Desert Aire SelectAire Plus SP Series, Инструкция по установке и эксплуатации

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The auxiliary heating outputs come set from the factory for control of staged control or
modulating control as specified at the time of order. When set for Staged, the dry contact
associated with the heating output will close on a drop in temperature of the zone set point
minus the deadband minus the differential. The contact will remain closed until the
temperature reaches the zone set point minus the differential.
Heater On = Zone Set Point – Heating Deadband – Heating Differential
Heater Off = Zone Set Point – Heating Deadband
Example:
- Zone Set Point: 85°F
- Heating Deadband: 2°F
- Heating Differential: 1°F
In this example, the heater output will close at 82°F and will open at 83°F. Due to
some system capacitance and sensor hysteresis, the actual zone condition may
overshoot these values slightly, but should not overshoot these values to cause the
unit to shift into a cooling mode. Should the heater be very oversized and the
overshoot significant, it may be necessary to increase the deadband to prevent
cycling between modes.
It should be noted that the nature of the staged heating will create a significant variation in
the supply air temperature as the heater is turned on and off. Heaters are sized for extreme
conditions (typically the 99th percentile heating capacity). At many times of the year the
heater is essentially oversized. Depending on the location of the supply ducts and diffuser
configurations, the variations may create drafts within the space. Also, if the air temperature
is very low and the heater cycles off, the supply air temperature may be lower than the space
dew point. This would cause condensation on ducts, diffusers, and surfaces.
Should there be issues with supply temperature variations, modulating heat should be
considered.
Modulating Heating
When the application has a moderate to extreme climate and outdoor air is specified, it is
recommended that auxiliary heating be modulating.
When the controls are set for Modulating heat output, both the binary heat output contact and
the modulating heat output are active. The binary heat output acts as an enable contact that
can activate a gas heater enable signal or start a hot water coil pump system. The modulating
output is intended to vary the gas valve, SCR electric heater, or hot water coil water flow rate.
The modulating heating sequence works based on a Zone Reset of the Supply Air
Temperature. When the zone temperature decreases to the Zone Temperature minus the
Heating Deadband, the controller enables heating mode and starts to increase the calculated
Desert Aire - SP Manual