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HVAC Systems
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When deciding on at HVAC system, the first question to answer is “Do I need humidity control?” Many industrial processes are hygroscopic and require humidity control in both summer and winter. We generally regard 40% RH at 68 F as the lowest humidity achievable with refrigeration. HVAC systems for humidity control are much more expensive because more tonnage is required and a reheat coil and humidifier are added to the system. For human comfort, most clean rooms use office type roof-top equipment.
The figure below shows a typical system using a simple office type roof-top unit. The conditioned air duct is connected to a plenum box on top of the fan-filter unit. the pelnum box is open on the sides to allow mixing of return air with the supply air. Never put straight conditioned air through a HEPA unit without mixing as the air will drop down on the occupants. With this type system, the return air flows freely back to the fan-filter units and the air conditioning unit. The return air also picks upu additional heat if the adjacent space is not air conditioned. For this condition, an enclosed system would be the best choice. Room pressure is maintained by the opening at the wall. Gerbig Enginieering can provide this dimension for the desired pressure.
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