Wednesday, March 28, 2007

How Does a Heat Pump Work?

An air-source heat pump can provide very efficient heating and cooling for your home, especially in our hot humid climate. The U.S. Department of Energy offers a very good explanation of how a heat pump works and why it works so well in our region.

When properly installed, an air-source heat pump can deliver one-and-a-half to three times more heat energy to a home than the electrical energy it consumes. This is possible because a heat pump moves heat rather than converting it from a fuel, like in combustion heating systems.

How They Work

A heat pump's refrigeration system consists of a compressor and two coils made of copper tubing (one indoors and one outside), which are surrounded by aluminum fins to aid heat transfer. In the heating mode, liquid refrigerant extracts heat from the outside coils and air, and moves it inside as it evaporates into a gas. The indoor coils transfer heat from the refrigerant as it condenses back into a liquid. A reversing valve, near the compressor, can change the direction of the refrigerant flow for cooling as well as for defrosting the outdoor coils in winter.

When outdoor temperatures fall below 25- 30°F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. The efficiency and performance of today's air-source heat pumps is one-and-a-half to two times greater than those available 30 years ago. This improvement in efficiency has resulted from technical advances and options such as these:

• Thermostatic expansion valves for more precise control of the refrigerant flow to the indoor coil

• Variable speed blowers, which are more efficient and can compensate for some of the adverse effects of restricted ducts, dirty filters, and dirty coils

• Improved coil design

• Improved electric motor and two-speed compressor designs

• Copper tubing, grooved inside to increase surface area.

My advice is to make the most of your dollars you spend on your HVAC and invest in the savings that a heat pump can offer you.


Anonymous said...

My house was built in 1995.If I replace my AC unit with a 14 SEER. Do I need to replace my furnace also. In your opinion which is the best AC unit for your money. Heat pump is not for us. I don't want to be freezing if we happen to have a sub-zero temp. winter. Thank you so much

My name is Paul LaGrange.... said...

The questions you ask have a number of different answers depending on where you live. Regardless of your location, you should always match your indoor and outdoor units, which would mean you should replace both the condenser and the indoor machine at the same time to reap the benefits of the full 14 SEER. Air source heat pumps work well in the south, but in areas that have lots of sub-zero temperatures in the winter, ground source heat pumps (AKA geothermal heat pumps) are the most efficient. They are pricey, but they have a rather short payback period. Geothermal heat pumps get their cooling and heating from the ground temperature which stays constant througout the winter and summer. I would caution you, though, to find someone who is very familiar with servicing and installing these machines. This is not your everyday, run of the mill HVAC system. Also, there are federal tax credits associated with purchasing one of these systems. Check out our blog on how geothermal heat pumps work. Good luck!

Anonymous said...

I'm trying to understand how my heat pump works. It's 36 degrees here in Va beach. I'm running in the normal heat mode and sometimes the condensing unit Fan) is on when the inside air handler is off? Additionally, there are times when the reverse is true. The temperature in the house may be one degree lower than the set temperature and the air handler is blowing but he condenser fan is not. This is the first winter with this unit and I'm not sure it's working properly. The installer insists the unit is working properly. Please help!


My name is Paul LaGrange.... said...


In the heating mode, the condenser and indoor unit sould be running at the same time. Unless you have the fan turned to "on" instead of "auto". Make sure that your fan is in the "auto" position and if there is still a discrepancy between the indoor and outdoor equipments' run times, call your A/C man back and have him take a look at your heat pump.

Anonymous said...


We've just moved into a home that uses a heat pump for heating/cooling in Ohio. We are having temperatures in the 20's right now and I find the air coming out of the vents to be consistently cool. The thermostat reads about a degree or two lower than we have it set and the pump can't seem to catch up. In my research I see that these pumps aren't the most efficient with the weather I'm describing. Is there something I should do to supplement the heat to this home in the winters. Am I actually spending more on electric than I would with conventional heat?


My name is Paul LaGrange.... said...


I don't know if you have a geothermal heat pump or an air source heat pump, but it sounds like you do not have any "back-up" heat installed in your unit. I would recommend looking into installing back-up heat strips or making the unit a dual fuel heat pump (i.e. natural gas furnace that backs up the heat pump when it gets too cold). It is difficult to say whether you are spending more on electricity without seing your home and your energy bills. Please contact an HVAC subcontractor who is familiar with heat pumps and can offer some sound advice on your particular system.

kelvin said...


I am a mechanical student having interest in thermodynamics .I found your blog and related posts very useful and interesting .Please provide some information on solenoids also.

OleManErny said...

Hi Paul,

We have a heat pump for our house and it works quite well, but there is one peculiar thing... The drain pipe coming off the condenser (presume this is correct) just empties into the garage. So I have to use a bucket to catch the water and empty by hand. The house was built 10 years ago so it seems strange that this was not integrated into the plumbing or something more automatic.

Any idea if this is common or what a good solution would be?

Thanks in advance,

My name is Paul LaGrange.... said...

This is very odd, indeed. The pipe should be run completely out of the house or into the plumbing system.Is this the pipe from your emergency pan or from your air handler? If it is from your emergency pan, then you may have more problems if there is water in your pan. I would recommend having a plumber or handyman run the pipe outside and have an HVAC contractor look at the machine of you have water in your emergency pan. Good luck!

glenn said...

Paul ... I have a heat pump and aux backup heat. It seems like the aux heat runs more than the heat pump. The pump will come on for about 5 mins and blow Luke warm air then the aux heat comes on and warms the house . However my light bill runs four to five hundred dollars. This is killing me , last winter my bill was never over $250 .. any suggestions?

My name is Paul LaGrange.... said...

Do you live in a warmer climate, like in Louisiana or are you located up north? The answers to you question will vary depending on your climate.


glenn said...

I live in Mississippi .. we had a cold snap last month . But $500 a month? I'm in the poor house

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My name is Paul LaGrange.... said...

Chances are that your back-up heat strips are running instead of just your heat pump. You may want to have an HVAC contractor who is familiar with your particular brand of heat pump take a look at the wiring on the condenser. There is an outdoor thermostat that can often be adjusted so that the heat strips only come on when the temperature gets below 30 degrees. Heat strips are very expensive to run, so, without seeing your home, this would be my first thought as to what is causing your high bills. Hope this helps!

Mikes said...

As a result, a heating system that can operate with lower flow temperatures, such as underfloor heating which typically operates at around 55oC, allows the pump to maximize its effectiveness and minimize both its carbon production and the fuel costs for the homeowner.

Hvac contractors

Alexander said...

Good post very interesting. I have a heat pump, it saves me a lot of money.

Fire Fly said...

great post. thanks for the info.

Heat pumps have been evolving ever since they were first invented over fifty years ago. Since 1993, the Department of Energy more commonly known as the DOE and the Environmental Protection Agency (EPA) consider ground source heat pumps to be one of the most effective and environmentally friendly ways to heat and cool buildings.