Modulating Hot Gas Reheat
For McQuay RoofPak™ Applied and Maverick™II Commercial Rooftop Systems
In a packaged rooftop system, hot refrigerant gas leaving the
compressor can be channeled to a separate coil to reheat the
air leaving the cooling coil, as pictured below. This reheat
costs no energy and is an excellent way to optimize
dehumidification. It is available as a factory-installed
option on McQuay RoofPak applied rooftop systems and
on Maverick II commercial rooftop systems.
For best performance, McQuay precisely controls or modulates
the supply of the hot gas to the reheat coil. This modulation helps
to maintain a constant, desired supply air temperature. Without it,
supply air temperatures can vary significantly as the unit’s
compressors cycle on and off. See Figure 1.
• MicroTech®III controls with integrated compressor and
reheat control. Reheat is automatically energized whenever
dehumidification is needed.
• Modulating valves on both the condenser coil and reheat coil
for more precise modulation.
• Enhancements on RoofPak systems that allow +/-1 degree of
supply air temperature control. These include an averaging
discharge sensor and VFDs that modulate condenser fan speed
and maintain a constant head pressure.
• Microchannel reheat and condenser coils, which are more
robust than traditional fin-tube coils and more resistant to
corrosion. Flat tubes and microchannel flow allow more heat
transfer per square foot of coil. And, because microchannel coils
require far less charge, refrigeration service is less expensive. No
receivers or oil flushing cycles are required and subcooling is
always provided. See Figure 3.
• Effective humidity control without using additional energy
to reheat the cooled air. Without hot gas reheat, a separate
heating system would be required to reheat the cooled,
dehumidified air to the desired level, which often violates
ASHRAE 90.1-2007 guidelines. Or, higher humidity levels
would have to be accepted in the conditioned space.
Engineered for flexibility and