77
ECONOMIZER OPERATION
There are four potential elements which are considered concur-
rently which determine whether the economizer is able to pro-
vide free cooling:
1. Dry bulb changeover (outside-air temperature qualification)
2. Enthalpy switch (discrete control input monitoring)
3. Economizer changeover select (
E.SEL
economizer
changeover select configuration option)
4. Outdoor dewpoint limit check (requires an installed out-
door relative humidity sensor installed)
Dry Bulb Changeover
Outside-air temperature may be viewed under
Tempera-
tures
AIR.T
OAT
. The control constantly compares its out-
side-air temperature reading against the high temperature OAT
lockout (
OAT.L
). If the temperature reads above
OAT.L
, the
economizer will not be allowed to perform free cooling.
NOTE: If the user wishes to disable the enthalpy switch from run-
ning concurrently, a field-supplied jumper must be installed be-
tween TB201 terminals 3 and 4.
Enthalpy Switch
The state of the enthalpy switch can be viewed under
Inputs
GEN.I
ENTH
.
Enthalpy switches are installed as standard
on all P Series rooftops. When the switch reads high, free cool-
ing will be disallowed.
The enthalpy switch opens (reads high) when the outdoor en-
thalpy is above 24 Btu/lb or dry bulb temperature is above
70°F and will close when the outdoor enthalpy is below
23 Btu/lb or the dry bulb temperature is below 69.5°F.
NOTE: The enthalpy switch has both a low and a high output. To
use this switch as designed, the control must be connected to the
low output. Additionally, there is a switch logic setting for the en-
thalpy switch under
Configuration
SW.LG
ENT.L
. This set-
ting must be configured to closed (CLSE) to work properly when
connected to the low output of the enthalpy switch.
There are two jumpers under the cover of the enthalpy switch.
One jumper determines the mode of the enthalpy switch/receiver.
The other is not used. For the enthalpy switch, the factory setting
is M1 and should not need to be changed. See
Fig. 10 for a dia-
gram showing the settings on the enthalpy switch.
The enthalpy switch may also be field converted to a differen-
tial enthalpy switch by field installing an enthalpy sensor
(33CSENTSEN or HH57ZC001). The enthalpy switch/receiv-
er remains installed in its factory location to sense outdoor air
enthalpy. The additional enthalpy sensor (33CSENTSEN) is
mounted in the return airstream to measure return air enthalpy.
The enthalpy control jumper must be changed from M1 to M2
for differential enthalpy control. For the 2-wire return air en-
thalpy sensor, connect power to the Vin input and signal to the
4 to 20 mA loop input. See Fig. 10 for diagram showing the
settings and inputs on the enthalpy switch.
There is another way to accomplish differential enthalpy con-
trol when both an outdoor and return air relative humidity sen-
sor are present. See Economizer Changeover Select section be-
low for further information.
Fig. 10 — Enthalpy Switch Jumper Positions
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 standard external 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/disabling of free cooling. If this option
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 P 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 hu-
midity sensor. A control expansion module (CEM) is required.
Once the sensor and board are installed, enable
Configura-
tion
ECON
ORH.S
, the outdoor relative humidity sensor
configuration option. This will automatically enable the CEM
board, if it is not enabled already.
If the user selects one of the Honeywell curves, A, B, C, or D,
then
OA.E.C
options 1-4 should be selected. See Fig. 11 for a
diagram of these curves on a psychometric 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 compare of outdoor enthal-
py versus an enthalpy set point is done. This outdoor enthalpy set
point limit is configurable, and is called
Configuration
ECON
OA.EN
.
Depending on what
Configuration
ECON
OA.E.C
is con-
figured 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.
NOTE: If the user wishes to disable the standard enthalpy control
from running concurrently, a field-supplied jumper must be in-
stalled between TB201 terminals 5 and 6.
Differential Enthalpy Changeover
This option compares the outdoor-air enthalpy to the return-air en-
thalpy and chooses the option with the lowest enthalpy. This op-
tion should be used in climates with high humidity conditions.
This option uses both humidity sensors and dry bulb sensors to
calculate the enthalpy of the outdoor and return air. An accessory
outdoor-air humidity sensor (
ORH.S
) and return-air humidity sen-
sor (
RRH.S
) are used. The outdoor-air relative humidity sensor
configuration (
ORH.S
) and return-air humidity sensor configura-
tion (
Configuration
UNIT
SENS
RRH.S
) must be enabled.
NOTE: If the user wishes to disable the standard enthalpy control
from running concurrently, a field-supplied jumper must be in-
stalled between TB201 terminals 5 and 6.
M3
M2
M1
OFF
100%
50%
0%
Summary of Contents for Weathermaster 48P2030-100
Page 130: ...130 Fig 19 Typical Power Schematic Sizes 040 075 Shown ...
Page 131: ...131 Fig 20 Main Base Board Input Output Connections ...
Page 132: ...132 Fig 21 RXB EXB CEM SCB Input Output Connections ...
Page 133: ...133 Fig 22 Typical Gas Heat Unit Control Wiring 48P030 100 Units Shown ...
Page 134: ...134 Fig 23 Typical Electric Heat Wiring 50P030 100 Units Shown ...
Page 135: ...135 Fig 24 Typical Power Wiring 115 V ...
Page 136: ...136 Fig 25 Typical Gas Heat Section Size 030 050 Units Shown ...
Page 138: ...138 Fig 27 Component Arrangement Size 030 035 Units ...
Page 139: ...139 Fig 28 Component Arrangement Size 040 075 Units ...
Page 140: ...140 Fig 29 Component Arrangement Size 090 100 Units ...
