Absorption devices
Gas-powered absorption devices, including heat pumps, operate based on a patent by Albert Einstein and Leo Szilard from 1930. It is nearly 100 years old, but it is still used in refrigeration equipment capable of transferring thermal energy from a lower-temperature location to a higher-temperature one. All of this is made possible by differences in pressure and density, the use of an absorbent, and the supply of heat generated by the combustion of liquefied gas. Remember that a heat pump is essentially a heating device capable of transferring heat from a lower-temperature environment (the lower source) to a higher-temperature environment (the upper source) using a refrigeration system. In typical, commonly used compressor-based heat pumps, one of the components is an electrically powered compressor that forces the refrigerant to circulate within the system. However, the situation is different with an absorption heat pump powered by liquefied petroleum gas (LPG). In this case, the fuel is LPG, which, when burned in the burner, provides heat that then powers the entire system.
How does an absorption heat pump work?
It operates in a manner very similar to an electric compressor; however, instead of a compressor, absorption heat pumps use a generator-absorber system. Everything is powered by gas, and during its combustion, heat is generated and supplied to the evaporator. Under its influence, ammonia evaporates from the ammonia-water solution. The high-pressure, high-temperature vapor passes through the rectifier trays. It is also worth noting that during the rectification process, the ammonia vapor comes into contact with the rich solution, causing it to leave this part of the evaporator virtually devoid of water vapor.
The refrigerant is transferred to the deflagrator, where the ammonia vapor is purified of residual water vapor. The ammonia vapor releases heat in the condenser, heating water for central heating or for domestic hot water, while the liquid refrigerant flows to the expansion valve.
Just beyond the pump valve, low-pressure, low-temperature liquid ammonia is fed to the evaporator, where it absorbs heat from the lower source and evaporates. In the absorber, however, the ammonia vapor is absorbed by a lean solution, which is directed to the absorber from the lower part of the evaporator. It is expanded to low pressure and sprayed in the form of a “mist” in the absorber. The water droplets absorb the ammonia, forming a rich solution. This mixture is directed to a shell-and-tube heat exchanger, where it transfers heat to the heating water.
Types of absorption heat pumps
You can choose from various types of gas-fired absorption heat pumps, which differ in their specific features and thermal efficiency. They utilize energy from renewable sources such as air, water, and the ground. The following types are available:
- Condensing gas absorption air-to-water heat pump – it features 165% thermal efficiency. It can heat rooms and produce domestic hot water.
- Gas-fired reversible air-to-water absorption heat pump – it features 149% thermal efficiency. It can heat or cool rooms.
- Condensing gas absorption heat pump for use with a ground-source heat exchanger – it features 170% thermal efficiency. It can heat and cool rooms and produce domestic hot water.
- Water/water condensing gas absorption heat pump – it features 174% heating efficiency and 244% efficiency when simultaneously utilizing heat and cooling. It can heat and cool rooms and produce domestic hot water, or simultaneously produce hot and cold water.
It is worth noting that these units are powered by heat generated in a gas burner through the combustion of, for example, LPG.
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