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Manual 2100-574
Page 10 of 23
MD4000
decidesLead
unit
Spyder1islead
SignalsSpyder2
aslag.
Spyder2islead
SignalsSpyder1
asLag
DCAmploadisreadand
convertedtobuildingload
withtheequationDCA*
106.4-.2455=BTUH
Calculate
AvailableCooling
(AC)for1econ
Availablecooling=(SP-
MTD-OAT)*1.08*Airflow
IfAC>BL
CalculateMAT
StartEcon1
StopEcon2
StopBlower2
Yes
No
Calculate
Availablecooling
for2econ
IfAC*2>BL
Yes
No
StartLead
Compressor
StartLeadBlower
No
IsOATsuitable
forCooling
Yes
IfOAT<=SP-MTD
andEnthalpyisbelow
curve(ifequipped
DetermineBuilding
Load
CalculateMAT
StartEcon1
StartEcon2
StartBlower2
CalculateMAT
StartEcon1
StartEcon2
StartBlower2
IsRT
aboveSP
Yes
No
StopLead
Compressor
IsRT
above or
belowSP
No
Yes
Calculateadjusted
buildingLoad
(BL)
MATwillbeadjustedtotake
intoaccountdeviationfrom
setpoint
BL+((RT-SP)*Airflow*1.2)
IsRT
BelowSP
No
Yes
IsRT
AboveALarn
Setpoint
Yes
StartLag
Compressor
No
Allowecon
operationwith
Compressor
No
Yes
StopEcon1
StopEcon2
Stop Blower2
Is2
nd
comp
Allowed
Yes
NO
MD4000-BCESDC/MD4000-BESDC
W/ AC UNITS W/ DC CONTROL
ECONOMIZERS
OAT=OutdoorAirTemperature
BL=BuildingLoad
MDT=MinimumTemperatureDifferential
RT=RoomTemperature
SP=Setpoint
AC=AvailableCooling
HEATING SEQUENCE OF OPERATION
Note: All heating sequences for air conditioners with
electric heat or heat pumps will automatically operate
in Alternating Lead/Lag/Lead/Lag sequence even if
controller is set to Non-Alternating for cooling with or
without economizers.
1. Air Conditioners with Electric Heat
1
st
stage heating set point is the dead-band (db) below
the 1
st
stage cooling set point (the SP entered into the
program). The dead-band is adjustable from 2-40F, and
factory default is 27F.
2
nd
stage heating set point will operate at same inter
stage differential as set for cooling mode.