Bard MD4000 - Manual (Page 10)

Manual 2100-574
Page 10 of 23
MD4000
decides Lead
unit
Spyder 1 is lead
Signals Spyder2
as lag.
Spyder 2 is lead
Signals Spyder1
as Lag
DC Amp load is read and
converted to building load
with the equation DCA *
106.4-.2455 = BTUH
Calculate
Available Cooling
(AC) for 1 econ Available cooling =( SP-
MTD-OAT)*1.08*Airflow
If AC > BL
Calculate MAT
Start Econ 1
Stop Econ 2
Stop Blower 2
Yes
No
Calculate
Available cooling
for 2 econ
If AC*2 > BL
Yes
No
Start Lead
Compressor
Start Lead Blower
No
Is OAT suitable
for Cooling
Yes
If OAT <= SP-MTD
and Enthalpy is below
curve(if equipped
Determine Building
Load
Calculate MAT
Start Econ 1
Start Econ 2
Start Blower 2
Calculate MAT
Start Econ 1
Start Econ 2
Start Blower 2
Is RT
above SP
Yes
No
Stop Lead
Compressor
Is RT
above or
below SP
No
Yes
Calculate adjusted
building Load
(BL)
MAT will be adjusted to take
into account deviation from
setpoint
BL+((RT-SP)*Airflow*1.2)
Is RT
Below SP
No
Yes
Is RT
Above ALarn
Setpoint
Yes
Start Lag
Compressor
No
Allow econ
operation with
Compressor
No
Yes
Stop Econ 1
Stop Econ 2
Stop Blower 2
Is 2 nd comp
Allowed
Yes
NO
MD4000-BCESDC/MD4000-BESDC
W/ AC UNITS W/ DC CONTROL
ECONOMIZERS
OAT = Outdoor Air Temperature
BL = Building Load
MDT = Minimum Temperature Differential
RT = Room Temperature
SP = Setpoint
AC = Available Cooling
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.