38
COOL MODE SELECTION PROCESS
The A Series
Comfort
Link controls offer three distinct meth-
ods by which it may select a cooling mode.
1. Thermostat (
C.TYP
= 3 and 4): The thermostat does not de-
pend upon the state of occupancy and the modes are called
out directly by the discrete inputs from the thermostat (
In-
puts
STAT
Y1
and
Y2
).
2. Occupied VAV cooling types (
C.TYP
= 1 and 2) are called
out in the occupied period (
Operating Modes
MODE
OCC
= ON).
3. Unoccupied VAV cooling types (
C.TYP
= 1 and 2) are called
out in the unoccupied period (
Operating Modes
MODE
OCC
= OFF). They are also used for space sensor control
types (
C.TYP
= 5 and 6) in both the occupied and unoccu-
pied periods.
This section is devoted to the process of cooling mode determi-
nation for the three types outlined above.
VAV Cool Mode Selection during the Occupied Period
(C.TYP = 1,2 and Operating Modes
MODE
OCC = ON)
There is no difference in the selection of a cooling mode for ei-
ther VAV-RAT or VAV-SPT in the occupied period. The actual
selection of a cool mode, for both control types, is based upon
the controlling return-air temperature (
Temperatures
AIR.T
CTRL
R.TMP
). Typically this is the same as the return
air temperature thermistor (
Temperatures
AIR.T
RAT
)
except when under CCN Linkage.
VAV Occupied Cool Mode Evaluation Configuration
There are VAV occupied cooling offsets under
Setpoints
.
Cool Mode Determination
If the machine control type (
Configuration
UNIT
C.TYP
) = 1 (VAV-RAT) or 2 (VAV-SPT) and the control is oc-
cupied (
Operating Modes
MODE
OCC
= ON
), then the
unit will not follow the occupied cooling setpoint (
OCSP
). In-
stead, the control will follow two offsets in the determination
of an occupied VAV cooling mode (
Setpoints
V.C.ON
and
Setpoints
V.C.OF
), applying them to the low-heat off trip
point and comparing the resulting temperature to the return-air
temperature.
The
Setpoints
V.C.ON
(VAV cool mode on offset) and
Set-
points
V.C.OF
(VAV cool mode off offset) offsets are used
in conjunction with the low heat mode off trip point to deter-
mine when to bring cooling on and off and in enforcing a true
“vent” mode between heating and cooling. See Fig. 6. The oc-
cupied cooling setpoint is not used in the determination of the
cool mode. The occupied cooling setpoint is used for supply air
reset only.
The advantage of this offset technique is that the control can
safely enforce a vent mode without worrying about crossing
setpoints. Even more importantly, under CCN linkage, the oc-
cupied heating setpoint may drift up and down and this method
ensures a guaranteed separation in degrees Fahrenheit between
the calling out of a heating or cooling mode at all times.
NOTE: There is a sub-menu at the local display (
Run Status
TRIP
) that allows the user to see the exact trip points for both the
heating and cooling modes without having to calculate them. Re-
fer to the Cooling Mode Diagnostic Help section on page 42 for
more information.
To enter into a VAV Occupied Cool mode, the controlling tem-
perature must rise above
[
OHSP
minus
L.H.ON
plus
L.H.OF
plus
V.C.ON
].
To exit out of a VAV Occupied Cool mode, the controlling tem-
perature must fall below
[
OHSP
minus
L.H.ON
plus
L.H.OF
plus
V.C.ON
minus
V.C.OF
].
NOTE: With Vent mode, it is possible to exit out of a cooling
mode during the occupied period if the return-air temperature
drops low enough. When supply-air temperature reset is not con-
figured, this capability will work to prevent over-cooling the space
during the occupied period.
Supply Air Setpoint Control and the Staging of Compressors
Once the control has determined that a cooling mode is in ef-
fect, the cooling control point (
Run Status
VIEW
CL.C.P
) is calculated and is based upon the supply air setpoint
(
Setpoints
SASP
) plus any supply air reset being applied
(
Inputs
RSET
SA.S.R
).
Refer to the SumZ Cooling Algorithm section on page 42 for a
discussion of how the A Series
Comfort
Link controls manage
the staging of compressors to maintain supply-air temperature.
VAV Cool Mode Selection during the Unoccupied Period
(C.TYP = 1,2; Operating Modes
MODE
OCC=OFF)
and Space Sensor Cool Mode Selection (C.TYP = 5 and 6)
The machine control types that use this type of mode selection are:
•
C.TYP
= 1 (VAV-RAT) in the unoccupied period
•
C.TYP
= 2 (VAV-SPT) in the unoccupied period
•
C.TYP
= 5 (SPT-MULTI) in both the occupied and unoc-
cupied period
•
C.TYP
= 6 (SPT-MULTI2) in both the occupied and unoc-
cupied period
These particular control types operate differently than the VAV
types in the occupied mode in that there is both a LOW COOL
and a HIGH COOL mode. For both of these modes, the control
offers two independent setpoints,
Setpoints
SA.LO
(for
LOW COOL mode) and
Setpoints
SA.HI
(for HIGH COOL
mode). The occupied and unoccupied cooling setpoints can be
found under
Setpoints
.
The heat/cool setpoint offsets are found under
Configuration
D.LV.T
.
See Table 37.
ITEM
EXPANSION
RANGE UNITS CCN POINT DEFAULT
V.C.ON
VAV Occ. Cool On Delta 0 to 25
^F
VAVOCON
3.5
V.C.OF
VAV Occ. Cool Off Delta 1 to 25
^F
VAVOCOFF 2
ITEM
EXPANSION
RANGE
UNITS
CCN
POINT
DEFAULT
OCSP
Occupied Cool Setpoint
55 to 80
dF
OCSP
75
UCSP
Unoccupied Cool Setpoint 75 to 95
dF
UCSP
90
Fig. 6 — VAV Occupied Period Trip Logic
L.H.OF
L.H.ON
V.C. ON
V.C. OF
OHSP
Summary of Contents for WEATHERMAKER 48A2020
Page 112: ...112 Fig 20 Typical Main Control Box Wiring Schematic 48 50A Units ...
Page 113: ...113 Fig 21 Typical Auxiliary Control Box Wiring Schematic ...
Page 114: ...114 Fig 22 Typical 2 Stage Gas Heat Wiring Schematic Size 060 Units Shown ...
Page 115: ...115 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown TO NEXT PAGE ...
Page 116: ...116 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown cont ...
Page 117: ...117 Fig 24 Typical Electric Heat Control Schematic 50 Series Size 060 Units Shown ...
Page 118: ...118 Fig 25 Typical Controls Option Wiring Schematic SW1 SW2 OR DEHUMIDIFY SWITCH ...
Page 119: ...119 Fig 26 Typical Power Schematic 48 50A2 A3 A4 A5 060 Unit Shown ...
Page 120: ...120 Fig 27 Typical Power Schematic of Greenspeed Low Ambient Option 48 50A 060 Unit Shown ...
Page 121: ...121 Fig 28 Typical Small Chassis Component Location Size 020 035 Units ...
Page 122: ...122 Fig 29 Typical Large Chassis Component Locations Size 040 060 Units ...
Page 185: ...185 APPENDIX C VFD INFORMATION cont Fig F Internal Enclosure Fan Replacement A48 7716 ...