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JOHNSON CONTROLS
FORM 145.05-NOM2 (807)
“AC-S/A DEW MAX” – This establishes the maximum
allowable derived Dew Point Control set point. The
default value is 60.0° F.
“AC-DEW DIF” - This establishes the differential below
the Slab Temperature that the unit will try and control
to. The default value is 5.0° F.
Sequence of Operation
The Unit Control takes the Slab Temperature and
subtracts the
“AC-DEW DIF” value. It then compares
this value to the “AC-S/A DEW MIN” and the “AC-S/A
DEW MAX” . The derived “DEW POINT COOLING”
set point is determined as follows:
•
If the Slab Temperature minus the
“AC-DEW
DIF” is less than or equal to the “AC-S/A DEW
MIN” the control sets the “DEW POINT COOL-
ING” set point to the “AC-S/A DEW MIN”
programmed value.
•
If the Slab Temperature minus the
“AC-DEW
DIF” is between the “AC-S/A DEW MIN” and
the “AC-S/A DEW MAX” the control sets the
“DEW POINT COOLING” set point to the Slab
Temperature minus the “AC-DEW DIF” .
•
If the Slab Temperature minus the
“AC-DEW
DIF” is greater than or equal to the “AC-S/A
DEW MAX” the control sets the “DEW POINT
COOLING” set point to the “AC-S/A DEW
MAX” programmed value.
ECONOMIZER OPERATION
There are two economizer options available – outdoor
air economizer or none.
Based on the type of economizer that is installed the
following parameters must be programmed through
the
“Setpoints” section of the Keypad / Display or by
a communicated input.
“O/A ECON EN” – This value can be turned ON, if
outdoor air economizer is desired, or OFF if not, the
default value is OFF.
“O/A MIN POS” – If outdoor air economizer is enabled
this value must also be programmed. This is the
minimum allowable position for the outdoor air damper
when outdoor air economizer is enabled in the Occupied
mode. The default value is 15%.
“ECON –S/A TMP EN” – When the outdoor air
economizer is selected, the type of control, supply air or
return air must be selected. This value must be turned
ON to use Supply Air Temperature Control. The default
value is ON.
“AC / ECON S/A SP” - this is the set point the controller
will control to if the unit is confi gured for “ECON –S/A
TMP EN” . The default value is 55.0° F.
“ECON – R/A TMP EN” - When the outdoor air
economizer is selected, the type of control, supply air or
return air, must be selected. This value must be turned
ON to use Return Air Temperature Control. The default
value is OFF.
“AC / ECON R/A SP” – this is the set point the controller
will control to if the unit is confi gured for “ECON – R/A
TMP EN” . The default value is 75.0° F.
Sequence of Operation
Outdoor Air Economizer
If the “OUTSIDE AIR TEMP” is less than the “RETURN
AIR TEMP” the control will switch into the economizer
mode. The unit will remain in the economizer mode
until the
“OUTSIDE AIR TEMP” is 1.0° F greater than
the “RETURN AIR TEMP” .
If the unit is confi gured to use Supply Air Temperature
Control, the control will compare the actual supply air
temperature to the
“AC / ECON S/A SP” and generate
an analog output based on the difference and the amount
of response to a given change in output.
If the unit is confi gured to use Return Air Temperature
Control, the control will compare the actual return air
temperature to the
“AC / ECON R/A SP” minus 1.0° F
and generate an analog output based on the difference
and the amount of response to a given change in
output.
If both Supply Air and Return Air Temperature Control
is selected, the Unit Control will use the lower of the
two outputs to control the economizer water valve.
On a FlexSys unit if Dew Point Control is selected, the
control will compare the derived Dew Point Control set
point minus 2.0° F and the dew point of the supply air;
and generate an analog output based on the difference
and the amount of response to a given change in
output.
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