Honeywell AUTOMATIC CONTROL, Engineering Manual

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ENGINEERING CMANUAL OF AUTOMATION CONTROL
AIR HANDLING SYSTEM CONTROL APPLICATIONS
244
C2562-2
RA 76 ° F DB,
50% RH
MA
OA 80 ° F DB,
78 ° F WB
1
2
3
5
4
COOLING COIL
DISCHARGE
55
° F DB
WATER COIL FACE AND BYPASS SYSTEM CONTROL
Functional Description
M10473
SA
11
6
5
2
70
90
32
SUPPLY
FAN
COOL
HEAT
ON
1
CONTROL
PROGRAM
3
4
7
9
76
50
50
72
74
MA
8
10
0
60
10
100
COOL OR
DEHUMIDIFIER
DEMAND
CHW
VALVE
0
100
0
100
FACE
DAMPER
In the following chart it is assumed that:
1. Desired space condition is 76 ° F DB and a maximum of
50% RH.
2. OA condition is 80 ° F DB and 78 ° F WB.
3. Air entering the system is from the ECONOMIZER
CYCLE DECISION application. The system operates on
25 percent OA during the cooling cycle.
4. Cooling coil leaving air temperature is 55 ° F.
The following results are obtained:
Item
No. Explanation
1 Mixed air temperature at cooling design
condition.
2 Air entering the cooling coil is cooled along a
line of constant moisture content until
saturation is approached. Near saturation the
moisture content is reduced as the air is
cooled. This process involves both latent and
sensible cooling.
3 The final leaving air temperature necessary to
satisfy space requirements will be maintained
by reheating along a constant moisture line.
4 Heating coil discharge.
5 This process line represents the increase in
temperature and humidity that occurs due to
the sensible and latent heat gains in the space.
Item
No. Function
1 Control system energizes when fan is turned
on (See FAN SYSTEM START-STOP
CONTROL)
.
2-4 Space temperature PI control loops have heat
and cool setpoints with deadband.
5,6 Space humidity sensor and setpoint enable
dehumidification.
7-9 Heating and cooling valves and face and
bypass dampers position for heating, cooling,
and dehumidifying cycles.
10 Stages chilled water and face-and-bypass
damper loading.
11 Control program coordinates cooling, heating,
dehumidifying, and fan and hot water
interlock control.