Free Energy from Air Heat Pumps – is that Magic?

October 30th, 2011 by Susan Kraemer

Moving back to my native New Zealand this year, I had the chance to try a different kind of heating system for our house here. One of the most intriguing technologies I’m hearing about here is something I never heard of – an air heat pump.

I was familiar with the very eco correct “geothermal” or ground heat pump, only because I write about green building. This pumps air through pipes that loop through your house and down about 5 feet underground where the temperature is a relatively constant 55 degrees F, summer and winter, from Maine to Miami, bringing up a moderate temperature, even though above-ground temperatures can veer from below 0 to over 100 through the seasons. Staying at a moderate 55 F year round makes it a lot easier to make up the difference (with heating or cooling) to the comfortable 65 or so that we humans evolved to like best.

So I was surprised to find that here, “air” heat pumps appear to be such a normal and everyday way to heat a home, that flashy advertisements vie for your attention in every hardware store, showing how comfortable and warm your family will be with a heat pump to complete the happy home.

But strangely, no marketing emphasis is put on the incredible energy efficiency of the air heat pump! Yet the only energy it needs is the small amount of electricity needed to drive the fan to squirt the heated air, and an air compressor.

It delivers more energy than a 100% efficient heater, which uses 9 kw of electricity to deliver 9 kw of heat. But heat pumps transfer 3 to 4 times the energy that it takes to operate, so they can deliver the same 9 kw of heating from under 3 kw of power.

They extract heat from ambient air outside, filter out particles, molds and pollens and bring heated, dried air inside, using a process a bit like the refrigerator working in reverse. Air heat pumps are controlled by a thermostat so you can adjust heating levels, just like with an actual heater.

That heat pumps can warm a home with no electricity for heating – even when it is colder outside than inside – makes them seem to work by something akin to magic.

The way it actually works is science. It’s kind of how a fridge works:

1. A refrigerant gas is contained inside a copper tube that runs from the outside to inside, and this gas has the ability to absorb heat from air.
2. The gas is passed through a compressor, which heats it up to over 140 degrees F.
3. The gas carries the heat through copper pipes that enter the house to be stored in the heat exchange unit.
4. Fans blow the heat in.

In the summer, you can simply run them in reverse, to cool the inside of the house, sending the heat out.

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Tags: air heat pump, efficient heating

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.

Charles

Susan
I live in Barbados and I have been trying to find coolers that are suitable for homes. This sounds very interesting. Where can I find more information. There is a scarcity of information on the web.
Jeremy R

If I didn’t live in NZ and also have a heat pump I would be confused by this sentence: “They extract heat from ambient air outside, filter out particles, molds and pollens and bring heated, dried air inside, using a process a bit like the refrigerator working in reverse.”

The part where you wrote: “bring heated, dried air inside,” makes it sound as though air comes from outside to the inside. I think you understand that is not the case but just wanted to clear it up.

The radon comment below should be retracted based on how impossible that there is any relationship between basements and heat pumps.
NickC

Important to note how outside temperature effects efficiency. The same principle that supplies the “magic,” decreases efficiency substantially with air source units as you approach the more extreme ends of the temperature spectrum. In Arizona if its 110 outside your air source heat pump will operate at much lower efficiently than its rated at, same things if its 30 degrees or colder outside. A place like San Diego? Perfect. For most of the country though backup heat is always required.
Anonymous

“It’s kind of how a fridge works:”

It’s exactly how a fridge works.

In ordinary heat engines,
High-temp thermal energy –> low-temp thermal energy + electrical energy.

Heat pumps reverse the process:
Low-temp thermal energy + electrical energy –> high-temp thermal energy.

Which is why air-source heat pumps don’t work so well in cold climes. The lower the temperature of the air, the higher the proportion of heat delivered has to come from electricity.
Crock48

I can see this being a viable option in some areas of the country but we also have to remember that Radon can exist below a dwellings basements so the air heat pump system needs to be highly evaluated depending on which area of the country you are in.
- Susan Kraemer
  
  No they don’t pull air from basements. Typically they are on an outside wall, piping the treated air in.
Dismissed

this is a poorly written article and difficult to read. there is so much information that is missing
Bob

I also live in Arizona USA like Susan who posted below. Since we have abundant sunshine, I heat my 1600 sq ft home with solar heat. I built 4×8 collector panels and force air through them into the home.
It is about as close to free heat that you can get and eliminated about 80 percent of the propane I had been using for winter..
Tom Garven

Susan:

I live in Arizona, USA and there are literally hundreds of thousands of heat pumps in the more moderate temperature zones in the U.S.[Nevada, Utah, California, Oregon, Texas, New Mexico, etc.]. These units are usually about 3 times more efficient than electric heating and the units work well down to about 35 degrees F. Newer models with a different refrigerant gas like R410 will operate down to about 10-20 degrees F and some companies are working on experimental models using CO2 which will work far below freezing. Newer heat pumps can be purchased with super-critical water heating units so you heat or cool your home while also heating your water.

I could not imagine living without my air source heat pump.
- Susan Kraemer
  
  Thanks, Tom. So, I guess I learned something by leaving – I never knew about air heat pumps while in the US. (It did seem odd that such a good idea would be unknown in the US!)
Colin

I used an “air heat pump” to heat and cool my 3500 Sq Ft house for some 15 years in a Northern Canadian location. Spring, Summer and Fall it worked as advertised, however, when outside temp dropped below -5C it stopped working and the bank of 8KW radiant heaters took over and then any overall power savings evaporated. I replace it with a very effective ground source system as soon as I could afford it.
Bob

What I understand is that a ground source heat pump is considerably more efficient than an air source type. I am 100 percent off grid and cannot use either due to start up power required to start the compressor.
- Anonymous
  
  Perhaps an inverter with a larger surge capacity? I picked my inverter based largely on how much surge power it could handle so that I wouldn’t have problems powering my shop tools.
  
  Or a ‘soft start’ controller on the compressor. My submersible well pump has a soft start ability which allows me to power it with smaller gauge wire between house inverter and well. Without the low surge I would have had to spend a heck of a lot more money for copper.
Anonymous

Isn’t that just another name for a reverse cycle air conditioner?
- Anonymous
  
  Basically, yes.
- Susan Kraemer
  
  Why don’t the companies simply call them air conditioners then? It is intriguing. Maybe air conditioners are less marketable here: even average people are very green.
  - Anonymous
    
    Air conditioners only cool spaces. Heat pumps are designed to work in two directions, to move heat in from the outside or heat out from the inside.
    
    Here’s a good overview. Looks like the first heat pump was built in the 1850s.
    
    http://en.wikipedia.org/wiki/Heat_pump#History
    
    Part of the issue might be NZ vs. US terminology. I think of most of NZ as having a moderate climate. Just the right place for heat pumps.
    
    Some place I’ve traveled calls air conditioners “chillers”. Took me a bit to figure out what they were talking about.
    - Susan Kraemer
      
      Terminology changes: tell me about it!
      
      In that case then, why don’t US air conditioner manufacturers use air conditioners/”heat pumps” to also move heat indoors in winter (and not just move heat outdoors in summer) if the technology is the same? Other than ground heat pumps, I am not aware of heat pump use in the US.
      - Anonymous
        
        Heat pumps have been in use for many years (decades) in the US. They probably slipped below your radar while you were visiting us here.
        
        But, thanks for bringing the concept of “free heat”. I had never thought of heat pumps in that way, and it’s right. Heat pumps can capture heat that’s lingering around outside and move it inside for less money than what it would take to make “new heat”.
      - Susan Kraemer
        
        A form of green energy that seems below everyone’s radar! I knew nothing about it, despite writing (and hence reading) about such matters for the last 4 years! While ground heat exchanges are well known.
  - Anonymous
    
    Heat Pump is a bit of a generic term… In Australia they’re just called reverse cycle air conditioners and it has been a standard feature for decades. It only requires a solenoid value within the unit to switch between heating and cooling modes. Perhaps the “name” has more to do with climate as I would expect (although I’ve never been there) that NZ is a fair bit cooler than Aust so heating is more in demand than cooling!
    
    In Aust there is also a range of hot water heaters that use a small AC system on top that are referred to as “heat pump” models. They are ALOT more energy efficient than conventional electric water heater as they ‘move’ heat rather than ‘make’ heat in a resistive element.
    - Susan Kraemer
      
      Yes, at least up around Auckland; temperatures are pretty moderate – about like the Bay Area of San Francisco. Never far too hot or freezing cold.
Doug

This really is nothing new, and certainly not free. It does consume power to run the condenser (compressor) and for the fan motor in the evaporator.
It is in fact, an air conditioner that essentially works in reverse.
There is no mechanical system that I know of that is more that 100% efficient, as you suggest. If this were true, we could heat or cool our homes with a heat pump, and send electric back to the electric company for a credit!
Wouldn’t that be sweet!
- Anonymous
  
  Well, there is an element of free heat. The heat is extracted from the outside air. There’s no charge for using that heat when it is available.
  Calling it a free heat source is something I haven’t heard before, but it’s technically correct. The condenser and fan are not creating heat, just moving it from one place to another.
Hakam_z

is the author talking about air-source heat pumps?
Anonymous

Heat pumps work great in some climates. Where it gets really cold then one has to add a heating element.