Desert Aire Aura QS, Инструкция по установке и эксплуатации

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5.4.3 Dehumidification Operation
For Aura™ Products
5.4.3.1 Packaged Units
Dehumidification operation is enabled when the IA dewpoint is greater than the dewpoint
set point. The standard IAQ controller allows for a wide range of operating conditions through
the use of predictive capacity equations embedded in the controller. Based on the unit size,
airflow, dry bulb and wet bulb temperatures, and design supply dewpoint, the controller
calculates the IA enthalpy which dictates when the lag compressor is required. Short-cycling
will not occur since IA conditions do not change rapidly.
5.4.3.2 Q-Pump In Units
Dehumidification operation is enabled when the intake air dewpoint (air entering the DX
evaporator, downstream of the enthalpy wheel, if equipped) is greater than the dewpoint
set point. The controller allows for a wide range of operation conditions by varying the speed
of the compressors to meet demand. Since the air downstream of the evaporator but prior to
the reheat condenser is saturated, the temperature of this air is equal to the dewpoint of the
supply air. As the dewpoint temperature rises, the compressor speed increases to drive the
temperature back down. For 30-ton capacity units, an additional fixed speed compressor is
present for a greater range of capacity. Modulating valves then reheat the air to reach the
desired supply air set point. The compressor speed may ramp up periodically to maintain oil
level in the compressor. This provides optimal energy efficiency while meeting the design
conditions in a very stable manner. Short cycling will not occur since intake air conditions do
not change rapidly.
For TotalAire™ and VerticalAire™ Products
Dehumidification operation is enabled when the IA dewpoint is greater than the dewpoint set point.
The standard IAQ controller allows for a wide range of operating conditions through the use of
predictive capacity equations embedded in the controller. Based on the unit size, airflow, dry bulb
and wet bulb temperatures, and design supply dewpoint, the controller calculates the IA enthalpy
which dictates when the lag compressor is required. For units greater than 30-tons capacity, one,
two, three or all four compressors may be cycled to more closely match the unit capacity to the load.
This provides optimal energy efficiency while meeting the design conditions in a very stable manner
as the IA enthalpy condition is independent of the output of the control. Short-cycling will not occur
since IA conditions do not change rapidly.
Running one compressor in a four compressor system during the dehumidification mode does have
one caveat. Since the IA has a relatively low sensible load, additional warmer supply air may be
required to attain a neutral temperature. Also, the supply air for the indoor space may require
additional sensible heating to maintain the required preset condition, especially if the outdoor air unit
serves a perimeter space or the unit was designed for very low dewpoints. When these
circumstances arise where there is a relatively low outdoor air load, the sensible load of the outdoor
air is relatively low compared to a proportionally higher latent load. In this case, energizing the
second stage compressor allows the unit to work as a relatively effective heat pump, converting the
Desert Aire - QS/QV Manual