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An HVAC mode equal to LOW COOL will cause the unit
to select the Setpoints
HVAC mode equal to HIGH COOL will cause the unit to
select the Setpoints
SA.HI set point to control to. Supply
air reset (if configured) will be added to either the low or
high cool set point.
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The control will utilize the SumZ cooling algorithm and
control cooling to a supply air set point. See the SumZ Cool-
ing Algorithm section on page 55 for information on con-
trolling to a supply air set point and compressor staging.
COOL MODE DIAGNOSTIC HELP
To quickly determine the current trip points for the cooling modes,
the Run Status sub-menu at the local display allows the user to
view the calculated start and stop points for both the cooling and
heating trip points. The following sub-menu can be found at the
local display under Run Status
Table 39 — Run Status Mode Trip Helper
ITEM
EXPANSION
TRIP
MODE TRIP HELPER
UN.C.S Unoccup. Cool Mode Start
UN.C.E Unoccup. Cool Mode End
OC.C.S Occupied Cool Mode Start
OC.C.E Occupied Cool Mode End
TEMP
Ctl.Temp R.TMP,S.TMP or Zone
OC.H.E Occupied Heat Mode End
OC.H.S Occupied Heat Mode Start
UN.H.E Unoccup. Heat Mode End
UN.H.S Unoccup. Heat Mode Start
HVAC
the current HVAC MODE
The controlling temperature is "TEMP" and is in the middle of Ta-
ble 39 for easy reference. The HVAC mode can also be viewed at
the bottom of the table.
For non-linkage applications and VAV control types (C.TYP = 1
or 2), "TEMP" is the controlling return air temperature
(R.TMP). For space sensor control, "TEMP" is the controlling
space temperature average occupied zone temperature (S.TMP).
For linkage applications, "TEMP" is zone temperature: average
occupied zone temperature (AOZT) during occupied periods and
average zone temperature (AZT) during unoccupied periods.
SUMZ COOLING ALGORITHM
The SumZ cooling algorithm is an adaptive PID (proportional,
integral, derivative) which is used by the control whenever more
than 2 stages of cooling are present (C.TYP = 1, 2, 3, and 4).
This section will describe its operation and define the pertinent
parameters. It is generally not necessary to modify parameters in
this section. The information is presented primarily for reference
and may be helpful for troubleshooting complex operational
problems.
The only configuration parameter for the SumZ algorithm is locat-
ed at the local display under Configuration
See Table 37.
Capacity Threshold Adjust (Z.GN)
This configuration affects the cycling rate of the cooling stages by
raising or lowering the threshold that capacity must build to in or-
der to add or subtract a stage of cooling.
The cooling algorithm's run-time variables are located at the local
display under Run Status
COOL. See Table 40.
Current Running Capacity (C.CAP)
This variable represents the amount of capacity currently running
in percent.
Current Cool Stage (CUR.S)
This variable represents the cool stage currently running.
SA.LO set point to control to. An
TRIP. See Table 39.
UNITS
CCN POINT
dF
UCCLSTRT
dF
UCCL_END
dF
OCCLSTRT
dF
OCCL_END
dF
CTRLTEMP
dF
OCHT_END
dF
OCHTSTRT
dF
UCHT_END
dF
UCHTSTRT
String
COOL
Requested Cool Stage (REQ.S)
This variable represents the requested cool stage. Cooling relay
timeguards in place may prevent the requested cool stage from
matching the current cool stage.
Maximum Cool Stages (MAX.S)
This variable is the maximum number of cooling stages the con-
trol is configured for and capable of controlling.
Active Demand Limit (DEM.L)
If demand limit is active, this variable will represent the amount of
capacity that the control is currently limited to.
Capacity Load Factor (SMZ)
This factor builds up or down over time and is used as the means
of adding or subtracting a cooling stage during run time. It is a
normalized representation of the relationship between "Sum" and
"Z". The control will add a stage when SMZ reaches 100 and de-
crease a stage when SMZ equals –100.
Next Stage EDT Decrease (ADD.R)
This variable represents (if adding a stage of cooling) how much
temperature should drop (in degrees) depending on the R.PCT
calculation and exactly how much additional capacity is to be
added.
ADD.R = R.PCT * (C.CAP — capacity after adding a cooling
stage)
For example: If R.PCT = 0.2 and the control would be adding
20% cooling capacity by taking the next step up, 0.2 times 20 =
4°F (ADD.R)
Next Stage EDT Increase (SUB.R)
This variable represents (if subtracting a stage of cooling) how
much the temperature should rise (in degrees) depending on the
R.PCT calculation and exactly how much capacity is to be
subtracted.
SUB.R = R.PCT * (C.CAP — capacity after subtracting a cooling
stage)
For example: If R.PCT = 0.2 and the control would be subtracting
30% capacity by taking the next step down, 0.2 times –30 = –6°F
(SUB.R)
Rise Per Percent Capacity (R.PCT)
This is a real time calculation that represents the number of de-
grees of drop/rise across the evaporator coil versus percent of cur-
rent running capacity.
R.PCT = (MAT – EDT)/ C.CAP
Cap Deadband Subtracting (Y.MIN)
This is a control variable used for Low Temp Override (L.TMP)
and Slow Change Override (SLOW).
Y.MIN = -SUB.R*0.4375
Cap Deadband Adding (Y.PLU)
This is a control variable used for High Temp Override (H.TMP)
Z.GN.
and Slow Change Override (SLOW).
Y.PLU = -ADD.R*0.4375
Cap Threshold Subtracting (Z.MIN)
This parameter is used in the calculation of SMZ and is calculated
as follows:
Z.MIN = Configuration
* 0.6
Cap Threshold Adding (Z.PLU)
This parameter is used in the calculation of SMZ and is calculated
as follows:
Z.PLU = Configuration
* 0.6
55
COOL
Z.GN * (–10 + (4* (–SUB.R)))
COOL
Z.GN * (10 + (4* (–ADD.R)))
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