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Heat pumps

Heat pumps

What is a heat pump

A heat pump is a device that draws heat energy from a hot tank (referred to as a source) at a low temperature to a sink (usually air or water) at a higher temperature either (a) using mechanical work or (b) ) with the help of a very high temperature hot tank.


The principle of operating the heat pump was primarily applied to standard refrigerators and freezers, air conditioners and subsequently to hot water generators. The term Heat Pump is often identified with the air conditioner. The difference between a heat pump and a common air conditioner is that the heat pump can be used for both heating and cooling by operating on the same thermodynamic cycle whose operation can be reversed as needed (heating or cooling). In cold climates it is even common to design and market heat pumps only for heating, while in warmer climates it is common to use these machines for both heating and cooling.


In an air conditioner requiring mechanical work (which in turn usually requires electricity consumption) to maintain the thermodynamic cycle, the term heat pump refers to engines operating on compressed gas as a means of transferring energy between source and sink. . This machine consists of a pump, compressor, expansion valve and heat exchangers so that the direction of pumping of the thermal energy can be reversed. For this reason it usually provides indoor heating and cooling as well as hot water. The most common sources of heat pumping for such machines are atmospheric air and soil. Depending on the nature of the source and the sink, the heat pumps are separated into air-to-air, air-to-water.




The operation of heat pumps is based on the cooling cycle, a perpetual cycle of expansion and compression of a fluid as in the following figure:





The fluid (coolant) flowing through the pipes at position 4 is liquid at high pressure and temperature after the compressor. In position 4, heat is eliminated, and after cooling, it expands (lowering pressure) on the expansion valve (6), and evaporates (due to pressure drop) in the evaporator in position 2, where it cools and absorbs heat. Then the cold refrigerant, in still gaseous form, is compressed into the compressor, liquefied, heated, expels heat, and so on. The important thing is that in each cycle, heat is eliminated at position 4 and is absorbed at position 2, so as long as the cycle is continuous there is a constant heat transfer from point 2 to point 4 and so with the cooling cycle we can transfer heat (energy) between two points, and this is why the devices that operate in this way are called heat pumps. In order to be able to take advantage of the ability to pump energy, at points 2 and 4, the tube must be shaped so that it can absorb and discharge fluid more easily. The intake and exchange of energy is done by means of special devices called heat exchangers.