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Cooling Towers
If a chiller is used to provide chilled water for building air conditioning, then the heat energy that is absorbed through that process must be rejected. The two mon ways to reject thermal energy from the pression process are either directly to the air or through a cooling tower. In a cooling tower, water is recirculated and evaporatively cooled through direct contact heat transfer with the ambient air. This cooled water can then be used to absorb and reject the thermal energy from the condenser of the chiller. The mon cooling tower used for HVAC applications is the mechanical draft cooling tower (Figure ). The mechanical draft tower uses one or more fans to force air through the tower, a heat transfer media or fill that brings the recirculated water into contact with the air, a water basin (sump) to collect the recirculated water, and a water distribution system to ensure even dispersal of the water into the tower fill.
Figure shows the relationship between the recirculating water and air as they interact in a counterflow cooling tower. The evaporative cooling process involves simultaneous heat and mass transfer as the es into contact with the atmospheric air. Ideally, the water distribution system causes the water to splash or atomize into smaller droplets, increasing the surface area of water available for heat transfer. The approach to the wet-bulb is monly used indicator of tower size and performance. It is defined as the temperature difference between the cooling water leaving the tower and the wet-bulb of the air entering the tower. Theoretically, the water being recirculated in a tower could reach the wetbulb temperature, but this does not occur in actual tower operations.
FIGURE Air/water temperature relationship in a counterflow cooling tower.
The range for a chiller/bination is determined by the condenser thermal load and the cooling water flow rate, not by the capacity of the cooling tower. The range is defin