Cooling tower water consumption is a growing concern among building owners as water and sewer rates are constantly on the increase. Water consumption can also be a major concern for engineers involved with the design of new cooling tower systems. During the permitting process, city or town officials will often want to know the expected average and peak water consumption in gallons per day (gpd) as well as the peak flow rate in gpm. The water consumption associated with toilets, sinks, showers, process loads, etc., can be estimated fairly easily from known population and expected occupancy rates. Cooling tower consumption on the other hand, is completely dependant upon the weather.
Although the total heat transfer will always be the same, the sensible and latent components are always changing because the entering air temperature and humidity conditions are always changing. The amount of water evaporated is obtained from the latent component, or the difference in entering and leaving humidity ratio. At peak design conditions, the evaporation rate can be 1.0% to 1.5% of the total circulation rate depending on the range. Note that the evaporation rate is much less in colder temperatures because the sensible component increases as the outside air temperature decreases.