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HVAC School - For Techs, By Techs

Jan 15, 2018

Jeremy Smith goes over floating suction and floating head refrigeration strategies. He also talks a bit more about low-ambient equipment operation.

Floating suction controls developed when we started using low-pressure controls on rack refrigeration. As the electronics advanced, we developed controls that could control temperature, which impacts pressure as well. Nowadays, controls can cross data and be much more effective at controlling pressure and temperature.

Suction pressure is the greatest contributor to a system's compression ratio. The higher the compression ratio, the less efficient a system is; a high compression ratio can be costly for grocery business owners or managers. Therefore, floating suction controls set the temperature exactly to what it should be based on the system's load, not lower than what the suction temperature should be.

Floating head controls attempt to minimize the compression ratio from the high side of the system. The floating head attempts to maintain head pressure by matching condenser fans closely with ambient temperatures. Ambient temperature controls the floating head control's set points. These floating head controls can set the condensing temperature as low as 68 degrees (F). The main factor that prevents the temperature from getting any lower is the expansion valve. It is possible that EEV usage could enable even lower temperatures, but they have been quite problematic so far. Jeremy recommends taking advantage of natural subcooling to get the most out of your floating head strategy.

These controls have to decrease capacity before they hit their targets. As such, these floating head and suction controls can be erratic and "swing" from extremes upon startup.

Jeremy also covers:

  • Energy and monetary savings
  • Pressure differentials caused by floating head controls
  • Expansion valves in refrigeration
  • Superheat "floating"
  • "Drain" leg or regulator

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