44
JOHNSON CONTROLS
FORM 145.05-NOM2 (807)
Sequence of Operation
There is a one minute delay from the time the air
proving switch closes until the heating sequence can
be initiated.
Supply Air Temperature Control
There is a one minute delay from the time the air-
proving switch closes until heating operation is allowed.
Heating operation will be enabled when the supply air
temperature is 5.0° F less than the
“HEAT- S/A TMP
SP”
set point. Heating operation will be disabled
when the supply air temperature is 2.0° F greater than
the
“HEAT- S/A TMP SP”
set point. The control waits
one minute from the time the supply air temperature
increases 2.0° F above the set point before it disables
the Heating operation.
The control compares the supply air temperature to
the
“HEAT- S/A TMP SP”
set point and generates a
variable percentage output based on the difference and
the amount of change in the supply air temperature to
a change in output.
Return Air Temperature Control
There is a one minute delay from the time the air-
proving switch closes until heating operation is allowed.
Heating operation will be enabled when the return air
temperature is 1.0° F less than the
“HEAT- S/A TMP
SP”
set point. Heating operation will be disabled
when the supply air temperature is 1.0° F greater than
the
“HEAT- S/A TMP SP”
set point. The control waits
one minute from the time the supply air temperature
increases 1.0° F above the set point before it disables
the Heating operation.
The control compares the return air temperature to
the
“HEAT- R/A TMP SP”
set point and generates a
variable percentage output based on the difference and
the amount of change in the return air temperature to a
change in output.
When both Supply Air and Return Air Control are
enabled, the Unit Control will control the heat operation
to the lower of the two variable percentage outputs.
Staged Heat Operation
The number of steps of capacity will vary with the
type and capacity of the heat. Each of the stages of
operation is assigned a window of operation based on
the percentage of the total operating range 0 to 100%.
To determine the window of operation for each stage
divide 100% by the number of stages. Table 12 gives
the window of operation for each stage.
The Unit Control will send the lower of the supply
air temperature or the return air temperature variable
voltage output to the hydronic heat valve and the valve
will modulate open and close based on the variable
voltage output.
We will use a 4-stage system in the following
example:
When the percentage is equal to or greater than 25%,
the control will wait 30 seconds and then initiate a
demand for the fi rst stage of operation. If the percentage
output drops to 5% or below, the demand for fi rst stage
operation would continue for 30 seconds. During this
30 second off delay if the percentage output is equal to
or greater than 25% again, the fi rst stage demand would
continue and the 30 second off delay would be turned
off. If at any time the heating demand is lost for three
seconds the demand for fi rst stage operation would be
turned off.
When the percentage output is equal to or greater
than 50%, the control will wait 30 seconds and then
initiate a demand for the second stage of operation.
If the percentage output drops to 30% or below, the
demand for second stage operation would continue for
30 seconds. During this 30 seconds off delay if the
percentage output is equal to or greater than 50% again,
the second stage demand would continue and the 30
TABLE 12 – WINDOW OF OPERATION, STAGED HEAT
1-STAGE
2-STAGES
3-STAGES
4- STAGES
TURN OFF
TURN ON
TURN OFF
TURN ON
TURN OFF
TURN ON
TURN OFF
TURN ON
STAGE 1
80%
100%
30%
50%
13.5%
33.5%
5%
25%
STAGE 2
-
-
80%
100%
46.6%
66.5%
30%
50%
STAGE 3
-
-
-
-
80%
100%
65%
75%
STAGE 4
-
-
-
-
-
-
80%
100%
Sequence of Operation
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