Networked Space Co 2 Sensor Capability; Ashrae Cycle Ii; Outdoor Air Fan Operation - Daikin MicroTech II Operation And Maintenance Manual

OM 752-4
The UVC can optionally be factory configured 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 modifies the heating, ventilat-
ing, and cooling functions (as available) to prevent the discharge air temperature from
falling below the VCLL set point.

Outdoor Air Fan Operation

The UVC is configured with a fan on delay that delays OA fan operation for a time
period (10 seconds, default) after the compressor starts. The OA fan stops with the
compressor.
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