How Does A Heat Pump Work? | Rasmussen Mechanical

5 min readSep 1, 2020

A heat pump is a mechanical-compression cycle refrigeration system which operates as both a heating and cooling system. Think of a heat pump as a transporter which moves heat from place to place. When you’re done with this article you will be able to answer the questions: How Does a Heat Pump Work?

The Basics: How Does A Heat Pump Work?

In its most basic sense, heat pumps transfer heat by circulating refrigerant. Refrigerant undergoes evaporation and condensation during this process causing increased heat transfer. The compressor pumps refrigerant between two heat exchange coils. Refrigerant evaporated by lowering pressure which allows for heat absorption. On its way to the other coil the refrigerant compresses at a high pressure causing it to release the heat it absorbed earlier.

Heat Pump in Air Conditioning Mode

In the summer the heat pump removes warm air from inside the space and relocates it outside, thus cooling it. When functioning correctly, a heat pump will keep a space comfortable and cool while reducing the level of humidity inside. The process is as follows:

A motorized fan pulls warm air from the interior of the space into the ductwork.
The refrigerant is circulated via a compressor between the outdoor condensing units and indoor evaporator.
Warm indoor air then travels to the air handler while refrigerant is pumped from the exterior condenser coil to the interior evaporator coil.
Heat is absorbed by the refrigerant as it passes over the indoor air.
The dehumidified air is pushed through connecting indoor ducts to air vents throughout the space, cooling it.
This method cycles over and over making your space consistently cool and comfortable during the warm months.

Heat Pump in Heat Mode

Heat pumps are more common in areas with moderate temperatures. However, air-source heat pump technology has advanced, allowing these systems to combine with an additional heater. This makes them more suitable for areas with long periods of cold weather. When the heat pump switches from air conditioning mode to heat mode:

The outside coil functions as the evaporator and the indoor coil functions as the condenser.
The refrigerant flows through a closed system of refrigeration lines between the outdoor and the indoor unit.
Even when outdoor temperatures are cold, the condenser coil absorbs heat energy from the outside air and releases it inside by the evaporator coil.
A motorized fan pulls air from the inside of your space into ductwork.
Heat is absorbed from the air when the refrigerant is pumped from the exterior coil to the interior coil.
The heat is released from the refrigerant in the interior space due to phase change heats the air.
This method cycles over and over making your space consistently warm and comfortable during the cold months.

Advantages of a Heat Pump

Energy Efficiency: Heat pumps move heat energy rather than generate it, giving you more energy efficiency.
Lower Running Costs: Initial cost of a heat pump can be steep, but the increase in energy efficient results in greater long-term savings.
Less Maintenance: Heat pumps require less maintenance than combustion heating systems. You can perform most maintenance yourself.
Long Life Span: The average lifespan of a heat pump is around 15 years.
Tax Credit: In some states, you can receive a tax credit for installing alternative energy equipment, like heat pumps.

Disadvantages of a Heat Pump

High Upfront Cost: The initial cost of a heat pump tends to be more than some of its alternatives.
Can Be Difficult to Install: Without a little research you may not want to install a Heat Pump. The research generally examines the movement of heat. Specifically, local geology for ground source heat pumps, and the heating and cooling requirements for your space.
Cold Weather: Heat pumps cannot be used to their full capacity in extremely cold weather. Although there are possibilities of an upgraded heat pump system, which helps overcome this problem.

What are the Main Parts of a Heat Pump?

Before you can perform regular maintenance for your heat pump, it helps to know and understand the main parts.

Reversing valves change the flow of refrigerant, which determines if your interior space is cooled or heated.
Thermostatic expansion valves regulate the flow of refrigerant, just like a faucet valve regulates the flow of water.
The accumulator is a reservoir that adjusts the refrigerant charge depending on seasonal needs.
Refrigeration lines and pipes connect the inside and outside equipment.
Heat strips are an electric heat element that is used for auxiliary heat. A component that adds heat on cold days or helps recover from lower set back temperatures rapidly.
Ducts serve as air tunnels to the various areas of your space.
Thermostat or the control systems set your desired temperature.

Illustration of a Heat Pump¹

General Tips:

Set your thermostat to a consistent temperature. Constant adjusting can cause higher utility costs.
Do not set your thermostat lower than 65 degrees during heating months.
While in cooling mode, do not set the thermostat below 70 degrees. This may cause the indoor coil to freeze, leading to condensation on the floor and around windows.
Schedule regular maintenance with a technician every year.

Recommended Preventative Maintenance Checks

Not only will this checklist help your energy bills decrease, but you’ll see improved efficiency. You can now answer the question “how does a heat pump work?” and give advice on how to maintain it.

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