Honeywell PRESTIGE THX9321 - Manual (Page 109)

THX9321 PRESTIGE ® 2.0 AND THX9421 PRESTIGE ® IAQ WITH EIM
109 68-0311—02
Dehumidification - Commercial
The thermostat reads the indoor humidity level and allows the
user to set a dehumidification setting. The thermostat controls
the humidity level using the cooling system or a dehumidifier.
If humidification and dehumidification are setup to operate in
the same system mode (Heat, Cool, Off) and you are sensing
humidity from one location, the thermostat will automatically
enforce a 15% deadband between the humidification and
dehumidification settings. The thermostat will automatically
switch between humidification and dehumidification to maintain
the desired humidity level.
If humidification and dehumidification are setup to operate in
the same system mode (Heat, Cool, Off) and you are sensing
humidity from two different locations using a remote wireless
indoor sensor (for example, main level and crawl space), the
thermostat will allow humidification and dehumidification to
operate at the same time, and there is no deadband between
humidification and dehumidification settings.
Dehumidification Equipment Options: (ISU 9000)
• A/C with Low Speed Fan
• A/C with High Speed 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 9080):
Fig. 234.
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.
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.
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.
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.
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). 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 9080 and 9090): 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, U2, or U3 as
normally open or normally closed (ISU 9050) and wire to the
Low Speed Fan terminal on the equipment. For example, if the
U1, U2, or U3 terminal is normally closed, it will open when the
thermostat calls for dehumidification.See “Wiring IAQ
Equipment or a Heat/Cool Stage to the Universal Terminals”
beginning on page 149.
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 9000. See
Fig. 235.
Fig. 235.