Honeywell AUTOMATIC CONTROL User Manual

ENGINEERING MANUAL OF AUTOMATIC CONTROL
VALVE SELECTION AND SIZING
444
Assume the following:
System flow at design, 1000 gpm
Pump head at design, 48 ft
Pump head at 90 percent flow, 50 ft
Pressure across mains at AHU 1 at design flow, 28 ft
Chiller pressure drop, 12 ft
Chiller piping loop design pressure drop, 8 ft
With full system flow, Valve V5 is closed. Pressure drop
across V5 equals the pump head minus the friction drops to
V5. Pressure drop across Valve V5 is then 48 ft – 12 ft
(chiller drop) – 4 ft (supply drop) – 4 ft (return drop) or 28 ft.
With system flow at 90 percent, the pump head rises to
50 ft, while the friction drops fall to the lower values shown
in Figure 16. For additional information on chiller bypass
operation see Chiller, Boiler, and Distribution System
Applications section. Pressure drop across V5 equals the
pump head minus the friction drops to V5. Pressure drop
across Valve V5 is then 50 ft – 9.6 ft (chiller drop) – 3.2 ft
(supply drop) – 3.2 ft (return drop) or 34 ft. Converting ft to
psi, 34 ft x 0.4335 psi/ft = 14.7 psi (see General
Engineering Data section).
Substituting the flow of water, specific gravity of water, and
pressure drop in the C
v
formula shows that the Valve V5
should have a C
v
of 235.
Fig. 16. Chiller Bypass Application.
RETURN
SYSTEM STRAINER
HEAT/
COOL
COIL
1
V1
B1
HEAT/
COOL
COIL
2
V2
B2
HEAT/
COOL
COIL
3
V3
B3
HEAT/
COOL
COIL
4
V4
B4
V5
PUMP
SUPPLY
DP SETPOINT = 34'
180 GPM
PER
AHU COIL
DP
M10605
CHILLER
12
9.6
36
40.4
48
50
PD
4
3.2
4
3.2
PD
4
3.2
PD
ZERO REFERENCE
0
32
37.2
NUMBERS IN CIRCLES = GAGE PRESSURES
PUMP INLET = ZERO FOR SIMPLICITY
TOP NUMBERS = FULL FLOW
BOTTOM NUMBER = 90% FLOW
PD = PRESSURE DROP
EXAMPLE 3:
Sizing water valves for heating coils is especially critical.
In Figure 17, a valve with a C
v
of 12 will have 30 percent
of the available pressure drop when full open, while a valve
with a C
v
of 5 will have 70 percent of the available pressure
drop. As shown in Figure 18, the valve with 70 percent of
the available pressure drop essentially provides the equal
percentage water flow control, resulting in linear coil heat
transfer and stable temperature control. The valve with only
30 percent of the available pressure drop has a more linear
flow control which results in nonlinear coil heat transfer.
See EQUAL PERCENTAGE VALVE section for further
information.
C
v
=
900
1
14.7
= 235

Honeywell AUTOMATIC CONTROL Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL
Category	Controller
Language	English