How Does a Heat Pump Operate?

When you think about cooling a hot building, your first thought might be an air conditioner. However, heat pumps can both heat and cool a building — but how exactly do heat pumps work?

Simply stated, a heat pump is a device that moves heat from one location to another using minimal energy. This process isn't complicated. Heat pumps generally extract heat from the air or ground to warm a space, but they can also be reversed to cool it down.

If you're familiar with how an air conditioner works, you're already halfway to understanding how a heat pump operates. Heat pumps and air conditioners function in remarkably similar ways.

A major advantage of using a heat pump over a traditional HVAC system is that you don't need separate units for heating and cooling. Heat pumps are highly efficient because they transfer heat rather than generating it through burning fuel. This makes them more eco-friendly than a gas-powered furnace.

Heat pumps don't just regulate temperature — they excel in moderate climates. So, if you live in an area with mild temperatures, using a heat pump could help you save on energy costs each month.

Keep reading to learn more about how one of the most widely used types of heat pumps functions.

Heat Transfer and Air-Source Heat Pumps

Although there are various types of heat pumps, they all share a fundamental principle: heat transfer. Instead of burning fuel to produce heat, a heat pump moves heat from one location to another. The process relies on thermodynamics, which states that heat naturally moves from hotter areas to cooler ones.

A heat pump works by using a small amount of energy to reverse this process, drawing heat from a cooler environment and pushing it into a warmer space. Essentially, heat is transferred from a source — like the air or ground — into a sink — such as your home.

One of the most widely used types of heat pumps is the air-source heat pump. These devices pull heat from the outdoor air and circulate it inside using refrigerant-filled coils, similar to those found on the back of your refrigerator. The air-source variety is relatively simple, featuring two fans, refrigerant coils, a reversing valve, and a compressor to facilitate the process.

The reversing valve is the key component that enables the air-source heat pump to cool. This adaptable part changes the direction of the refrigerant flow, allowing the system to function in reverse. Instead of pushing heat inside your home, the heat pump releases it, just like an air conditioner. When the refrigerant flow is reversed, it absorbs heat from the indoor unit and moves outside, where it releases the heat. This process cools the refrigerant, which then flows back indoors to collect more heat. The cycle repeats, keeping you comfortably cool.

Ground-Source and Absorption Heat Pumps

By now, you understand that air-source heat pumps use an external fan to draw air over refrigerant-filled coils. Two sets of these coils move the heat indoors, where a second fan blows the air away from the coils and disperses it throughout your home, providing cool relief. Some air-source heat pump systems feature a single packaged unit containing both sets of coils, all housed in one box. This unit is typically installed on the roof of a building, with ductwork extending through the walls. Larger systems for commercial buildings are often set up this way.

Residential heat pumps generally feature a split system, with components installed both outdoors and indoors through the wall. Depending on the system type, it may include one or more indoor units to distribute heat throughout the space.

Ground-source heat pumps (also known as geothermal heat pumps) work a bit differently. They capture heat from the earth or an underground water source and move it indoors — or vice versa. The most common kind of ground-source heat pump extracts heat directly from the ground via pipes buried underground, filled with water or refrigerant.

These liquid-carrying pipes come in two types: closed-loop or open-loop systems, and they function exactly as their names imply. In a closed-loop system, the same refrigerant or water circulates repeatedly through the pipes. In an open-loop system, water is pumped from an underground source, such as a well or man-made lake, and heat is extracted from it. The water then returns to the well or lake, and more water is drawn to continue the cycle in an open loop.

If you're seeking something more advanced, consider the absorption heat pump — a type of air-source pump powered by natural gas, solar power, propane, or geothermal-heated water instead of electricity. These pumps, typically used in large-scale applications, are now also available for residential use.

The main distinction between a standard air-source heat pump and an absorption pump is the method of operation. Instead of compressing a refrigerant, an absorption pump absorbs ammonia into water, which is then pressurized by a low-power pump. The heat source causes the ammonia to boil out of the water, and the cycle begins anew.

When evaluating an absorption heat pump, it’s important to understand how they’re rated. Manufacturers use a metric called the coefficient of performance (COP), which may sound complex. However, all you need to remember is to look for a COP of at least 1.2 for heating and 0.7 for cooling. Don't worry, we'll also cover ratings for standard heat pumps later on.

While air-source, ground-source, and absorption heat pumps are the most common types, they may not be suitable for every situation. Keep reading to discover other kinds of heat pumps.

Other Types of Heat Pumps

If your home lacks air ducts for heat distribution, don’t worry. Consider installing a unique type of heat pump known as a mini-split heat pump. It connects an outdoor air-source unit to multiple indoor units, which can be linked to water or space heaters. These ductless mini-split systems are ideal for retrofitting homes with heat pump technology, offering flexibility in their placement both inside and outside the home.

Another benefit of mini-split systems is that the installation only requires a small 3-inch (7.6-centimeter) conduit to pass through the wall, making it relatively unobtrusive. These systems are versatile, as indoor air handlers can be mounted on walls, ceilings, or floors — and they’re compact. However, the installation does occupy some indoor space, and they do not circulate as much air as larger heat pumps, making them best suited for smaller living or commercial spaces.

While most heat pumps use air, the reverse cycle chiller (RCC) design uses water, making it more efficient in colder climates. In an RCC system, the heat pump connects to an insulated water tank, heating or cooling it as needed. A fan and coil system then circulate the heated or cooled air through ductwork to various heating zones in the home.

RCC systems can also circulate hot water through a radiant floor heating system, which is especially beneficial in cold climates during the winter months. So, when your feet are cozy on a warm tile floor this winter, you can thank these cold-climate heat pumps for the comfort.

In a standard air-source heat pump, a backup burner is used to provide temporary heat when the system switches to reverse in order to defrost the coils. This backup burner prevents the system from blowing cold air through the vents during the defrost cycle, which is crucial for maintaining warmth during that process.

Some argue that the RCC system holds an advantage because it utilizes hot water from the tank to defrost the coils, eliminating the need for a backup burner. This also ensures that the system never blows cold air when it's not supposed to, keeping you consistently warm.

A more recent development is the cold climate heat pump, designed to operate efficiently in colder temperatures, even below 0 degrees Fahrenheit (-18 degrees Celsius). This heat pump determines the minimum energy required to maintain the desired level of heating or cooling, adjusting its output accordingly to prevent energy waste.

Even advanced heat pumps have their limitations. Keep reading to discover the benefits and drawbacks of heat pumps, as well as the essential factors to consider before purchasing one.

Pros and Cons of Heat Pumps

Heat pumps offer savings on utility bills, but they have some limitations. They are less effective in colder regions where temperatures frequently dip below freezing, although advancements are being made to address this challenge. This is because transferring heat from a very cold area to a warmer one requires more energy than moving heat between areas with less of a temperature difference.

In a moderate climate, there is generally more heat available outside than in a cold one. Even in freezing conditions, the outside air still contains some heat that can be extracted and pumped indoors. However, the system needs to work harder to capture the available heat, and supplemental energy may be necessary to generate enough warmth to heat your home when temperatures dip below freezing.

The warmth produced by heat pumps is typically milder than that of a gas or oil-burning furnace. For those accustomed to traditional furnaces, this gentler heat can feel less intense. However, many people prefer the even distribution of warmth provided by heat pumps, which eliminates cold spots throughout the house.

Heat pumps cycle on and off less frequently than gas furnaces, and most modern systems have improved to prevent the cold air blast that once occurred during the temporary reverse cycle used to defrost the coils.

Now that you're aware of the pros and cons of heat pumps, let's explore what factors you should consider when shopping for one.

Shopping for Heat Pumps

Before installing a heat pump, it's essential to determine what type of supplemental or backup heating you'll require when the heat pump isn't performing at its best. While many heat pumps rely on supplemental electric heating, options like oil burners or modified gas furnaces are also viable alternatives.

The most efficient and cost-effective backup heating solution will likely align with the heating systems commonly used in your area. It's always a good idea to consult your local utility company for more details before proceeding with a heat pump installation.

Ground-source heat pumps are superior dehumidifiers compared to standard air conditioners. This is due to their larger, flat return coils, which can handle and dehumidify more air than the smaller coils typically found in air conditioning systems. In contrast, air-source heat pumps offer dehumidifying performance similar to that of regular air conditioners. Keep these capabilities in mind if you have specific humidity control needs.

What To Look for in a Heat Pump

When you begin your search for a heat pump, there are a few key factors to keep in mind. One of the most important is the unit's efficiency, which is typically measured using SEER and HSPF ratings. The higher the SEER and HSPF ratings, the more efficient the heat pump will be.

Heat pumps often include features designed to enhance efficiency. Some of these features are:

Though many of these features are typically found in higher-end heat pumps, the long-term energy savings often offset the initial investment, making them a worthwhile consideration for improved efficiency and energy savings over the pump's lifetime.

Now that you're familiar with how to select a heat pump, the next question is: will it truly save you money in the long run?

Do Heat Pumps Save You Money?

The price to install and operate different types of heat pumps can vary significantly. Ground-source heat pumps tend to be more costly to install compared to air-source models, as they require digging to reach a heat source and involve more sophisticated heat transfer systems. The cost may vary depending on your property's terrain. However, the superior efficiency of ground-source heat pumps can lead to long-term savings on your energy bills.

Many areas in the United States offer tax incentives for installing high-efficiency climate control systems, which can help reduce the costs of both parts and installation.

The operating and repair costs of a heat pump depend on the type of system you have. Ground-source heat pumps are generally more affordable to run because the ground and water temperatures stay relatively constant, enhancing the pump's efficiency. Additionally, ground-source systems aren't exposed to harsh weather, which reduces wear and tear. However, repairs can be expensive if access to underground parts is required.

Air-source systems are simple to access and maintain but may need more frequent upkeep due to their exposure to the elements. Moreover, air-source heat pumps may require additional energy, especially in colder climates, which can result in higher utility costs.

Heat pumps can lower your energy costs by up to 40 percent, but failure to maintain the system can significantly decrease its efficiency over time. It's crucial to consider the climate in your area when choosing a heat pump to ensure optimal performance. Ultimately, heat pumps can provide substantial savings on utility bills if you choose the right type of system and properly maintain it.

Keep reading to learn about the ongoing costs for running and maintaining your new heat pump.

Heat Pump Maintenance

If you use your heat pump frequently, you should replace the filter approximately once a month. However, if the unit is only used occasionally, changing the filter every three months should suffice. Make sure to clean the fans and coils regularly to keep them free of debris, and have your heat pump checked by a professional twice a year—once before the heating season and again before the cooling season.

Common issues with heat pumps include low airflow, leaky or noisy ducts, temperature inconsistencies, incorrect refrigerant levels, and various sounds like rattling, squeaking, or grinding. If you encounter these problems, try to pinpoint the source. Is the airflow low from just one register, or is it affecting all registers? Is the noise coming from the air ducts or the heat pump unit itself?

There are several steps you can take to identify and potentially resolve a heat pump issue before seeking professional help. If the unit isn't working, first attempt to reset its motor. Check for issues with the pump's ignition system, and ensure that the circuit breaker hasn't been tripped or the fuse hasn't blown. Verify the thermostat is functioning correctly. If needed, replace the dirty filter and check for any airflow blockages.

If the air ducts are noisy as they expand and contract, consider installing rubber pads around them to reduce noise. Rattling sounds may be resolved by securing any loose parts, and squeaks within the unit could indicate that the fan belt needs adjusting or replacing. A grinding sound may suggest worn motor bearings, which will likely require professional attention.

Remember, if you're not experienced with mechanical work, it's probably best to avoid attempting these repairs yourself. Additionally, because heat pumps may contain hazardous substances, it's a wise decision to seek professional help. Chemical leaks are dangerous, and mishandling a malfunctioning unit can result in injury.

A heat pump typically lasts between 10 and 25 years, with regular inspections and maintenance being the key factors in extending its lifespan. Heat pumps in milder climates tend to last longer. However, technology may evolve before your heat pump reaches the end of its useful life, meaning you could find it outlives the technician's ability to service it. New innovations might make heat pumps safer or more efficient, so it's worth keeping an eye on emerging models.