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Size large riser
(Riser carrying largest part of load)
The larger line carries 6.5 tons capacity at full load. Select
from figure 14 a 11/8 inch O.D. line (smallest line with ac
ceptable velocity). When operating at 6.5 tons capacity,
this line will operate at 2500 fpm and will produce 4.5 psig
drop per 100 feet.
Putting the Segments Together
Next, you must determine if the line sizes you selected will
result in satisfactory pressure drop between the condens
ing unit and the evaporator
.
Start by finding the total equivalent feet of the large (B) ris
er. See figure 18. Fifteen feet of pipe, plus two tees (branch
side of tee at 4.5 equivalent feet each), plus four ells (1.8
equivalent feet each) = 31.2 equivalent feet length:
15 + 9 (two 4.5 foot tees) + 7.2 (four 1.8 foot ells ) = 31.2
Now, find the total equivalent feet of the small (A) riser. See
figure 18. Fifteen feet of pipe, plus one ell (1.5 equivalent
feet), plus one tee (branch side of tee at 3.5 equivalent
feet), plus one tee (line side of tee at 1.0 equivalent feet) =
21.0 equivalent feet length:
15 + 1.5 + 3.5 + 1.0 = 21.0
Use the total equivalent length of each riser to compute the
pressure drop of each riser. For the large (B) riser, 11/8
inch O.D. suction line with 6.5 tons capacity has 4.5 psig
drop per 100 feet. Multiply (4.5/100) by 31.2 equivalent feet
to calculate the total friction loss of 1.4 psig.
(4.5
100) X 31.2 = 1.4
For the small (A) riser, a 7/8 inch O.D. suction line with 3.5
tons capacity has 6 psig drop per 100 feet. Multiply (6/100)
by 21 equivalent feet to calculate the total friction loss of
1.26 psig:
(6
100) X 21 = 1.26 psig.
The total pressure drop for the riser is equal to the average
of the pressure drop in both risers:
1.4 (B riser drop) + 1.26 (A riser drop) = 2.66
2.66
2 = 1.33
(average pressure drop through A
and B risers)
Find the pressure drop for the horizontal run of pipe. A
13/8 inch pipe at 10 tons capacity and has 3.3 psig drop
per 100 feet. Multiply 3.3/100 by 61 equivalent feet to cal
culate the total friction loss of 2.01 psig:
3.3
100 X 61 = 2.01
Add the pressure drop through the risers to the pressure
drop through the horizontal run to find the total pressure
drop for the system:
2.01 psig (horiz. run) + 1.33 psig (avg. riser) = 3.34
Use figure 14 to calculate the pressure drop in 25 feet of
13/8 inch line. Multiply 3.3/100 by 25 feet to calculate the
friction loss of 0.825 psig.
3.3
100 X 25 = 0.825
The Btuh capacity lost in the total equivalent length"
of the refrigerant line (using figures 12 and 14) = 1% x
(3.34 − 0.825) x 120,000:
Btuh lost = 0.01 x (2.515) x 120,000 = 3018
Capacity loss for the line selected is approximately 2.5 per
cent.
Service Valves
The liquid line and suction line service valves and gauge
ports are accessible inside the unit. These gauge ports are
used for leak testing, evacuating, charging, and checking
the charge. Condensing unit, lines, and evaporator need to
be evacuated.
Liquid Line Service Valve
HS29−072/090/120 units use the liquid line service valve
shown in figure 19. A Schrader valve core is factory
installed. A service port cap is supplied to protect the
Schrader valve from contamination and serve as the pri
mary leak seal.
Accessing the Schrader Valve:
1 − Remove service port cap with an adjustable wrench.
2 − Connect gauge to the service port.
3 − When testing is complete, replace service port cap.
Tighten finger tight, then tighten an additional 1/6 turn.
