What Is a Heat Pump & How Does It Work? (Explained)

Imagine if you could magically move heat from one place to another, like a genie in a bottle granting your thermal wishes. Well, that’s basically what heat pumps do – they pump heat! 

By manipulating the refrigerant temperature within a closed loop, heat pumps can collect ambient heat from the air and concentrate it. It’s a game of temperature tug-of-war, with the refrigerant constantly changing phases between a gas and a liquid.

How Does a Heat Pump Work?

air source heat pump diagram

Here’s how it works: the refrigerant starts off at ambient temperature and is compressed using an electric motor, which makes it really hot. This hot refrigerant is then used to heat water by passing it through a coil inside a hot water tank, which in turn cools the refrigerant down. 

The cooled refrigerant is then passed through an expansion valve, causing it to evaporate and cool even further.

But the story doesn’t end there – the cold refrigerant is then passed through a series of metal pipes with metal fins exposed to the outside air, which warms it up as air passes over the fins, like a natural hair dryer. 

And as long as the refrigerant is colder than the outside air, it can continue to collect heat, which can then be concentrated using the condenser to heat water and start the whole cycle over again.

To understand this process better, think of it like pumping up a bicycle tire. 

When you compress air in a pump and force it into the tire, the air warms up and can be felt as it warms the pump shaft and the tire. But if you let the tire sit, it will cool down to the temperature of the surrounding air. 

By releasing the compressed air within the tire through the valve, the air will expand, cooling it below the temperature of the surrounding air.

Unlike a resistive electric element that can only generate as much heat as is available in the energy of the electricity consumed, heat pumps can use electricity to collect heat from the surrounding air, allowing them to collect more heat than is available in the energy of the electricity. 

Not only are heat pumps like magical genies granting unlimited thermal wishes, but they’re also incredibly efficient. In fact, they’re up to four times more efficient than electric resistive heating systems and much more efficient than gas systems.

Using hot water heat pumps as an example. Gas hot water systems typically have gas-to-hot water efficiencies of around 65-75%. In contrast, heat pumps can collect and concentrate heat from the surrounding air, making them much more efficient at heating water. 

It’s like having a thermal superhero that can save the day with incredible efficiency! With a heat pump, you get all the heat you need without wasting energy or money.

Heat Pump Efficiency: What Makes Them Amazing

Have you ever heard of a machine that can move multiple units of heat per unit of electricity consumed? 

Well, that’s precisely what a heat pump does, measured by its coefficient of performance (COP). However, as the name suggests, heat pumps require a heat source to work their magic, and for air-source heat pumps, this is usually the ambient air.

The efficiency of an air-source heat pump is greatly influenced by the temperature of the surrounding air. 

In hot climates, where the air is warm, heat pumps can collect heat easily, achieving very high efficiency and significantly reducing the energy required. 

However, in colder conditions, the heat pump’s efficiency decreases, and in less efficient models, it can drop below that of a standard electric resistive heating unit.

To account for the seasonal fluctuations in ambient temperature, the average efficiency of a heat pump over the year is described by its seasonal performance factor (SPF). 

This value is generally lower than the stated COP because it considers when the heat pump will operate at reduced efficiency due to unfavorable ambient temperatures.

For locations that experience very cold winter conditions, coupling the heat pump with an alternative heat source can improve efficiency and reduce energy consumption. 

Ground, exhaust air from the ventilation system, large bodies of water, and solar thermal collectors are common alternative heat sources. 

In hot and humid climates that require regular cooling, the heat rejected from the cooling system can be used as a heat source.

Heat pumps are so efficient that Passive House certification assumes that each occupant will consume 25 L of hot water per day, which can be generated using a heat pump with a seasonal performance factor of 2.25 and associated heat losses, equating to approximately 250 kWh per annum per occupant. 

It’s like having a thermal wizard that can create heat out of thin air!

Heat Pump Cooling: These Magic Boxes Can Do More Than Heat

That’s correct. Heat pumps can provide heating and cooling through the same system, and they can be used to cool a home in the same way they are used for heating. 

During cooling mode, the heat pump absorbs heat from the indoor air and releases it to the outside, resulting in a cooler indoor temperature. This process can be delivered through the ventilation system or through direct cooling of air within a room using a recirculation fan coil unit. 

In a high-efficiency home, cooling may only be required for a few hours on the year’s hottest days. Cooling the occupied rooms may be sufficient to meet the occupants’ comfort requirements, while the ventilation system scavenges cooling for the rest of the home.

Operating & Efficiency of Cooling With Heat Pumps

Regarding air-source heat pumps, their cooling efficiency is closely tied to the surrounding environment. As the temperature rises, the system’s efficiency drops, which means that claims of high COPs may not always reflect real-world performance. 

In fact, many heat pumps will reduce their cooling output during extremely hot conditions to avoid overheating. And once temperatures hit a certain threshold, usually around 104°F, the heat pump will no longer be able to provide cooling altogether.

But fear not because there are ways to work around this issue. For instance, if you live in a climate where temperatures only spike for a few days out of the year, you can manage the conditions inside your home by adjusting the building envelope and reducing ventilation rates. 

By cooling the house before the day’s heat sets in, you can maintain comfortable temperatures throughout the peak hours, even if the heat pump can no longer provide additional cooling.

For those living in more extreme climates, other options exist. For example, heat pumps can be coupled with alternative heat sinks, such as the ground or a nearby water body, which can significantly improve their efficiency and operate at peak capacity even during the hottest parts of the day. 

So if you’re looking to stay cool no matter how high the mercury rises, plenty of strategies and tools are at your disposal to help you beat the heat.

Split System Heat Pumps: Perfect for Mild Climates

A split reverse cycle heat pump system may be a cost-effective solution when it comes to cooling homes in mild climates. However, the system can cause discomfort if hot air is blown directly onto occupants. Which often happens with ductless mini-split heat pumps.

To prevent this, the unit should be located to maximize air distribution while avoiding direct airflow on people. Some homeowners also like to hide mini-spilts as well.

A split system located in the living space where internal heat sources are present can effectively maintain a comfortable temperature throughout the home.

In conjunction with a heat recovery ventilation system, cooling from the living space can be distributed throughout the home via a heat exchanger. 

The split system can also provide flexibility to the heating system, allowing it to be used for on-demand cooling in the living space while heating the rest of the home via the ventilation system.

To ensure maximum efficiency, the distance between the head unit and the condenser should be minimized, and all pipes and connections must be insulated to prevent condensation and energy loss. Additionally, the head unit must have a condensate drain to prevent moisture buildup, and noise levels should be kept within acceptable levels to maintain acoustic comfort.

Overall, a split reverse cycle heat pump system can be an effective solution for cooling homes in mild climates, as long as proper installation and location techniques are used to maximize efficiency and occupant comfort.

What is a Cold Climate Heat Pump?

A cold climate heat pump is a highly efficient heating and cooling system for regions with low outdoor temperatures. It utilizes advanced technology to extract heat from the outside air, even in freezing conditions and transfers it indoors to provide warmth.

Conversely, in warmer months, the heat pump can reverse its operation to cool the indoor space by transferring heat from inside to outside.

These heat pumps are characterized by their ability to operate efficiently in temperatures as low as -20°F (-29°C), making them an ideal, energy-saving solution for homes and businesses in cold climate regions.

Types of Heat Pumps Available

Now that you have the answers to the questions, “what is a heat pump?” and “how does a heat pump work?” the next thing you should read about is the types of heat pumps.

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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.