2) The Chilled Water Plants can be used for the Large Multi Storey Buildings
In the direct expansion types of the central air conditioning plant, the refrigerant like R22 flows through the whole air conditioning system including the air handling unit. When the refrigerant flows in the refrigeration piping there is lots of drop in its pressure. Due to this the length of the refrigeration tubing and the distance between the condenser and the air handling unit should be kept minimum possible.
If the air handling unit is kept at the height more than the condenser, the loss in pressure is pronounced since refrigerant travelling from the condenser to the air handling unit is in liquid state. As the distance between the air handling unit and the condenser increases the loss in pressure also increases. At certain point the losses may be so high that the refrigerant may not be able to reach the air handling unit, leading to complete failure of the system. At the larger height difference there is also oil return problem from the refrigerant to the compressor.
Due to these reasons, in direct expansion type of the central air conditioning plant there is limitation on the distance between the condenser and the air handling unit. The distance between the two cannot be too high. This limits the application of the direct expansion type of central air conditioning systems to the small buildings or a number of rooms on the single floor. In such cases the plant room and air handling room and the rooms to be cooled are located on the same floor. The height difference between the condenser and the air handling units has to be quite reasonable so that they can function well.
One of the solutions to increase the capacity of the DX systems can be to increase the number of air handling units on upper floors. But with this will be additional number of joints in the refrigerant tubing from which there will be higher chances of leakage of highly expensive refrigerant. This leads to too many operational and maintenance problems.
One may think that we can employ compressor of very high capacity to increase the refrigerant pressure, but this will lead to highly excessive capital and running costs of the plant. This is because we will have to install the compressor of capacity much higher than needed.
Thus the direct expansion types of the air conditioning plants can be used only for smaller buildings or various rooms on the same floor.
There are no pressure loss problems in the chilled water system. In this system chilled water is pumped by the pump at very high pressure, which is good enough to carry it to various floors of the multi storey building. The losses in the pressure of water are accommodated by the sufficient capacity of the pump, which has low capital and running cost. Further, the water doesn’t carry any oil so there are no oil return problems.
In case of the chilled water system the compressor, condenser, expansion valve and the chiller are all kept at the same level in the single plant room. There is no problem as such of the height difference between the condenser and the air handling unit since the refrigerant does not travels to the air handling unit. The flow of the refrigerant is limited to the chiller plant. The water chilled in the chilled flows to the various air handling units kept on different floors of the building. The whole arrangement and the structure of the chilled water type of central air conditioning plant makes it more suitable for cooling the large multi storey buildings and even for very long distances along the same floor level. This makes the chilled water central air conditioners more popular than the direct expansion type ones.