How Do Heat Pumps Work?

Many types of equipment used to heat a home do so by burning fuel to produce heat. A furnace keeps a home warm by burning oil or gas, for example. A boiler works by using fuel to heat water past the boiling point, converting it to steam.

Heat pumps are different. When comparing a heat pump vs. a furnace or boiler, one of the most important things to understand is that, unlike boilers or furnaces, heat pumps do not produce heat. Instead, they move heat — similar to how appliances like your refrigerator operate. If you are considering switching to a heat pump at your home, get to know more about how they work and the advantages of using one instead of other types of heating equipment.

What Is a Heat Pump?

The definition of a heat pump is a device that moves heat from one location to another. During the colder months of the year, a heat pump provides heat to a residence by transferring it from either the air outside or from the ground. Although the devices have the word “heat” in their name, they can also double as air conditioners. When it is hot outside, you can reverse the operation of the heat pump, so that it moves hot air from inside your home to the outside.

Heat pumps tend to be considerably more energy efficient when compared to other types of heating systems. Since they move heat instead of producing it, they are often able to heat the same size home as a furnace or boiler for about one-quarter of the cost.

Usually, heat pumps are recommended for homes in areas that have moderate temperatures, meaning in areas that do not get too hot in the summer or that do not see the temperature fall well below freezing in the winter. You can still install a heat pump in your home if you live in an area that does see freezing temperatures in winter or sweltering heat in the summer, though. You just might also need to install a back-up or ancillary heating or cooling system, too.

Heat pumps are typically made up of the following components:

Air handler: Heat pumps are divided into two primary parts: the indoor unit, or air handler, and the outdoor unit. The air handler can be attached to the ductwork in your home if you have it, or it can be a separate unit that is attached to a wall, known as a mini-split system. The unit contains a coil and a fan. The coil provides the heating and cooling while the fan spreads the heated or cooled air into the ducts or into the room.
Outdoor unit: The outdoor unit of a heat pump sits outside of the house, next to the wall. It also contains a coil and a fan. The fan in the outdoor unit blows warm or cool air from the source into the heat pump, allowing it to travel indoors to the air handler.
Compressor: The compressor is responsible for pressurizing refrigerant and forcing it to move through the heat pump system.
Refrigerant: Refrigerant courses through the heat pump system, either rejecting or absorbing heat.
Expansion valve: The expansion valve controls the flow of refrigerant through the heat pump.
Reversing valve: The reversing valve controls whether the heat pump is used to heat the home or to cool it.

How does a heat pump work in the winter? A heat pump uses the principle of heat transfer to effectively do its job. In the winter, that means transferring heat from one area, such as from the air outside or from under the ground, to the inside of a residence. In the summer, the process is flipped — the heat pump cools a home by transferring heat from indoors to the outdoors. Meanwhile, cool air is moved inside, lowering the temperature indoors.

The function of a heat pump is actually the same as the function of a refrigerator or air conditioner. The primary difference between an air conditioner or refrigerator and a heat pump is that refrigerators and air conditioners are only used to cool. Heat pumps, on the other hand, can both heat and cool.

A heat pump’s efficiency comes from its ability to pull the heat either from below the ground or from the air. Even when the temperature outdoors is what the average person would consider cold or chilly, there is still some heat to be found.

The simplest way to understand how a heat pump works is to describe it as a process of condensation and evaporation

How Heat Pumps Move Heat

When a heat pump is in “heat” mode, it pulls warmth from the air or ground, transferring it into your home. The process goes as follows:

Liquified refrigerant travels through the expansion valve inside the heat pump. As the refrigerant passes through the valve, it is transformed into a low-pressure gas-liquid mixture.
The refrigerant travels to the evaporator coil, which is located on the outside unit. It absorbs heat from the source (such as the air or ground). As it absorbs heat, it transforms into a vapor (gas).
In gas form, the refrigerant moves into the reversing valve, entering the condensing coil. In the condensing coil, the gas is further pressurized, which increases its heat.
As the warm refrigerant gas travels through the condenser, its heat travels into the air indoors. As the gas loses heat, it condenses, turning back into a liquid.
From there, the refrigerant moves back into the expansion valve, and the process repeats.

The less heat there is in the ground or air outside, the less a heat pump will be able to provide heat to the home.

How Heat Pumps Move Cool Air

You can reverse a heat pump so that it cools the interior of your home, rather than heats it. The process goes as follows:

Refrigerant moves through the expansion valve, transforming into a low-pressure gas-liquid mixture.
The mixture travels into the evaporator coil, which is now located on the inside unit. The refrigerant absorbs heat from the air indoors.
As the refrigerant absorbs heat, it eventually boils, transforming into a gas.
The gas moves into the reversing valve, then into the compressor, where it is pressurized. The compression causes the gas to heat even more.
The very hot gas moves into the condenser coil, which is now on the outside unit. There, it releases its heat into the air outside. As it loses heat, it turns back into a liquid.
Liquified refrigerant travels back to the expansion valve, and the process repeats.

When acting as an air conditioner, heat pumps also lower the humidity of the air indoors. Moisture from the air condenses on the surface of the indoor coil. It then collects in a pan beneath the coil before draining away from the heat pump.

Types of Heat Pumps

The most notable difference between heat pump types is the source of heat each one uses. Generally speaking, there are two main categories of heat pump: geothermal and air-source. Within each category are sub-categories, such as open-loop or closed-loop heat pumps. Take a look at how each type of heat pump functions.

Geothermal Heat Pumps

While the temperature of the air outside can fluctuate radically throughout the year, dropping below 40 degrees F in the winter and climbing above 90 degrees F in the summer, the temperature of the ground just a few feet below the surface remains somewhat steady. Depending on location, the ground temperature several feet below the Earth’s surface is between 45 and 75 degrees Fahrenheit year-round. A geothermal heat pump taps into the heat below the ground to keep homes warm in the winter.

Geothermal heat pumps have some advantages when compared to air-source types. Since ground temperature remains pretty much constant, a geothermal heat pump is often able to provide more consistent heating. Often, geothermal heat pumps have long lifespans and fewer maintenance needs. They also operate pretty quietly.

The two main types of geothermal heat pump systems are:

Closed-loop: A closed-loop heat pump sends a solution of anti-freeze through a closed, plastic tubing system that is either submerged in a body of water, such as a lake or pond or buried underground.
Open-loop: An open-loop heat pump system uses water, such as groundwater, as the fluid for heat exchange. It can be used in areas where there is an ample supply of clean water. Instead of cycling through the system, water flows in one end and back out the other.

Air-Source Heat Pumps

An air-source heat pump pulls heat from the outside air, rather than from the ground. Traditionally, they were not as effective at heating homes during very cold weather, as the air temperature is considerably less stable than ground temperature. For that reason, air-source heat pumps were once primarily found in areas that did not often experience freezing weather. Today’s air-source heat pumps are better able to effectively heat a home even when it is very cold outside, so the systems are now found throughout the U.S.

Ducted vs. Ductless Heat Pumps

A heat pump system can also be ducted or ductless. In a ducted system, the heated or cooled air travels through ducts that are located in the walls and ceilings of a house. Ductless systems have an air handler that distributes the cooled or heated air directly into the room it is located in.

If you are considering installing a heat pump in a new addition to your home, it can make sense to go with a ductless system so that you do not also need to run ductwork into the addition. However, if your home already has ducts and you are upgrading to a heat pump from another type of heating system, a ducted model might be more appropriate.

Advantages of Heat Pumps

Compared to other heating systems, heat pumps offers several advantages:

Improved efficiency: Since heat pumps transfer or move heat instead of burning fuel to generate it, they are usually much more energy-efficient than other heating and cooling systems. The fact that they do not rely on fossil fuels means they can also be a good pick for environmentally-conscious homeowners.
Lower energy bills: Heat pumps use less energy than furnaces or boilers, so your home is likely to notice a drop in your energy bills after installation. You also do not have to worry about keeping enough heating fuel on hand to power your heat pump.
Improved home comfort: Temperature is not the only factor that determines the comfort level of your home. Humidity also affects how comfortable a home is. Heat pumps are often better at reducing humidity levels compared to air conditioners. They are less likely to dry out the air excessively when used to heat the home as well.
Low-maintenance: While an annual inspection and cleaning are recommended to keep your heat pump operating at its peak, the systems are otherwise pretty low-maintenance.
No risk of carbon monoxide: Carbon monoxide is an odorless, colorless gas that can make you and your loved ones sick. It is produced when fossil fuels, such as gas or oil, burn. Since heat pumps generally run on electricity and do not burn fossil fuels, they do not produce carbon monoxide.

Is a Heat Pump Right for You? SMO Energy Can Help You Decide

There are many reasons why a heat pump might be the right option for your home in Southern Maryland. If you are looking to reduce your dependence on fossil fuels, a heat pump can help you do so. Heat pumps, particularly ductless mini-split systems, can also be good choices if you are interested in setting up separate heating and cooling zones in rooms throughout your home or if you are putting an addition onto your house.

SMO Energy offers installation and replacement of heat pumps and ductless mini-split systems, as well as many other options to keep your home comfortable all year round. Contact us today to learn more and to schedule a free, in-home energy consultation.