Heat pump

A heat pump moves heat from one place to another.

In winter, it moves heat from outside to your home. In summer, it can move heat from your house to the outside. This keeps you comfy.

It uses a special liquid to carry the heat. The liquid turns into a gas to pick up heat. Then it turns back into a liquid.

These machines are very good at their jobs. They use less power than some other heaters. This helps the Earth stay healthy.

They can even heat your water or dry your clothes. It is a very smart way to use energy.

A heat pump is a clever tool. It moves heat from one place to another.

Most models get heat from the air. These are called air-source heat pumps. Other types use water or the ground.

Heat pumps do not make heat. They just move it. This makes them very efficient. For every 1 kWh of power used, they can move 1 to 4.5 kWh of heat. This helps the planet stay healthy.

How does it work? It uses a liquid called a refrigerant. This liquid moves through a set of steps. First, the liquid turns into a gas. This gas picks up heat from outside. Next, a compressor squeezes the gas. This makes the gas very hot. The hot gas flows inside your home. It lets out its heat to warm the room. Then, the gas turns back into a liquid. The cycle starts again.

Some heat pumps can do both jobs. They can heat a home in winter. In summer, they move heat out to cool the house. They can even heat your water or dry clothes.

A heat pump is a clever machine that moves heat from one place to another.

It does not create heat itself like a fire or a gas boiler. Instead, it uses energy to shift heat between spaces. This makes it very efficient for keeping buildings comfortable. For every 1 kWh of electricity used, a heat pump can move 1 to 4.5 kWh of heat. This high efficiency helps reduce carbon emissions. Many people use them to heat their homes or even to dry clothes.

How does this movement happen? The machine uses a special liquid called a refrigerant. In a common type, the refrigerant flows through coils and absorbs heat. This causes the liquid to turn into a gas. A compressor then squeezes this gas to make its temperature rise.

This hot gas flows to an indoor heat exchanger to warm the room. As it loses heat, the gas turns back into a liquid. This liquid then travels to an outdoor unit to repeat the cycle.

The machine can even reverse this process to cool a house in summer.

People have been studying how to move heat for a long time. In 1748, William Cullen showed how to make artificial refrigeration. Later, in 1852, Lord Kelvin explained the theory behind how heat pumps work. Between 1855 and 1857, Peter von Rittinger built the very first heat pump. In 1877, a real working system was installed at a salt works in Switzerland.

Later, in 1928, Aurel Stodola built a heat pump for the Geneva city hall. That system still provides heat from Lake Geneva today.

There are many different ways to find heat for these machines. Air-source heat pumps are the most common models used today. Other versions include ground-source heat pumps and water-source heat pumps.

Some even use exhaust air from a building to find warmth. In 2023, the largest water-source heat pump was installed in Esbjerg, Denmark. Sales of these machines are growing quickly around the world. In 2023, people in Europe bought 3 million heat pumps. This helps countries move away from using natural gas.

You can think of a heat pump like a moving truck for heat. Just as a truck carries boxes from one house to another, the refrigerant carries heat. It picks up heat from a cool place and drops it off in a warm place. This works even when it is cold outside. The machine just needs a little bit of work to push the heat uphill. This is why they are so useful for modern living. They provide a flexible way to manage the temperature in our homes.

A heat pump is a sophisticated device designed to transfer thermal energy from one location to another. Unlike a gas boiler, which generates heat by burning fuel, a heat pump uses mechanical or thermal energy to move existing heat. This distinction makes the technology highly efficient. By shifting heat rather than creating it, these machines can provide significant warmth or cooling with relatively little energy input. They play a vital role in modern climate change mitigation because they can run on electricity from renewable sources.

The mechanism relies on a process called the vapor-compression refrigeration cycle. This cycle uses a substance called a refrigerant, which flows through various components. First, a liquid refrigerant flows through coils in a cooling unit and absorbs heat. This absorption causes the liquid to change state into a gas. A compressor then performs work on this gaseous refrigerant, increasing both its pressure and its temperature.

Once compressed, the hot gas moves to a heat exchanger in the indoor space. As the gas releases its thermal energy into the room, it condenses back into a liquid. This liquid then travels to an outdoor heat exchanger. In this outdoor unit, the pressure falls, causing the liquid to evaporate and the temperature of the gas to drop. This gas is now colder than the outdoor environment. Because it is colder, it can once again absorb energy from the heat source before returning to the compressor.

Heat pumps are categorized by the source of the thermal energy they use. Air-source heat pumps are the most common variety. Ground-source heat pumps extract heat from the earth, while water-source heat pumps pull heat from bodies of water.

There are also exhaust air heat pumps, which extract heat from a building's exhaust air. Some specialized versions include thermoacoustic heat pumps, which use standing sound waves instead of refrigerants, and solid-state electrocaloric heat pumps.

The history of this technology spans several centuries of scientific discovery. In 1748, William Cullen demonstrated artificial refrigeration. Later, in 1852, Lord Kelvin described the underlying theory of heat pumps. Between 1855 and 1857, Peter von Rittinger developed and built the first heat pump. By 1877, a functional vapor compression system was installed at the Bex salt works in Switzerland. In 1928, Aurel Stodola constructed a closed-loop water-source heat pump for the Geneva city hall. That specific system, which uses water from Lake Geneva, continues to provide heating today.

Efficiency is measured by the coefficient of performance, or COP. This ratio compares the heat delivered to the work required. A heat pump is more efficient than electrical resistance heating because its COP is greater than one. For example, at a specific temperature, an ideal heat pump might have a COP of 28. This means one joule of work delivers 28 joules of heat. In practical applications, heat pumps can transfer 1 to 4.5 kWh of thermal energy for every 1 kWh of electricity consumed. As the temperature of the indoor space rises, the COP typically decreases.

Heat pumps are essential for large-scale energy transitions. In 2021, heat pumps met only 10% of global space and water heating needs, though they could potentially satisfy over 80%. However, adoption is accelerating. In 2023, 3 million heat pumps were sold in Europe. Large-scale versions are also used in district heating systems. These machines are versatile, used for heating, ventilation, and air conditioning (HVAC). They can even be used for domestic hot water or drying clothes.