67
Dehumidification Configuration (
D.SEL) — The dehumidi-
fication configuration can be set for the following settings:
• D.SEL = 0 — No dehumidification and reheat.
• D.SEL = 1 — The control will perform dehumidification
and reheat with staged gas only.
• D.SEL = 2 — The control will perform both dehumidifi-
cation and reheat with third party heat via an alarm relay.
In the case of D.SEL=2, during dehumidification, the
alarm relay will close to convey the need for reheat. A
typical application might be to energize a 3-way valve to
perform hot gas reheat.
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 discrete input.
Economizer Disable in Dehum Mode (
D.EC.D) — This
configuration determines economizer operation during Dehu-
midification mode.
• D.EC.D = YES — Economizer disabled during dehu-
midification (default).
• D.EC.D = NO — Economizer not disabled during dehu-
midification.
Vent Reheat Set Point Select (
D.V.CF) — This configuration
determines how the vent reheat set point is selected.
• D.V.CF = 0 — Reheat follows an offset subtracted from
return air temperature (D.V.RA).
• 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 dur-
ing the vent mode. The air will be reheated to this set point.
Dehumidify Cool Set Point (
D.C.SP) — This is the dehu-
midification cooling set point.
Dehumidity RH Set Point (
D.RH.S) — This is the dehumidi-
fication relative humidity trip point.
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
→
DEHU
→
D.SEL must be set to 2.
If the machine’s control type is a TSTAT type (Configura-
tion
→
UNIT
→
C.TYP=3 or 4) and the discrete input selection
for the sensor is not configured (D.SEN not equal to 3),
dehumidification will be disabled.
If the machine’s control type is a TSTAT type (Configura-
tion
→
UNIT
→
C.TYP=3 or 4) and the economizer is able to
provide cooling, a dehumidification mode may be called out,
but the control will not request mechanical cooling.
If a 2-stage control type is selected (Configuration
→
UNIT
→
C.TYP = 4 or 6), then the economizer, if active, locks out
mechanical cooling during the Dehumidification mode.
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
→
DEHU
→
D.SEL = 1 or 2, then
either staged gas or hot water valve control will be automati-
cally 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
perform free cooling, will have its control point (Run
Status
→
VIEW
→
EC.C.P) set to Configuration
→
DEHU
→
D.C.SP. If Configuration
→
DEHU
→
D.EC.D is dis-
abled, 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
→
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
→
DEHU
→
D.SEL = 2), then no heating will be
initiated and the alarm relay will be energized. If
Configuration
→
DEHU
→
D.SEL = 1 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
cooling 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 (Configu-
ration
→
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
→
DEHU
→
D.RH.S) or the discrete input reads
“LOW”, the Dehumidification mode will end.
Temperature Compensated Start — This logic is
used when the unit is in the unoccupied state. The control will
calculate early Start Bias time based on Space Temperature
deviation from the occupied cooling and heating set points.
This will allow the control to start the unit so that the space is at
conditioned levels when the occupied period starts. This is
required for ASHRAE 90.1 compliance. A space sensor is re-
quired for non-linkage applications.
SETTING UP THE SYSTEM — The settings for tempera-
ture compensated start can be found in the local display under
Configuration
→
UNIT.
TCST-Cool Factor (
TCS.C) — This is the factor for the start
time bias equation for cooling.
TCST-Heat Factor (
TCS.H) — This is the factor for the start
time bias equation for heating.
NOTE: Temperature compensated start is disabled when these
factors are set to 0.
ITEM EXPANSION RANGE UNITS CCN POINT
TCS.C Temp.Cmp.Strt.Cool Factr 0 - 60 min TCSTCOOL
TCS.H Temp.Cmp.Strt.Heat Factr 0 - 60 min TCSTHEAT
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