246653-YTG-E-0108
Johnson Controls Unitary Products
11
SELECTION PROCEDURE
GIVEN:
Required Cooling Capacity
460,000 Btuh
Required Sensible Cooling
390,000 Btuh
Required Heating (Gas)
320,000 Btuh
Entering Air on Evaporator
83° F DB/ 67° F WB
Outside Design Temperature
95° F
Supply Fan CFM
13,000 CFM
External Static Pressure
1.25 IWG
Electrical Supply Voltage
460-3-60
Economizer Required
2” Throw Away Filters
Constant Volume
SELECT UNIT:
1.
Determine nominal tons:
460,000 / 12,000 = 38.33 Tons
Thus, a nominal 40 ton unit is selected.
2.
Reference Cooling Capacity Table for a 40 ton unit with
standard evaporator coil.
a.
Locate the table for a standard evaporator coil with
95° F air on the condenser.
b.
Enter table at 13,000 CFM and 67°F WB air on
evaporator
c.
Trace to 83° F Entering Dry Bulb column.
d.
Read 493 MBH total capacity and 403 MBH sensi-
ble capacity.
The 40 ton unit will meet the cooling requirements. From
the nomenclature, the unit will be a Y34. Choose the
appropriate configuration for the next digit. Assuming
bottom return and supply, the fourth digit would be an
“A,” making the model Y34A.
3.
Find Gas Heating Capacity Table.
a.
Trace down Output column.
b.
Find output which exceeds 320,000 Btuh require-
ment. The N5 option gives 426 MBH output.
c.
Ensure that it is offered in the Y34 unit. Read option
model as N5.
From the basic nomenclature, the model now becomes
Y34AN5. Add voltage code of “4” for 460-3-60. Nomen-
clature becomes Y34AN54.
SELECT FAN SPEED AND HORSEPOWER
REQUIREMENTS OF SUPPLY AIR FAN
1.
Find Supply Air Performance Tables for the 40 ton unit.
a.
Check footnotes and make necessary additions or
deductions to static resistance of ductwork:
Ductwork static resistance 1.25
IWG
Economizer static resistance addition
(interpolate) =.25 IWG + Gas Heat (High) =
0.5 IWG
Total Static Resistance
2.0 IWG
b.
Enter Fan Performance Table at 13,000 CFM and
2.0 IWG static pressure:
RPM = 690
BHP = 10.7
NOTE:
Either a Class I or Class II blower could be used.
c.
Enter the Fan Motor Drive Tables. Selecting a 15 hp
motor allows (service factor of 1.5) for a maximum
operating BHP greater than the 10.7 BHP require-
ment.
SIZE OVERCURRENT PROTECTION DEVICE AND
DETERMINE CIRCUIT AMPACITY
1.
Find electrical tables for the basic 40 ton unit.
a.
Enter table for 460-3-60 voltage.
b.
Find 15 hp in the Supply Air Fan column.
c.
Trace to Minimum Circuit Ampacity column - read
104.
d.
Trace to Max. Fuse/Breaker Size column - read 110.
e.
Size wire and overprotection device accordingly.
f.
Check all footnotes.
TABLE 2: REFRIGERANT CHARGE
UNIT (T
ONS
)
MODEL
TYPE
F
ACTORY
/ F
IELD
C
HARGED
C
HARGE
SYS #1
SYS #2
SYS #3
SYS #4
25
wo/HGBP
R22
Factory
25 lb. / 8 oz.
26lb / 0oz
-
-
25
w/HGBP
R22
Factory
26 lb. / 0 oz.
26 lb. / 0oz
-
-
30
wo/HGBP
R22
Factory
13 lb. / 4 oz.
13 lb. / 8 oz.
13 lb. / 8 oz.
-
30
wo/HGBP
1
R22
Factory
14 lb. / 6 oz.
14 lb. / 10 oz.
14 lb. / 10 oz.
-
30
w/HGBP
R22
Factory
14 lb. / 0 oz.
13 lb. / 8 oz.
13 lb. / 8 oz.
-
30
w/HGBP
1
R22
Factory
15 lb. / 2 oz.
14 lb. / 10 oz.
14 lb. / 10 oz.
-
40
wo/HGBP
R22
Factory
15 lb. / 5 oz.
15 lb. / 4 oz.
15 lb. / 5 oz.
15 lb. / 15 oz.
40
w/HGBP
R22
Factory
15 lb. / 13 oz.
15 lb. / 4 oz.
15 lb. / 5 oz.
15 lb. / 15 oz.
1.
With high capacity evaporator coil.
