Set Up Dehumidification With Cooling System - Honeywell VisionPRO 8000 Product Data

humidification and dehumidification settings. The thermostat
will automatically switch between humidification and
dehumidification to maintain the desired humidity level.
Dehumidification Equipment Options: (ISU 900)
• A/C with Low Fan
• A/C with High Fan
• Hot Gas Bypass
• Dehumidifier
NOTE: Hot Gas Bypass - During a call for dehumidifica-
tion, 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.
Dehumidification using the Cooling System
Dehumidification using A/C with Low Speed Fan, A/C with High
Speed Fan or Hot Gas Bypass, has the following methods of
dehumidification control (ISU 908):
Fig. 144.
Basic (ISU 908): This option uses the cooling system to reach
the desired humidity level. Minimum On Time, Cooling Droop
and Reheat are not used with this method. This setting is
commonly used if your dehumidification equipment is Hot Gas
Bypass.
Minimum On Time (ISU 908 and 909): 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.
Cooling Droop (ISU 908 and 910): 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
Dehum Over Cooling Limit range is from 1° to 5° F.
Cooling Droop with Minimum On Time (ISU 908, 909, and
910): This method uses both options above to reduce humidity
while maintaining a comfortable temperature.
Reheat (ISU 908): 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). This
feature requires a conventional forced air heating system (gas,
oil, or electric) in the application.
NOTE: 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.
NOTE: Reheat can be used on systems where the A-Coil
is located after the heating coil (heat exchanger),
but it is not effective at removing humidity.
Reheat with Minimum On Time (ISU 908 and 909): This
method uses both Reheat and Minimum On Time options
above to reach the desired humidity level.
If set for A/C with Low Speed Fan, configure U1 as normally
open or normally closed (ISU 905) and wire to the Low Speed
Fan terminal on the equipment. For example, if the U1 terminal
is normally closed, it will open when the thermostat calls for
dehumidification.
NOTE: The thermostat will not lower the fan speed when
the second stage of cooling is on.
Set up Dehumidification With Cooling
System
Some screens shown in this section may not appear on the
thermostat, depending on how you set up dehumidification.
1. Select the Dehumidification Equipment in ISU 900. See
Fig. 145.
2. Select the terminals wired to the A/C with Low Speed
Fan or Hot Gas Bypass. See Fig. 146.
3. Select whether the U1 terminal is Normally Open or
Normally Closed. See Fig. 147.
• Normally Open – contacts are normally open and will
close during a call for dehumidification
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VISIONPRO 8000 WITH WI-FI
Fig. 145.
Fig. 146.
33-00096—01
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