45
The main elements to be calculated and used in the calcula-
tion of SumZ are:
1) the rise per percent capacity (
R.PCT
)
2) the amount of expected rise for the next cooling stage
addition
3) the amount of expected rise for the next cooling stage
subtraction
The calculation of “Z” requires two variables,
Z.PLU
used
when adding a stage and
Z.MIN
used when subtracting a stage.
They are calculated with the following formulas:
Z.PLU
=
Z.GN
* (10 + (4*(–
ADD.R
))) * 0.6
Z.MIN
=
Z.GN
* (–10 + (4*(–
SUB.R
))) * 0.6
Where:
Z.GN
= configuration used to modify the threshold levels used
for staging (
Configuration
→
COOL
→
Z.GN
)
ADD.R
=
R.PCT
*
(
C.CAP
– capacity after adding a cooling
stage)
SUB.R
=
R.PCT
* (
C.CAP
– capacity after subtracting a cool-
ing stage)
Both of these terms,
Z.PLU
and
Z.MIN
,
represent a thresh-
old both positive and negative upon which the “SUM” calcula-
tion must build up to in order to cause the compressor to stage
up or down.
Comparing SUM and Z
— The “SUM” calculation is com-
pared against
Z.PLU
and
Z.MIN
.
• If “SUM” rises above
Z.PLU
, a cooling stage is added.
• If “SUM” falls below
Z.MIN
, a cooling stage is subtracted.
There is a variable called
SMZ
which is described in the
reference section and which can simplify the task of watching
the demand build up or down over time. It is calculated as
follows:
If SUM is positive:
SMZ
= 100*(SUM/
Z.PLU
)
If SUM is negative:
SMZ
= –100*(SUM/
Z.MIN
)
Mixed Air Temperature Calculation (MAT)
— The mixed-
air temperature is calculated and is a function of the economiz-
er position. Additionally there are some calculations in the con-
trol which can zero in over time on the relationship of return
and outside air as a function of economizer position. There are
two configurations which relate to the calculation of “MAT”.
These configurations can be located at the local display under
Configuration
→
UNIT
.
MAT Calc Config
(
MAT.S
)
—
This configuration gives the
user two options in the processing of the mixed-air temperature
(MAT) calculation:
•
MAT.S
= 0
There will be no MAT calculation.
•
MAT.S
= 1
The control will attempt to learn MAT over time. Any time
the system is in a vent mode and the economizer stays at a
particular position for long enough, MAT = EDT. Using
this, the control has an internal table whereby it can more
closely determine the true MAT value.
•
MAT.S
= 2
The control will not attempt to learn MAT over time.
To calculate MAT linearly, the user should reset the MAT
table entries by setting
MAT.R
to YES. Then set
MAT.S
= 2
.
The control will calculate MAT based on the position of the
economizer and outside air and return air temperature.
To freeze the MAT table entries, let the unit run with
MAT.S
= 1
. Once sufficient data has been collected, change
MAT.S
= 2
. Do not reset the MAT table.
Reset MAT Table Entries?
(
MAT.R
)
—
This configuration
allows the user to reset the internally stored MAT learned
configuration data back to the default values. The defaults are
set to a linear relationship between the economizer damper
position and OAT and RAT in the calculation of MAT.
SumZ Overrides
—
There are a number of overrides to the
SumZ algorithm which may add or subtract stages of cooling.
• High Temp Cap Override (
H.TMP
)
• Low Temp Cap Override (
L.TMP
)
• Pull Down Cap Override (
PULL
)
• Slow Change Cap Override (
SLOW
)
Economizer Trim Override
—
The unit may drop stages of
cooling when the economizer is performing free cooling and
the configuration
Configuration
→
ECON
→
E.TRM
is set to
Yes. The economizer controls to the same supply air set point
as mechanical cooling does for SumZ when
E.TRM
= Yes.
This allows for much tighter temperature control as well as cut-
ting down on the cycling of compressors.
For a long cooling session where the outside-air tempera-
ture may drop over time, there may be a point at which the
economizer has closed down far enough were the unit could
remove a cooling stage and open up the economizer further to
make up the difference.
Mechanical Cooling Lockout (
Configuration
→
COOL
→
MC.LO
)
—
This configuration allows a configurable outside-
air temperature set point below which mechanical cooling will
be completely locked out.
DEMAND LIMIT CONTROL — Demand Limit Control
may override the cooling algorithm and clamp or shed
cooling capacity during run time. The term Demand Limit
Control refers to the restriction of the machine capacity
to control the amount of power that a machine will use.
Demand limit control is intended to interface with an external
Loadshed Device either through CCN communications, exter-
nal switches, or 4 to 20 mA input.
The control has the capability of loadshedding and limiting
in 3 ways:
• Two discrete inputs tied to configurable demand limit set
point percentages.
• An external 4 to 20 mA input that can reset capacity back
linearly to a set point percentage.
• CCN loadshed functionality.
NOTE: It is also possible to force the demand limit variable
(
Run Status
→
COOL
→
DEM.L
).
To use Demand Limiting, select the type of demand limiting
to use. This is done with the Demand Limit Select configura-
tion (
Configuration
→
DMD.L
→
DM.L.S
).
To view the current demand limiting currently in effect,
look at
Run Status
→
COOL
→
DEM.L
.
The configurations associated with demand limiting can be
viewed at the local display at
Configuration
→
DMD.L
.
See
Table 57.
Demand Limit Select (
DM.L.S
) — This configuration deter-
mines the type of demand limiting.
• 0 = NONE — Demand Limiting not configured.
• 1 = 2 SWITCHES — This will enable switch input
demand limiting using the switch inputs connected to the
CEM board. Connections should be made to TB6-4,5,6.
• 2 = 4 to 20 mA — This will enable the use of a remote 4
to 20 mA demand limit signal. The CEM module must
be used. The 4 to 20 mA signal must come from an
externally sourced controller and should be connected to
TB6-7,8.
• 3 = CCN LOADSHED — This will allow for loadshed
and red lining through CCN communications.
ITEM
EXPANSION
RANGE
CCN
POINT
DEFAULTS
UNIT
UNIT CONFIGURATION
MAT.S
MAT Calc Config
0 - 1
MAT_SEL
1
MAT.R
Reset MAT Table
Entries?
Yes/No
MATRESET
No
Summary of Contents for WEATHERMAKER 48AJ020
Page 95: ...95 Fig 13 Typical Main Control Box Wiring Schematic A48 7787 ...
Page 96: ...96 TO NEXT PAGE Fig 14 Auxiliary Control Box Wiring Schematic A48 7294 ...
Page 98: ...98 Fig 15 Typical 2 Stage Gas Heat Wiring Schematic Size 051 and 060 Units Shown A48 6866 ...
Page 102: ...102 TO NEXT PAGE Fig 18 Typical Power Schematic Size 051 and 060 Units Shown A48 7298 ...
Page 104: ...104 Fig 19 Controls Option Wiring Schematic A48 7810 ...
Page 105: ...105 Fig 20 Small Chassis Component Location Size 020 035 Units A48 7301 ...
Page 106: ...106 Fig 21 Large Chassis Component Locations Size 036 060 Units A48 7302 ...