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Table 6—Puron System Suction Pressure Drop
Nominal
Size
(Btuh)
Suction Line
OD
(in.)
Pressure
Drop
(psi/100 ft)
Suction
Velocity
fpm
Puron Suction Line Pressure Drop (psig)
Total Equivalent Line Length (ft)
20 50 80 100 125 150 175 200 225 250
18000
18000
18000
1/2 9.9 1649 2 5 8 10 12 15 17 20 22 25
5/8 3.1 1018 1 2 2 3 4 5 5 6 7 8
3/4 1.2 678 0 1 1 1 1 2 2 2 3 3
24000
24000
24000
1/2 16.7 2199 3 8 13 17 21 25 29 33 38 42
5/8 5.2 1357 1 3 4 5 7 8 9 10 12 13
3/4 2.0 904 0 1 2 2 2 3 3 4 4 5
7/8 1.0 678 0 0 1 1 1 1 2 2 2 2
30000
30000
30000
5/8 7.8 1696 2 4 6 8 10 12 14 16 18 20
3/4 2.9 1130 1 1 2 3 4 4 5 6 7 7
7/8 1.5 848 0 1 1 1 2 2 3 3 3 4
36000
36000
36000
5/8 10.9 2036 2 5 9 11 14 16 19 22 24 27
3/4 4.1 1356 1 2 3 4 5 6 7 8 9 10
7/8 2.0 1017 0 1 2 2 3 3 4 4 5 5
42000
42000
42000
42000
5/8 14.1 2375 3 7 11 14 18 21 25 28 32 35
3/4 5.4 1582 1 3 4 5 7 8 9 11 12 14
7/8 2.7 1187 1 1 2 3 3 4 5 5 6 7
11/8 0.8 696 0 0 1 1 1 1 1 2 2 2
48000
48000
48000
3/4 6.9 1808 1 3 6 7 9 10 12 14 16 17
7/8 3.5 1357 1 2 3 3 4 5 6 7 8 9
11/8 1.0 796 0 0 1 1 1 1 2 2 2 2
60000
60000
60000
3/4 10.4 2260 2 5 8 10 13 16 18 21 23 26
7/8 5.2 1696 1 3 4 5 6 8 9 10 12 13
11/8 1.4 995 0 1 1 1 2 2 3 3 3 4
Line set application not recommended
Example1
While on a service call, after checking for proper indoor and
outdoor airflow, Tom finds the following pressures and
temperatures at the service valves of a Puron air conditioner:
S Liquid line pressure = 340 psig
S Liquid line temperature = 97°F
S Suction line pressure = 125 psig
S Suction line temperature = 70°F
Using a Puron PT chart, the subcooling is determined to be 8°F,
which is within ±3 of the 10°F listed on the rating plate. Tom
believes the charge is correct. He calculates the superheat to be
approximately 27°F superheat. The apparently high superheat has
Tom concerned.
Tom uses the Pseudo Evaporator Superheat method to check the
TXV performance. The system is a 3--ton Puron air conditioner
with 75 feet equivalent length of 3/4” suction line. Based on Table
6, the system has approximately 3--psig pressure drop in the vapor
line. Per the instructions, he takes the suction line temperature at
the outlet of the evaporator and finds it to be 53°F. Tom adds 3
psig to the 125--psig suction pressure at the outdoor unit to get 128
psig evaporator pressure. The saturated pressure of 128 equates to
44°F. Tom calculates the evaporator superheat to be (53°F--44°F
=) 9°F. The TXV appears to be operating properly.
NOTE: The additional superheat at the compressor is due
principally to heat gain in the 75 feet of suction line with a minor
contribution by the pressure drop. Because the suction line of the
lineset was the same size as the vapor service valve fitting and less
than 80 feet, Tom could have ignored the pressure drop in the
suction line and obtained the evaporator superheat by using the
vapor service valve pressure of 125 psig (saturated temperature =
43°F) and the evaporator outlet temperature of 53°F. The
evaporator superheat is calculated to be (53°F–43°F=)10°F.