OT - GeoThermal Heating & A/C

[rws]

In the County where I work, they do a lot of geo thermals, and it is done by bored wells. Due to space constraints, there could be as many as 20 bored wells for a not so big building. Of course, these holes are bored by a well drilling rig, the loops are grouted in place, piping buried to the building. VERY expensive. But by golly they get those LEED points for it!

I guarantee most of the components will wear out and be replaced before they ever break even on costs.

[firbikrhd1]

In my opinion, the feasibility of geothermal depends greatly upon the circumstances. I installed a Florida Heat Pump geothermal type HVAC in my home in S. FL over 30 years ago. By today's standards it isn't as efficient as it should be but in my 1400 square foot house my electric bills have never been higher than $120/month and are generally less. My neighbors with similar sized homes bills are well over $200/month in summer.
Now I am building a new home in the mountains of NC. I checked out a geothermal system for that house since my FL one worked out so well. The recovery on investment in NC would be longer than I will be alive. The difference? In FL I went 26 feet for a good well (hit water at 8 feet) and my return line goes into a watershed behind my home so no need for a return well. In NC, the well for domestic water went 825 feet and got 1 GPM and cost $7300 for the well and casing alone, no pump. Even if 1 GPM was enough to satisfy the requirements of the system the cost of a return well would negate the cost effectiveness of the system. OK, so a ground loop system might be an option, except excavation costs, steep slopes and rock are an issue. With enough money you can do anything, build anywhere, but when it comes to return on investment an LPG furnace coupled with a high efficiency heat pump HVAC wins out in this situation.

[wmgeorge]

In the County where I work, they do a lot of geo thermals, and it is done by bored wells. Due to space constraints, there could be as many as 20 bored wells for a not so big building. Of course, these holes are bored by a well drilling rig, the loops are grouted in place, piping buried to the building. VERY expensive. But by golly they get those LEED points for it!

I guarantee most of the components will wear out and be replaced before they ever break even on costs.

The loops will never "wear out" the equipment which are compressors and fan motors will of course but they are inside... life on those items depend on the usage but will be 15-20 years and that seems to be what they are getting out of the ones already installed.
Cost effective and pay back? After working in the field doing service work for nearly 30 years, I taught for the last 12 years before I retired. Had the privilege of working with some pretty smart engineers working for the state of Iowa. They did the math, proved its economics and convinced me to introduce geothermal into our HVAC program. In the mean time this State was replacing old systems in state owned buildings with geothermal. New state owned buildings were built with geothermal from day one when they had the space for either the ground loops or wells. The installed loops and wells are not that expensive. Backhoe work and plastic pipe is cheap. The City I live in uses geothermal in all its schools. Must be a reason.

[rws]

Of course the loops won't wear out. I meant the compressors, valves, pumps, etc. So after spending over $50K to sink a bunch of wells, you're saying how many years it will take to offset the electric costs over air exchanged units?

Backhoe work is not that cheap, you need the real estate to put in it. Plastic pipe, yes, that's cheap.

[wmgeorge]

Well I just covered the wear on the compressors and fan motors, about the same as a standard AC unit and high efficiency gas furnace about 15-20 years. You realize the wells are not lined nor bored as a standard water wells? Just a 12 inch (or smaller) bore hole that stays open long enough to shove a pre plastic welded loop down, once it is down the top is sealed with Bentonite grout, when the wells are in and grouted the home runs back to the mechanical room are also thermally welded. Wells are much cheaper than your standard water well. Usually in this area one 200 ft well per 12,000 Btu's is required. Three ton standard size for residential system requires 3 wells and the plastic pipe and connections. I've been away from it long enough I don't have current prices but it used to be about $2,000 per well plus the trenches. The pumps are cheap and inexpensive to run, all they need to do since it is a sealed system is just push the water around the loop. I've seen systems with pumps as small as 1/6 hp.
Residential areas, they can put bore holes under the driveway, front and back yards. Holes can be drilled at an angle. In fact they can horizontal bore a loop system around your building All depends on the soil they have to work with. Usually the "Looper" will contract out just to put in the loops or wells and the rest of the dirt work. The rest is done by the HVAC installer. Takes a couple years for the ground to settle in around the plastic pipe at that time you will start to get the maximum heat transfer to and from the ground.

[Guido]

If'n I remember a twit of college thermo, efficiency of heat transfer from one medium t'other is best when the temperature differential is at a maximum. The earth/groundwater in Florida is relatively warm compared to earth/groundwater temperatures in, say Minnesota. Slick salesmen will juggle the numbers, always in their/your favor.

Concerning ground loops, best to visit with a driller/installer who's been raised and bred locally, and knows the area like the back of his hand. Whole lotta luck is involved when putting a plastic loop in a mud filled borehole, versus a borehole requiring grouting, versus a hole which is hammered through hard/soft rocks of all sizes. We've worked more than one project where the driller threw up his hands, and walked away. Infinite possibilities, which cost money. How's your luck?????????? YMWV

[wmgeorge]

Geothermal is not for everyone or every location. I'd hope that anyone I hired to do the ground work as a Looper would know enough not to put in a system in rocks or rocky soils. I'd also pick someone with a professional track record in geothermal not just the low bidder. In Iowa drillers have been required for many, many years to file reports with the state on the core samples they bring up.

[becksmachine]

Now I am building a new home in the mountains of NC. I checked out a geothermal system for that house since my FL one worked out so well. The recovery on investment in NC would be longer than I will be alive. The difference? In FL I went 26 feet for a good well (hit water at 8 feet) and my return line goes into a watershed behind my home so no need for a return well. In NC, the well for domestic water went 825 feet and got 1 GPM and cost $7300 for the well and casing alone, no pump. Even if 1 GPM was enough to satisfy the requirements of the system the cost of a return well would negate the cost effectiveness of the system. OK, so a ground loop system might be an option, except excavation costs, steep slopes and rock are an issue. With enough money you can do anything, build anywhere, but when it comes to return on investment an LPG furnace coupled with a high efficiency heat pump HVAC wins out in this situation.

Not wanting to ruffle feathers here, but you are assuming that you would also use a "pump and dump" system in the North Carolina location. The point here is that you don't need to find water in the hole you would drill/dig/make to use for a ground source heat pump. It is just a different way of creating a ground loop that doesn't take up as much area as a trench system. Consequently a 100'-300' foot hole, dry or wet, will work just fine and certainly cost less than drilling 825 feet!

Holy cow, what does it cost just to change out a pump?? I would assume this needs to be a high budget submersible unit?

Also, one clarification here, for myself as well. wmgeorge has stated

A 1 HP compressor will transfer 12,000 Btu's of heat either one way or the other.

This would seem to be somewhat misleading as it does not account for difference in "desired effect" between heating mode and cooling mode. Assuming that the 12,000 btu figure is correct, in cooling mode, the amount heat rejected from the structure is somewhat less than this as the heat generated by the system also needs to be rejected. Thus the cooling effect is somewhat less than the stated 12,000 btu's

This is just the opposite of the heating mode, where the heat generated by the unit is utilized to achieve the "desired effect", thus resulting in a heat input to the building greater than 12,000 btu's.

Or am I looking at this wrong?

Dave

[Sophiedoc]

We have had vertical loop GSM for early 24 year in central Missouri.Some observationsoes lower energy bills.Cooling more efficient than heating.When backup electric coils go on @ around 25 degrees the meter spins.Leave it @ same temp day and night as recovery time is much slower than conventional system.Don't waste the money on the hot water heat reclaimer unless you have a water softener or water low on minerals as the system clogs up frequently.(Not the main system -only the heat reclaimer.)

[wmgeorge]

We have had vertical loop GSM for early 24 year in central Missouri.Some observationsoes lower energy bills.Cooling more efficient than heating.When backup electric coils go on @ around 25 degrees the meter spins.Leave it @ same temp day and night as recovery time is much slower than conventional system.Don't waste the money on the hot water heat reclaimer unless you have a water softener or water low on minerals as the system clogs up frequently.(Not the main system -only the heat reclaimer.)

The cut in temperature for the back up heat can be changed. Plus you have an older system newer ones are more efficient but it would not be cost effective to replace until it fails. Yes liming of the hot water heater is a known issue of not just geothermal but any water heating system in our areas.

[wmgeorge]

Not wanting to ruffle feathers here, but you are assuming that you would also use a "pump and dump" system in the North Carolina location. The point here is that you don't need to find water in the hole you would drill/dig/make to use for a ground source heat pump. It is just a different way of creating a ground loop that doesn't take up as much area as a trench system. Consequently a 100'-300' foot hole, dry or wet, will work just fine and certainly cost less than drilling 825 feet!

Holy cow, what does it cost just to change out a pump?? I would assume this needs to be a high budget submersible unit?

Also, one clarification here, for myself as well. wmgeorge has stated

This would seem to be somewhat misleading as it does not account for difference in "desired effect" between heating mode and cooling mode. Assuming that the 12,000 btu figure is correct, in cooling mode, the amount heat rejected from the structure is somewhat less than this as the heat generated by the system also needs to be rejected. Thus the cooling effect is somewhat less than the stated 12,000 btu's

This is just the opposite of the heating mode, where the heat generated by the unit is utilized to achieve the "desired effect", thus resulting in a heat input to the building greater than 12,000 btu's.

Or am I looking at this wrong?

Dave

Dave a Pump and Dump well system is really not the best because of minerals in the water tend to clog up the heat exchanger, a lake or pond (soft water) would be a better choice. The pump would also need to be much larger since your pumping up and out, not back into a loop. Larger pump, more expense running. Sealed loop system is really the better way to go.
Actually 12,000 Btu's of cooling would generate slightly more heat, when gas is compressed it becomes hotter... heat of compression. Also since the compressor is suction cooled from the returning cool gas, it also picks up heat from the motor windings.
My complaint with any heat pump system is the discharge air in the heating mode is really not hot, more like 95-110 degrees, some people call it cold air. The newer units with the variable speed ECM motors take care of a lot of that cold air complaint problems.

[Boucher]

There are lots of different ways to implement the earth coupled heat pumps. Some vary with the geographic/geological location. The fundamental benefit is that it is cheaper to move energy than to create it. There are probably more incopetent contractors than good ones but that is getting sorted out.
Around here the plumbing is a looped 1 1/4" poly pipe that is grouted into the drill hole using thermally enhanced grout. It is filled with a enviromentally friendly antifreze solution. A 1/12 hp pump is all that is needed to overcome the pipe friction. The systems are very quite and the temperature much more uniform than convental systems. Cost savings on a 2500sf home runs $400-$500 per month and takes around 7 years to break even dollar wise.

[epanzella]

[QUOTE=Boucher;898240]There are lots of different ways to implement the earth coupled heat pumps. Some vary with the geographic/geological location. The fundamental benefit is that it is cheaper to move energy than to create it. There are probably more incopetent contractors than good ones but that is getting sorted out.
Around here the plumbing is a looped 1 1/4" poly pipe that is grouted into the drill hole using thermally enhanced grout. It is filled with a enviromentally friendly antifreze solution. A 1/12 hp pump is all that is needed to overcome the pipe friction. The systems are very quite and the temperature much more uniform than convental systems. Cost savings on a 2500sf home runs $400-$500 per month and takes around 7 years to break even dollar wise.[/QUOTE
You're right on the money with the payback interval. When I installed my system 7 years ago the payback worked out to about 12 years but numerous rate increases have me on track to break even late next year then it's all gravy.

[JeffKranz]

Thanks for all the good info on this - I didn't really expect to get this much response. I think that I will now ditch the idea of the hot water warmer idea - I really think since I have natural gas in the house, it would be cheaper to just heat water with that system. One of the guys I work with said he had to replace a pump and the cost of the pump and the original hot water tank on his GeoThermo system, could no way payback the $'s he would save using a normal hot water tank (either electric or Natural gas).

I'm a little concerned with the contactor the builder is using since he gave me his quote and the detail was almost blank. I am going to call him and discuss before the final decision is made but with the tax credit from our government I think the payback would be in the 5-6 year. The total cost difference between a standard Heat / AC system and the Geothermal system after rebate is about $4500. Since my soil is 100% sand, and the water table is pretty high, I should have conditions that are good for the thermal transfer.

I would think the trench should be around 5-6' deep and I have plenty of real estate to put these in.

[wmgeorge]

Thanks for all the good info on this - I didn't really expect to get this much response. I think that I will now ditch the idea of the hot water warmer idea - I really think since I have natural gas in the house, it would be cheaper to just heat water with that system. One of the guys I work with said he had to replace a pump and the cost of the pump and the original hot water tank on his GeoThermo system, could no way payback the $'s he would save using a normal hot water tank (either electric or Natural gas).

I'm a little concerned with the contactor the builder is using since he gave me his quote and the detail was almost blank. I am going to call him and discuss before the final decision is made but with the tax credit from our government I think the payback would be in the 5-6 year. The total cost difference between a standard Heat / AC system and the Geothermal system after rebate is about $4500. Since my soil is 100% sand, and the water table is pretty high, I should have conditions that are good for the thermal transfer.

I would think the trench should be around 5-6' deep and I have plenty of real estate to put these in.

Jeff those are ideal conditions for a geothermal system. Most of the time either with Water Furnace or Climate Master (and others) the cost of the add on inside the unit itself to heat water is not adding much to the system cost. Have your installer break down the costs. You can always use the geo to pre-heat the water that feeds your natural gas water heater. Make sure the geo installer has done all this before. If your going though the builders general contractor for all this I'd really do some double checking on his qualifications. Get it in writing. BG

PS It depends on Code where you are located. Some areas you can not have a direct heat exchange from a refrigerant condenser to potable water ( for human consumption). They would need to use a hot water to water heating exchanger, not worth the expense in your case, probably.