net loss on that wall, unless it was a really bad single pane with no storm.

In my own house, there are walls with a ratio of over 20 to one of wall to window area. The wall may exceed the worst window in net loss.

And, even the "most advanced" new window does not cut the normal window losses down "that" much.

Evan says the window is the lossiest part, and I don't argue with that..... But that is a far cry from saying that "new windows are an obvious no-brainer"......

To be a "no brainer", the window has to actually BE BETTER than the old one. otherwise you are just 'churning", spending money for no point.

if you have a wall with window loss equal to wall loss, but the window is already a good type....... Replacing the window will get you little or nothing. But the WALL may be able to be insulated better, which will actually have a payback.

The fact that the window still loses heat is only 'fixable" by boarding it up..... but if you can significantly cut the heat loss through the wall by blown-in insulation, or the like, you can win. You need to check the cost of insulation against the savings, and against the increased comfort, but there is a good chance you can get a net gain over the time you are in the house. And in the future, the house sale price may be better.

Evan: please tell me how your comment makes sense:


My point is, AND IT CONTINUES TO BE, that it is IMPOSSIBLE to make a blanket statement as to what will definitely improve heat loss and heating efficiency without actually studying the house in question.

your response:


That is simply not true. Radiation gains and losses must be considered as part of a solution to insulating a house. Why do you think thermal scans are used so much?

So doing an IR scan is NOT "studying the house"? Nonsense...... This makes even less sense than prior statements.

better quit while you are ahead..... You are making NO sense, as anyone can see, and I am getting quite bored.

I may not bother to look at this thread any more, so you probably have a free hand to 'get the last word'.

ptjw7uk
02-13-2010, 12:32 PM
In the UK you cannot have a habitable home that has no windows as the regs say you must have 1/20 floor area as window.
Mind you they are having problems keeping to regulations and keeping a buildings character intact.
Whatever happened to the vacuum sealed units that were abouit in the sixties! I expect they were to coctly to make.

peter

Evan
02-13-2010, 01:42 PM
Evan says the window is the lossiest part, and I don't argue with that..... But that is a far cry from saying that "new windows are an obvious no-brainer"......


So far you are the only one to say that, in your usual hyperbolic fashion that has nothing to do with anything anybody else stated.


So doing an IR scan is NOT "studying the house"? Nonsense...... This makes even less sense than prior statements.


Back pedalling now I see.

Incidentally there are excellent reasons to change perfectly good windows, especially ones that face to the north. If you have a room with windows to the north and some other direction making the north facing windows (in the northern hemi) smaller can be a big payback item. Also, breaking one large window into smaller lights can reduce the convection cells within double glazed windows. The smaller an individual light is the less heat it loses per unit area because convection doesn't operate as well.

Filling in windows is definitely an option and is one that I have used. I filled in one totally useless window in my basement grinding shop and installed a high intensity fluorescent light fixture in the spot with daylight bulb and a diffuser. It is very much like having some sunlight in the room and helps to fool the brain that it isn't really so dark outside in winter.

http://ixian.ca/pics7/window.jpg

dp
02-13-2010, 03:02 PM
The best way to prevent window losses is to take out all the windows and fill them in with wall. Not very practical.

Then it is not the best way, is it?


Windows are a big offender per unit area, of course. but, as DP admits, they are not necessarily the biggest NET loss on a section of the house.

Of all the means we have at our disposable to conserve energy, windows represent the best bang for the buck. Using the graphic from Scotland, 35% of the energy goes out the walls. What do you think it would cost to reduce that to 10%? 20%? 30%? Doesn't matter - it is not affordable and won't be done.

Windows can be improved dramatically simply by putting up any of a variety of curtains, drapes, poly sheeting, shutters, and more. And many of these solutions improve the appearance of the rooms. And they work for winter cold and summer heat.


I looked around as I went to work.... Many ,many houses had large wall expanses with only one or two smallish windows. Obviously the window was not the largest net loss on that wall, unless it was a really bad single pane with no storm.

They still represent the best investment. Insulating walls and attic spaces is hugely expensive and is not on the radar of a great many home owners, and doesn't show up even as a blip for renters. Window treatments appeal to renters and home owners so of all the possible heat loss vectors, windows are the ones that get the most treatment. It is not necessary to replace them to improve them. It is not possible to achieve the same level of efficiency as new windows by fiddling with old single-pane windows, but much can be done.


And, even the "most advanced" new window does not cut the normal window losses down "that" much.

Cite?


Evan says the window is the lossiest part, and I don't argue with that..... But that is a far cry from saying that "new windows are an obvious no-brainer"......

This does not compute. Of course new windows are a no-brainer.


To be a "no brainer", the window has to actually BE BETTER than the old one. otherwise you are just 'churning", spending money for no point.

It is irrational to introduce the notion that a buyer wishing to improve their energy loss situation will spend thousands to upgrade their windows and not consider they will achieve the desired result. You're struggling with this.


if you have a wall with window loss equal to wall loss, but the window is already a good type....... Replacing the window will get you little or nothing. But the WALL may be able to be insulated better, which will actually have a payback.

Or doing nothing in this case as doing the wall is not an option for many (renters).

J Tiers
02-13-2010, 11:45 PM
I did look back into this thread.....

DP, we are talking totally different things here......

I am talking about STRUCTURAL improvements. Actually changing some aspect of the house...... Like REPLACING windows. Or adding blown-in insulation, attic insulation, etc.

I took it that you and Evan were also talking about STRUCTURAL changes. The original poster seems to have those in mind.

ONLY things like that can make the house *as a structure* more efficient heat-wise. Whether or not they are "on the radar" for homeowners is irrelevant.

Sorry to break it to you, but if the house is insufficiently insulated, you need more insulation. You can do "work arounds", but the fact is if there isn't enough insulation, you need to add it. Blown-in insulation is a practical way to add insulation to a house with uninsulated walls, or walls "insulated" only with the so-called "insulating board" sheathing under the siding.

if the wall is solid, like brick, you don't have that option. Moving is your best bet. For a renter, moving is the ONLY choice, since structural changes won't be happening.

Replacing windows is widely touted as a "no-brainer", and is among the "structural" changes. But, as I pointed out, according to the table Evan himself showed, and his later admission, the best type 2 pane thermal windows are only around twice as good as the worst single pane. In other words, you get about a 50% cut in losses at best. if wall and window are equal, it is a 25% net cut. Significant, but only if you have bad windows.

if you already have exterior storms and tight windows, it is obvious that replacing the windows will net you a LOT less than the 50% reduction. It almost certainly won't pay in your lifetime.

if your windows are the bad type, it probably will pay off quite well, as it did for our neighbors, or for our basement windows.

But you cannot KNOW that without knowing something about the house. it is not possible to make a blanket statement that "replacing windows will save you "X" amount" unless you have knowledge of the house, by looking at it, measuring leakage, using IR, whatever. preferably all of those.


Now.....

YOU are talking about NON-structural things. That's totally different.

I already, long ago, mentioned the idea of tapestries, which are nothing but insulation hung up inside the structure. I have a small room in my brick house that has 4 side exposure, 3 walls and roof, in which I have jokingly threatened to hang up tapestries.... But a better approach would likely be to strip the plaster, and put up foam insulation, covered with wallboard, etc.

I've used the plastic over the window, etc, and it does work to an extent.

I've rented places where it did NOT work....... the windows were SO leaky that the plastic looked like sails on the Cutty Sark..... until they BLEW OFF the frames.

You are saying that the window may be the most effective because it is the only thing you can actually address... If that is the case, due to funds, renting, etc, you are correct.

But I took the OP to mean that he was interested in making actual physical structural changes if they made sense in a cost-benefit analysis.

If so, then he may or may not get the most bang for the buck in STRUCTURAL changes from replacing windows. We can't know, because we don't know about his house.

It may be that he needs attic insulation. or it may be that he has plenty already.... we don't know. Since the picture, IIRC was of a "semi-ranch style split level" house, the area of roof, and thus attic, is probably a very significant percentage of the total surface area, and worthy of consideration. the area of roof may be almost twice that of a two-story house with similar floor area.

Insulating an attic with rolled-out insulation batts is relatively cheap compared to many other 'structural" changes. And it can be done to part of the house at a time, as funds allow.

bsmith
02-17-2010, 05:28 PM
I happened to be looking over the www.buildingscience.com site and noticed this web page http://www.buildingscience.com/documents/insights/bsi-007-prioritizing-green2014it-s-the-energy-stupid where exterior walls are discussed.

We all agree that windows are a major culprit on home energy consumption. Nothing is more efficient than a home built like a refrigerator with no windows allthough such a home would be unhealthy in many other ways. Even so, it was funny to see the comment by Joe Lstiburek that "bad glass ruins good walls."

In Figure 1 on the above mentioned web page it can be seen that even very good and expensive energy efficient glass compromises greatly the overall energy efficiency of well insulated exterior walls. I guess the main lesson here is that if minimizing hvac operating costs is the primary goal then use the least amount of window area possible and use glass with as high of insulating quality as can be economically justified for the given situation.

aboard_epsilon
02-17-2010, 07:05 PM
what houses should have is automatic shutters that close at night so insulting the windows ..

just today ..i was sitting in the lounge ..the sun came out from behind a cloud.and my lounge gained 1.5 degrees C in a couple of Min's

so you could have heavy insulated bi-metallic controlled for simplicity .Venetian blinds..set so that they let the sun in in the winter.....when they are in the shade they close up.

all those thermal image heat loss pictures are for publicity ..

i would like to see one that is of a house using the new windows we have in the UK .some now are triple glazed, argon filled with coated heat reflective glass.

all the best.markj

JCHannum
02-17-2010, 09:20 PM
i would like to see one that is of a house using the new windows we have in the UK .some now are triple glazed, argon filled with coated heat reflective glass.

all the best.markj

You have to wonder what the carbon footprint created by the manufacturing of those looks like.