34 | PIR Ready VT76x7 Series-Installation Guide
H
UMIDITY
C
ONTROL
Humidity reset
Humidity setpoint reset by outside air temperature
If an outdoor air sensor is
connected
at
the
Terminal
Equipment Controller or a value
is received from the network, it
can be used to reset the
humidity setpoint during the cold
season
to
minimize
condensation on windows and
building structures.
When the outdoor temperature
falls below the selected high
temperature, parameter
RH
HT
(32
F in the example Figure 8),
the humidity setpoint will start to
decrease. The lowest humidity
setpoint will be reached at
selected
low
temperature,
parameter
RH LT
(-20
F).
The setpoint decrease from original setpoint to the lowest setpoint determined by the
parameter
RE
Sp
. In the example, Figure 8,
RE
Sp
was set to 20%, therefore the
humidity setpoint dropped from 45% to 20%.
If you don’t want to use this feature, set the
RE Sp
parameter to 90% RH.
High limit humidity sensor
The
VT76x7
series
includes
a
high
limit
sequence. This allows the
use of a remote 0 to 10
VDC humidity sensor to
limit the humidity in the
supply air. If no sensor is
detected
at
the
HL
connector, this sequence
is
disabled
at
the
Terminal
Equipment
Controller.
Note:
this
high
limit
function is not a safety
device.
For
critical
situations,
provide
installation with normal
protections required to
ensure a safe operation.
20%
25%
30%
35%
40%
-40°F -20°F 0°F 20°F 40°F
45%
%
R
H
S
et
p
oi
nt
Outside Air Temp.
RH HT = 32°F
RH LT = -20°F
RH Set = 45%
RE Sp = 20%
Fig.11
– Humidity setpoint reset by outside air
temperature
Fig.12
– High humidity limit vs. Control output level curve
Maximum Supply Humidity
100
%
0
%
50
%
Control
Output
Level
85
%
