69
YORK INTERNATIONAL
FORM 100.50-NOM1 (604)
5
•
Economizer Enable
= ON and econ o miz er con di -
tions are not available
Damper #1 (outdoor air damper) will modulated as
re quired to maintain the
"Minimum Outside Airfl ow"
by an ap pro pri ate PI control algorithm. The following
Þ
g ure illustrates the control function.
FIG. 36 –
FULL FLOW MEASUREMENT OPTION,
ECONOMIZER NOT AVAIL ABLE
Flow Control - Economizer Available
When the unit is in the occupied mode of operation,
and:
•
Airfl ow Meas Confi g
= 2 (full)
•
Economizer Enable
= ON and econ o miz er con di -
tions are available
Damper #1 will be controlled through an appropriate
algorithm to meet the fol low ing two requirements:
• The measured outdoor air
ß
ow is =>
Min i mum Flow
Setpoint
• The outdoor damper position is mod u lat ed to meet
the requirements of economizer operation or econ-
o miz er loading operation.
If the
“OA Damper Min Pos 1 or 2”
causes the air
ß
ow
to be above the
“Min Outside Airfl ow”
setpoint, the
damper will not close to allow the air
ß
ow to meet the
“Min Outside Airfl ow”
setpoint.
The following
Þ
gure illustrates the control re quire -
ments.
FIG. 37 –
FULL FLOW MEASUREMENT OPTION
ECONOMIZER
SEQUENCE
Open (100%)
OA Damper
Position
Closed (0%)
MAX CFM
OA Air Flow (CFM)
0 CFM
LD06567
Control Range for
Economizer
Operation
Open (100%)
OA Damper
Position
Closed (0%)
Min. Outside
Airflow
OA Flow (CFM)
Position to Meet OA
Setpoint
LD06568
Demand Ventilation
Demand Ventilation is a control sequence that can in-
crease or decrease the amount of ventilation introduced
to the building based on the level of contaminate in the
conditioned space. Typically this is CO2 however based
on the type of IAQ sensor used any contaminate could
be used to increase the ventilation level. We will use
CO2 in this example.
The demand for ventilation will be determined by com-
paring the level of CO2 in the building to the “
Demand
Ventilation”
setpoint. The CO2 level in the building
will be measured by an appropriate IAQ sensor con-
nected to the unit.
The Demand Ventilation control sequence will only be
allowed to function if:
• The
"IAQ Sensor Enable"
setting is set to ON.
• The unit is equipped with an econ o miz er and
Econ-
o miz er Enable
= ON.
• The
Airfl ow Meas Confi g
con
Þ
g u ra tion is = 0 or 2
• Occupancy status is = Occupied.
•
"Economizer Installed"
is set to YES.
Demand Ventilation control will operate in both heating
and cooling modes and will increase the position of the
economizer (OA Damper) from the minimum position
or the control positions of economizer or economizer
loading as required to meet the
"Demand Ventilation"
programmed parameter.
