What is a Heat Pump?

Okay let's get down to the basics. A heat pump is very similar to a residential air conditioner. So, then what is a heat pump? 

It uses the same equipment (compressor, fan, heat exchanger, etc.) and the same refrigeration cycle.

A heat pump does the opposite of an air conditioner. It pulls heat from a heat source (outdoor air, underground, ground water, etc.) and transfers it to the house, building, pool....or whatever surroundings you want to heat.

But there is something very cool about most heat pumps......it can also cool your surroundings!

By reversing the flow of refrigerant, one can obtain the effects as pictured below.

heat pump general concept

There are many types of heat pumps. The most common are:

- ground source
- water source
- air source

Both ground source and water source heat pumps are usually used in connection with geothermal energy. For more information, click on "geothermal heat pumps" on the left hand column. Geothermal is an exciting, money-saving, environmentally-friendly means of heating and cooling.

What is a heat pump that is "air source"?

These are very common in mild to warm climates. The downside to air source is that it can only be operated in temperatures above 40 F or 5 C. For this reason, auxiliary heating (such as electric or gas) may be needed for heating in colder weather.

How it works

Before explaining how a heat pump works, let's look at a standard residential air conditioner. Below is a diagram of a simplified air conditioner:

air conditioning concept

The evaporator is inserted into an air stream upon which air passes through a series of fins and tubes. The picture below is an example of an evaporator coil.

evaporator coil

The temperature of the refrigerant inside of the evaporator is less than the temperature of the air blowing across it.

The effect is cold air on a hot summer day!

But there is a problem.

The evaporator just absorbed heat from the air. Doesn't that mean the temperature of the evaporator is going to rise?


But we want the evaporator to be cold in order to keep the air cold. So we need to have a means of rejecting that heat.

Now enters......the compressor.

The compressor is a device that pumps refrigerant from the evaporator into the condenser (see the diagram above). The refrigerant leaving the compressor is hotter and has been compressed to a higher pressure.

The high pressure, high temperature refrigerant moves into the condenser, which is normally located outside. The condenser, condenser fan, and compressor packaged together are known as a condensing unit and is pictured below.

heat pump outdoor unit

As an example, let's say that the refrigerant in the condenser is 130 F or 54 C. The temperature outside will be lower than the temperature of the condenser refrigerant. The condenser fan moves outside air across the fins and tubes of the condenser. This process results in the air removing heat that absorbed in the evaporator.

Once the heat is removed from the refrigerant it moves back into the evaporator ready to absorb more heat from the home!

And the cycle repeats itself.

But that's an air conditioner.....what is a heat pump?

A heat pump uses the same cycle, except in reverse. Using a four-way reversing valve.

heat pump concept

Do you remember how the condenser rejected the heat that was absorbed in the evaporator?

A heat pump uses that condenser heat to warm up the home. So, instead of the condenser being located outside, a heat pump locates the condenser in the home.

Where is the evaporator?

You got it! Outside.

The compressor still moves the refrigerant in the same direction (evaporator to compressor, compressor to condenser, condenser to evaporator).

We just move the evaporator and condenser to different locations! We don't physically move them. We use a four-way reversing valve to do the trick.

Sounds simple, huh?

Well it gets a little more complicated.

Most heat pumps are designed to heat and cool a home, pool, or other space.

We'll save the complication for another page.

But hopefully this answered your question,

"What is a heat pump?"

If your curiosity isn't satisfied, click on "Heat Pump Info" on the left side of this page! Follow the links to the heat pump information that you're looking for.

Or take a look at this great video answering the question: "What is a heat pump?"

Return to Heat Pump Info

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