Application

Sequence of Operation
BTU Calculations
33
Siemens Industry, Inc.
Application Note, App 2928
140-1302
2015-07-07
CTL STPT = 70°F: OCC.UNOCC = UNOCC
If
TEMP LOOPOUT =
and
SUP AIR VOL =
then
DISCH STPT =
Formula for DISCH STPT:
CTL STPT +
(TEMP LOOPOUT x
100% ÷ SUP AIR VOL)
10°F
UOC SUP MAX
80°F
70° + (10° x 100% ÷ 100%)
10°F
0.5 ´ UOC SUP MAX
90°F
70° + (10° x 100% ÷ 50%)
–5°F
0.25 ´ UOC SUP MAX
50°F
70° + (–5° x 100% ÷ 25%)
0°F
any flow
70°F
70° + (0° x 100% ÷ x%)
While the actual number of BTUs is not explicitly calculated, DISCH STPT varies as
the supply flow varies in order to maintain a constant quantity of heat entering the
room.
This module also limits TEMP LOOPOUT to values that generate supply air
temperature setpoints that are less than DISCH MAX.
As the demand for heating decreases (TEMP LOOPOUT drops), DISCH STPT
eventually reaches DISCH MIN. If TEMP LOOPOUT drops further, then the value of
TEMP CTL VOL begins to rise from the currently active supply airflow minimum to the
currently active supply airflow maximum to provide more cool air to the space. If this
value is compatible with correct room pressurization, then it is used as the supply flow
setpoint, SUP FLOW STPT. If not, the actual setpoint may be higher or lower than
TEMP CTL VOL.
Temperature Control Sequence.