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90
•
D.V.CF
= 1 — Reheat follows a dehumidification heat set
point (
D.V.HT
).
Vent Reheat RAT Offset (D.V.RA)
Set point offset used only during the vent mode. The air will be
reheated to return-air temperature less this offset.
Vent Reheat Set Point (D.V.HT)
Set point used only during the vent mode. The air will be re
-
heated to this set point.
Dehumidify Cool Set Point (D.C.SP)
This is the dehumidification cooling set point.
Dehumidity RH Set Point (D.RH.S)
This is the dehumidification relative humidity trip point.
Dehumidify RH Deadband (DH.DB)
This is the dehumidification relative humidity sensor's deadband.
Dehum Discrete Timeguard (DH.TG)
This is the dehumidification discrete switch's time guard.
OPERATION
Dehumidification and reheat can only occur if the unit is
equipped with either staged gas or hydronic heat. Dehumidifi
-
cation without reheat can be done on any unit, but
Configura
-
tion
DEHU
D.SEL
must be set to 5.
If the machine’s control type is a TSTAT type (
Configura
-
tion
UNIT
C.TYP
=3) and the discrete input selection for
the sensor is not configured (
D.SEN
not equal to 3), dehumidi
-
fication will be disabled.
If the machine’s control type is a TSTAT type (
Configura
-
tion
UNIT
C.TYP
=3) and the economizer is able to pro
-
vide cooling, a dehumidification mode may be called out, but
the control will not request mechanical cooling.
NOTE: Configuring
Configuration
DEHU
D.SEN
to 1, 2, or
3 will enable the CEM board along with the sensor selected for
control.
NOTE: If
Configuration
HEAT
HT.CF
is inconsistent,
Con
-
figuration
DEHU
D.SEL
will automatically revert to 0.
If a tempering, unoccupied, or “mechanical cooling locked
out” HVAC mode is present, dehumidification will be disabled.
An HVAC: Off, Vent or Cool mode must be in effect to launch
either a Reheat or Dehumidification mode.
If an associated sensor responsible for dehumidification fails,
dehumidification will not be attempted (
SPRH
,
RARH
).
Initiating a Reheat or Dehumidification Mode
To call out a Reheat mode in the Vent or the Off HVAC mode,
or to call out a Dehumidification mode in a Cool HVAC mode,
one of the following conditions must be true:
• The space is occupied and the humidity is greater than the
relative humidity trip point (
D.RH.S
).
• The space is occupied and the discrete humidity input is
closed.
Dehumidification and Reheat Control
If a dehumidification mode is initiated, the rooftop will attempt
to lower humidity as follows:
• Economizer Cooling — The economizer, if allowed to
perform free cooling, will have its control point (
Run
Status
VIEW
EC.C.P
) set to
Configuration
DE
-
HU
D.C.SP
. If
Configuration
DEHU
D.EC.D
is
disabled, the economizer will always be disabled during
dehumidification.
• Cooling — For all cooling control types: A High Cool HVAC
mode will be requested internally to the control to maintain
diagnostics, although the end user will see a Dehumidification
mode at the display. In addition, for multi-stage cooling units
the cooling control point will be set to
Configuration
DE
-
HU
D.C.SP
(no SASP reset is applied).
• Reheat When Cooling Demand is Present — For reheat
control during dehumidification: If reheat follows an offset
subtracted from return-air temperature (
Configura
-
tion
IAQ
DEHU
D.SEL
= 3), then no heating will be
initiated and the alarm relay will be energized. If
Configu
-
ration
IAQ
DEHU
D.SEL
= 2 or1 and
Configura
-
tion
HEAT
HT.CF
= staged gas or hot water valve,
then the selected heating control type will operate in the
low heat/modulating mode.
• The heating control point will be whatever the actual cool
-
ing set point would have been (without any supply air reset
applied).
• Reheat During Vent Mode — If configured
(
Configura
-
tion
DEHU
D.V.CF
= 0), the heating control point will
be equal to RAT -
D.V.RA
. If configured (
Configura
-
tion
DEHU
D.V.CF
=1
), the heating control point will
be equal to the
D.V.HT
set point.
Ending Dehumidification and Reheat Control
When either the humidity sensor falls below relative humidity
sensor's dead band % (
Configuration
DEHU
DH.DB
) or
below the set point (
Configuration
DEHU
D.RH.S
),
or the
discrete input reads “LOW”, and discrete switch time guard ex
-
pires (
Configuration
DEHU
DH.TG
), the Humidi-MiZer
mode will end.
Humidi-MiZer Adaptive Dehumidification System
Units with the factory-equipped Humidi-MiZer
®
option are ca
-
pable of providing multiple modes of improved dehumidifica
-
tion as a variation of the normal cooling cycle. The design of the
Humidi-MiZer system allows for 2 humidity control modes of
operation of the rooftop unit, utilizing a common subcooling/re
-
heat dehumidification coil located downstream of the standard
evaporator coil. This allows the rooftop unit to operate in both a
Dehumidification (Subcooling) mode and a hot gas Reheat
Mode for maximum system flexibility. The Humidi-MiZer pack
-
age is factory installed and will operate whenever there is a de
-
humidification requirement present. The Humidi-MiZer system
is initiated based on input from a factory-installed return air hu
-
midity sensor to the large rooftop unit controller. Additionally,
the unit controller may receive an input from a space humidity
sensor, a discrete input from a mechanical humidistat, or third-
party controller. Dehumidification and reheat control are al
-
lowed during Cooling and Vent modes in the occupied period.
SETTING UP THE SYSTEM
The settings for Humidi-MiZer system can be found at the lo
-
cal display at
Configuration
DEHU
. See Table 60.
Dehumidification Configuration (D.SEL)
The dehumidification configuration for Humidi-MiZer option
is
D.SEL
= 4 (DH – HUMDZR).
Dehumidification Sensor (D.SEN)
The sensor can be configured for the following settings:
•
D.SEN
= 1 — Initiated by return air relative humidity sensor.
•
D.SEN
= 2— Initiated by space relative humidity sensor.
•
D.SEN
= 3 — Initiated by discrete input.
The default sensor is the return air relative humidity sensor
(
D.SEN
= 1). Units ordered with the Humidi-MiZer option will
have factory-installed return air relative humidity sensors.
Economizer Disable in Humidi-MiZer Mode (D.EC.D)
When
D.SEL
= 4 (DH – HUMDZR), this configuration is au
-
tomatically set to
D.EC.D
= YES (Economizer disabled during
dehumidification).
Vent Reheat Set Point Select (D.V.CF)
This configuration determines how the vent reheat set point is se
-
lected. This set point becomes the supply air set point when the
Humidi-MiZer function is initiated and the unit enters a Reheat
mode (relative humidity above set point with no cooling demand).
Summary of Contents for WeatherExpert 48N2
Page 135: ...135 Fig 18 48 50N Typical Power Schematic Nominal 075 Ton Unit Shown ...
Page 136: ...136 Fig 19 48 50N Typical Power Schematic Nominal Ton 90 150 Units Shown ...
Page 137: ...137 Fig 20 48 50N Main Base Board Input Output Connections ...
Page 138: ...138 Fig 21 48 50N RXB EXB CEM Input Output Connections a48 9307 ...
Page 139: ...139 Fig 22 48 50N EXV SCB Input Output Connections a48 9308 ...
Page 140: ...140 Fig 23 48N Typical Modulating Gas Heat Unit Control Wiring ...
Page 141: ...141 Fig 24 50N Typical Electric Heat Unit Control Wiring ...
Page 144: ...144 Fig 27 48N Typical Gas Heat Section Wiring Nominal Ton 120 to 150 Units ...
Page 145: ...145 Fig 28 48 50N Typical Power Component Control Wiring 460 v ...
Page 146: ...146 Fig 29 48 50N Component Control Wiring 575 v Nominal Ton 075 to 150 Units ...
Page 147: ...147 Fig 30 48 50N Component Arrangement Power Box ...
Page 148: ...148 Fig 31 48 50N Component Arrangement Control Box ...
Page 240: ...240 APPENDIX D VFD INFORMATION CONT Fig G VFD Bypass Wiring Diagram WHEN USED ...