78
Fig. 11 — Psychrometric Chart for
Enthalpy Control
Outdoor Dewpoint Limit Check
If an outdoor relative humidity sensor is installed, the control is
able to calculate the outdoor air dewpoint temperature and will
compare this temperature against the outside air dewpoint tem-
perature limit configuration (
Configuration
ECON
O.DEW
).
If the outdoor air dewpoint temperature is greater than
O.DEW
,
free cooling will not be allowed. Fig. 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 vertically, angle to the left and then fold over. This corre-
sponds to the limits imposed by dry bulb changeover, outdoor
enthalpy changeover and outdoor dewpoint limiting respec-
tively. 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 constructed on a psychrometric
chart.
Control Angle Alarm Configuration
The economizer actuator determines its end stops through a
calibration at the factory. Field-installed actuators may be cali-
brated in the Service Test mode. When an actuator learns its
end stops through calibration, it also determines its control an-
gle. The actuator will resolve this control angle and express its
operation in a percent (%) of this learned range.
If the economizer has not learned a sufficient control angle
during calibration, the economizer damper will be unable to
control ventilation and free cooling. For this reason, the econo-
mizer actuator used in the P Series control system has a config-
urable control angle alarm low limit (
Configuration
ECON
ACT.C
C.A.L1
or
C.A.L2
). If the control angle
learned through calibration is less than
C.A.L1
or
C.A.L2
, an
alert will occur and the actuator will not function.
NOTE: This configuration does not typically need adjustment. It
is configurable for the small number of jobs which may require a
custom solution or workaround.
UNOCCUPIED ECONOMIZER FREE COOLING
This Free Cooling function is used to start the supply fan and
use the economizer to bring in outside air when the outside
temperature is cool enough to pre-cool the space. This is done
to delay the need for mechanical cooling when the system en-
ters the occupied period. This function requires the use of a
space temperature sensor.
When configured, the economizer will modulate during an un-
occupied period and attempt to maintain space temperature to
the occupied cooling set point. Once the need for cooling has
been satisfied during this cycle, the fan will be stopped.
Configuring the economizer for Unoccupied Economizer Free
Cooling is done in the
UEFC
group. There are three configura-
tion options,
FC.CF
,
FC.TM
and
FC.LO
.
Unoccupied Economizer Free Cooling Configuration
(FC.CF)
This option is used to configure the type of unoccupied econo-
mizer free cooling control that is desired.
0 = disable unoccupied economizer free cooling
1 = perform unoccupied economizer free cooling as available
during the entire unoccupied period.
2 = perform unoccupied economizer free cooling as available,
FC.TM
minutes before the next occupied period.
Unoccupied Economizer Free Cooling Time Configuration
(FC.TM)
This option is a configurable time period, prior to the next oc-
cupied period, that the control will allow unoccupied econo-
mizer free cooling to operate. This option is only applicable
when
FC.CF
= 2.
Unoccupied Economizer Free Cooling Outside Lockout Tem-
perature
(FC.LO)
This configuration option allows the user to select an outside-
air temperature below which unoccupied free cooling is not al-
lowed. This is further explained in the logic section.
Unoccupied Economizer Free Cooling Logic
The following qualifications that must be true for unoccupied
free cooling to operate:
• Unit configured for an economizer
• Space temperature sensor enabled and sensor reading
within limits
• Unit in the unoccupied mode
•
FC.CF
set to 1 or
FC.CF
set to 2 and control is within
FC.TM
minutes of the next occupied period
• Not in the Temperature Compensated Start mode
• Not in a cooling mode
• Not in a heating mode
• Not in a tempering mode
• Outside-air temperature sensor reading within limits
• Economizer would be allowed to cool if the fan were re-
quested and in a cool mode
• OAT >
FC.LO
(1.0°F hysteresis applied)
• Unit not in a fire smoke mode
• No fan failure when configured for unit to shut down on a
fan failure
CONTROL CURVE
CONTROL POINT
(approx Deg) AT 50% RH
A
73
B
68
C
63
D
58
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 ...