HEAT PUMP / part 1 - principle of operation and structure

The principle of operation of the heat pump

The heat pump is designed to transform thermal energy from a low-temperature heat source: air, soil, water) to a high-temperature consumer. According to the type of work, heat pumps are classified into different types, in particular, sorption (absorption/adsorption) and jet (steam injection) heat engines, which are used to dispose of excess heat, and thermoelectric heat pumps, which we use in small portable car refrigerators.

The most popular type of heat pump on the market is a vapor-compression unit - a device that you install at your facilities. The operation of a vapor-compression heat pump is based on one of the fundamental principles of thermodynamics - the Carnot cycle. This is the only reversible cycle that occurs in a closed system and can be carried out in both forward and reverse directions. Accordingly, an installation based on the Carnot cycle can operate as an air conditioner or heat pump, or combine heating and cooling functions in one device. Compression heat pumps apply mechanical energy using electricity as a power source. Learn more about the benefits of heat pumps in the Hajster blog.

The structure and principle of operation of a steam-compression heat pump

The source of heat extraction of the steam compression pump is the environment. The design of a steam-compression heat pump consists of the following main components: capacitor, throttle valve, evaporator and compressor.

In the hermetic circuit of the heat pump, there is a refrigerant (working body), mainly freons are used, which do not contain chlorine and are safe for the ozone layer of our planet. The work cycle of the heat pump is based on the transfer of temperature by the working body (refrigerant) as a result of a change in pressure and a phase transition - from a liquid state to a gaseous state and vice versa, under the influence of mechanical action.

Being under low pressure in the evaporator, the refrigerant is able to boil at a low temperature, which allows it to extract heat from a low-potential energy source: air, soil, water. Next, the working body (gaseous state) enters the compressor, where it is compressed due to mechanical action, which leads to a sharp increase in temperature. Then the refrigerant is fed to the heat exchanger - the condenser, where it begins to condense at high pressure. As a result of condensation, heat is released, which is transferred to the coolant of the heating system. After the condenser, the working body passes through the throttle valve, which reduces the pressure, which also leads to a decrease in temperature. At this point, the thermodynamic cycle is closed and the refrigerant is again ready for boiling and heat removal in the evaporator. Thus, 80% of the thermal power of heat pumps consists of regenerative energy from the environment, and only 20% of the energy is used for the operation of the heat pump itself. Heat pumps provide space heating and hot water supply. And if there is a reversing valve in the circuit of the heat pump, they are able to work in the reverse mode - to cool the premises. 

The compressor is the heart of the heat pump. All the technical characteristics and parameters of the installation depend on the compressor. Below are the main types of compressors used in steam-compressor heat pump units:

• rotary, mainly used for low power installations. In modern air heat pumps, two-rotor compressors are most often used, which are characterized by increased resource and reliability. Thanks to this design, the compressor can work at a low rotation speed, thereby reducing the number of start and stop cycles, which significantly increases the efficiency of heat pumps. The use of two rotors also reduces vibration and noise.

• spiral, the most common for the configuration of heat pumps of small and medium power. The advantages of such compressors are: high efficiency, noiselessness during operation, durability, high reliability (insignificant number of moving parts).

• piston, for installations of medium and high power

• screw, for high power systems up to 1000 kW.

The use of inverter technology makes it possible to ensure high efficiency of heat pumps with spiral compressors in the entire power range. A combination of two "tandem compressors" compressors is used for the manufacture of heat pumps of medium and higher power. Such systems guarantee high efficiency when the heat load changes, which allows optimal adaptation to different operating conditions.

Classification of heat pumps by energy source

The main condition for the operation of the heat pump is the presence of an energy source, that is, the heat from which it will be taken to ensure the process of boiling the working fluid in the evaporator. According to the type of source, heat pumps are divided into the following groups:

• geothermal: use the heat of the soil or underground water

• air: use the heat of the surrounding air

• heat pumps that use the secondary heat of another thermal process that needs to be disposed of - for example, the heat of a technological process or waste water - can be singled out separately.