UFAD VAV with Baseboard Heating
UFAD VAV with Baseboard Heat
This system is similar to a VAV system with baseboard heat, except that:
1. the supply air is delivered via an underfloor plenum and,
2. a return-air bypass arrangement is assumed in order to provide sufficient dehumidification without the need for reheat.
Because this system delivers air via an underfloor plenum, be sure to include a raised floor/underfloor plenum height when drawing the rooms that will be assigned to this system. At design cooling conditions, the supply air is delivered from floor diffusers at a warmer supply-air temperature (default = 65°F) and at a lower velocity than is typical for overhead delivery methods. Because the supply air is introduced from the pressurized floor plenum, a warmer supply-air temperature is necessary to avoid an uncomfortable temperature difference between ankle and head heights. A modulating damper varies the amount of air introduced to the room based on the space temperature sensor.
If the zone thermostat calls for heat, the damper is closed to minimum position, and a convector (located in a trench that is not open to the floor plenum) or baseboard heater (located above the raised floor) activates to add heat to the zone. For any underfloor air distribution system, the floor diffusers should be as close to the supply shaft as possible to minimize the heat gain as the cool supply air travels through the underfloor plenum.
In this option, cooling and ventilation air are provided by the central system. As illustrated above, perimeter subdivisions of the plenum are created below each zone. A pressure-dependent modulating damper varies the amount of air introduced to the zone based on a space temperature sensor. In heating, the damper goes to minimum position and a convector in a trench that is not open to the plenum, or a baseboard heater located above the raised floor, engages to add heat to the zone.