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EXAMPLE Indoor Coil Below Outdoor Unit
VAPOR LINE
SUCTION RISER
20 FT.
INDOOR COIL
2 FT.
FIGURE 15
From table 3, four ells at 1.8 equivalent feet each equals 7.2
equivalent feet. When added to the 82 feet of pipe, the total
equivalent feet becomes 89.2 feet (round up to 90 feet).
Multiply 6/100 by 90 equivalent feet to calculate total friction
loss of 5.4 psi.
Use figure 14 to calculate the pressure drop in 25 feet of 1 1/8
inch line. Multiply 6/100 by 25 feet to calculate friction loss of
1.5 psi. This loss has already been included in the capacity
given in Lennox' Engineering Handbook, so it should be sub
tracted from the total.
The capacity lost in the total equivalent length" of the re
frigerant line (using figures 12 and 14) equals 1 percent x
(5.4 - 1.5) x 90,000.
Btuh lost= 0.01 x (3.9) x 90,000 = 3510
Capacity loss for the line selected is approximately 3.9
percent.
The preceding calculation shows that this is a workable
system, but it will result in losses in both capacity and effi
ciency.
Alternative Sizing: Using the same (7 1/2 ton) example,
this time select 1 3/8 inch O.D. line. 1 3/8 inch O.D. line with
2 psi per 100 feet pressure drop has 1760 fpm velocity. Now
calculate pressure drop due to friction loss to determine if
this is a better selection.
From figure 3, four ells at 2.4 equivalent feet each equals
9.6 equivalent feet. When added to the 82 feet of pipe, the
total equivalent feet becomes 91.6 feet (round up to 92
feet).
Multiply 2/100 by 92 equivalent feet to calculate total friction
loss of 1.8 psi.
Use figure 14 to calculate the pressure drop in 25 feet of
1 3/8 inch line. Multiply 2/100 by 25 feet to calculate friction
loss of 0.5 psi. This loss has already been included in the
capacity given in Lennox' Engineering Handbook, so it
should be subtracted from the total.
The capacity lost in the total equivalent length" of the re
frigerant line (using figures 12 and 14) equals 1 percent x
(1.8 - 0.5) x 90,000.
Btuh lost= 0.01 x (1.3) x 90,000 = 1170
Capacity loss for the line selected is approximately 1.3
percent.
60 FT.
OIL TRAP
Page 15
The conditions in this example will allow either 1 1/8 inch or
1 3/8 inch vapor line to be used, since capacity loss is mini
mized and velocity is sufficient to return oil to the compres
sor.
Service Valves
The liquid line and vapor line service valves and gauge
ports are accessible inside of the unit. These gauge ports
are used for leak testing, evacuating, charging and check
ing charge.
IMPORTANT - Service valves are closed to line set con
nections. Do not open until refrigerant lines and indoor coil
have been leak tested and evacuated. All precautions
should be exercised to keep the system free from dirt,
moisture and air.
Liquid Line Service Valve
All HP29 units use liquid line service valves as shown in fig
ure 16. A Schrader valve is factory installed. A service port
is supplied to protect the Schrader valve from contamina
tion and serve as the primary leak seal.
LIQUID LINE SERVICE VALVE (VALVE OPEN)
INSERT HEX
WRENCH HERE
INLET (TO
INDOOR
COIL)
SCHRADER
VALVE
SERVICE
PORT
CAP
SERVICE PORT
LIQUID LINE SERVICE VALVE (VALVE CLOSED)
RETAINING RING
INLET (TO
INDOOR
COIL)
SERVICE
PORT
SERVICE
PORT
CAP
SCHRADER VALVE OPEN
TO LINE SET WHEN VALVE IS
CLOSED (FRONT SEATED)
FIGURE 16
STEM CAP
OUTLET (TO
COMPRESSOR)
STEM CAP
INSERT HEX
WRENCH HERE
(VALVE
FRONT
SEATED)
OUTLET (TO
COMPRESSOR)
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