Quantity Of Water; Water Valve Pressure Drop - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

VALVE SELECTION AND SIZING
REPRINTED BY PERMISSION FROM ASHRAE HANDBOOK—
1996 HVAC SYSTEMS AND EQUIPMENT
1.6
50% BY MASS
1.5
40%
1.4
30%
1.3
20%
1.2
1.1
10%
1.0
WATER
0.9
0.8
-20 -10 0 10
TEMPERATURE, C
Fig. 15. Pressure Drop Correction for
Propylene Glycol Solutions.

QUANTITY OF WATER

To find the quantity of water (Q) in cubic meters per hour
use one of the following formulas:
watts
Q =
S • T w
1. When heat flow rate is known:
Where:
watts = Heat flow rate.
T w = Temperature difference of water entering
and leaving the coil.
S = Value from Table 3; based on temperature of
water entering the coil.
Table 3. Water Flow Formula Table.
Water
Temp C S
20 1158
30 1154
40 1150
50 1145
60 1141
75 1134
90 1128
PROPYLENE GLYCOL SOLUTION
20 30 40 50 60
M15320
Water
Temp C S
105 1121
120 1114
135 1108
150 1101
165 1094
180 1088
200 1080
2. For hot water coil valves:
1202.4
Q =
S
Where:
3
m /s = Airflow through the coil.
1202.4 = A scaling constant.
Ta = Temperature difference of air entering and
leaving the coil.
S = Value from Table 3; based on temperature of
water entering the coil.
T w = Temperature difference of water entering
and leaving the coil.
70
3. For fan system chilled water coil valves:
Q = 1.02
Where:
3
m /s = Airflow through the coil.
Heat removed =Heat per kilogram of dry air removed in kJ/
kg. Includes both sensible and latent heat.
1.02 = A scaling constant.
T w = Temperature difference of water entering
and leaving the coil.

WATER VALVE PRESSURE DROP

To determine valve pressure drop:
1. For two-way valves consider the following guidelines for
valve pressure drop:
a. Include the pressure drop in the design of the
water circulating system.
— In systems with two-way valves only, it is often
necessary to provide a pump relief bypass or
some other means of differential pressure
control to limit valve pressure drops to the
valve capabilities. For control stability at light
loads, pressure drop across the fully closed
valve should not exceed triple the pressure drop
used for sizing the valve.
— To avoid high pressure drops near the pump,
reverse returns are recommended in large
systems.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
438
m 3
T a
• •
s Tw
m 3
Heat removed
•
s Tw