Quantity Of Steam; Steam Valve Pressure Drop; Proportional Applications; Two-Position Applications - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

VALVE SELECTION AND SIZING

QUANTITY OF STEAM

To find the quantity of steam (Q) in kilograms per hour use
one of the following formulas:
1. When heat output is known:
Heat Output
Q =
2325 kJ/kg
Where:
Heat output = Heat output in kJ/kg.
2325 kJ/kg = The approximate heat of vaporization of
steam.
2. For sizing steam coil valves:
m 3 /s x
T a x 4330
Q =
2325 kJ/kg
Where:
3
m /s = Volume of air from the fan in cubic meters
per second.
Ta = Temperature difference of air entering and
leaving the coil.
4330 = A scaling constant.
2325 kJ/kg = The approximate heat of vaporization of
steam.
3. For sizing steam to hot water converter valves:
Q = L/s x DTw x 6.462
Where:
L/s = Water flow through converter in liters per
second.
Tw = Temperature difference of water entering
and leaving the converter.
6.462 = A scaling constant.
4. When sizing steam jet humidifier valves:
( )
W 1 – W 2 g moisture
Q =
kg air
Where:
W1 = Humidity ratio entering humidifier, grams of
moisture per kilogram of dry air.
W2 = Humidity ratio leaving humidifier, grams of
moisture per kilogram of dry air.
3
1.2045 kg/m = The specific weight of air at standard
conditions of temperature (20 C) and
atmospheric pressure (101.325 kPa).
3
m /s = Volume of air from the fan in cubic meters
per second.
3600 s/h = A conversion factor from second to hours.
m 3
1.2045 kg air 3600s
• • •
m 3
s h
Simplifying:
(
Q = 4.3362

STEAM VALVE PRESSURE DROP

Proportional Applications

When specified, use that pressure drop ( P) across the valve.
When not specified:
1. Calculate the pressure drop ( P) across the valve for good
modulating control:
P = 80% x (P
NOTE: For a zone valve in a system using radiator orifices
use:
P = (50 to 75)% x (P
Where
P = Pressure in supply main in kPa absolute.
1
P = Pressure in return in kPa absolute.
2
2. Determine the critical pressure drop:
critical = 50% x P
P
Where:
P a = Pressure in supply main in kPa (absolute
1
pressure)
Use the smaller value P or P critical when calculating K v .

Two-Position Applications

Use line sized valves whenever possible. If the valve size
must be reduced, use:
P = 20% x (P
Where
P = Pressure in supply main in kPa absolute.
1
P = Pressure in return in kPa absolute.
2
ENGINEERING MANUAL OF AUTOMATIC CONTROL
442
)
W 1 – W 2 kg moisture
hr
– P )
1 2
– P )
1 2
a
1
-P )
1 2