Evap condenser fan control


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We are looking to add a variable speed drive to an existing industrial evaporative condenser. Normally we would control the drive through algorithms in the main refrigeration controller.

I'm looking for a stand alone unit that can take an input signal from a transducer and control fan speed accordingly. Does anyone make a device specifically for this application?
Why don't you just use the intelligence provided in most commercial VSDs? We have used and programmed the Hitachi L200 series drive with a PID control loop that will work directly from a pressure transducer input. One thing we did discover, however, is that to achieve the most effective control of the system the air on temperature of the condenser is a key element in achieving fine control. We now make condenser control systems that measure the air on, air off, gas in & liquid off temperatures as well as the discharge pressure.