VCES-DDC-IOM-1C
6
Adjust the following setpoints:
#147 – Summer Zone Setpoint
• Limits: 60–80°F [15–25°C]
• Factory set: 70°F
• BACnet variable: AV84
• Function: The summer zone setpoint is the room or
return air setpoint for summer mode.
#150 – Winter Zone Setpoint
• Limits: 60–80°F [15–25°C]
• Factory set: 70°F
• BACnet variable: AV87
• Function: The winter zone setpoint is the room or re-
turn air setpoint for winter mode.
Override Contact Control (Optional)
Alternatively the unit may be controlled by its heating,
cooling, dehumidification contacts. The heating contact is
only provided on units with heating options and the cool-
ing/dehumidification contact is only provided on units with
cooling options. An optional room thermostat (or contact
closure) may be used to provide a dry contact closure
across terminals FW 314–315 for cooling, or FW 318–319
for heating.
These override contacts can be used in any of the three
temperature control modes listed above. When the unit
is running normally, it will run based on its corresponding
setpoints. When an override contact is made, the unit will
change its setpoints as follows:
#118 – Coil Override Leaving Setpoint
• Limits: 40–65°F [4–18°C]
• Factory set: 50°F
• BACnet variable: AV146
• Function: The coil override leaving setpoint is the
temperature that the cooling coil will cool the coil
leaving air temperature down to during room air
temperature/humidity control (summer mode only).
#121 – Heating Override Setpoint
• Limits: 50–105°F [10–40°C]
• Factory set: 90°F
• BACnet variable: AV140
• Function: The heating override setpoint is the tem-
perature that the post heat will heat the supply air up
to during room air temperature control (winter mode
only).
An optional humidistat may be used to provide a dry contact
closure across terminals FW 316–317 for dehumidification.
In order to give more flexibility to the user, the setpoints
are fully adjustable from the BacStat interface. For a full
modulating system (ex. SCR electric heat) you only need to
adjust the setpoint value. When using a binary switch (ex.
summer/winter changeover) or when staging a device (ex.
compressors), a span or differential is needed to separate
the ‘On’ and ‘Off’ point to eliminate the fast cycling. In
this case, Venmar CES uses the Setpoint-Span-Reset ad-
justment method.
• The Setpoint is the value to reach.
• The Span is the band width between the ‘On’ and
‘Off’ point.
• The Reset is the percentage of the span value under
the setpoint (refer to Figure 3).
Setpoint Adjustment
60°F
40°F
100°F
Summer setpoint (60°F)
59°F off
64°F on
Reset = 20%
OA temp
Summer mode
On = 64°F
Summer mode
Off = 59°F
OAT ºF
Span = 5
Δt (Change in time)
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For this example:
Sum_Stp = 60°F Sum_Span = 5 Sum_Reset = 20
To calculate:
Summer switch On = Sum_Stp + (Sum_Span * ((100 - Sum_Rst) / 100))
Summer switch Off = Sum_Stp - (Sum_Span * (Sum_Rst / 100))
Figure 3: Setpoint adjustment example
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