Installation and Operation Manual

© 2012 557_D - 11/12
35 of 48
A Watts Water Technologies Company
Relative Humidity Operation
Section F
Relative Humidity (RH) is controlled by maintaining the Minimum Humidity using
humidification and by maintaining Maximum Humidity using dehumidification. The RH
is maintained within a 5% differential. The differential is applied above the minimum
setpoint, and applied below the maximum setpoint.
To avoid condensation on windows, the minimum relative humidity setting can be
changed according to the following outdoor temperatures.
Outdoor Temperature
-10°F (-23°C) 0°F (-18°C) 10°F (-12°C) 20°F (-7°C) 30°F (-1°C)
Suggested RH Min
20% 25% 30% 35% 35%
RH is affected by changes in the ambient air temperature. When using a programmable
schedule, the thermostat calculates the relative humidity setpoint with respect to the Set
Heat Room setting when in heat mode, the Set Cool Room when in cool mode,
and the average between Set Heat Room and Set Cool Room when in auto mode.
This may result in changes in displayed RH when the mode is changed.
When the mode is set to off, the humidification and dehumidification systems do not
operate.
The thermostat has three humidification modes.
Operation Mode Required
Relay(s)
Sensor
Required
Stand Alone Humidifier
Humidifier operates independently of the HVAC
system.
Available in all modes except off.
HM1 ACC RELAY
= HUM
None
Humidifier with Fan
Humidifier ducted together with HVAC system.
The system fan is operated whenever the humidi-
fier is operating.
Available in all modes except off.
HM2 ACC RELAY
= HUM
None
Humidifier with Air Heating
Humidifier ducted together with HVAC system.
The air system must be heating (heat pump,
furnace, electric or hydronic fan coil) in order to
allow the humidifier to operate.
Available when heating.
HM3 ACC RELAY
= HUM
None
Fan Post Purge
------------------------------------------------------
------------------------------------------------------
The fan relay includes a post purge feature that operates the fan after the heating or
cooling system has shut off. When a duct temperature sensor is installed the length
of post purge is based on the air duct temperature and the Heatpurge or Coolpurge
temperature settings. When there is no duct temperature sensor installed, the length
of post purge is based upon the Heatpurge and Coolpurge time settings.