Trane IntelliPak 2 Series, Installation, Operation And Maintenance Manual

Page: 99 / 220

RT-SVX24Q-EN 99
of cumulative compressor run time while the reheat
condenser coil pumpout relay is in a certain state. If
compressors accrue an amount of run time equal to the
HI-adjustable purge interval time without the pumpout
relay changing states a purge cycle will be initiated
lasting for three minutes.
During this cycle all compressors but the 2nd
compressor on circuit #1 will be energized if not
already, the reheat valve and cooling valves will be set
to 50%, and the reheat coil pumpout relay will be
toggled to its opposite state. After the three-minute
purge cycle completes the purge interval timer will be
reset and all system components will return to the state
they were in prior to entering purge.
During hot gas reheat control an evaporator frost
control function designed specifically for reheat modes
will be active. This function will reduce refrigeration
circuit capacity to 50% (1st compressor on each circuit
remaining on) when the Entering Evaporator Temp
drops below a non-adjustable limit of 35° F for 10
continuous minutes. Once capacity is reduced, it will
remain reduced until the current cycle of hot gas reheat
is terminated or a purge cycle occurs.
If the Entering Evaporator Temp remains below 35° F
for an additional 10 minutes both circuits will be de-
activated and remain off until the Entering Evaporator
Temp rises above 45°F. Even though all compressors
have been de-activated the unit will remain in
dehumidification mode and re-enable compressors up
to 50% capacity when the Entering Evaporator Temp
rises to 45°F or greater.
Energy Recovery Sequence of Operation
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The primary components of the energy recovery
system are the energy recovery wheel, exhaust air
bypass damper, outdoor air bypass damper, and the
energy recovery preheat output. See
Figure 69, p. 100
and Figure 70, p. 101 . A filter is also placed between
the wheel and the outdoor air damper and an indicator
scheme similar to that for final filters is provided to
notify the user when that filter needs to be changed.
The energy recovery wheel will only be energized
when both the Supply Fan and Exhaust Fan are
requested on by the various functions that control
them. Energy recovery is a passive function and can
not request fan operation.
Once the required airflow is present the wheel will be
commanded on if the indoor vs. outdoor conditions are
such that energy can be recovered. This is assessed
differently in cooling and heating modes.
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/
lb. greater than indoor enthalpy the wheel is activated
to remove energy from the incoming outdoor air. In
heating mode the wheel is activated based on indoor
vs. outdoor dry bulb temperature. If the outdoor
temperature is 5° F less than the indoor temperature.
the wheel is activated to recover heat energy from the
exhaust air.
In cooling mode the exhaust air bypass damper is held
closed, providing 100% energy recovery capacity
during cooling modes of operation. In heating modes,
including CV heating, VAV Heating, CV Supply Air
Tempering, VAV Supply Air Tempering, Morning
Warm-up, and Daytime Warm-up the exhaust air
bypass damper is controlled to discharge air
temperature. The damper is modulated to keep the
supply air temp at the Supply Air Heating setpoint for
VAV control, or for CV control, supply air temp will be
controlled to a calculated Supply Air Heat Setpoint
based on conditions in the space.
If the wheel is active, supplemental heat (electric,
hydronic, gas) control algorithms will be disabled until
the exhaust air bypass damper is fully closed
(maximum heating capacity from the wheel). At this
point, supplemental heat algorithms are released to
calculate supplemental heat capacity requests using
standard setpoints until the setpoints are satisfied. In
VAV occupied modes the energy recovery wheel will
remain active after termination of supplemental heat
above heating setpoint until the exhaust air bypass
damper is opened fully for 3 minutes (indicating
minimal capacity requested from the wheel). In CV
occupied heating mode the wheel will remain active
after termination of a heating cycle until the zone temp
rises above the Occupied Zone Heating Se 1.0°F
and the exhaust air bypass damper is fully open. The
wheel will remain active if these conditions persist
continuously until the expiration of a HI-adjustable
time-out period or until the zone temp rises above the
Occupied Zone Cooling Setpoint - 0.5°F.
During active Economizing control the energy wheel
will be disabled but the outdoor air bypass damper will
open an amount that tracks the opening of the OA
damper proportionally from minimum position to fully
open.
To protect the wheel from frost build-up in heating
modes a frost avoidance function is included. This
feature will energize the energy recovery preheat
output (if configured) and modulate the outdoor air
bypass damper open (to reduce incident cold outdoor
air on the wheel) as necessary when the Leaving
Recovery Temp Sensor value is less than the Recovery
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