CHAPTER 2 _LTY _Case study1.pdf - tHERMAL SCIENCE trouble-free hvac cooling towers A MAI NTE NANCE G U I D E Air conditioning and refrigeration systems

CHAPTER 2 _LTY _Case study1.pdf - tHERMAL SCIENCE...

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Air conditioning and refrigeration systems ranging from light commercial to industrial applications may rely on cooling towers to remove waste heat. While there are many different types of cooling towers and evaporative condensers used with HVACR systems, the basic methods of operation and maintenance are fairly common to all designs. Because of the inherently rugged construction of modern cooling towers, proper maintenance is often overlooked until major cooling system problems develop. Such problems are avoidable if you understand the basic principles of cooling tower operation, and perform periodic inspection and maintenance of the cooling tower system. It also helps to understand that a cooling tower is a collection of systems that work together. Here’s an overview of how these systems operate: Hot water from the condenser is delivered to the cooling tower by the condenser pump through distribution piping. The hot water is sprayed through nozzles onto the fill (heat transfer media) inside the cooling tower. Some cooling towers feed the nozzles through pressurized piping, others use a water distribution basin and feed the nozzles through gravity. A cold water collection basin at the base of the cooling tower gathers cool water after it has passed through the heat transfer media. The cool water is pumped back to the condenser to complete the cooling water loop. Cooling towers use evaporation to release waste heat from an HVAC system. Hot water flowing from the condenser is slowed down and spread out in the fill. A portion of the hot water is evaporated in the fill area, which cools the bulk water. Cooling tower fill is typically arranged in packs of thin corrugated plastic sheets or, alternately, as splash bars supported in a grid pattern. trouble-free hvac cooling towers A MAINTENANCE GUIDE THERMAL SCIENCE Large volumes of air flowing through the heat transfer media help increase the rate of evaporation and cooling capacity of the cooling tower. This airflow is generated by fans powered by electric motors. The cooling tower fan size and airflow rate are selected for the desired cooling at the design conditions of hot water, cold water, water flow rate and wet bulb air temperature. HVAC cooling tower fans may be propeller type or squirrel cage blowers depending on the cooling tower design. Small fans may be connected directly to the driving motor, but most designs require an intermediate speed reduction provided by a power belt or reduction gears. The fan and drive system operates in conjunction with a starter and control unit that provides start/stop and speed control. As cooling air moves through the fill, small droplets of cooling water become entrained and can exit the cooling tower as carry-over or drift. Devices called drift eliminators are used to remove carry- over water droplets. Cooling tower drift becomes an annoyance when the droplets fall on people and surfaces downwind from the cooling tower. Efficient drift eliminators remove virtually all of the entrained cooling water droplets from the air stream.
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