Heating Control Processes; Control From Supply Air - Honeywell AUTOMATIC CONTROL Engineering Manual

SPECIFICATIONS
See FAN SYSTEM START-STOP CONTROL.
Anytime the supply fan runs, the OA, exhaust, and RA
dampers shall position to a minimum ventilation position and
shall be further modulated by an SA PID control loop to
maintain the SA temperature setpoint. The SA temperature
setpoint shall be varied from no less than 55°F to no more than

HEATING CONTROL PROCESSES

The following applications show various ways to control
heating in an air conditioning system.

CONTROL FROM SUPPLY AIR

Functional Description
2
NORMAL
MA
N.O.
5
1
00
PERCENT
6
OPEN
Item
No. Function
1-2 Control system energizes when fan is turned
on (See FAN SYSTEM START-STOP
CONTROL).
3,5 SA temperature maintained by modulating the
hot water valve.
4 Setpoint for SA temperature control.
6 Control program coordinates temperature
control and fan interlock.
FEATURES
1. Air is discharged at a minimum temperature.
2. Valve opens upon loss of motive force (electricity or
compressed air) and closes upon fan shutdown.
SA
ON
3
75
CONTROL
75
PROGRAM
M10458
AIR HANDLING SYSTEM CONTROL APPLICATIONS
75°F as the space temperature PID loop cooling demand varies
from 100 to 0%. Anytime the economizer program is invoked,
the SA temperature control shall be enabled.
PSYCHROMETRIC ASPECTS
For the psychrometric aspects of this application, refer to
MIXED AIR CONTROL WITH ECONOMIZER CYCLE. The
psychrometric aspects of the two applications are the same.
CONDITIONS FOR SUCCESSFUL OPERATION
1. A multiple inline coil arrangement should be used if a
high temperature rise is required.
2. Heating medium and flow must be available.
SPECIFICATIONS
See FAN SYSTEM START-STOP CONTROL.
Anytime the supply fan runs, the hot water valve shall be
modulated by an SA PID control loop to maintain the SA
temperature setpoint. The hot water valve shall close upon fan
shutdown and open upon loss of motive force.
PSYCHROMETRIC ASPECTS
4
1. The SA temperature remains constant until the entering
air temperature exceeds the desired SA temperature.
2. In the following chart it is assumed that the SA PID
control loop is set at 75°F.
MA
The following results are obtained:
Item
No. Explanation
1 Coil discharge is 75°F DB until MA exceeds
75°F DB, above which the coil valve is
closed, no heat is added, and SA condition is
equal to MA.
223 ENGINEERING CMANUAL OF AUTOMATION CONTROL
75°F COIL DISCHARGE
CONTROLLER SETPOINT
1
C2549-1