Candy Coating

Requirement:

Deliver 50 degree dry bulb and 33 degree dew point controlled air to coating and polishing pans and maintain the processing room in which they are located at 65 degree dry bulb and 48 degree dew point, all on a year round basis with intermittent use of the pans.

Solution:

Install "split direct expansion systems" that will allow for the accurate control of air environment regardless of the room use. Separate systems are used for "Process" and "Room" environmental control.

The 33 degree dew point temperature requirement at the pan inlet dictated the use of 30 degree set point controlled refrigerant temperature in the "Process" evaporator.

This is accomplished by controlling the evaporator refrigerant temperature with "Compensated Evaporator Pressure Regulation" in heat exchanger coils that have enough surface to obtain the 33 degrees leaving air dew point temperature with a 30 degree evaporator temperature that without the creation of ice...The air quantities delivered by the air handlers is constant even though the air quantity required by the process pans varies with use. The anomaly is accommodated with a pressure sensitive damper controlled air bypass.

The need for air side flushing at the completion of production runs is accommodated with a namual system of diverting dampers that "dump" the contaminated air to the outdoors for a short period of time. At the end of this "dump" cycle, the refrigeration system returns to full dew point control.

The required reheat is obtained by modulating 120 degree warm water through 3 way bypass valves that feed water type reheat coils.

The humidification of each system is obtained from SCR controlled electric duct type humidifiers located in the supply duct to each system.

by:

Kenneth W. Wicks

ASHRAE Fellow

5/3/99