Water Coil Face And Bypass System Control - Honeywell AUTOMATIC CONTROL Engineering Manual

AIR HANDLING SYSTEM CONTROL APPLICATIONS
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.
3
COOLING COIL
DISCHARGE
55°F DB

WATER COIL FACE AND BYPASS SYSTEM CONTROL

Functional Description
COOL
2
HEAT
70
8
MA
90
9
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.
ENGINEERING CMANUAL OF AUTOMATION CONTROL
OA 80°F DB,
78°F WB
2
MA
1
RA 76°F DB,
5
50% RH
4
C2562-2
3
76
11
CONTROL
74
PROGRAM
72
4
32
7
SUPPLY
FAN
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.
6
50
COOL OR
50
DEHUMIDIFIER
DEMAND
5
0
60
SA
10
100
1
ON
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.
244
10
CHW
FACE
VALVE
DAMPER
0
100
0
100
M10473