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airflow from the unit, thereby effectively preventing overpres-
surization and its accompanying problems.
A 48/50A2,A4 unit can be equipped with a VFD for staged air
volume control. The speed of the fan is controlled directly by
the
Comfort
Link controls based on the operating mode of the
unit. A 4 to 20 mA signal is sent to the VFD to control the fan
speed.
The four most fundamental configurations for most applica-
tions are
Configuration
SP
SP.CF
, which is the static
pressure control type,
Configuration
SP
CV.FD
, used to
indicate CV unit with VFD (staged air volume).
Configuration
SP
SP.S
, used to enable the static pressure sensor, and
Configuration
SP
SP.SP
, the static pressure setpoint to
be maintained.
OPERATION
On VAV units equipped with a VFD and a proper static pres-
sure sensor, when
SP.CF
,
SP.S
and
SP.SP
are configured, a
PID routine periodically measures the duct static pressure and
calculates the error from setpoint. This error is simply the duct
static pressure setpoint minus the measured duct static pres-
sure. The error becomes the basis for the proportional term of
the PID. The routine also calculates the integral of the error
over time, and the derivative (rate of change) of the error. A
value is calculated as a result of this PID routine, and this value
is then used to create an output signal used to adjust the VFD to
maintain the static pressure setpoint.
Static pressure reset is the ability to force a lowering of the
static pressure setpoint through an external control signal. The
unit controls support this in two separate ways, through a 4 to
20 mA signal input wired to the unit’s isolator board input ter-
minals (third party control) or via CCN.
When employing the CCN, this feature uses the communica-
tions capabilities of VAV systems with ComfortID™ terminals
under linkage. The system dynamically determines and
maintains an optimal duct static pressure setpoint based on the
actual load conditions in the space. This can result in a signifi-
cant reduction in required fan energy by lowering the setpoint
to only the level required to maintain adequate airflow
throughout the system.
OPERATION
On CV units equipped with a VFD (Staged Air Volume) when
SP.CF
,
CV.FD
,
SP.FN
are configured, the
Comfort
Link con-
trols will control the speed of the supply fan based on the oper-
ating mode of the unit. The VFD speed setting points are
SP.MN
,
SP.MX
,
HT.VM
. When in LOW COOL mode and the
compressor stage less than 50%, fan will be as
SP.MN
mini-
mum speed. When in HIGH COOL, the fan will be at
SP.MX
maximum speed. In heating mode, the fan will operate at
SP.MX
maximum speed when the heating stage is 75% or
greater and at
HT.VM
heating minimum speed when the heat-
ing stage is less than 75%. On units configured for two-stage
thermostat operation, the fan will be at
SP.MX
on a call for W2
and at
HT.VM
on a call for only W1.
SETTING UP THE SYSTEM
The options for static pressure control are found under the Lo-
cal Display Mode
Configuration
SP
. See Table 59.
Static Pressure Configuration (SP.CF)
This variable is used to configure the use of
Comfort
Link controls
for static pressure control. There are the following options:
0 (None)
There will be no static pressure control by
Comfort
Link con-
trols. This setting would be used for a constant volume (CV)
application when static pressure control is not required or for a
VAV application if there will be third-party control of the VFD.
In this latter case, a suitable means of control must be field in-
stalled. This setting must be used on CV units with VFD
(staged air volume).
Table 59 — Static Pressure Control Configuration
* Some defaults are model number dependent.
† 67 when
CV.FD
= Yes.
CAUTION
Failure to correctly configure
SP.CF
and
SP.FN
when oper-
ating in VFD Bypass mode will result in the indoor fan mo-
tor running continuously. Damage to unit could result.
ITEM
EXPANSION
RANGE
UNITS
CCN POINT
DEFAULT
SP
SUPPLY STATIC PRESS.CFG.
SP.CF
Static Pres. VFD Control?
0, 1
STATICFG
0*
CV.FD
Constant VOL IDF is VFD
Yes/No
CVIDFVFD
No
SP.FN
Static Pres. Fan Control?
Yes/No
STATPFAN
Yes*
SP.S
Static Pressure Sensor
Enable/Disable
SPSENS
Disable*
SP.LO
Static Press. Low Range
–10 to 0
in. W.C.
SP_LOW
0
SP.HI
Static Press. High Range
0 to 10
in. W.C.
SP_HIGH
5
SP.SP
Static Pressure Setpoint
0 to 5
in. W.C.
SPSP
1.5
SP.MN
VFD Minimum Speed
0 to 100
%
STATPMIN
20†
SP.MX
VFD Maximum Speed
0 to 100
%
STATPMAX
100
SP.FS
VFD Fire Speed Override
0 to 100
%
STATPFSO
100
HT.V.M
VFD Heating Minimum Speed
75 to 100
%
VFDHTMIN
75
SP.RS
Stat. Pres. Reset Config
0 to 4
SPRSTCFG
0
SP.RT
SP Reset Ratio (
/dF)
0 to 2.00
SPRRATIO
0.2
SP.LM
SP Reset Limit in iwc (
)
0 to 2.00
SPRLIMIT
0.75
SP.EC
SP Reset Econo.Position
0 to 100
%
ECONOSPR
5
S.PID
STAT.PRESS.PID CONFIGS
SP.TM
Static Press. PID Run Rate
1 to 200
sec
SPIDRATE
2
SP.P
Static Press. Prop. Gain
0 to 100
STATP_PG
20
SP.I
Static Press. Intg. Gain
0 to 50
STATP_IG
2
SP.D
Static Press. Derv. Gain
0 to 50
STATP_DG
0
SP.SG
Static Press. System Gain
0 to 50
STATP_SG
1.0
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 ...