30
McQuay IM 487-4
Introduction
Refrigerant Charge
Factory-installed DX coils are designed to use R-22. The total
charge per circuit is the sum of the following three values:
•
Condenser section charge. Refer to manufacturer’s data.
•
Evaporator coil charge.
•
Charge for length of interconnecting piping, installed by
field.
Note:
Factory-installed DX coils are intended for one
refrigerant circuit on unit size 800 and two refrigerant
circuits containing identical weights of refrigerant on all
other sizes. The values shown in Table 8, Table 9 and
Table 10 are for each circuit.
Note:
The total operating charge per circuit should not exceed
the pumpdown capacity per circuit.
* The RDS 802C unit has two refrigerant circuits.
Unit Piping
Condensate Drain Connection
•
The unit is provided with a 1.5" male NPT condensate drain
connection. Refer to certified drawings for the exact
location. For proper drainage, level the unit and drain pan
side to side and install a P-trap
•
Units may have positive or negative pressure sections. Use
traps in both cases with extra care given to negative pressure
sections. In Figure 33, dimension “A” should be a minimum
of 8" (203 mm). As a conservative measure to prevent the
cabinet static pressure from blowing or drawing the water
out of the trap and causing air leakage, dimension A should
be two times the maximum static pressure encountered in
the coil section in inches w.c.
•
Draining condensate directly onto the roof may be
acceptable; refer to local codes. Provide a small drip pad of
stone, mortar, wood, or metal to protect the roof against
possible damage.
•
If condensate is piped into the building drainage system,
pitch the drain line away from the unit a minimum of 1/8"
per foot. The drain line must penetrate the roof external to
the unit. Refer to local codes for additional requirements.
Sealed drain lines require venting to provide proper
condensate flow.
•
Where the cooling coils have intermediate condensate pans
on the face of the evaporator coil, copper tubes near both
ends of the coil provide drainage to the main drain pan.
Check that the copper tubes are in place and open before the
unit is put into operation.
•
On units with staggered cooling coils, the upper drain pan
drains into the lower coil drain pan through a copper tube
near the center of the drain pan. Check that this tube is open
before putting the unit into operation and as a part of routine
maintenance.
Table 8: Approximate DX coil refrigerant charge per circuit
Unit size
DX Coil R-22 charge (lbs./circuit)
Flat coil
Staggered coil
047C
3 x no. of DX rows
3.5 x no. of DX rows
077C
5 x no. of DX rows
6.5 x no. of DX rows
Table 9: Approximate refrigerant charge per circuit
Unit size
Evaporator coil (lbs/ckt/coil row)
802
3.30
802C*
2.45
Table 10: Weight of refrigerant R-22 in copper lines
(pounds per 100 feet of Type L tubing)
O.D.
line
size
Vol. per
100 ft.
in cubic
feet
Weight of refrigerant, lbs./100 feet
Liquid @
100°F
Hot gas
@ 120°F
cond.
Suction gas (superheat to
85°F)
30°F
40°F
3/8"
0.054
3.84
0.202
0.052
0.077
1/2"
0.100
7.12
0.374
0.098
0.143
5/8"
0.162
7.12
0.605
0.158
0.232
7/8"
0.336
24.00
1.260
0.323
0.480
1 1/8"
0.573
40.80
2.140
0.550
0.820
1 3/8"
0.872
62.10
3.260
0.839
1.250
1 5/8"
1.237
88.00
4.620
1.190
1.770
2 1/8"
2.147
153.00
8.040
2.060
3.060
2 5/8"
3.312
236.00
12,400
3.180
4.720
3 1/8"
4.728
336.00
17.700
4.550
6.750
3 5/8"
6.398
456.00
24.000
6.150
9.140
4 1/8"
8.313
592.00
31.100
8.000
11.190
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