Instruction manual

www.DaikinApplied.com 33 OM 751-4
desCrIptIon of operatIon
Networked Space Humidity Sensor Capability
A networked space humidity sensor can be network interfaced with the Space Humidity
Input variable. When the Space Humidity Input variable is used (valid value), it auto-
matically overrides the hard-wired space humidity sensor (if present).
Networked Outdoor Humidity Sensor Capability
A networked outdoor humidity sensor can be network interfaced with the Outdoor Hu-
midity 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 xed damper positions to determine the amount
of OA for proper ventilation within the space. Most commonly, the xed position of the
OA damper is based on the maximum number of occupants the space is designed to
accommodate. However, this xed 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 xed damper control for ventilation is
energy wasteful since you are treating OA not actually needed for ventilation during low
occupancy levels.
People produce CO
2
when they breath; the CO
2
level within the space has a direct
relationship with the number of people within that space.
The UVC can optionally be factory congured to provide CO
2
-based Demand Con-
trolled 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 occu-
pancy levels below maximum design. The CO
2
DCV function uses a 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 typically is 20% then when using CO
2
DCV, you could set the new
minimum OA damper position as low as 4% (e.g., 20% × 0.20 = 4%). This new, smaller
minimum OA damper position then should provide enough ventilation to keep odors in
check within the space for most applications.
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 become a problem, 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 position at a later date.
– If the CO
2
Demand Controlled Ventilation (DCV) option is used, the UVC only uses
the IA fan 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 IA fan
high speed OA damper minimum position is factory set at 5%.
Networked Space CO
2
Sensor Capability
A networked space CO
2
sensor can be network interfaced with the Space CO
2
Input
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 modies the heating, ventilat-
ing, and cooling functions (as available) to prevent the discharge air temperature from
falling below the VCLL set point.