Sequences of operation
Several functions can drive the economizer, including minimum position, free cooling, economizer
loading, and minimum outdoor air supply.
Economizer minimum position
The economizer minimum position is set during occupied mode when the outside air (OA) is not
suitable for free cooling. The position of the damper is set proportionally between the Economizer
Minimum Position and the Economizer Minimum Position Low Speed Fan setpoints in relation to
the VFD output percentage.
Note:
On a constant volume single speed supply fan system both setpoints should be set to
the same value.
Free cooling
Four types of free cooling options are available: dry bulb changeover, single enthalpy, dual enthalpy
changeover, and auto.
Dry Bulb Changeover
– For dry bulb economizer operation, the outside air is suitable for free
cooling if the outside air temperature (OAT) is 1.0°F below the Economizer OAT Enable setpoint and
1.0°F below the RA temperature (RAT). Free cooling is no longer available if the OAT rises above
either the Economizer OAT Enable setpoint or the RAT.
Single/Dual Enthalpy Changeover
– For single enthalpy economizer operation, the outside air is
suitable for free cooling if the OA enthalpy is at least 1 Btu/lb below the economizer OA enthalpy
setpoint and the OAT is no greater than the RAT plus 9.0°F.
If the OAT rises above the RAT plus 10.0°F, free cooling is no longer available. The OAT must drop to
no greater than RAT plus 9.0°F to enter free cooling again.
Free cooling is no longer available if the OA enthalpy rises above the economizer OA enthalpy
setpoint. For dual enthalpy economizer operation, the OA enthalpy must be lower than the RA
enthalpy by 1 Btu/lb and the OAT is no greater than the RAT plus 9.0°F.
Auto
– The control determines the type of free cooling changeover based on which sensors are
present and reliable. Conditions include:
•
Return and outside air dry bulb = dry bulb changeover
•
Return and outside air dry bulb and outside air humidity = single enthalpy
•
Return and outside air dry bulb and return and outside air humidity = dual enthalpy
•
If either the return or outside air dry bulb sensors are unreliable, free cooling is not available
For detailed installation and operation instructions, refer to
Airside Economizer Kit
(
Form 145.10-
NO2
).
Dimensions
Table 1: Dimensions
Mixing box dimension
Damper dimension
Vertical unit Economizer
A
B
C
D
E
DSV060C
VASE-060C-1
49.00
27.75
24.00
40.00
14.00
DSV096C/120C VASE-120C-1
66.50
36.25
26.50
58.00
19.50
DSV144C
VASE-144C-1
78.00
35.75
28.50
70.00
19.50
DSV180C
VASE-180C-1
82.00
37.75
28.50
74.00
21.50
DSV240C
VASE-240C-1
86.00
41.00
34.00
78.00
25.00
DSV300C
VASE-300C-1
104.00
45.00
34.00
90.00
25.00
D-Series Vertical (DSV060C-300C) Air-Cooled Self-Contained Units, C Generation with Smart Equipment Controller
20
Johnson Controls
