Heat pump: principle of operation, areas of application
Mar 26, 2021
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We get heat by burning wood, coal, oil products and gas. But these methods of heating that are familiar to us are actually primitive and dangerous: they irretrievably waste the resources of the earth and pollute the atmosphere. This cannot go on for long. Therefore, traditional methods are being replaced by energy efficient technologies that can generate heat from the earth and air without harming nature.
What is a heat pump?
Heat is found everywhere: in the air, water and earth. A heat pump is a step-up heat transformer, a device that takes heat from the environment and transfers it to the heating and hot water supply system. When a heat pump is operating, energy is spent not on direct heating of the coolant, but on pumping and converting heat from the environment into the house. This is how a high energy efficiency of the device is achieved: when 1 kilowatt of electricity is consumed for the operation of the compressor, 3-5 kW of thermal energy is generated (thermal coefficient of COP is 3-5 units).
What kind of heat pumps are there?
Heat pumps are classified into three types:
- Aerothermal (air), which receive thermal energy from the atmosphere.
- Geothermal, extracting heat from the earth.
- Aquathermal (aquatic) - a class of equipment that uses the heat of the aquatic environment: rivers, lakes, sea, underground aquifer.
The aerothermal pump draws heat through an air heat exchanger - an outdoor radiator. Ground source pumps receive heat energy from the ground through geothermal fields - these are laid horizontally below the surface of the earth pipes, or boreholes (probes), where the pipes are installed vertically. The probes can also be positioned at an angle, since not all areas have the ability to drill into depth. The collectors of the aquathermal pump are placed in a reservoir or water well.
Ground source heat pumps operate more efficiently due to stable ground temperatures all year round. With aerothermal pumps, the thermal coefficient (COP) drops at an outdoor temperature of -15 ° C. Water heat pumps depend on the quality of the water: algae, limescale, corrosion - these factors significantly reduce the performance of the device.
How does an air source heat pump work?
The operation of any heat pump is divided into three stages:
- collection of heat from the environment;
- an increase in the temperature of the collected heat;
- heat transfer to the heating and hot water system.
The only difference is the method of obtaining low-grade heat from the environment. With an air source heat pump, this is done as follows:
- The refrigerant circulates through the evaporator of the air heat pump - freon. It is an antifreeze and highly volatile liquid that boils at low temperatures. The freon temperature is always lower than the air temperature and, therefore, under its influence, the refrigerant boils and is converted into steam. This is called thermal differential heat transfer.
- Freon vapor enters the compressor, where it is compressed. Under the influence of high pressure, the refrigerant vapor heats up: the temperature of the compressed freon vapor can reach 128 ° C. This heat enters the condenser.
- In the condenser, hot freon steam transfers heat energy to the heating and water heating circuit. When the heat energy is released, the steam cools down and again becomes a liquid state, but at the same time maintains a high pressure. And also the temperature of the refrigerant at this stage is still insufficient for a new cycle of heat absorption from the environment. Therefore, after the heat exchanger, the freon passes through the throttle valve, where the pressure drops and the temperature drops. After that, the refrigerant goes to the external circuit for a repeated cycle.
How does a geothermal and aquathermal heat pump work?
The principle of operation of these heat pumps differs only in the extraction of heat from the environment. Here, a circuit of pipes laid underground or immersed in water acts as a heat exchanger. It is not a refrigerant that circulates through the pipes, as in air pumps, but an intermediary - propylene glycol, alcohol or a water-glycol mixture. It is these liquids that accumulate heat obtained from water or soil and transfer it to the evaporator of the installation.
The coolant enters the evaporator, heats the freon, converting it into steam. Freon vapor passes through the compressor, where it is compressed and heated. After that, it also enters the condenser, where it transfers heat to heating and hot water supply. The cycle ends when the refrigerant passes through the throttling valve, where the depressurization and cooling process takes place. The cooled freon enters the evaporator again.
To put it simply: the heat of air, water or earth is required only in order to boil freon and turn it into steam. Further, in the compressor, steam is heated under the influence of pressure to high temperatures, the energy of which is used to heat water in the heating system and hot water supply. In this way, the low-grade heat of the external environment is converted into high temperatures of the heating medium of the heating circuit.
How to improve the efficiency of a heat pump?
The heating system plays an important role in the performance of a heat pump. The equipment operates most efficiently with low-temperature heating systems: warm water floor; fan coil units (fan heat exchangers). The fact is that the heat pump works as efficiently as possible at a temperature of 35-40 ° C at the outlet, and this corresponds to the optimal temperature of the heating medium in the water underfloor heating system or air heating.
Can the heat pump cool?
Heat pumps can not only heat but also cool - used for air conditioning. That is, the device can take heat from the room and remove it outside according to the same principle, but only in the reverse order. A refrigerator is also a heat pump. This household appliance does not produce cold, it simply removes all heat from the sealed thermal insulation chamber.
In what areas are heat pumps used?
Heat pumps are used for heating and air conditioning industrial facilities, municipal buildings, multi-storey and private residential buildings. This technology is capable of replacing all traditional heating methods. An example of this is Sweden, where more than 90% of buildings for various purposes are heated with the help of heat pumps. Geothermal and aerothermal pumps are widespread in Europe, USA, Japan.
Who is this type of heating suitable for?
The heat pump only needs electricity to function. This type of heating is suitable for private houses located far from gas mains or where gas connection is unreasonably expensive. The heat pump is perfect for non-gasified settlements where there is not enough power to install an electric boiler. This type of heating is popular with those who do not want to live on a "powder keg", that is, it is suitable for people who fear suffocation or explosion if gas leaks. The heat pump can be used in commercial buildings as energy efficient heating.
What are the dangers of a heat pump?
The heat pump does not burn fuel; it does not produce harmful emissions into the atmosphere and waste into the environment. It is a fire / explosion proof and environmentally friendly device. The refrigerant circulates in a closed circuit and does not pose a danger to nature and humans.
What to look for when choosing a heat pump?
As we mentioned, heat pumps are divided into three types: aerothermal, aquathermal and geothermal. The first ones work from atmospheric heat and they have two significant drawbacks: temperature drops and regular pollution of the radiator. In severe frosts, the thermal coefficient (COP) drops to 1, instead of the declared 3-5. And also the constant pollution of outdoor radiators reduces the efficiency of the aerothermal pumps. These installations are more suitable for temperate climates with mild winters.
Aquathermal pumps are demanding on the quality of the water and their efficiency drops when the coolant circuit becomes dirty or covered with deposits.
For our conditions, the best choice is geothermal heat pumps. The "soil-water" system is the most convenient, reliable and efficient for heating and hot water supply at home. This is due to the almost constant soil temperature throughout the year. The geothermal field is laid below the freezing point of the soil, which allows the installation to function stably and produce a high thermal coefficient. For example, COP of FH series geothermal heat pumps (ФХ-401, FH-405, FH-415) up to 5 units!
When choosing equipment, it is important that it not only heats water banally, but also has advanced characteristics that meet the requirements of a modern heat pump. Take for example geothermal heat pump IQ (inverter) ФХ-415. The installation is equipped with: a device for remote access; automatic restart in the event of a power outage; protection of circulation pumps; phase imbalance protection; climate control mode for air temperature; weekly work schedule; weather-dependent mode; control of the heating element of the hot water tank; non-volatile memory; soundproofed housing. This guarantees the reliability, durability and high energy efficiency of the equipment.
How do you feel about such heating systems? Write in the comments.
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