Carrier 38BA - Manual (Page 2)

64 F evaporator entering air wb temperature,
the system has a total capacity (TC) of 600,800
Btuh, and a calculated sensible heat capacity
(SHC) of 498,800 Btuh. For close-coupled
systems (15 ft or less of interconnecting pipe),
an additional 2% may be added to both TC and
SHC. As this system is not close-coupled, the
ratings are used directly from the combination
ratings. At this point, the sensible heat capacity
is adjusted for the evaporator entering air db
temperature. For 20,000 cfm, the bypass factor
is 0.18. The adjusted sensible heat capacity is:
Adj SHC = SHC + [1.09 X cfm x (1—bf)
X (edb-80)]
= 498,800 + [1.09 X 20,000
X (1-.18) X (77-80)]
= 498,800- 53,600
= 445,200 Btuh
Therefore, the selected system will meet all
cooling requirements.
Find heating capacity of selected fan-coil unit.
Enter Table 3, page 10, for 40RR054 and
20,000 cfm. A one-row nonfreeze steam coil
will deliver 915,000 Btuh based on 60 F enter­
ing air temp, and 2 psig steam. To find the
corrected heating capacity, enter Table 1, page
10, for steam coils at 5 psig steam and 58 F
entering air temperature. By interpolation, the
correction factor is 1.062.
Corrected capacity =
Leaving air db
915,000 X 1.062
971,700 Btuh
corrected capacity
1.09 X cfm
edb -t-
58 +
97\_J00
1.09 X 20,000
= 102.6 F
The heating coil has sufficient capacity and the
leaving air db is less than the maximum
temperature of 140 F.
IV Determine fan rpm and bhp.
Refer to Table 14, page 17, for a 40RR054 at
20,000 cfm and 1.12 in. wg external static
pressure, plus 0.07 in. wg for the heating coil
(Table 4), indicates a fan rpm of 828 and
requires 12.6 bhp. As this rating point is within
the shaded area, the fan drive must be selected
and purchased locally.
V Determine size of liquid and suction lines.
Table 11, page 14, indicates the pipe sizes for
the various condensing units. These sizes are
based on an equivalent length equal to the
maximum length indicated plus 50% for fit­
tings. A more accurate estimate may result in
smaller pipe sizes. Enter the table with the
condensing unit (38AD024) and the estimated
length of interconnecting pipe (90 ft). The
suction line will be 2 1/8-in. OD and the liquid
line is 7/8-in. OD. Similarly, for the 38AD016,
the suction line is 2 1/8-in. OD and the liquid
line is 7/8-in. OD. If a 38AD034 — 38AE054
condensing unit is used with more than 25 ft of
piping, a double suction riser may be required.
VI Find size nozzle, TXV and solenoid valve.
To determine the nozzle(s), TXV(s), and sole­
noid valve(s), enter Table 6, page 13, with the
system number. Tables 7, 8, 9, and 10 give the
part numbers for the keys indicated in the
previous table. For this example, a C12 nozzle
would be used in each of the 3 distributors.
Also, the TXV’s and solenoid valves used would
be (using Carrier Part No.):
FAN
COIL
40RR054
COND
UNIT
38AD024
38AD024
38AD016
COIL
SECT
u
M
L
TXV
EA03PC503
SOLENOID
VALVE
EF11BS28
EE11BS28
None Requ ired
Part numbers for Alco and Sporlan valves are
obtained in a similar fashion. Also, for several
systems, a single solenoid valve will control
both the middle and lower coil sections as
exemplified by system no. 49. These systems
should be piped in accordance with Fig. 5, page
16. When the condensing unit is below the
fan-coil unit, the maximum liquid lift as pre­
sented in Table 13, page 15, should be adhered
to.