Simple Diagram & Operation of Heat Pumps Pump up Your Heat Pump Knowledge

1. Operation of a heat pump

1.1    Evaporation (evaporator)

1.2    Compression (compressor)

1.3    Condensing (condenser)

1.4    Expansion (expansion valve)

2. Air source heat pumps

2.1    Diagram of an air-to-air heat pump

2.2    Diagram of an air-to-water heat pump

2.3    How does an air-to-water heat pump work?

3. Diagram of a geothermal heat pump

4. Diagram of water to water heat pump

5. Comparison of various heat pumps

Heat pumps are an eco-friendly solution. We can use heat pumps to heat or cool houses efficiently and economically. They use free energy sources such as water, air, and soil and consume a small amount of electricity to achieve heating or cooling. Before choosing a heat pump, it may be necessary to understand how it works. We can do this by referring to the heat pump diagram and its thermodynamic cycle.

1. Operation of a heat pump  

The heat pump operation is based on a thermodynamic cycle. In cold weather conditions, the heat pump operates in heating mode, extracting heat from the air, water, or ground and going through the evaporator, compressor, condenser, and expansion valve to provide heating, hot water, floor heating, etc.

In hot weather conditions, the heat pump is in cooling mode, operating oppositely. The heat pump draws heat energy from the air inside the home. The refrigerant changes from a liquid to gas, then back to liquid and finally to a gas state through various functions of the evaporator, compressor, condenser and expansion valve. Finally, it transfers the heat to the outside air to cool the house.

The heat pump’s heating mode and cooling mode are repeated.

In heating mode, all heat pumps go through the following steps and realize the heating function through the following components:

1.1 Evaporation (evaporator)

1.2 Compression (compressor)

1.3 Condensing (condenser)

1.4 Expansion (expansion valve)

Below is a breakdown of the main operating steps.

1.1 Evaporation (evaporator)

Firstly, the evaporation phase begins with the liquid refrigerant in the evaporator absorbing heat from the external ambient air. Then the refrigerant turns from a liquid state to a low-temperature and low-pressure gas state.

1.2 Compression (compressor)

The compression stage starts when the compressor draws in the low-temperature, low-pressure gaseous refrigerant. The compressor consumes a small amount of electricity to do work and converts the low-temperature, low-pressure gas into a high-temperature, high-pressure gas.

1.3 Condensation (Condenser)

In the condensing stage, the heated high-temperature and high-pressure gaseous refrigerant passes through the heat pump condenser and transfers its heat to the water in the heating circuit. It then becomes liquid again.

1.4  Expansion (expansion valve)

During the expansion phase, the liquid refrigerant passes through a heat pump expansion valve to reduce the refrigerant pressure and temperature until it evaporates into a low-temperature, low-pressure wet vapor (gas-liquid mixture), which is then returned to the evaporator.

The refrigerant then resumes its thermodynamic cycle.

It should be added that a reversible heat pump operates differently in summer in cooling mode. This equipment absorbs heat indoors and then expels it outdoors to lower the room's temperature.  

Please refer to the heat pump diagram to get to know the operation.

This diagram shows how a heat pump works.

2. Air source heat pump (ASHP)

An air source heat pump (ASHP) One heat exchanger equipped with fins is outside the building. The fan forces air in through it, and the other heat exchanger is used to heat the air inside the building or heat water through radiators or floor heating, releasing the heat into the building.

In cooling mode, ASHPs extract indoor heat through an internal heat exchanger and release it into the ambient air through an external heat exchanger.

Here are the ASHP’s heating and cooling cycle diagrams detailing the different components and cycle processes.

2.1 Diagram of an air-to-air heat pump

Air-to-air heat pumps heat a space by absorbing heat from the outside air and eventually transferring it to the room through a fan coil. Conversely, air-to-air heat pumps absorb heat from the room and transfer it outside for cooling purposes. However, air-to-air heat pumps do not perform hot water functions. You need to add a hot water unit to make up for it.

2.2 Diagram of an air-to-water heat pump

Like an air-to-air heat pump, an air-to-water heat pump also extracts heat from the outside air. It then transfers this heat to the house's hydraulic heating circuit such as a  radiator, hot water heating, or hot water supply.

2.3 How does an air-to-water heat pump operate?

Air-to-water heat pumps use air and refrigerant to operate. Specifically, the air-to-water heat pump extracts energy from the air. The refrigerant transfers energy through a thermodynamic cycle of the heat pump's four main components (evaporator, compressor, condenser, and expansion valve).

To better understand its working principle, see the schematic diagram of an air-to-water heat pump.

As shown in the diagram, the air inhaled by the outdoor unit will transfer its heat to the refrigerant, which will be converted into gas after passing through the evaporator. It will then be sent to the compressor, which increases the refrigerant's pressure and temperature after work. The fully heated refrigerant will transfer its heat to the water in the condenser heating circuit. Then, it will lose its heat and become liquid again. At last, it will pass through the expansion valve, reducing its pressure and capturing the heat in the air again, distributing heat through geothermal heating, radiators, or fan coils.

It is worth noting that in monobloc heat pumps, the four stages of the thermodynamic cycle of the refrigerant are carried out in a single compartment. In contrast, a split heat pump includes an outdoor and indoor unit.

3.  Diagram of a geothermal heat pump

The operation principles of air source and geothermal heat pumps are generally the same. The difference between air to air, water to water, ground to air, and ground to water heat pumps is how they use the energy to heat the refrigerant and distribute the heat in the room.

A ground source heat pump ("GSHP") or geothermal heat pump is a house heating/cooling system leveraging the Earth's relatively constant temperature through the seasons by using a heat pump to transfer heat into or out of the ground. Ground source heat pumps (GSHPs) are one of the most energy-efficient technologies for heating, ventilation, air conditioning and water heating because they use far less energy than burning fuel or using resistive electric heaters.

The efficiency of GSHPs is the Coefficient of Performance (CoP), typically in the range of 3-6, which means that the equipment provides 3-6 joules of heat for every joule of electricity.

GSHP extracts the heat contained in the ground through a special sensor (horizontal, vertical, or groundwater). The captured energy heats the heat transfer fluid, which passes through the evaporator, compressor, condenser, and expansion valve, heating the room's interior floor or radiators.

4. Diagram of a water to water heat pump

A water-to-water heat pump can take heat from a lake, river, or groundwater for heating a refrigerant, which is then used to heat a home or produce domestic hot water, according to its thermodynamic cycle. The system involves a supply well and a return well to achieve the heating/cooling function. The heat pump extracts groundwater from the supply well. The cooled groundwater flows back into the ground through a return well.

5.  Comparison of various heat pumps

In this part, I am going to compare the different heat pumps, illastrating their respective advantages and disadvantages, lifespan.

Generally speaking, air source heat pumps are relatively cheaper and easier to install in the short term.

Of all types, geothermal heat pumps have the highest upfront costs. Because installation requires drilling and excavating large areas of land or ditches, it is highly disruptive to the soil. However, in the long run, they can  still save money.

Water source heat pumps are expensive to install but have a high payback in the long run. They are relatively easier and cheaper to install compared to geothermal heat pumps. However, they require high quality and a sufficient quantity of water nearby. Clean water is better, especially if you're installing an open-loop system.

After a brief comparison, you may have a general understanding of the three types of heat pumps. If you have any queries about heat pumps, please contact us directly by email: inquiry@sprsunheatpump.com or follow us on facebook, twitter, linkedin. Stay tuned!