Fan-Powered Mixing Boxes

Fan-powered mixing boxes are variable air volume (VAV) devices that modulate the amount of air that enters the space. A damper located in the supply airstream modulates the amount of conditioned air that enters the space in response to space thermostat requirements. The difference between a fan-powered mixing box and a standard VAV box is the addition of a fan inside the box. This fan induces air from the ceiling plenum and mixes it with the primary air, hence the name mixing box. By introducing ceiling plenum air back into the space, the fan box is able to capture waste heat from the lights to help offset any space heating demands, thereby saving energy.

On a "series" box, the fan runs continuously whenever the system is energized to supply a constant quantity of total supply air to the space. This total air is made up of a mixture of primary air (from the air handler) and ceiling plenum air. As the space cooling load becomes satisfied, the primary air damper begins to close. As this damper closes a proportional amount of plenum air is induced through a port on the side of the box such that the total quantity of air entering the space stays constant.

On a "parallel" box, the fan runs only when there is a call for heating from the space thermostat. As the cooling load becomes satisfied the primary air damper closes to a minimum position. On a call for heat the fan is energized and pulls air from the ceiling plenum through the box and into the space. If the space temperature drops further, optional supplemental heat (either electric resistance or hot water) is energized to provide additional heat to the space.

45S Series Fan-Powered Mixing Box

The 45S Series Fan-Powered Mixing Box provides variable volume cooling/heating for large zones. Available in six sizes from nominal 500 to 3,000 cfm for cooling only, heating only or cooling & heating. Heat is available in either electric or hot water.

45T Parallel Fan-Powered Mixing Box

The 45T Parallel Fan-Powered Mixing Box provides variable volume cooling/heating for large zones. Available in six sizes from nominal 500 to 4,000 cfm for cooling only, heating only or cooling & heating. Heat is available in either electric or hot water. The parallel fan operates in the heating mode only and mixes varying quantities of plenum air with heat from the box to provide precise temperature control over a wide range of operating conditions.