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View Full Version : OT Wired claims "Air-Conditioning Actually Emits Less C02 Than Heating"



gellfex
12-16-2008, 12:11 AM
This was linked from kunstlercast.com, a "Peak Oil" podcast and forum.

http://www.wired.com/science/planetearth/magazine/16-06/ff_heresies_02ac

Sounds like BS to me, I don't buy the premise that cooling is more efficient. There's lots of inefficiencies all along the line from generation, transmission loss, and the efficiency of the heat pump. A modern condensing gas fired boiler can be 95% efficient, so little heat goes out the vent that the pipe is PVC.

Anyone got a better grip on the numbers?

bruto
12-16-2008, 01:06 AM
I can see the point, but it's kind of a false dichotomy. It's not a contest. You don't win by saying "I can waste energy in Arizona because people have to use more in Minnesota." You're still consuming energy, and if you're doing it unnecessarily it doesn't matter how much crap the folks in Vermont and Michigan are putting up their chimneys to keep warm. It's still unnecessary.

dp
12-16-2008, 01:08 AM
I can see the point, but it's kind of a false dichotomy. It's not a contest. You don't win by saying "I can waste energy in Arizona because people have to use more in Minnesota." You're still consuming energy, and if you're doing it unnecessarily it doesn't matter how much crap the folks in Vermont and Michigan are putting up their chimneys to keep warm. It's still unnecessary.

You would think that would be the case, but Kyoto is exactly about that. It's a scam.

Evan
12-16-2008, 02:17 AM
Anyone got a better grip on the numbers

Sure. Heating with electricity is more efficient per degree of temperature deviation from ambient than any other possible method. Electric heat in the home is always 100% efficient and the transmission and distribution losses can be as low as 10% or even less. Large combined cycle power plants approach the Carnot limit within a few percent in some cases and if hydroelectric power is used then it is a renewable energy resource.

The real kicker though is the electric heat pump system. It's fridgeration in reverse and does what fridgeration can't do which is to multiply the energy used by applying mechanical advantage to the process leveraged from the environment. In a relatively warm climate multiplication factors of 2 to 3 times can be had with a heat pump system.

An air conditioner is limited by the temperature difference of the heat rejector and the ambient temperature. Radiation occurs as the forth power of temperature difference so a heater is many time further ahead than a cooler. The cooling coils must be kept above freezing or they will stop working in short order as they become covered in ice. A radiator in a heating system has no such theoretical problem. I measured the surface temperature of my gas heater and it runs about 600F. It is able to move more energy per sq foot of area than a cooling system of the same size. Also, a cooling system is bottom limited by absolute zero. A heating system has no such limitation and can be hot to an almost arbitrary degree.

The biggest factor though is the simple fact air conditioning is largely optional but in most cases heating is not. While it is possible to die of heat stroke it is also possible to avoid it by simple actions. However, if you are in a very cold climate heating is a requirement to live, not a luxury.

derekm
12-16-2008, 10:40 AM
Sure. Heating with electricity is more efficient per degree of temperature deviation from ambient than any other possible method. Electric heat in the home is always 100% efficient and the transmission and distribution losses can be as low as 10% or even less. Large combined cycle power plants approach the Carnot limit within a few percent in some cases and if hydroelectric power is used then it is a renewable energy resource.

The real kicker though is the electric heat pump system. It's fridgeration in reverse and does what fridgeration can't do which is to multiply the energy used by applying mechanical advantage to the process leveraged from the environment. In a relatively warm climate multiplication factors of 2 to 3 times can be had with a heat pump system.

An air conditioner is limited by the temperature difference of the heat rejector and the ambient temperature. Radiation occurs as the forth power of temperature difference so a heater is many time further ahead than a cooler. The cooling coils must be kept above freezing or they will stop working in short order as they become covered in ice. A radiator in a heating system has no such theoretical problem. I measured the surface temperature of my gas heater and it runs about 600F. It is able to move more energy per sq foot of area than a cooling system of the same size. Also, a cooling system is bottom limited by absolute zero. A heating system has no such limitation and can be hot to an almost arbitrary degree.

The biggest factor though is the simple fact air conditioning is largely optional but in most cases heating is not. While it is possible to die of heat stroke it is also possible to avoid it by simple actions. However, if you are in a very cold climate heating is a requirement to live, not a luxury.

Evan,
The biggy as regards heat capacity is the water vapour in the air. The Air con when it acts as a dehumidifier is extracting the latent heat of vapourisation. This is substantial.. 2.2 MJ/Kg... however very cold air means no water vapour.

I have a dehumidifier in my shop.

Derek in the relatively warm and damp UK

Evan
12-16-2008, 10:51 AM
The biggy as regards heat capacity is the water vapour in the air. The Air con when it acts as a dehumidifier is extracting the latent heat of vapourisation. This is substantial.. 2.2 MJ/Kg... however very cold air means no water vapour.



So what does that have to do with efficiency? Extraction of water vapour is a side effect of cooling as cooling is the desired result rather than drying (in most cases). Extreme humidity is mostly associated with proximity to warm water which includes the Atlantic coast area on both sides of the pond thanks to the Atlantic Conveyor circulation.

Lew Hartswick
12-16-2008, 10:53 AM
Talk about "convoluted reasoning" . I wonder if the underlying reasoning
is to try and get more people to move to the desert southwest. :-)

So: Don't all you folks believe it. Stay up there in the "frozen north"
and leave us alone here in Albuquerque etc. There are too many here
already. :-)
...lew...

derekm
12-16-2008, 11:25 AM
So what does that have to do with efficiency? Extraction of water vapour is a side effect of cooling as cooling is the desired result rather than drying (in most cases). Extreme humidity is mostly associated with proximity to warm water which includes the Atlantic coast area on both sides of the pond thanks to the Atlantic Conveyor circulation.

It has everything to do with it because:

Imagine a sealed room with people in it with just enough dry fresh air allowed to keep the people alive (sounds like modern living) The people are dumping some heat and quite a bit of water vapour into the room. the room temp is 15C but the desired temp is 18C

The options are:

just heat the room electrically with say 500w
use a dehumidifier with a max power consumption of 500w.

you will get more heat from the dehumidifier.... as we have a source of water vapour to extract heat from...

deHumidifiers are no good at heating very dry, very cold, uninhabited rooms (Who wants to heat them anyway). But once the room is close to temperature and inhabited... they work quite well at maintaining the temp...

And why would you want to live more than 70 miles from a sea that doesnt freeze ?:D

Evan
12-16-2008, 01:21 PM
deHumidifiers are no good at heating very dry, very cold, uninhabited rooms (Who wants to heat them anyway). But once the room is close to temperature and inhabited... they work quite well at maintaining the temp...


The heat coming from a dehumidifier is mainly waste process heat due to inefficiency, not latent heat of condensation. While water has a very high specific heat air doesn't hold that much water. At room temperature at sea level and 100% saturated humidity a cubic meter contains appoximately 20 grams of water.

If you remove half of that by condensation you gain about 1/4 kilocalorie of heat per gram or about 2.5 kilocalories. A teaspoon of sugar metabolizes to about 3 kilocalories of body heat so you would be better off to just add a spoon of sugar to your tea.


And why would you want to live more than 70 miles from a sea that doesnt freeze

My tools don't rust. Even steel left outside doesn't rust for several years. :D

derekm
12-16-2008, 04:46 PM
The heat coming from a dehumidifier is mainly waste process heat due to inefficiency, not latent heat of condensation. While water has a very high specific heat air doesn't hold that much water. At room temperature at sea level and 100% saturated humidity a cubic meter contains appoximately 20 grams of water.

If you remove half of that by condensation you gain about 1/4 kilocalorie of heat per gram or about 2.5 kilocalories. A teaspoon of sugar metabolizes to about 3 kilocalories of body heat so you would be better off to just add a spoon of sugar to your tea.



My tools don't rust. Even steel left outside doesn't rust for several years. :D


My shop is only 2.8 by 3 by 2.5m and this still gives 110 Kcalories or 1/8 Kwhr or in proper units 462KJ with your figures

but my dehumidifier extracts about 5 litres per day => 11MJ => 3Kwhr


True a heat pump working on the 30 tonnes of water immediately underneath the shop would be better... but we are getting there...

aah but the exhiliration of sailing on the sea on christmas day with ice on the deck and having a christmas dinner cooked afloat..
Well if you dont have "salt water in the veins"as my mother likes to say
you wouldn't understand....

Evan
12-16-2008, 05:15 PM
I was born in sight of the ocean and grew up there. However, I like rust free tools even better. :)