Table 6. “C” values used to determine rupture disc vent line sizes
Evaporator
Size
(EVSZ)
(a)
Condenser
Size (CDSZ)
(b)
“C” Values for Unit Components
Total C val-
ue
Short H.R.
Condenser
Long H.R.
Condenser
Auxiliary
Condenser
With Free
Cooling
050 Short
050 Short
64.05
23.56
31.45
15.28
6.16
050 Short
050 Long
71.94
050 Long
050 Long
83.02
080 Short
080 Short
86.28
29.06
38.80
15.28
5.87
080 Short
080 Long
96.02
080 Long
080 Long
111.29
142 Extended
142 Long
142.20
N/A*
Design Special
15.28
Design Special
142M
142 Long
126.37
50.50
7.10
142 Long
142 Long
136.76
210 Long
210 Long
149.28
56.72
250 Extended
250 Long
173.33
62.12
Notes:
1.
Rupture disc diameter is 3 inches (76 mm).
2. To determine the total “C” value for a specific unit, add the appropriate “C” values for the evaporator, standard condenser and economizer. If
the unit is equipped with any options (e.g., heat recovery, free cooling or an auxiliary condenser, add the applicable “C” values to this total.
to determine the vent line pipe diameter.
(a) EVSZ = Evaporator shell size
(b) CDSZ = Condenser shell size
For CenTraVacs using a rupture disc relief:
•
L
= equivalent length of discharge piping, ft (m)
•
Cr
= rated capacity as stamped on the relief device in lb/min (kg/s), or SCFM multiplied by 0.0764 lb/min (convert
multiplier in lb/min to kg/s for SI)
Cr
(convert C in lb/min to kg/s for SI)
•
f
= Moody friction factor in fully turbulent flow
•
d
= inside diameter of pipe or tube, in (mm)
•
ln = natural logarithm
•
P2
= absolute pressure at outlet of discharge piping, psi (kPa)
•
P0
= allowed back pressure (absolute) at the outlet of pressure relief device, psi (kPa)
P0
= (0.50
P
) + atmospheric pressure
Note:
For rupture discs on CenTraVac chillers, P is 15 lb. Atmospheric pressure is at the elevation of the installation
above sea level; a default value is the atmospheric pressure at sea level, 14.7 psi (101.325 kPa).
RELEASED 10/Mar/2020 06:59:20 GMT
