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This "SUM" will be compared against the "Z" calculations
in determining whether cooling stages should be added or
subtracted.
Z Calculation — For the "Z" calculation, the control attempts
to determine the entering and the leaving-air temperature of the
evaporator coil and based upon the difference between the two
during mechanical cooling, and then determines whether to
add or subtract a stage of cooling. This is the adaptive element.
The entering-air temperature is referred to as MAT
(mixed-air temperature) and the leaving-air temperature of the
evaporator coil is referred to as EDT (evaporator discharge
temperature). They are found at the local display under the
Temperatures
CTRL sub-menu.
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
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"
calculation 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
SumZ Cooling Algorithm 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.
ITEM
EXPANSION
UNIT
UNIT CONFIGURATION
MAT.S
MAT Calc Config
MAT.R
Reset MAT Table
Entries?
MAT Calc Config (MAT.S) — This configuration gives the
user two options in the processing of the mixed-air temperature
(MAT) calculation:
COOL
Z.GN)
CCN
RANGE
DEFAULTS
POINT
0 - 2
MAT_SEL
1
Yes/No
MATRESET
No
• 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
method, 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 al-
lows the user to reset the internally stored MAT learned config-
uration 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
Yes. The economizer controls to the same supply air setpoint as
mechanical cooling does for SumZ when E.TRM = Yes. This
allows for much tighter temperature control as well as cutting
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
MC.LO) — This configuration allows a configurable outside-
air temperature setpoint below which mechanical cooling will
be completely locked out.
DEMAND LIMIT CONTROL — Demand Limit Control
may override the cooling algorithm to limit or reduce cooling
capacity during run time. The term Demand Limit Control re-
fers to the restriction of machine capacity to control the amount
of power that a machine will use. This can save the owner
money by limiting peaks in the power supply. Demand limit
control is intended to interface with an external Loadshed De-
vice either through CCN communications, external 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
setpoint percentages.
• An external 4 to 20 mA input that can reset capacity back
linearly to a setpoint percentage.
• CCN loadshed functionality.
NOTE: It is also possible to force the demand limit variable
(Run Status
COOL
To use Demand Limiting, select the type of demand limiting
to use. This is done with the Demand Limit Select configura-
tion (Configuration
To view the current demand limiting currently in effect,
look at Run Status
COOL
42
ECON
E.TRM is set to
DEM.L).
DMD.L
DM.L.S).
DEM.L.
COOL
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