88
OPERATION — Dehumidification and reheat can only occur
if the unit is equipped with either staged gas or hydronic heat.
Dehumidification without reheat can be done on any unit but
Configuration
IAQ
DEHU
D.SEL must be set to 2.
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
IAQ
DEHU
D.SEN to 1, 2 or 3 will enable the CEM board along with the
sensor selected for control.
NOTE: If Configuration
IAQ
DEHU
D.SEL = 1 or 2,
then either staged gas or hot water valve control will be auto-
matically enabled (Configuration
HEAT
HT.CF will be
set to either 3 or 4).
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 dehumidifica-
tion mode is initiated, the rooftop will attempt to lower
humidity as follows:
• Economizer Cooling — The economizer, if allowed to per-
form free cooling, will have its control point (
Run Sta-
tus
VIEW
EC.C.P
) set to
Configuration
IAQ
DEHU
D.C.SP
. If
Configuration
IAQ
DEHU
D.EC.D
is disabled, the economizer will always be dis-
abled 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
IAQ
DEHU
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 (Configu-
ration
IAQ
DEHU
D.SEL = 2), then no heating
will be initiated and the alarm relay will be energized. If
Configuration
IAQ
DEHU
D.SEL = 1 and Con-
figuration
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
cooling set point would have been (without any supply
air reset applied).
• Reheat During Vent Mode — If configured (Configura-
tion
IAQ
DEHU
D.V.CF = 0), the heating control
point will be equal to RAT - D.V.RA. If configured (Con-
figuration
IAQ
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 ei-
ther the humidity sensor fall 5% below the set point (Configu-
ration
IAQ
DEHU
D.RH.S) or the discrete input reads
“LOW”, the Humidimizer mode will end.
Humidi-MiZer
®
Adaptive Dehumidification
System —
Units with the factory-equipped Humidi-MiZer
option are capable of providing multiple modes of improved
dehumidification as a variation of the normal cooling cycle.
The design of the Humidi-MiZer system allows for two humid-
ity control modes of operation of the rooftop unit, utilizing a
common subcooling/reheat dehumidification coil located
downstream of the standard evaporator coil. This allows the
rooftop unit to operate in both a Dehumidification (Subcool-
ing) mode and a hot gas Reheat Mode for maximum system
flexibility. The Humidi-MiZer package is factory installed and
will operate whenever there is a dehumidification requirement
present. The Humidi-MiZer system is initiated based on input
from a factory-installed return air humidity sensor to the large
rooftop unit controller. Additionally, the unit controller may re-
ceive an input from a space humidity sensor, a discrete input
from a mechanical humidistat, or third-party controller. Dehu-
midification and reheat control are allowed during Cooling and
Vent modes in the occupied period.
SET UP THE SYSTEM — The settings for Humidi-MiZer
system can be found at the local display at Configura-
tion
IAQ
DEHU. See Table 60.
Dehumidification Configuration (
D.SEL) — The dehumidi-
fication configuration for Humidi-MiZer option is D.SEL = 4
(DH – HUMDZR).
Dehumidification Sensor (
D.SEN) — The sensor can be con-
figured 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).
Table 60 — Dehumidification Configuration
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
DEHU DEHUMIDIFICATION CONFIG.
D.SEL Dehumidification Config 0-5 DHSELECT 0
D.SEN Dehumidification Sensor 1-3 DHSENSOR 1
D.EC.D Econ disable in DH mode? Yes/No DHECDISA Yes
D.V.CF Vent Reheat Setpt Select 0-1 DHVHTCFG 0
D.V.RA Vent Reheat RAT offset 0-8 deltaF DHVRAOFF 0
D.V.HT Vent Reheat Setpoint 55-75 dF DHVHT_SP 70
D.C.SP Dehumidify Cool Setpoint 40-55 dF DHCOOLSP 45
D.RH.S Dehumidify RH Setpoint 10-90 % DHRELHSP 55
H.SEL Heat Reclaim Config 0-2 RCLM_CFG 0
HZ.RT Humidi-Mizer Adjust Rate 5-120 HMZRRATE 30
HZ.PG Humidi-Mizer Prop. Gain 0-10 HMZR_PG 0.8
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