Waste Heat Recovery From Air Conditioners

August 29th, 2009 by Susan Kraemer

If you live in one of the states now sweltering through heat waves; even more frequent sweltering days are in your future as a result of climate change.

But it’s not only your children’s children who will suffer heat waves more often. Your property values in these states will also sink over time as your neighborhoods heat up to unlivable levels over the next decades.

A/C will be a necessity. But adding a heat recovery system will at least cut those losses to your home values:

Because it will save future owners half their energy costs.

Heating hot water can account 40% of your energy use. Your A/C unit makes excess heat in the process of cooling your home. Why use energy twice, if you can reuse it?

You can use your waste heat instead of the gas or electricity you now use to heat water, by putting an Enviro Pac waste heat recovery unit between the A/C and the water heater. These pick up the heat that your A/C generates as it it cools your home, and use it to heat water in your hot water tank.

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Tags: Build It Solar, climatewizard.org, Enviro-Pak, heat recovery systems, home values and climate change, most efficient air conditioners, regional climate predictions by state, why vote for cap and trade climate bill

About the Author

Susan Kraemer writes at CleanTechnica, CSP-Today, PV-Insider , SmartGridUpdate, and GreenProphet. She has also been published at Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times. Follow Susan on Twitter @dotcommodity.

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http://cleantechnica.com/author/susan Susan Kraemer

Great idea. It would be easy to incorporate the savings upfront. One company that does, though is PVT Solar that combines solar pv (electricity) with solar thermal for heat by Vinod Khosla
http://cleantechnica.com/author/susan Susan Kraemer

Great idea. It would be easy to incorporate the savings upfront. One company that does, though is PVT Solar that combines solar pv (electricity) with solar thermal for heat by Vinod Khosla
http://www.olivetreeenergy.com Thomas H. Hebert

With regard to previous comments, first, when an A/C system has additional condenser coil surface added, the efficiency goes up not down (if the friction related pressure loss is low), secondly, refigerators do not have enough compressor horsepower to provide significant amounts of recoverable heat, thirdly there is a waste heat recovery unit that produces more hot water over a years period of time than a pumped heat recovery unit, that has no pump or electrical input whatsoever (go to http://www.olivetreeenergy.com , to see). Finally, the maintenance costs alone, make this system more cost efffective than solar (or pumped heat recovery).
http://www.olivetreeenergy.com Thomas H. Hebert

With regard to previous comments, first, when an A/C system has additional condenser coil surface added, the efficiency goes up not down (if the friction related pressure loss is low), secondly, refigerators do not have enough compressor horsepower to provide significant amounts of recoverable heat, thirdly there is a waste heat recovery unit that produces more hot water over a years period of time than a pumped heat recovery unit, that has no pump or electrical input whatsoever (go to http://www.olivetreeenergy.com , to see). Finally, the maintenance costs alone, make this system more cost efffective than solar (or pumped heat recovery).
http://www.greenlifeanswers.com Dave Kay

The thermodynamics support the claim of improving compressor efficiency. As long as the rate of heat removal to the 55-degree water is greater than the rate of heat removal to, say, the 90-degree air the AC was designed to dump to(which should be the case, given the relative temperatures and heat capacities of the air and water), the refrigerant will return just as cool if not cooler. It really does reclaim “waste” heat.

But I agree that solar hot water heating seems a lot simpler than intercepting the refrigerant on a central AC — and the units might also keep your roof cooler if mounted on the roof!
http://www.greenlifeanswers.com Dave Kay

The thermodynamics support the claim of improving compressor efficiency. As long as the rate of heat removal to the 55-degree water is greater than the rate of heat removal to, say, the 90-degree air the AC was designed to dump to(which should be the case, given the relative temperatures and heat capacities of the air and water), the refrigerant will return just as cool if not cooler. It really does reclaim “waste” heat.

But I agree that solar hot water heating seems a lot simpler than intercepting the refrigerant on a central AC — and the units might also keep your roof cooler if mounted on the roof!
russ

The water heater connection is available from some AC models now.

Problem is that it only works when the AC is on and in the heating mode the AC (heat pump) has to run additional time.

Better to just have solar hot water panels. I turned off the electric connection to the hot water tank on 1 April and will turn it on again in November. Zero power except for a very small recirc pump.
russ

The water heater connection is available from some AC models now.

Problem is that it only works when the AC is on and in the heating mode the AC (heat pump) has to run additional time.

Better to just have solar hot water panels. I turned off the electric connection to the hot water tank on 1 April and will turn it on again in November. Zero power except for a very small recirc pump.
MD

Same could be said for a refrigerator too, yet no one does it for the same reason Jean explained…
MD

Same could be said for a refrigerator too, yet no one does it for the same reason Jean explained…
- Mike
  
  Not really, a refrigerator has nowhere near the same capacity as a home air conditioner. No one does it because its there is not much heat to be gained.
http://jean.posterous.com Jean

Recovering ‘waste’ heat from an air conditioning unit would decrease its efficiency, make the unit under-perform when most needed and eventually require more energy to compensate for the losses than recovered.

This is another one of these greats ideas that recover energy by wasting more energy than recovered.
http://jean.posterous.com Jean

Recovering ‘waste’ heat from an air conditioning unit would decrease its efficiency, make the unit under-perform when most needed and eventually require more energy to compensate for the losses than recovered.

This is another one of these greats ideas that recover energy by wasting more energy than recovered.
- Mike
  
  Jean, based on your statement it appears that you have no idea how neither an air conditioner nor a waste heat recovery system works. An air conditioner works by removing heat from inside a house to outside the house. Don’t believe me? Put your hand where the air exits the outdoor unit, that is the heat that is being removed from the house. That heat is just dumped into the outside air by the air conditioning unit (now keep in mind that it took a lot of energy to move that heat[running the blower, and the AC]). What this device does is takes this otherwise wasted heat and uses it to heat your water. Its free heat, or i should say heat that you have already paid for and putting it to use. This reduces the amount of energy you have to use for your water heater to heat up the water.