Does Your Evaporative Cooling System Circulate Enough Water?

Important that the water distribution system is capable of circulating a minimum of 0.75 gallons/min for every foot of pad system length (GPM/ft). This means, for instance, that a 60' pad section should have a water distribution system capable of circulating a minimum 45 gallons of water over and through the pads each minute. Before you get too concerned, realize that only a small fraction of this water will actually evaporate. In fact, the recommended circulation rate is about ten times the max...imum evaporation rate. So why do we need to circulate so much water? First, it is important to keep in mind that unlike fogging pads, with six-inch-pad systems water is only applied at the very top of the pad and as a result it takes a lot of water to insure that the pads get thoroughly wetted all the way to the bottom. Thus, you will find dry spots and/or streaking are more likely to occur in systems where the water circulation rate is below 0.75 GPM/ft. Streaking will, of course, lead to decreased cooling as some of the air entering the house moves through sections of dry pad instead of wet pad (Figure 1).