DUMP BOX (VARIABLE AIR VOLUME) SYSTEM This type of system allows each area’s thermostat to vary the amount of cold air entering the occupied space, addressing the varying cooling loads. The dump box (bypass box) illustrated, always (in theory), consumes the same CFM from the main supply duct. The air is bypassed to the return air duct, forced into the occupied space or split between the two destinations. At a practical level the total CFM is different when the box is positioned to full bypass or full air flow to the occupied space relative to mixing positions between these two points. The main fans do not require a means of varying their CFM as the system requirement in the main supply and return ducts does not vary. As with all the fan systems, the air balancing should be performed by a qualified and experienced Air Balancing Technician. DUMP (BYPASS) BOX SYSTEM CONSTANT VOLUME RETURN FAN EXHAUST NC RETURN AIR AIR DUMP (BYPASS) BOX NO SUPPLY FAN THERMOSTAT SUPPLY OUTDOOR NC MIXED AIR AIR AIR I 7.57 M
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