D-EIMWC01308-16EN - 27/40
Common Header Vent Line
When valves are piped together, the common piping must follow the rules according to ASHRAE
Standard 15. The minimum line size of a common header application is based on the
sum of the relief
valve discharge areas and the sum of the rated discharge capacities.
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. First, sum the discharge areas of the relief valves using actual I.D. values from
Table 6 for Sch. 40 pipe :
Min. Common Header Diam (in) = ( ID
1
2
+
ID
2
2
+
ID
3
2
+
ID
4
2
+
……
+
ID
n
2
)
1/2
Compare the calculated min. common header diameter to the internal diameter values in Table 6 and
choose the minimum size which meets or exceeds the sum of the relief valve discharge areas.
For example, if for E5426/C5426 the min. common header diameter is 2.90 inches. From Table
we see
that 3” pipe (3.068” I.D.) is the minimum size which meets or exceeds the sum of the relief valve
discharge areas.
Next, sum of the rated discharge capacities (Cr) to determine required flow capacity.
Total Flow Capacity (lbm air / min ) = Cr
1
+ Cr
2
+ Cr
3
+ ………. Cr
n
For example, if E5426/C5426 has the total flow capacity 604 lbm air/min then for this capacity use
1.803*(L)
0.2
(this equation is only true for relief valve setting of 200 psig, relief valve discharge capacity
of 75.5 lbm air/min and average friction factor of 0.02) in order to compute the approximate required
diameter of the common header diameter if this diameter is constant for the entire length of pipe for a
required length (L) of the Sch 40 piping.
“L” Represents the distance in feet from the relief valves where they are vented to atmosphere.
Finally, select a pipe I.D. from Table 6 equivalent or bigger than the required diameter. If the result is
bigger than 3” pipe which was the result for the common header diameter above then use the bigger
diameter pipe.
The above information is a guide only. Consult local codes and/or latest version of ASHRAE Standard 15
for sizing data.
Pumpdown
To facilitate compressor service, all Daikin centrifugal chillers are designed to permit pumpdown and
isolation of the entire refrigerant charge in the unit’s condenser. In no case would a combination of
evaporator and condenser sizes require more refrigerant than the pumpdown capacity of the condenser.
There is a factory-installed check valve in the compressor discharge line leading to the condenser and a
liquid line valve in the condenser refrigerant outlet liquid line, to allow isolation and storage of the
refrigerant charge in the condenser for servicing for the compressor, economizer, and evaporator. This
feature eliminates extra labor, time and the usage of remote storage vessels. Any tubing lines connected to
the condenser should also be isolated by closing off the factory provided service angle valves only after
the compressor shuts off as a result of pumping down.
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