Honeywell THX9321 Prestige 2.0 System Installation Manual page 22

System Installation Guide
Commercial dehumidification
The thermostat reads the indoor humidity level and allows the user to set a dehu-
midification setting. The thermostat controls the humidity level using the cooling
system or a dehumidifier.
Dehumidification Equipment Options: (ISU 9000)
• A/C with Low Speed Fan
• A/C with High Speed Fan
• Hot Gas Bypass
• Dehumidifier
When set for A/C with Low Speed Fan, A/C with High Speed Fan or Hot Gas
Bypass, there are six methods of dehumidification control: (ISU 9080) See
descriptions of each, below.
1 Basic: This option uses the cooling system to reach the desired humidity
level. Minimum On Time, High Humidity Comfort Reset and Reheat
are not used with this method. This setting is commonly used if your
dehumidification equipment is Hot Gas Bypass.
2 Minimum On Time (ISU 9090): This option ensures that the compressor runs
long enough to effectively reduce humidity when the cooling equipment is
cycled on. The compressor will run for the minimum "on time" you set until
the desired humidity level is reached.
3 High Humidity Comfort Reset (ISU 9100): This option uses the cooling
system to lower the temperature up to 5° F below the current cool setpoint
until the desired humidity is reached. The high humidity comfort range is
from 1° to 5° F.
4 High Humidity Comfort Reset with Minimum On Time (ISU 9090 and 9100):
This method uses both options above to reduce humidity while maintaining
a comfortable temperature.
5 Reheat (ISU 9080): This option allows heating to run during dehumidification
to help maintain a comfortable temperature. If only cooling stage 1 is used,
during the "off" cycle, both cooling and heating run at the same time as
needed to dehumidify without overcooling. This option cannot be used in
the Heat mode. This option is effective only if using a system with the A-Coil
located before the heating coil (heat exchanger).
6 Reheat with Minimum On Time (ISU 9080 and 9090): This method uses
both Reheat and Minimum On Time options above to reach the desired
humidity level.
The Dehumidifier option requires a dedicated unit for dehumidification. The ther-
mostat can be setup to control dehumidification in all modes (Heat, Off, Cool [ISU
9120]).
Hot Gas Bypass - During a call for dehumidification, the cooling capacity will be used to remove more latent heat
than sensible heat. The operation of Hot Gas Bypass varies by equipment. For more details, contact the equipment
manufacturer.
Reheat can be used on heat pump applications that have a forced air backup heat source (gas, oil or electric). The
thermostat will turn on the first stage of forced air backup heat during Reheat.
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