This is a HVAC chilled water system cooling tower fan for a large chilled water system. Four large cooling towers for two chiller plants in a data center. Data center cooling systems generally are redundant not only for emergency situations but also for maintenance. The cooling tower fan typically has vibration switches installed in the fan assembly to shut the fan off in the event of too much vibration. A fan this large (approximately 6 foot diameter) needs to be balanced to prevent vibration that could possibly shake the cooling tower apart and create a safety hazard for workers. The fan is driven by a variable frequency drive that ramps the cooling tower fan up and down depending on demand. Demand or the load is typically based on outside air temperature and sometimes other temperature variables, A reset schedule is used to ramp the fan up or down based on those other variables and the outside air temperature. The faster the fan turns the more air is pulled through the cooling tower and the louvers inside the cooling tower. That means more heat is removed from the water but also more evaporation. For this reason, especially in a critical facility, it is important to have a back supply for the make up water. Some critical facilities have their own storage tanks for make up water in case the main source fails in some way. Depending on the load factors and the control of the system the fan will ramp up and down based on load or demand. The fan pulls air through the cooling tower and across the louvers where the water falls. As the water falls along the louvers the air is pull across the water where a heat exchange process takes place by the process of evaporation. Once the heat is removed using the process of evaporation it is then returned to condenser barrel to absorb more heat and return to the cooling tower to release the heat. To learn more about critical facilities and HVAC click here.