Description of Operation
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OM 1280-2 • MICROTECH UNIT CONTROLLER
Network Space Humidity Sensor
Capability
A space humidity value can be provided to the UVC using
the Space Humidity Input network variable. When the Space
Humidity Input variable is used (valid value), it automatically
overrides the hard-wired space humidity sensor (if present).
Network Outdoor Humidity Sensor
Capability
An outdoor humidity value can be provided to the UVC using
the Outdoor Humidity Input variable. When the Outdoor
Humidity Input variable is used (valid value), it automatically
overrides the hard-wired outdoor humidity sensor (if present).
CO
2
Demand Controlled Ventilation
(optional)
Ventilation equipment typically uses fixed damper positions to
determine the amount of Outdoor Air (OA) for proper ventilation
within the space. Most commonly, the fixed position of the OA
damper is based on the maximum number of occupants the
space is designed to accommodate. However, this fixed OA
damper operation ignores the fact that most spaces during the
day have varying occupancy levels and may only rarely reach
maximum design occupancy levels. This type of fixed damper
control for ventilation is often less energy efficient when outdoor
air is treated during periods of low occupancy.
Since occupants inherently produce CO
2
as they exhale, the CO
2
level is directly related to the number of people in a given space.
The UVC can optionally be factory configured to provide
CO
2
-based Demand Controlled Ventilation (DCV). The CO
2
DCV function is useful in saving the energy typically wasted in
treating OA not actually needed for ventilation within a space
during occupancy levels below maximum design. The CO
2
DCV function uses PI-loop control to adjust the OA damper
above the minimum position as needed to maintain the Space
CO
2
Setpoint (1200 PPM default).
The minimum damper position used with CO
2
DCV typically
can be set at ~20% of the minimum position that would be
used without CO
2
DCV. For example, if the minimum OA
damper position is 20% then when using CO
2
DCV, set the new
minimum OA damper position as low as 4% (e.g., 20% × 0.20
= 4%). For most applications this new, smaller minimum OA
damper position should provide enough ventilation to control
undesirable conditions such as odors within the space.
NOTE:
The CO
2
DCV function can increase the OA damper
position past that required by the economizer and
vice versa.
– If odors within the space are a nuisance,
increase the OA damper minimum position
as needed to eliminate these odors. It may
be necessary with new construction or after
renovation to raise the minimum position for
some time period to help reduce odor buildup
due to the out-gassing of new construction
material, and then return the minimum OA
damper to its previous position.
– If the CO
2
Demand Controlled Ventilation (DCV)
option is used, the UVC only uses the IAF high
speed OA damper minimum position regardless
of fan speed. The DCV function adjusts the OA
damper above this minimum as needed. In this
case, the IAF high speed OA damper minimum
position is set at 5%.
Network Space CO
2
Sensor Capability
A network space CO
2
value can be provided to the UVC using
the Space CO
2
Input network variable. When the Space CO
2
Input variable is used (valid value), it automatically overrides
the hard-wired space CO
2
sensor (if present).
ASHRAE Cycle II
The UVC supports ASHRAE Cycle II operation. The basis of
ASHRAE Cycle II is to maintain the required minimum amount
of ventilation whenever possible, which can be increased
during normal operation for economizer cooling or CO
2
DCV
control or reduced to prevent excessively cold discharge air
temperatures.
A discharge air temperature sensor is installed in all unit
ventilators. If necessary, the ASHRAE II control algorithm
overrides room control and modifies the heating, ventilating,
and cooling functions (as available) to prevent the discharge
air temperature from falling below the VCLL setpoint.
Summary of Contents for MicroTech
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