13
To determine the damper setpoint position, perform the
following procedure for each condition setpoint, with
mechanical cooling OFF:
Calculate the appropriate supply air temperature using the
following formula:
TS = (TO x Vbz/CFM) + TR x (CFM – Vbz)/CFM
TS = Supply Air Temperature
TO = Outdoor Air Temperature
Vbz = Design Maximum Ventilation CFMr
CFM= Unit Supply Airflow Rate
TR = Return Air Temperature
As an example:
Unit Airflow Rate at High Speed is 4000 CFM
Ventilation CFM at design occupancy Vbz is 1200 CFM
TO = 60 F
TR = 75 F
Required TS = 60 x (1200/4000) + 75 x (4000 – 1200/4000)
=60x0.30+75x0.70=18.0+52.5
= 70.5
At the W7220 keypad, enter the parameter SETUP -->
VENTMAX H and adjust the setpoint value until the
observed Supply Air Temperature (MA TEMP) reaches
70.5. Press the
“Enter” key to save this setpoint to
controller memory.
When determining VENTMIN setpoints, substitute the
value for Va in place of Vbz in the formula.
DCV Setpoint — The SETPOINTS parameter DCV SET
defines the space CO
2
level above which the DCV mode
begins to open the outside air damper beyond its
VENTMIN ventilation lower limit. This setpoint should
be a minimum of 100 ppm greater than the outdoor
ambient CO
2
level to ensure the outside air will be
capable of diluting the space CO2 level. A typical value
for outdoor CO
2
is 400 ppm; adjust the setpoint DCV SET
to 500 ppm if outdoor CO
2
level is not known. The
factory default value for DCV SET is 1100 ppm.
Economizer Occupancy Control
The 24--v signal that terminates at the W7220’s OCC
input to place the economizer control in Occupied mode
when the supply fan starts is routed through the rooftop
unit’s Central Terminal Board at its OCCUPANCY
jumper. To implement an occupancy control for the
economizer operation, connect a contact set at CTB
OCCUPANCY quick--connect terminals and cut jumper
JMP2. To allow automatic occupancy mode, close the
control contacts. To place the economizer in Unoccupied
mode, open the control contacts.
OCCUPANCY
TERMINALS
CUT JUMPER JMP2
TO IMPLEMENT
OCCUPANCY
CONTROL
C12169
Fig. 9 -- Central Terminal Board (CTB)
LLECON--02SI
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