120
Table 99 — Cooling Information Display Table
Next Stage EDT Decrease (ADD.R)
This variable represents (if adding a stage of cooling) how much
the temperature should drop in degrees depending on the R.PCT
calculation and 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 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 subtract-
ing 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 amount 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)
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
COOL
Z.GN * (–10 + (4*
(–SUB.R))) * 0.6
Cap Threshold Adding (Z.PLU)
This parameter is used in the calculation of SMZ and is calculated
as follows:
Z.PLU = Configuration
COOL
Z.GN * (10 + (4*
(–ADD.R))) * 0.6
High Temp Cap Override (H.TMP)
If stages of mechanical cooling are on and the error is greater than
twice Y.PLU, and the rate of change of error is greater than 0.5F,
then a stage of mechanical cooling will be added every 30 sec-
onds. This override is intended to react to situations where the load
rapidly increases.
Low Temp Cap Override (L.TMP)
If the error is less than twice Y.MIN, and the rate of change of er-
ror is less than –0.5F, then a mechanical stage will be removed
every 30 seconds. This override is intended to quickly react to sit-
uations where the load is rapidly reduced.
Pull Down Cap Override (PULL)
If the error from set point is above 4F, and the rate of change is
less than –1F per minute, then pulldown is in effect, and “SUM”
is set to 0. This keeps mechanical cooling stages from being added
when the error is very large, but there is no load in the space. Pull-
down for units is expected to rarely occur, but is included for the
rare situation when it is needed. Most likely pulldown will occur
when mechanical cooling first becomes available shortly after the
control goes into an occupied mode (after a warm unoccupied
mode).
Slow Change Cap Override (SLOW)
With a rooftop unit, the design rise at 100% total unit capacity is
generally around 30F. For a unit with 4 stages, each stage rep-
resents about 7.5F of change to EDT. If stages could reliably be
cycled at very fast rates, the set point could be maintained very
precisely. Since it is not desirable to cycle compressors more
than 6 cycles per hour, slow change override takes care of keep-
ing the PID under control when “relatively” close to set point.
ITEM EXPANSION RANGE UNITS CCN POINT WRITE STATUS
COOL COOLING INFORMATION
C.CAP Current Running Capacity % CAPTOTAL
CUR.S Current Cool Stage COOL_STG
REQ.S Requested Cool Stage CL_STAGE
MAX.S Maximum Cool Stages CLMAXSTG
DEM.L Active Demand Limit % DEM_LIM forcible
SUMZ COOL CAP. STAGE CONTROL
SMZ Capacity Load Factor –100 to +100 SMZ
ADD.R Next Stage EDT Decrease ^F ADDRISE
SUB.R Next Stage EDT Increase ^F SUBRISE
R.PCT Rise Per Percent Capacity RISE_PCT
Y.MIN Cap Deadband Subtracting Y_MINUS
Y.PLU Cap Deadband Adding Y_PLUS
Z.MIN Cap Threshold Subtracting Z_MINUS
Z.PLU Cap Threshold Adding Z_PLUS
H.TMP High Temp Cap Override HI_TEMP
L.TMP Low Temp Cap Override LOW_TEMP
PULL Pull Down Cap Override PULLDOWN
SLOW Slow Change Cap Override SLO_CHNG
HMZR HUMIDIMIZER
CAPC Humidimizer Capacity HMZRCAPC
C.EXV Condenser EXV Position COND_EXV
B.EXV Bypass EXV Position BYP_EXV
RHV Humidimizer 3-Way Valve HUM3WVAL
C.CPT Cooling Control Point COOLCPNT
EDT Evaporator Discharge Tmp EDT
H.CPT Heating Control Point HEATCPNT
LAT Leaving Air Temperature LAT
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