Honeywell AUTOMATIC CONTROL Engineering Manual page 456

VALVE SELECTION AND SIZING
QUANTITY OF STEAM
To find the quantity of steam (Q) in pounds per hour use one
of the following formulas:
1. When Btu/hr (heat output) is known:
Btu/hr
Q =
1000 Btu/lb steam
Where:
Btu/hr = Heat output.
1000 Btu/lb = A scaling constant representing the
approximate heat of vaporization of steam.
2. For sizing steam coil valves:
C F M x T D a x 1.0
Q =
1000 Btu/lb steam
Where:
cfm = Cubic feet per minute (ft
the fan.
TDa = Temperature difference of air entering and
leaving the coil.
1.08 = A scaling constant. See NOTE.
1000 Btu/lb = A scaling constant representing the
approximate heat of vaporization of steam.
NOTE: The scaling constant 1.08 is derived as
follows:
0.24 BTU
1.08 = x
lb air ˚F
Where:
The specific volume of air at standard
1 lb air
=
conditions of temperature and atmospheric
3
13.35 ft
pressure.
Simplifying the equation:
14.40 Btu min
1.08 =
˚F hr 13.35 f
To find the scaling constant for air conditions other
than standard, divide 14.40 Btu by specific volume of
air at those conditions.
3. For sizing steam to hot water converter valves:
Q = gpm x TDw x 0.49
ENGINEERING MANUAL OF AUTOMATIC CONTROL
3
/min) of air from
60 min 1 lb air
x
3
1 hr 13.35 ft
3
Where:
gpm = Gallons per minute of water flow through
converter.
TDw = Temperature difference of water entering
and leaving the converter.
0.49 = A scaling constant. This value is derived as
follows:
8.33 lb water
0.49 =
1 gal
Simplifying the equation:
0.49 min lb steam
0.49 =
gal hr ˚F
4. When sizing steam jet humidifier valves:
( )
W 1 – W 2 lb moisture
Q =
lb air
Where:
W1 = Humidity ratio entering humidifier, pounds
of moisture per pound of dry air.
W2 = Humidity ratio leaving humidifier, pounds of
moisture per pound of dry air.
13.35 ft 3
= The specific volume of air at standard
conditions of temperature and atmospheric
lb air
pressure.
ft 3
= Cubic feet per minute (cfm) of air from the
min
fan.
60 min
= A conversion factor.
hr
Simplifying:
(
W 1 – W 2 lb moisture
Q = 4.49
5. When Equivalent Direct Radiation (EDR) is known:
Q = EDR (Total) x 0.24
Where:
EDR (Total) = Radiators are sized according to Equivalent
Direct Radiation (EDR). If controlling
several pieces of radiation equipment with
one valve, add the EDR values for all pieces
to obtain the total EDR for the formula.
0.24 = A scaling constant, lb steam/unit EDR. See
Table 4.
446
60 min 1 lb steam
x x x
1 hr 1000 Btu lb water ˚F
ft 3
1
x x
13.35 ft 3
min
lb air
)
hr
1 Btu
60 min
x
hr