47
Economizer Control Modes —
Determine the Economizer control
mode before set up of the control. Some modes of operation may
require different sensors. Refer to Table 15. The Economizer is
supplied from the factory with a supply air temperature sensor, a low
temperature compressor lockout switch, and an outdoor air temper-
ature sensor. This allows for operation of the Economizer with
outdoor air dry bulb changeover control. Additional accessories can
be added to allow for different types of changeover control and
operation of the Economizer and unit.
OUTDOOR DRY BULB CHANGEOVER—
The standard
controller is shipped from the factory configured for outdoor dry bulb
changeover control. The outdoor air and supply air temperature
sensors are included as standard.
For this control mode, the outdoor temperature is compared to
a
selectable set point on the sensor See Fig. 44
.
If the outdoor--air
temperature is above the set point, the Economizer will adjust the
outdoor air dampers to minimum position. If the outdoor--air
temperature is below the set point, the position of the outdoor--air
dampers will be controlled to provide free cooling using outdoor
air. When in this mode, the LED next to the free cooling set point
potentiometer will be on. The changeover temperature set point is
set using the switches on the sensor. See Fig. 44 for the
corresponding temperature changeover values.
EXHAUST FAN
SETPOINT
LED LIGHTS WHEN
EXHAUST CONTACT
IS MADE
MINIMUM DAMPER
POSITION SETTING
MAXIMUM DAMPER DEMAND
CONTROL VENTILATION
SETPOINT
LED LIGHTS WHEN
DEMAND CONTROL
VENTILATION INPUT
IS ABOVE SETPOINT
DEMAND CONTROL
VENTILATION SETPOINT
LED LIGHTS WHEN
OUTDOOR AIR IS
SUITABLE FOR FREE
COOLING
ENTHALPY
CHANGEOVER SETPOINT
A09708
Fig. 43 -- Economizer Controller Potentiometer and LED
Locations
(8.9°C)
(11.7°C)
(12.8°C)
(14.4°C)
(17.2°C)
(20°C)
(22.8°C)
(25.6°C)
A10134
Fig. 44 -- Outdoor Air Temperature Changeover Set Points
OUTDOOR ENTHALPY CHANGEOVER—
For enthalpy
control, accessory enthalpy sensor (part number HH57AC078) is
required. Replace the standard outdoor dry bulb temperature sensor
with the accessory enthalpy sensor in the same mounting location.
RETURN DUCT
(FIELD-PROVIDED)
RETURN AIR
SENSOR
ECONOMIZER
A09710
Fig. 45 -- Enthalpy Sensor Mounting Location
85
(29)
90
(32)
95
(25)
100
(38)
105
(41)
110
(43)
80
(27)
75
(24)
70
(21)
65
(18)
60
(16)
55
(13)
50
(10)
45
(7)
40
(4)
35
(2)
A
B
B
C
C
D
D
35
(2)
40
(4)
45
(7)
50
(10)
55
(13)
60
(16)
65
(18)
70
(21)
75
(24)
80
(27)
85
(29)
90
(32)
95
(36)
100
(38)
105
(41)
110
(43)
A
APPROXIMATE DRY BULB TEMPERATURE — ˚F (˚C)
ENTHALPY – BTU PER POUND DRY AIR
12
14
16
18
20
22
24
26
28
30
100
90
80
70
60
50
40
32
34
36
38
40
42
44
46
CONTROL
CURVE
CONTROL POINT
APPROX ˚F (˚C)
AT 50% RH
A
73 (23)
67 (19)
63 (17)
70 (21)
B
C
D
30
20
10
REL
A
TIVE HUMIDITY (%)
A09711
Fig. 46 -- Enthalpy Changeover Setpoints
674D
--
--
A
Summary of Contents for Legacy 674D
Page 3: ...3 A09473 Fig 2 674D A24 36 Unit Dimensions 674D A...
Page 4: ...4 A09474 Fig 3 674D A42 60 Unit Dimensions 674D A...
Page 24: ...24 A10207C Fig 14 208 230 1 60 Connection Wiring Diagram Unit 674D 674D A...
Page 25: ...25 A10207L Fig 14 Cont 208 230 1 60 Ladder Wiring Diagram Unit 674D A 674D A...
Page 26: ...26 A10208C Fig 15 208 230 3 60 Connection Wiring Diagram Unit 674D A 674D A...
Page 27: ...27 A10208L Fig 15 Cont 208 230 3 60 Ladder Wiring Diagram Unit 674D A 674D A...
Page 28: ...28 A08019 Fig 16 Cooling Charging Table Subcooling 674D A...
Page 49: ...49 A10059 Fig 49 Economizer Wiring Diagram 674D A...
