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Since it is obvious that during dehumidification mode the cooling of the air to the design
dewpoint will also provide more sensible capacity, dehumidification stages will take
precedence over cooling stages. Also note that the single compressor staging in a four
compressor unit will take place without the caveat described in the dehumidification section.
5.4.5 Heating Operation
5.4.5.1 Water Source Heat Pump
For Aura™ Products
For water source heat pump units, Desert Aire does not use a reversing valve in the
refrigeration circuit. Instead, Desert Aire uses solenoid valves which direct the refrigerant flow
such that it always travels counter to the water flow in the coaxial heat exchanger.
Heating operation is enabled when the intake air temperature (air entering the DX
evaporator, downstream of the enthalpy wheel, if equipped) is below the supply air
temperature set point and the supply air temperature dewpoint.
The supply air set point is achieved by varying the speed of the compressor for more or
less capacity based on the temperature of the supply air. As more capacity is required,
the compressor speed will increase. The compressor speed may ramp up periodically
to maintain oil level in the compressor, the supply air temperature is above the set point,
a bypass valve will open to prevent overheating of the space.
Should auxiliary heating be installed, a modulating output will activate when the
capacity of the heat pump is insufficient to heat the air to the desired leaving air
temperature. Use of the modulating output is determined when the reheat valves
reach 100% for a set period of time, capability is available should there be higher
airflow than anticipated.
For TotalAire™ and VerticalAire™ Products
For water source heat pump units, Desert Aire does not use a reversing valve in the
refrigeration circuit(s). Instead, Desert Aire uses solenoid valves which direct the
refrigerant flow to either a DX coil (cooling or dehumidification mode) or a water to
refrigerant exchanger (heating mode). The Desert Aire sequence allows for constant
control of the SAT without the swings typically experienced with a reversing valve
system. In addition, Desert Aire also utilized a fully modulating hot gas reheat valve
which provides for more precise control of the SAT.
The standard IAQ controller allows for predictive operation of the heat pump heating
stages. While compressor operation is still allowed at IA temperatures below 68°F, the
use of a predictive calculation based on unit size and airflow determines the number of
compressor stages required to meet the SAT set point. This can be accurately predicted
based on the unit nominal capacity and the airflow.
Desert Aire - QS/QV Manual
Summary of Contents for Aura QS
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