Variable Air Volume Dump Bypass Air System
The variable air volume dump bypass air system supplies a constant volume of air at a constant pressure and temperature in a single run of duct.
Dump bypass boxes supply air to the ceiling mounted air diffusers throughout the building. The volume of air delivered by the supply fan is set at a constant volume.
The air handling fan should be sufficient to maintain a minimum operating pressure at all control boxes. Operating at higher duct static pressure than necessary wastes energy and results in a higher noise level at the control boxes due to throttling.
Wall mounted thermostats sensing zone temperature, regulate the volume of air allowed to enter the controlled area through the above suspended ceiling mounted variable volume air control boxes.
On a call for cooling, the vav bypass system delivers an increased volume of air to the zone. Full cooling is the maximum air flow that the box is set to deliver. Minimum cooling, is the minimum air flow that the control is set to deliver.
The minimum air flow is usually 25% of maximum air flow and ensures that there is ventilating air available for the occupants during the heating season.
Some rooms such as conference and interior training rooms have bypass boxes with electric reheat coils and usually require a higher minimum air flow to ensure safe operating conditions.
When the VAV dump bypass system boxes are in the minimum position, air is bypassed to the above suspended ceiling space. Each box is equipped with a bypass balancing damper at the top. This balancing damper should be set, ensuring that too much air does not bypass to the ceiling space. This ensures other boxes are not deprived of their required supply air.
Perimeter thermostats also control pneumatic control valves for the perimeter hot water heating system.
The return air fan which draws air back from the space provides the return link in the air circulation for the zone.
The air system is comprised of the:
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