Brief introduction of chillers
Chillers are one of the components of an air conditioning system that bring the system activity to temperature equilibrium. The job of a chiller is not to generate cold, but to remove heat. This heat is the heat generated for a fluid or refrigerant by activities inside the system and must be removed from the system. A chiller is a device that does this by rotating the refrigerant in its various parts.
An overview of the classification of different types of chillers
The chiller is composed of different parts and the variety of functions of some of these parts can make different types of chillers. As compression and absorption chillers, it talks about how the part works, especially between the evaporator and the condenser. In fact, it can be said that one of the most important divisions of chillers goes back to the way they work and their cycle mechanism. In this regard, two types of compression and absorption are defined for the chiller.
Differences between compression and absorption chillers in terms of structure and internal components
If we look briefly at the general components of the chiller that make up its cycle, we come across fixed components such as the evaporator, condenser and expansion valve. The evaporator is the first component of this cycle and the expansion valve is its last point. But there is a difference between the two components of evaporator and condenser in chillers depending on their compression and absorption.
Compression chiller bases its work on condensing refrigerant. In this way, the compressor is used in this part of the cycle. The compressor takes the refrigerant vapour from the evaporator, compresses it, and raises its temperature and pressure. This gas refrigerant enters the condenser section with this new high pressure and temperature to dissipate heat from it.
Therefore, in a compression chiller, a single device was used to compress the refrigerant. But this is done in the absorption chiller by four separate devices. In this way, in the absorption chiller, the absorber set, heat exchanger, pump and generator are replaced by the compressor.
Comparison of absorption and compression chillers based on performance
As mentioned in the previous section, in an absorption chiller, instead of a single device, a set of components is used to compress the refrigerant. It can be said that in terms of performance, the basis of the absorption chiller, like the compression chiller, is based on the compaction of the refrigerant, but it does it in a different way.
One of the differences in the performance of the absorption chiller is due to its refrigerant. In addition to the refrigerant, which was equivalent to water in compression chillers, another fluid is used as an adsorbent in absorption chillers. This adsorbent has changed over time depending on advances in science and technology, but today lithium bromide is used.
The function of the adsorption chiller with the help of the adsorbent fluid is such that the refrigerant and the attractive fluid in the absorber or absorber part of the chiller, during a heating process; form a solution. This solution can not be led to the next part by the laws of thermodynamics and heat transfer, after which the pump moves from the absorber to the generator to transfer it. The solution of adsorbent and refrigerant enters the generator by the pump and there, by absorbing heat, the phase of the solution changes and the refrigerant evaporates. The refrigerant vapour then enters the condenser to change phase. As in the compression chiller cycle, the condenser would receive refrigerant vapour from the compressor and perform the same process on it. In the meantime, the diluted solution is returned from the generator to the absorber section. A heat exchanger is used to recover energy in this part. This device can be effective in the amount of energy consumed by the generator.
In fact, the rest of the absorption chiller cycle is like a compression chiller. Thus, in both chillers, the condenser and the evaporator are the two main starting and ending points, and the condenser has a type of input material in both of these chillers, performs a similar process on it, and finally returns a type of material to the expansion valve. But the difference between the performance of these two chillers in terms of compression in the compressor or absorber assembly, heat exchanger and generator. The operation of compression and absorption chillers is done by focusing on changing the phase of the refrigerant to bring it to different phases through thermodynamic processes so that it can dissipate heat.
Comparison of compression and absorption chillers based on application
The choice of the type of chiller used depends on the conditions, needs and demands of the facility and space. These criteria include the amount of budget, more or less access to water, access to energy consumption to operate the chiller, which is defined in terms of electricity or fossil fuels, the tolerance of the structure to maintain the chiller, as well as the area of available space.
The conditions and location of installation of absorption chillers require more care and safety because these chillers have more weight than other models of chillers (compression) due to the placement of more components inside. Therefore, the installation infrastructure should be considered during installation. Also, the dimensions of the absorption chiller are larger and require more space.
The absorption chiller consumes less electronic energy because it uses thermal energy and fossil fuels. However, this chiller can be considered as a pollutant by burning fossil fuels. Thus, as mentioned, depending on climatic conditions and access to energy can be considered positive or negative.
Absorption chiller – except for direct flame type – produces less vibration and noise pollution so it can be suitable for residential areas.
The difference between absorption and compression chillers in costs
If we assume other variables such as the capacity of chillers are the same, the cost of buying an absorption chiller is higher than a compression chiller. Also, due to the presence of more components and the more complex formation of the absorption chiller structure, the maintenance cost is higher for this chiller than for the compression chiller. From another perspective, due to the presence of absorbers in absorption chillers, the need for water is more and as a result, it consumes more water, and consequently, the cost of supplying water to absorption chillers is more than compression chillers.