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A Simple Diagram and Operation Guide of Heat Pump

Heat pumps are an environmentally friendly solution. We can use heat pumps to efficiently and economically heat or cool houses. They utilize free energy sources such as water, air, and soil, and consume a small amount of electricity for 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.


Operation of a Heat Pump

The operation of a heat pump 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 providing heating, hot water, floor heating, etc., through the evaporator, compressor, condenser, and expansion valve.


In hot weather conditions, the heat pump operates in cooling mode, working in the opposite way. The heat pump extracts heat from the indoor air and transfers it to the outside air through various functions of the evaporator, compressor, condenser, and expansion valve, changing the refrigerant from liquid to gas and back to liquid, ultimately cooling the house.


The heating and cooling modes of the heat pump are cyclical.

In the heating mode, all heat pumps go through the following steps and achieve heating functions through the following components:


1.1 Evaporation (Evaporator)


1.2 Compression (Compressor)


1.3 Condensation (Condenser)


1.4 Expansion (Expansion Valve)



The following is a breakdown of the main operating steps:


1.1 Evaporation (Evaporator)

First, the evaporation stage begins, where the liquid refrigerant in the evaporator absorbs heat from the external ambient air. Then, the refrigerant changes from liquid to a low-temperature, low-pressure gas state.


1.2 Compression (Compressor)

The compression stage starts when the compressor takes in the low-temperature, low-pressure gaseous refrigerant. The compressor consumes a small amount of electricity to convert the low-temperature, low-pressure gas into high-temperature, high-pressure gas.


1.3 Condensation (Condenser)

In the condensation stage, the heated high-temperature, high-pressure gaseous refrigerant passes through the heat pump condenser, transferring its heat to water in the heating circuit. It then turns back into a liquid.


1.4 Expansion (Expansion Valve)

In the expansion stage, the liquid refrigerant passes through the heat pump expansion valve to reduce the pressure and temperature of the refrigerant until it evaporates into a low-temperature, low-pressure wet vapor (a gas-liquid mixture) and returns to the evaporator.


Then, the refrigerant resumes its thermodynamic cycle.


It should be noted that the operation of reversible heat pumps is different in the cooling mode during summer. Such devices absorb heat from indoors and then discharge it outside to lower room temperature.


Please refer to the heat pump diagram to understand its operation.

heat pump heating and cooling cycle diargram

This diagram illustrates the working principle of a heat pump.


Air Source Heat Pump (ASHP)

An air source heat pump (ASHP) has a finned heat exchanger outside the building. A fan forces air to pass through it, and another heat exchanger is used to heat the indoor air or heat water for heating through radiators or underfloor heating, releasing heat into the building.


In cooling mode, the ASHP extracts heat from indoor air and releases it into the ambient air through the internal heat exchanger.


The following are the heating and cooling cycle diagrams of an ASHP, detailing the different components and the cycle processes.

heat pump cycle diargram

ASHP Cooling Cycle

heat pump heating and cooling cycle diargram

ASHP Heating Cycle


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An air-to-air heat pump absorbs heat from the outside air and ultimately transfers it to the room for space heating through a fan coil unit. Conversely, it absorbs heat from the room and transfers it to the outside air for cooling purposes. However, air-to-air heat pumps do not perform the function of heating water. You would need to add a water heating device to compensate for that.


Similar to an air-to-air heat pump, an air-to-water heat pump extracts heat from the outside air. It then transfers this heat to the hydraulic heating circuit of the house, such as radiators, domestic hot water heating, or supplying hot water.


How Does an Air-to-Water Heat Pump Work?

An air-to-water heat pump operates using air and refrigerant. Specifically, it extracts energy from the air. The refrigerant transfers energy through the thermodynamic cycle of the heat pump’s four main components: evaporator, compressor, condenser, and expansion valve.


To better understand its operation, please refer to the schematic diagram of the air-to-water heat pump.


Air-to-Water Heat Pump Schematic

As shown in the diagram, air drawn in by the outdoor unit transfers its heat to the refrigerant, which is converted into gas after passing through the evaporator. It is then sent to the compressor, where the compressor increases the pressure and temperature of the refrigerant after working. The fully heated refrigerant transfers its heat to the water in the condenser heating circuit. It then loses its heat and becomes a liquid again. Finally, it passes through the expansion valve, reducing its pressure, and captures heat from the air again, distributing heat through geothermal heating, radiators, or fan coil units.


It is worth noting that in a monobloc heat pump, the four stages of the refrigerant’s thermodynamic cycle occur within a single compartment. In contrast, a split heat pump includes an outdoor and indoor unit.


The operating principles of air source heat pumps and ground source heat pumps are similar. The difference between air-to-air, water-to-water, ground-to-air, and ground-to-water heat pumps lies in how they utilize energy to heat the refrigerant and distribute heat indoors.


A ground source heat pump (“GSHP”) or geothermal heat pump is a heating/cooling system for houses that transfers heat into or out of the ground using a heat pump, utilizing the relatively stable temperature of the earth throughout the seasons. GSHPs are one of the most energy-efficient technologies for heating, ventilation, air conditioning, and water heating, as they require far less energy compared to burning fuels or using resistance heaters.


The efficiency of GSHPs is measured by the coefficient of performance (COP), typically ranging from 3 to 6, which means the equipment provides 3-6 joules of heat for every joule of electrical power consumed.


GSHPs extract heat from the ground through a special sensor (horizontal, vertical, or groundwater). The captured energy heats a thermal fluid, which, through the thermodynamic cycle of the evaporator, compressor, condenser, and expansion valve, heats the interior floors or radiators of the building.


Water-to-water heat pumps can extract heat from lakes, rivers, or groundwater for heating the refrigerant and then, based on its thermodynamic cycle, use it for heating residential or production hot water. The system involves a supply well and a return well to achieve heating/cooling functions. The heat pump extracts groundwater from the supply well, which is then returned to the ground through the return well.


Comparison of Different Heat Pumps

In this section, we will compare different heat pumps, explaining their respective advantages, disadvantages, and lifespansions.


In general, air source heat pumps have relatively lower prices and are easier to install in the short term.


Among all types, ground source heat pumps have the highest upfront costs. Installation requires drilling and excavating a large area of land or trenches, which can be disruptive to the soil. However, in the long run, they can still save money.


Water source heat pumps have high installation costs, but they offer a high return on investment in the long run. Compared to ground source heat pumps, their installation is relatively easier and cheaper. However, they require nearby high-quality and sufficient water sources. Clean water is preferable, especially if you are installing an open-loop system.


After a brief comparison, you may have a rough understanding of these three types of heat pumps. If you have any further questions about heat pumps, please feel free to contact us directly via email.

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