How Does a Heat Pump Work?
Heat pump. The name sounds pretty cool. But what are they? Heat pumps use the same technology as air conditioners and share many of the same components. You can think of a heat pump as an air conditioner running in reverse but to make it all work a few extra components are required.
When Should You Consider a Heat Pump?
Heat pumps don’t make sense in every situation. They cost a little more upfront, have more mechanical components, and become less efficient as the temperature gets closer to freezing, but when used in the right situation they can save a lot of money on energy. The best uses for heat pumps are in relatively temperate areas such as the mid-atlantic or southeast where winter temperatures are usually between 35 and 50 degrees fahrenheit. An additional consideration is what energy sources you have available. The table below can help you decide whether a heat pump might make sense for your home.
| Energy Source | Heat Pump Recommended? |
| Electricity Only | Yes |
| Electricity and Natural Gas | No |
| Electricity and Propane | Hybrid Heat (Heat Pump and Gas Furnace) |
When natural gas is available it is generally the most cost-effective way to heat your home, and the extra cost of a heat pump will take longer to pay for itself. When propane is available it is usually quite expensive but provides more efficient heating than electricity so a hybrid heating solution is recommended. Hybrid heating uses the heat pump as the first stage of heating and then transitions to the propane furnace as the temperature gets near freezing. If electricity is your only method of energy then a heat pump will save you a lot of money over electric heat strips.
Heat Pump Components
Standard A/C Components
- Compressor – A/C works by compressing and expanding refrigerant. When refrigerant is compressed heat is created, when the pressure is released cold is created.
- Expansion Valve – The expansion valve releases the pressure created by the compressor creating a cooling effect at the evaporator coil.
- Evaporator Coil – The evaporator coil is a series of bends and fins designed to create the largest surface area possible in a compact space to transfer cold from the expanded refrigerant to the air passing through the coil.
- Condenser Coil – The condenser coil is a series of bends and fins designed to create the largest surface area possible in a compact space to transfer heat from the compressed refrigerant to the air passing through the coil.
Additional Heat Pump Components
- Reversing Valve
- Additional Expansion Valve – An additional expansion valve is located in the outside unit to allow compressed refrigerant pressure to be released before it is compressed again to create heat. The cooling effect created by the release of pressure is transferred to the air through the outdoor coil (condenser coil in A/C mode becomes the evaporator coil in heat pump mode).
- Defrost Control – Heat pumps must be defrosted during a normal running cycle because the normal outside air can’t remove enough of the cooling effect created by expansion of the refrigerant at the evaporator. When the defrost control board senses the coil needs to be defrosted the system goes back into A/C mode and the electric heat strips are activated to counteract the effect of the A/C in the home.
- Outdoor Thermostat – Since heat pumps become less efficient as it becomes colder outside, multi-stage heating is used. The indoor thermostat is setup to discontinue the use of the heat pump at a certain outdoor temperature (such as 38 degrees) and continue heating the home with second stage heat (usually a gas or electric furnace).
- Accumulator – The compressor is only designed to compress liquid refrigerant. In the heat pump operation mode the compressor is likely to see vapor as well as liquid and the accumulator allows this vapor to settle into a liquid state before entering the compressor.
