Heat Pump Guide – Air-Source, Water, Geothermal

A heat pump is an HVAC device that can transfer heat between locations – to both cool and heat.

Heat pumps move heat from one space to another to warm or cool a building; often more efficiently than other heating systems.

A heat pump can direct and reverse its flow of refrigerant to absorb heat and control the climate of buildings. The use of refrigerants to transfer heat from one place to another, using the refrigerant cycle, results in an incredibly efficient way to heat and cool a home.

A heat pump is an appliance, usually a pair of machines working together; one inside of the structure and one outside of the structure. This configuration is referred to as a heat pump split system, designed for controlling the interior environmental temperature, humidity, and air filtration of a structure.

A heat pump – also called a reversible heat pump – has the ability to reverse heat flow from outdoors to indoors. The key to a heat pump’s functionality is the four-way reversing valve, which changes the function of the evaporator and condenser sections of the unit, reversing the flow of refrigerant. A heat pump can both heat and cool; being able to pump heat back into the structure, which an air conditioner is unable to do without a refrigerant reversing valve. A heat pump does not add cold; it removes heat; transferring heat out for cooling the space or transferring heat in for warming a space. Sometimes, technically, cool-only split systems can still be referred to as heat pumps, since they are removing or “pumping” heat to cool a space. So, from a cooling perspective, minus a few technical details, heat pumps and air conditioning units are essentially the same when operating in cooling mode, with no significant difference in operation, efficiency, or energy costs.

How Does a Heat Pump Work?

Heat pumps use electricity to control the flow of the refrigerant which absorbs heat, circulating it throughout a building and transferring heat from one place to another.

Heat pumps do not create heat. They work by transferring heat from one place to another. Heat pumps use a refrigerant that circulates between the indoor unit and outdoor unit to transfer heat. A heat pump, by absorbing heat, is able to transfer heat between home’s indoors and the outside; transferring heat from the outside air, ground, or water into the home. In cooler months, a heat pump absorbs heat from the outside air and transfers it inside the home. In warmer months, it reverses the process, extracting heat from inside the home and releasing it outside.

A heat pump split system will have an air handler inside and a condenser unit outside. 

Within a heat pump, the condenser unit has three main functions:

  1. Enclose the compressor unit (an electric pump to circulate the refrigerant)
  2. Enclose the condenser coil (used to disperse heat to the outside in cool mode and to collect heat in heat mode)
  3. Move air through the coil using the fan unit.

Other parts involved with electrical, and refrigerant also reside here but are beyond the scope of this description. 

The air handler inside produces heat or cool air depending on the commanded mode. The air handler is made up of two main components:

  1. An evaporator coil (absorbs heat or emits heat depending on the selected mode).
  2. A fan assembly that moves air through the evaporator coil and onto the duct system).

The main chemical concept here is that refrigerant has two states, liquid under pressure and gas when not compressed. During compression, refrigerant heats up. During the release of the pressure, it gets very cold. The refrigerant constantly circulates through the system through piping. The condenser coil and evaporator coils are connected together as one circuit with this piping. The refrigerant is constantly circulating through both coils being pumped by the compressor pump. 

At a molecular level, the electrons and protons of warm air molecules (or any warm matter) circle the nucleus quickly. The electrons of a cooler matter (in our case, cooler refrigerant) are moving slower. So, the faster action of warm air electrons and protons energy transfers into the slower action electrons and protons of the refrigerant upon contact, thereby slowing down the faster by spending energy (causing the warm air molecules to slow down or cool). Hot goes to cold.

The pressurized refrigerant cools quickly when the pressure is released. So, we spray the high-pressure refrigerant into the inside of the evaporator coil using a metering device (small restrictive orifice, small capillary tubes, or a thermostatic expansion valve). This spraying releases pressure, causing the refrigerant to enter the evaporator coil in a very cold gas state. Now the evaporator coil has become very cold. As we force air through the coil, the cold coil absorbs the heat out of the air, making cold (air-conditioned) air to be distributed throughout the conditioned space. Now the refrigerant is warm and is circulated outside to the condenser coil to be forced away by the condenser fan unit. The refrigerant is then sent back to the evaporator coil to collect more heat. This is a constantly circulating system.

If we want heating mode, we reverse the direction of the refrigerant, and the whole process operates in a reverse manner. 

What Is a Heat Pump Evaporator?

The evaporator is the part of the heat pump that absorbs heat from the air inside your home. The cold evaporator absorbs the heat out of the passing air and into the refrigerant. This refrigerant is then circulated to the condenser coil, where it is compressed.

The evaporator is a low-temperature heat exchanger where the refrigerant enters as a low-temperature gas, absorbing heat from the heat source by contact. 

What Is a Heat Pump Condenser?

The condenser or condenser unit. The condenser unit contains a coil, a compressor motor, a fan unit, and other support components. The condenser unit’s purposes are to circulate the refrigerant and disperse collected heat.

A condenser unit (or AC condenser unit) is the outdoor portion of an air conditioner or heat pump that either releases or collects heat, depending on the command entered at the thermostat. Both split-system air conditioners and heat pump condensers are made of the same basic parts.

What Is a Heat Pump Compressor?

The compressor is the electric pump that keeps the refrigerant circulating through the system. It pumps the refrigerant in a gas state, putting it under pressure and creating a liquid state refrigerant, sending it from the condenser unit to the air handler evaporator coil.

What Is Heat Pump Expansion Valve?

The expansion valve (thermostatic expansion valve) is the part of the heat pump that regulates how much refrigerant flows into the evaporator coil. It helps maintain optimal operating pressure in the system so that it can operate efficiently.

Where Do Heat Pumps Work?

Heat pumps are popular in the Northeast and Midwest where temperatures vary, but are most effective in areas with a mild climate, where the temperature during the colder season typically remains above freezing. A heat pump can be combined with an existing gas or oil furnace to create a hybrid heating solution. A dual-fuel heat pump, or hybrid head pump alternates between traditional electric operation and a fossil fuel gas furnace to improve comfort and optimize efficiency, often paying for itself within three to five years. In this situation, as long as the heat pump is more efficient than the gas or oil furnace, it will be the primary source of heating. If the outside temperature drops too low for the heat pump to operate effectively and efficiently, the furnace will take over until the outside temperature rises. The ability of a hybrid heat solution to switch between the heat pump and the furnace depending on conditions makes it a leader in reduced energy consumption and costs.

At temperatures below freezing, heat pumps slow, and many are less efficient at lower temperatures. Heat pumps are best in the southern and coastal states where winters are mild, compared to furnaces which are better suited and preferred in northern locations.

Do Heat Pumps Work In the Winter?

A heat pump provides heat in the winter by extracting heat from the outside air and transferring it inside. In the summer, a heat pump works by reversing the process and extracts heat from inside the home and transfers it outside. This is possible because a heat pump has a reversing valve in the refrigerant circuit system that allows it to work both ways. During winter, it extracts available heat from the outdoor air and brings it to your home. At 0°F, a heat pump can still operate at 220% efficiency. Modern cold-climate heat pumps can heat a home efficiently at temperatures below -10 degrees. 

Effectiveness of a Heat Pump

The heat pump’s purpose is to provide the best possible comfort. This is achieved by controlling the temperature and humidity evenly, cleanly, and reliably. As time and technology advance, we look at the cost of acquiring this.

The main advantage of using a heat pump is the efficiency for both heating and air conditioning. A heat pump is one of the most efficient methods to heat and cool your home. HSPF – Heating Seasonal Performance Ratio is used to measure a heat pump’s heating efficiency. Heat pumps can be up to four times more energy efficient than traditional systems, and can save homeowners up to 50% on their energy bills. Heat pumps are also much quieter than traditional systems while requiring less maintenance. 

The new modern SEER2 heat pump systems are the ultimate climate control choice. These new designs provide extremely efficient operation, and when operated within the designed low and high outside temperatures, they can be completely and fully automated to maintain your inside climate while being trouble-free for many years with regular and correct maintenance.

Heat Pumps and the Coefficient of Performance

Heat pumps can be used for both heating and cooling, and the coefficient of performance (COP) is a measure of the efficiency of the heat pump in transferring heat from one location to another. The COP is calculated as the ratio of the heat output of the heat pump to the electricity input required to operate the pump.

In the case of cooling, the heat pump absorbs heat from the inside of a building and transfers it to a heat sink, such as the outdoor air or a body of water. This process is the reverse of heating, in which the heat pump absorbs heat from the outside air or a body of water and transfers it to the inside of a building.

The COP of a heat pump used for cooling is affected by the same factors as a heat pump used for heating, including the efficiency of the heat pump, the temperature of the heat reservoir, and the temperature difference between the heat reservoir and the conditioned space.

For example, a heat pump used for cooling in a warm climate will have a lower COP than a heat pump used for cooling in a cooler climate. This is because the temperature difference between the heat reservoir (outdoor air) and the conditioned space (indoor air) is smaller in the cooler climate, making it easier for the heat pump to transfer heat from the inside of the building to the outside.

By understanding the COP of a heat pump system, you can compare the energy efficiency of different heat pump systems and make informed decisions about which system is best suited for your cooling needs.

Why Choose a Heat Pump?

An energy efficient alternative to traditional HVAC systems for all climates, heat pumps offer heating, cooling, and dehumidification. Heat pumps operate by extracting heat from the outside air. While a traditional boiler system uses natural gas, propane, or heating oil, a heat pump will lower your heating fuel costs while requiring less maintenance than most fuel-source heaters.

Heat Pump Types

Heat Pumps, of which three main types exist, each with a unique use-case and implementation. Heat pump types are categorized as follows: air-source, geothermal, and water source. An air-source heat (AHSP) pump is the most common and most cost-effective option. A Geothermal heat pump (GHP) is more efficient, requiring more installation work while being more expensive. A water-source heat pump (WSHP) is most efficient and requires a water source to operate.

What is the Downside to a Heat Pump?

The main disadvantage of using a heat pump is the recent unstable cost of electricity, on top of the already higher price to run the units. Heat pumps may also not work well in extremely cold weather without the expensive emergency heat mode. Heat pumps that experience freezing may experience reduced efficiency; especially when temperatures drop below freezing. Although modern heat pumps have defrosting features that mitigate this. Also, if the system has any age at all, some people also find those heat pumps somewhat noisy when they are operating.

What Is a Heat Pump vs. a Furnace?

Heat pumps rely on electricity to transfer warmth from the surroundings, even when the temperature outside is low, and bring it indoors. Furnaces produce heat by burning either oil or gas. Heat pumps produce less heat in comparison to furnaces, and are best for use in milder climates, such as zones 1-3 on the U.S. Department of Energy climate zone map. Unlike a furnace which exclusively produces heat, a heat pump can both heat a home in winter and cool it in summer. During hot weather, a heat pump operates in an identical manner to an air conditioner by reversing the pressure and the flow of refrigerant through its coils.

Heat pumps do not require fuel or create their own heat like furnaces do; rather, they utilize electricity and refrigerant to acquire heat from the outside atmosphere and disperse it indoors.

What Is the Difference Between a Heat Pump and an Electric Furnace?

Furnaces provide heat in heat exchanger boxes inside the unit, traditionally through gas, oil, or electric power. A key distinction between a heat pump and a furnace is that the former can both warm and chill a home, while the latter is only capable of heating. Nevertheless, if the temperature outside gets too frosty, heat pumps may not be able to adequately heat up the residence.

Are Heat Pumps the Future?

While only about 1 percent of American homes currently have heat pumps, it is becoming the energy-efficient system of choice for many homeowners. Around 40% of new U.S. homes will have a heat pump installed in them, according to Fortune Magazine. When designed and installed properly, a heat pump can provide a great return on investment.