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RT-SVX073A-EN
Figure 38. Energy recovery wheel economizer operation
Outside Air Intake Damper
(Mist Eliminator not shown)
Outside Air Bypass Damper
Path to
Filters
& Coil
Un-
Conditioned
Outside Air
Path to
Filters
& Coil
Unit Return
Airflow
Return Air Damper
Exhaust Air
Bypass Damper
Exhaust Air
Path to Exhaust Fan
Building Return Air
Energy Recovery Wheel Availability
In cooling mode, wheel activation conditions are assessed
based on indoor (return air) vs. outdoor enthalpy. Indoor
and outdoor enthalpy values are calculated using the same
sensors as used for comparative enthalpy. If the outdoor
enthalpy is 3 BTU/pound greater than indoor enthalpy, the
wheel is activated to remove energy from the incoming
outdoor air. Any time economizing operation is active
energy wheel operation is inhibited.
In heating mode, the wheel is activated based on indoor
(return air) vs. outdoor dry bulb temperature. If the outdoor
air temperature is 5° F less than the indoor (return) air
temperature the wheel is activated to recover heat energy
from the relief air.
Energy Recovery Cooling
During active energy recovery cooling modes, both bypass
dampers are driven closed to provide 100% energy
recovery cooling. VAV units only consider the enthalpy
evaluation to enable active cooling.Single Zone units not
only consider the enthalpy evaluation, but also checksif the
Space Temperature has exceeded the Space Temp
Cooling Setpoint. If the temperature fall below this setpoint,
active energy recovery wheel operation for cooling is
terminated.
Energy Recovery Heating
Energy recovery heating is available for occupied heating
modes VAV, Single Zone, Daytime Warmup, and SA
Tempering. Both VAV and Daytime Warmup modulate the
bypass dampers closed in sequence, Outdoor Air Bypass
first then Return Air Bypass, to provide capacity control of
discharge air temperature to the Active Heating Setpoint.
SA Tempering controls the dampers the same way to
maintain discharge air temperature to the SA Cooling
Setpoint. Single Zone units also consider the Space
Temperature relative to the Space Heating Setpoint for
active recovery wheel heating, enabling the wheel when
the temperature is less than the setpoint and disabling the
wheel when the temperature exceeds the setpoint.
Energy Wheel Frost Avoidance
During active heating modes, the control will attempt to
prevent frost forming on the wheel as the Leaving
Unit Startup
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