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Cooling towers are simple mechanisms.  Their operation is based on the natural occurrence of evaporative cooling – something most of us have experienced daily since the first time we got wet and felt a chill. But despite their simplicity, cooling towers play a crucial role in operational efficiency of the entire chilled water system. Not only are they the exit point for all those BTUs in a building that the chilled water system is working so hard to absorb and eliminate, their operation has the potential to significantly reduce the amount kWs going to the biggest energy hog in our system—the chiller.

To appreciate the role that cooling towers play, it’s important to take time to understand the refrigeration process in a chilled water system.

Each of these stages overlaps via some form of heat transfer, ultimately taking the heat from the building and releasing it to the atmosphere using sequential media.  In the middle of all of this is the refrigeration cycle.

So what happens in the refrigeration cycle?

Basically, the refrigeration cycle is responsible for transferring the heat absorbed by the return chilled water (coming back from the building) and transferring it to the condenser water which circulates to the cooling tower where it releases the heat to the atmosphere.  To better understand this, let’s start at the bottom of Figure 1, at the compressor motor.

Note that most chillers are packaged with all of the following components: compressor, condenser, expansion valve, and evaporator.  Each of these components is shown in Figure 1.  The refrigerant entering the compressor carries with it the BTUs transferred to it from the chilled water loop.  As it enters the compressor this refrigerant is in a low pressure/low temperature gaseous state.  The compressor “pumps up” the refrigerant into a high pressure/high temperature state, since temperature increases with pressure of any given refrigerant.