3. Auto Humidify
This feature is designed to eliminate the problem of
sweating windows in very cold weather. When selected, the
set point is automatically reduced by 1 percent for every
drop of 2°F in outdoor temperature between 50°F and 0°F.
The set point may be changed at any time, and it will
continue to track outdoor temperature from the new set
point and current outdoor temperature. The adjusted set
point range is still limited to between 10 and 45 percent
relative humidity. To use this feature, an outdoor tempera-
ture sensor MUST be attached. If not, E3 error message will
be displayed.
4. Auto and Fan Humidify
The 2 choices of AUTO and FAN can be selected together.
This provides both functions simultaneously.
5. Humidify Off
The humidify function can be turned off completely. This
does not require changing existing set points.
TO SELECT HUMIDIFICATION (BETWEEN NORMAL,
FAN, AUTO, FAN AND AUTO, OR OFF) (SEE TABLE 4.)
Press HUMIDITY button to bring up humidity select screen. It is
indicated by "hu" or "dhu" in clock display. Successive presses
will change between "hu" and "dhu" in clock display. Select "hu"
for humidity functions. The large display shows actual humidity
level. The smaller display (in heat set point location) shows
humidity set point (HSP) or OF (off). When HSP value is
displayed, its value can be changed with up and down buttons.
Successive presses of MODE button will move between 5 choices
described above and each will be indicated as shown in Table 4.
To exit humidity select screen, press END button.
ADDITIONAL HUMIDIFY COMMENTS
The humidifier is actually turned on when humidity is 2 percent
below set point and turned off when it reaches 2 percent above set
point. This built-in hysteresis prevents humidify output from
toggling on and off when humidity level is near set point.
The vacation mode provides some additional humidification func-
tions. These are specially designed to provide protection for an
unoccupied home while simultaneously minimizing energy use.
Refer to "Vacation" section for additional information.
B.
Dehumidification
Dehumidification is done only during cooling. Depending on type
of equipment used, compressor speed, blower speed, set point
adjustment, and equipment cycling are modified to provide added
dehumidification. A dehumidification set point (separate from
humidification set point) is available to the homeowner. It can
range from 50 to 90 percent relative humidity. When actual
humidity is higher than set point, a dehumidification demand
exists. The Thermidistat Control responds by activating its dehu-
midify output. It may also control the compressor and blower,
depending on equipment type and dehumidify selection choice.
The 3 available selections are described below.
The amount of extra dehumidification available is very dependent
on the type of equipment in the home. Without a variable-speed
blower, the system’s ability to adjust dehumidification is very
limited.
1. Normal Dehumidify Operation
When normal dehumidify is selected, the compressor will
not turn on without a cooling demand. If dehumidify
demand exists while cooling, dehumidify output will also
be active (24vac removed). This output commands variable-
speed blowers to reduce their airflow, which improves
water removal from the cooled air.
2. Cool to Dehumidify
The cool to dehumidify selection tells the system to operate
the compressor, within limits, when there is a dehumidify
demand even if there is no cooling demand. The limits are
that the system may overcool up to 3°, but no more, while
attempting to satisfy a dehumidify demand. Within this 3°
range, there is an additional balance between overcooling
and humidity satisfaction. When overcooling must occur,
the dehumidify set point is adjusted upward by 2 percent per
degree of overcooling. For example, a cooling set point of
76°F and a dehumidify set point of 60 percent is equivalent
to a cooling set point of 75°F and a dehumidify set point of
62 percent. This dehumidify set point change is internal to
the Thermidistat Control and is not shown on the display.
During cool-to-dehumidify demand, the compressor runs a
maximum of 10 minutes on, followed by 10 minutes off.
When the compressor turns off, the fan (G output) is also
turned off immediately. The immediate fan shutoff prevents
re-evaporation of water on the coil, improving dehumidifi-
cation. If fan is set to continuous, the G (fan on) signal is
removed for 5 minutes starting when compressor turns off.
In most furnaces and fan coils, the blower operates for 90
sec after both Y and G disappear. This 90-sec delay should
be removed, if possible, for maximum dehumidification
performance. Consult furnace or fan coil Installation In-
structions to see if delay can be disabled.
TABLE 2—EQUIPMENT OUTPUTS
1-SPEED AC
2-SPEED AC
1-SPEED HP
2-SPEED HP
Cool—0 to 2 minutes
Y, G
Y1, G
Y, G, O
Y1, G, O
Cool—2 to 4 minutes
Y, G
Y1, Y2, G
Y, G, O
Y1, Y2, G, O
Heat—0 to 2 minutes
W1
W1
Y, G
Y1, G
Heat—2 to 4 minutes
W1, W2
W1, W2
Y, G
Y1, Y2, G
Eheat—0 to 2 minutes
---
---
W1
W1
Eheat—2 to 4 minutes
---
---
W1, W2†
W1*
* Two-stage heat not available
NOTE: For Y—use terminal Y/Y2, for Y1—use terminal Y1/W2, for W2—use terminal O/W2,
for O—use terminal O/W2, for W1—use terminal W/W1, for W2†, use terminal Y1/W2
TABLE 4—HUMIDIFICATION SELECTIONS
SELECTION
MODE DISPLAY
FAN DISPLAY
HUMIDIFY SP
DISPLAY
Normal Humidify
Blank
Blank
HSP Value
Fan Humidify
Blank
FAN
HSP Value
Auto Humidify
AUTO
Blank
HSP Value
Auto and Fan
AUTO
FAN
HSP Value
Humidify Off
Blank
Blank
OF
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