D-EIMWC00804-14EN
Centrifugal Chillers
27
Vent piping is sized for only one valve of the set since only one can be in operation at a time. In
no case would a combination of evaporator and condenser sizes require more refrigerant than the
pumpdown capacity of the condenser. Condenser pumpdown capacities are based on the current
ANSI/ASHRAE Standard 15 that recommend 90% full at 90°F (32
°
C). To convert values to the
older ARI standard, multiply pumpdown capacity by 0.888.
Sizing Vent Piping (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 R-134a vessels is calculated using a
complicated equation that accounts for equivalent length of pipe, valve capacity, Moody friction
factor, pipe ID, outlet pressure and back pressure. The formula, and tables derived from it, is
contained in ASHRAE Standard 15-2001.
Daikin centrifugal units have relief valve settings of 180 psi, 200 psi, and 225 psi, and resultant
valve discharge capacities of 68.5 # air/min, 75.5 # air/min, and 84.4 # air/min respectively.
Using the ASHRAE formula and basing calculations on the 225 psi design yields a conservative
pipe size, which is summarized in Table 9. The table gives the pipe size required per relief valve.
When valves are piped together, the common piping must follow the rules set out in the
following paragraph on common piping.
Table 9. Relief Valve Piping Sizes
Equivalent length (ft)
2.2
18.5
105.8
296.7
973.6
4117.4
Pipe Size inch (NPT)
1 1/4
1 1/2
2
2 1/2
3
4
Moody Factor
0.0209
0.0202
0.0190
0.0182
0.0173
0.0163
NOTE: A 1-inch pipe is too small for the flow from the valves. A pipe increaser must always be installed at the valve
outlet.
Common Piping
According to ASHRAE Standard 15, the pipe size cannot be less than the relief valve outlet size.
The discharge from more than one relief valve can be run into a common header, the area of
which cannot be less than the sum of the areas of the connected pipes. For further details, refer
to ASHRAE Standard 15. The common header can be calculated by the formula:
DCommon
D
D
Dn
=
+
1
2
2
2
2
0 5
....
.
The above information is a guide only. Consult local codes and/or latest version of ASHRAE
Standard 15 for sizing data.
Electrical
Wiring, fuse and wire size must be in accordance with the National Electric Code (NEC).
Standard NEMA motor starters require modification to meet Daikin specifications. Refer to
Daikin Specification R35999901 or Daikin Product Manual PM DWSC/DWDC.
Important: Voltage unbalance not to exceed 2% with a resultant current unbalance of 6 to 10
times the voltage unbalance per NEMA MG-1, 1998 Standard. This is an important restriction
that must be adhered to.
Power Wiring
WARNING
Qualified and licensed electricians must perform wiring. Shock hazard exists.
Power wiring to compressors must be in proper phase sequence. Motor rotation is set up for
clockwise rotation facing the lead end with phase sequence of 1-2-3. Care must be taken that the
proper phase sequence is carried through the starter to compressor. With the phase sequence of
