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24 VAV-PRC003-EN
Application Tip Summary
Tip 1. Use comfort zones
Units serving thermal zones can
provide greater comfort by dividing the
thermal zones into “comfort zones”
using a changeover-bypass-VAV
system.
Tip 2. Create thermal zones
Create thermal zones which minimize
simultaneous heating and cooling
requirements. This will avoid
unnecessary changeover of the system
and maximize comfort. As an example,
a computer room would be a poor
candidate for one comfort zone of a
changeover-bypass-VAV system
because it will rarely, if ever, require
heating.
Tip 3. Use local heat
Zones which vary thermally by
requiring more heat than the other
zones or require heat when the HVAC
unit is in cooling mode should use local
heat. Local heat in the form of VariTrane
VAV units with electric or hot water
heat, or wallfin, or convectors, or duct-
mounted coils. The standard VariTrac
controller is capable of controlling the
heat based on zone temperature
demands.
Tip 4. Place dampers properly
The bypass damper should be ducted
between the supply and the return of
the unit as close to the unit as possible,
and should be sized to handle 80% of
the total system CFM.
Tip 5. Control building pressure
It may be necessary to provide a
modulating means to control building
pressure, especially when economizers
or demand-controlled ventilation are
used in conjunction with a changeover-
bypass-VAV system.
Tip 6. Use fan-powered VAV boxes
Consider using fan-powered VAV boxes
to provide local heat or to enhance
comfort levels in some of your zones.
Conference rooms, or zones with high
wall heat loss are ideal for either series
or parallel units.
Application
Considerations