Desert Aire Aura QS, Инструкция по установке и эксплуатации

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Desert Aire - QS/QV Manual
rotate as well. So if compressor 1 starts and then stops, a compressor in circuit B will be the
next to start.
5.4.8 CO
2
Operation
The standard IAQ controller that has CO
2
control will command more outdoor air into the space
when CO
2
levels rise and use less outdoor air when CO
2
levels fall. Although possible,
occupancy will not be commanded based on the CO
2
level. Since there is a minimum value
for room area regardless of CO
2
, occupancy must be either commanded independently by a
time schedule or manually overridden.
Additional hardware requirements for CO
2
control include two modulating actuators for the
outdoor air damper and the recirculation damper. A variable frequency drive (VFD) for the
supply air blower and a VFD for the exhaust air blower are also required. Three differential air
pressure transducers are included, one sensing the pressure drop across the reheat condenser
(P1), one sensing the heat wheel supply pressure drop (P2) and the third sensing the heat
wheel exhaust pressure drop (P3). A sensor mounted outdoors to provide a base reading as
well as a CO
2
sensor in the conditioned space will also be supplied.
A PID control loop has been added to determine the P2 set point based upon the CO
2
difference (the conditioned space reading minus the outdoor reading) and comparing this to a
set point of the ASHRAE recommended default set point of 700 ppm. The output of the PID
control loop will be the P2 set point and will vary from a low limit to a high limit. Both of the low
and high limits and the 700 ppm CO
2
set point are user adjustable. This varying set point is
used to control the modulating damper actuator.
A control loop has been added to control the damper actuator positions. The outside air
damper will vary from a minimum to a maximum based upon the heat wheel supply pressure
drop (P2) and the calculated P2 set point. The modulating damper actuators work in opposition
to each other. As the outside air damper opens “x”% the recirculation air damper closes “x”%.
The program also includes control loops for the supply blower VFD and the exhaust blower
VFD. The supply blower speed will vary as the output of a PID loop to maintain a constant
pressure drop across the reheat condenser. The P1 pressure set point is a fixed value for the
system and is adjustable by the user. The exhaust blower speed will vary as the output of a
PID loop to maintain a constant difference from the calculated P2 set point and the actual P2
pressure. This difference is adjustable from a negative 0.300” wc to a positive 0.300” wc by
the user as well to meet the building requirements.
5.4.9 Suction Pressure Operation
The suction pressure needs to protect the unit when a refrigerant circuit loses its charge. The
glycol concentration in the water circuit of the brazed plate heat exchanger may also allow for a
lower suction pressure cutout value when the compressors are running in the heat pump mode.
Also, restarting after an unoccupied cold soak condition needs to be addressed.