Economizer Operation - York eco2 050 Installation Operation & Maintenance

ECONOMIZER OPERATION

Economizer operation is described in the following
sec tions. A Þ nal section within Economizer operation
de scrip tion is on Economizer Loading. Economizer
Load ing is a variation on the Economizer operation.
Its func tion is to override the economizer to minimize
SAT swings resulting from turning cooling/heating
stages on and off.
Criteria for Economizer Operation
Economizer operation will be used for control when:
• Economizer - ON
• Economizer Enable - ON
• Required sensors are reliable
• Outside air conditions are suitable per criteria dis-
cussed in the following sections
Criteria for Economizer Suitable Decision
There are three different methods of Economizer
Operation:
• Differential Enthalpy Method: will be self-
con Þ g ured and used when sensors for Outdoor
Air tem per a ture, Outdoor Air humidity, Return
Air tem per a ture, and Return Air humidity are all
installed and re li able. This method is the highest
priority when sen sors are available.
• Outside Enthalpy Method: will be self-con Þ g ured
and used only when differential en thalpy meth od
is not available, and sensors for Outdoor Air tem-
per a ture and Outdoor Air humidity are installed and
re li able.
• Outside Temperature Method: will be self-con-
Þ g ured and used only when differential en thalpy
or out side enthalpy methods are not available, and
sensor for Outside Air temperature is installed and
re li able.
Economizer Suitable Calculations
Outside Temperature Method:
Economizer will be suitable when OAT < (SAT setpoint
+ 10°F). A 2°F hysteresis about the (SAT setpoint +
10°F) will be used. The 10°F offset rep re sents the high-
est outdoor air temperature that the DX cooling can
re li ably reduce to the SAT setpoint.
YORK INTERNATIONAL
Outside Enthalpy Method:
Economizer will be suitable when OA Enthalpy <
Out side Enthalpy Number parameter value and OAT <
(SAT setpoint + 10°F). A 2°F hysteresis about the (SAT
setpoint + 10°F) will be used. A 1 BTU/LB hys ter e sis
about the Outside Enthalpy Number will be used.
Differential Enthalpy Method:
Economizer will be suitable when OA Enthalpy < RA
Enthalpy and OAT < (SAT setpoint + 10°F). A 2°F hys-
ter e sis about the (SAT setpoint + 10°F) will be used.
A 1 BTU/LB hysteresis about the RA Enthalpy will be
used.
SAT Setpoints Used During Cooling With Econo-
mizer Operation
Under Economizer Operation, the following SAT set-
points will be used:
CV Cooling Mode:
• With a call for Þ rst stage cooling, the Econ o miz er
First Stage Setpoint value will be used as the Econ-
o miz er SAT setpoint.
• With a call for second stage cooling, Econ o miz er
Sec ond Stage Setpoint value will be used as the
Econ o miz er SAT setpoint.
VAV Cooling Mode:
• With a call for Þ rst stage cooling, the "VAV Cool
High Tem p" setpoint will be used as the Econ o miz er
SAT setpoint
• With a call for second stage cooling, the "VAV Cool
Low Tem p" setpoint will be used as the Econ o miz er
SAT setpoint
SAT control with Economizer
The economizer control will be based on a PI, direct
acting algorithm . If economizer is "suitable" (free
cool ing is available) and cooling is required (the unit
is not in satisÞ ed state), the algorithm will be active
and mod u late the economizer position (outside air and
return air dampers) in order to control SAT to the SAT
setpoint. If the economizer is not suitable, the Econo-
mizer Op er a tion is no longer used and control reverts
to the ap pro pri ate economizer not suitable mode of
operation.
FORM 100.50-NOM1 (604)
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