Page 15
Those fictitious lengths are shown in the table 2 and shall be considered effective for fully open valves.
Table 2:
Equivalent lengths (in meters) for concentrated drops.
The table1 is referred to a condensation temperature of 40°C.
In case of different condensation temperatures the following correcting values shall be applied to the cooling capacity.
Cond. Temp (°C)
20
30
40
50
K suction line
1.18
1.1
1
0.91
K discharge line
0.8
0.88
1
1.11
Table 2.a:
Cooling capacity of the correction factors in function of the condensing temperature.
Using the table 1 and the suggested correction factors it is possible to choose the proper diameter in accordance to the requested
cooling capacity and the evaluated pressure drops.
Once the choice is taken a check shall be made by calculating the real pressure drop using the following formula.
with symbols having the same meaning as in formula [1]
In order to verify if the selected diameter could be correct the following maximum pressure drops shall be considered according to
ASHRAE:
Liquid line:
Δ
Pmax
= 0,5÷1 K
Suction line:
Δ
Pmax
= 1 K
Discharge line:
Δ
Pmax
= 1 K
Example:
How to choose the proper tube diameter.
Input data:
Equivalent length calculated:
Leq
=60 m
Saturated suction temperature:
Tas
=5°C
Condensing temperature:
Tc
=50°C
Cooling capacity at the evaporator:
Pf
=30 kW
Since the values of cooling capacity indicated in Table 1 are relative to pressure drop values equal to 0.02 K / m , first check the
