63
Economizer Changeover Select (E.SEL)
The control is capable of performing any one of the following
changeover types in addition to both the dry bulb lockout and
the external switch enable input:
E.SEL
= 0
none
E.SEL
= 1
Differential Dry Bulb Changeover
E.SEL
= 2
Outdoor Enthalpy Changeover
E.SEL
= 3
Differential Enthalpy Changeover
Differential Dry Bulb Changeover
As both return air and outside air temperature sensors are in-
stalled as standard on these units, the user may select this op-
tion,
E.SEL
= 1, to perform a qualification of return and out-
side air in the enabling and disabling of free cooling. If this op-
tion is selected and outside-air temperature is greater than
return-air temperature, free cooling will not be allowed.
Outdoor Enthalpy Changeover
This option should be used in climates with higher humidity
conditions. The A Series control can use an enthalpy switch or
enthalpy sensor, or the standard installed outdoor dry bulb sen-
sor and an accessory relative humidity sensor to calculate the
enthalpy of the air.
Setting
Configuration
ECON
E.SEL
= 2 requires that
the user configure
Configuration
ECON
OA.E.C
, the
Outdoor Enthalpy Changeover Select, and install an outdoor
relative humidity sensor. Once the sensor is installed, enable
Configuration
ECON
ORH.S
, the outdoor relative hu-
midity sensor configuration option.
If the user selects one of the Honeywell curves, A,B,C or D,
then
OA.E.C
options 1 to 4 should be selected. See Fig. 11 for
a diagram of these curves on a psychrometric chart.
OA.E.C
= 1
Honeywell A Curve
OA.E.C
= 2
Honeywell B Curve
OA.E.C
= 3
Honeywell C Curve
OA.E.C
= 4
Honeywell D Curve
OA.E.C
= 5
custom enthalpy curve
If the user selects
OA.E.C
= 5, a direct comparison of outdoor
enthalpy versus an enthalpy setpoint is done. This outdoor en-
thalpy setpoint limit is configurable, and is called
Configuration
ECON
OA.EN
.
Depending on what
Configuration
ECON
OA.E.C
is
configured for, if the outdoor enthalpy exceeds the Honeywell
curves or the outdoor enthalpy compare value (
Configuration
ECON
OA.EN
)
, then free cooling will not be allowed.
Differential Enthalpy Changeover
This option compares the outdoor-air enthalpy to the return air
enthalpy and chooses the option with the lowest enthalpy. This
option should be used in climates with high humidity condi-
tions. This option uses both humidity sensors and dry bulb sen-
sors to calculate the enthalpy of the outdoor and return air. An
accessory outdoor air humidity sensor (
ORH.S
) and return air
humidity sensor (
RRH.S
) are used. The outdoor air relative hu-
midity sensor configuration (
ORH.S
) and return air humidity
sensor configuration (
Configuration
UNIT
SENS
RRH.S
) must be enabled.
Outdoor Dewpoint Limit Check
If an outdoor relative humidity sensor is installed, then the con-
trol is able to calculate the outdoor air dewpoint temperature
and will compare this temperature against the outside air dew-
point temperature limit configuration (
Configuration
ECON
O.DEW
). If the outdoor air dewpoint temperature is
greater than
O.DEW
, then free cooling will not be allowed.
Figure 12 shows a horizontal limit line in the custom curve of
the psychrometric chart. This is the outdoor air dewpoint limit
boundary.
Custom Psychrometric Curves
Refer to the psychrometric chart and the standard Honeywell A-D
curves in Fig. 11. The curves start from the bottom and rise verti-
cally, angle to the left and then fold over. This corresponds to the
limits imposed by dry bulb changeover, outdoor enthalpy change-
over and outdoor dewpoint limiting respectively. Therefore, it is
now possible to create any curve desired with the addition of one
outdoor relative humidity sensor and the options for changeover
now available. See Fig. 12 for an example of a custom curve con-
structed on a psychrometric chart.
Fig. 12 — Custom Changeover Curve Example
Fig. 11 — Psychrometric Chart for
Enthalpy Control
CONTROL CURVE
CONTROL POINT
(approx Deg) AT 50% RH
A
73
B
68
C
63
D
58
Summary of Contents for WEATHERMAKER 48A2020
Page 112: ...112 Fig 20 Typical Main Control Box Wiring Schematic 48 50A Units ...
Page 113: ...113 Fig 21 Typical Auxiliary Control Box Wiring Schematic ...
Page 114: ...114 Fig 22 Typical 2 Stage Gas Heat Wiring Schematic Size 060 Units Shown ...
Page 115: ...115 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown TO NEXT PAGE ...
Page 116: ...116 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown cont ...
Page 117: ...117 Fig 24 Typical Electric Heat Control Schematic 50 Series Size 060 Units Shown ...
Page 118: ...118 Fig 25 Typical Controls Option Wiring Schematic SW1 SW2 OR DEHUMIDIFY SWITCH ...
Page 119: ...119 Fig 26 Typical Power Schematic 48 50A2 A3 A4 A5 060 Unit Shown ...
Page 120: ...120 Fig 27 Typical Power Schematic of Greenspeed Low Ambient Option 48 50A 060 Unit Shown ...
Page 121: ...121 Fig 28 Typical Small Chassis Component Location Size 020 035 Units ...
Page 122: ...122 Fig 29 Typical Large Chassis Component Locations Size 040 060 Units ...
Page 185: ...185 APPENDIX C VFD INFORMATION cont Fig F Internal Enclosure Fan Replacement A48 7716 ...