Specifications

58 Catalog WSC/WDC-4
until the hot material is dipped into the water tank. Then, the load would increase drastically.
Large storage capacity will usually be required for this type of application.
System volume = {1000 gpm x 3 minutes} + {(5 increment of 10% increase) x (3 minutes) x 1000
gpm} = 18,000 gallons
Since there are many other factors that can influence performance, systems can successfully
operate below these suggestions. However, as the water volume decreases below these
suggestions, the possibility of problems increases. We believe that these guidelines should be an
industry standard and not just recommendations from McQuay.
Relief Valves
Vessel Relief Valves Figure 20, Typical Vent Piping
Relief valve connection sizes are 1-inch FPT and are in
the quantity shown in Table 10 and Table 11 for the
evaporator and condenser. In addition, there is a relief
valve (3/8 inch flare) on the top of the oil sump of all
units except variants of the 050 compressor, which
have the valve mounted on the motor end of the
compressor.
All relief valves must be piped to the outside of the
building in accordance with ANSI/ASHRAE 15-2001.
The new 2001 standard has revised the calculation
method compared to previous issues.
Twin relief valves, mounted on a transfer valve, are
used on the condenser so that one relief valve can be
shut off and removed for testing or replacement,
leaving the other in operation. Only one of the two
valves is in operation at any time. Where 4 valves are
shown, on some large vessels, they consist of two
relief valves mounted on each of two transfer valves.
Only two relief valves of the four are active at any
time.
Vent piping is sized for only one valve of the set since only one can be in operation at a time.
Relief Pipe Sizing (ASHRAE Method)
Relief valve pipe sizing is based on the discharge capacity for the given evaporator or condenser
and the length of piping to be run. Discharge capacity for HFC-134a vessels is calculated as
follows:
Inch-Pound Units
(
)
()
f
PPd
fC
PPd
L
O
r
O
6
/215.0
2
ln*
2
2
2
25
−
−
=
Where
L = equivalent length of discharge piping
R
r
= rated capacity as stamped on the relief valve in lb/min (kg/s)
f = Moody friction factor in fully turbulent flow. Typical values given in
Table 8, Moody friction factor (f)
Piping NPS DN ID (in.) f
1 25 1.049 0.0225
2 50 2.067 0.0190
3 80 3.068 0.0173
4 100 4.026 0.0163
SI Units
(
)
()
f
PPd
fC
PPdx
L
O
r
O
500
/104381.7
2
ln*
2
2
2
2515
−
−
=
−