Thermolec Application &Technical Notes - Manual (Page 18)

THREE EASY STEPS
STEP 2 - (continued)
Variable Air Volume units (VAV)
The
"Thermo-V"
electric heater developed by Thermolec eliminates the common problems that are
encountered in the application of an electric heater to a VAV box as described below:
A. When the VAV Box is in the minimum opening position, the air flow is often below the minimum
required to operate a standard electric heater, causing element overheating and possible tripping of
the thermal cut-outs. The common solution is to increase the minimum ventilation air flow to
accommodate the minimum air flow required to operate the heater which translates into energy waste.
B. The static pressure in the duct downstream is so low that even the most sensitive pressure
differential switch is unable to detect sufficient pressure to activate the electric heater.
The common solutions are:
1. To create an artificial pressure by adding restrictions at the outlet (perforated plate), which
creates a costly and unnecessary pressure loss when the box is in a fully open position.
2. To measure the pressure upstream of the VAV box, which could be dangerous, since, with a
restricted or totally closed box, there is pressure without air flow. The electric heater will have to
rely solely on it’s safety thermal protections to shut off.
Common Problems Encountered