Variable speed drive on cooling tower fans

Most of the duties in our cooling tower system only have manual valves. There are only two duties in which we have flow control valves to control the process temperature by varying the cooling water flow through the heat exchanger. The manual valves on the other duties are set based on based on the automatic valves being wide open. Then when the automatic valves modulate, the other duties, if anything, get more flow. This has not caused us any problems so long as the cooling tower system is sufficiently sized. Our process temperatures are less than 50 C and we keep the water quality reasonable. Perhaps that is why we haven't had any issues with heat exchanger fouling on the service side.

Our cooling tower pumps are fixed speed but we have variable speed drives on the cooling tower fans. These do a good job of controlling the cooling tower supply temperature except in those installations where the cooling tower sump size is excessive (China). With the flow control valves on the individual exchanges, the variable speed drive may not be absolutely necessary, but the process temperature control works better if it doesn't have to deal with daytime to nighttime or storm induced variation in supply temperature.

More control valves are being installed on the cooling water to our heat exchangers as our plants become more automated for the purposes of operability, improved quality and lower energy usage. Perhaps money is well invested in good control over cooling tower water quality.