Trane Genius PKG-PRC007-EN - Manual (Page 10)

PKG-PRC007-EN 10
Selection
Procedure
The selection of a Genius self-contained
unit can be accomplished in three easy
steps.
1
LOAD: Determine the load requirements
for heating and cooling (include outside
air) using Trane’s load estimate forms,
TRACE
® Easy/600 or any standard
method.
2
UNIT TYPE: Self-contained air
conditioners are available in either
water-cooled or remote air-cooled
models to match individual needs.
3
SELECT THE UNIT: The conditions under
which the unit must operate and the
design load will give the final selection.
SELECTION EXAMPLE
Design Conditions
Water-cooled unit
Entering air temperature — 80/67 F
Total gross capacity required —
55,000 BTUH
Entering water temperature — 85 F
Leaving water temperature — 92 F
Airflow — 1,950 CFM at 0.5” duct static
pressure.
Voltage
Unit Selection
Tentatively select a 5-ton unit — Model
SAVE050. Refer to Table PD-6 to obtain
gross total and sensible unit capabilities,
gpm, and leaving water temperature at
nominal conditions:
Total MBh — 60.6
Sensible MBh — 43.5
GPM — 14.5
LWT — 95
The SAVE-050 meets the total and
sensible design requirements.
Since the difference between entering
and leaving water is 7°F multiply the
capacities and water flow by correction
factors on Capacity Correction Factor
Table.
Cooling capacity multiplier 1.01
Sensible capacity multiplier 1.05
Water flow multiplier 1.39
60.6 x 1.01 = 61.21 MBh
43.5 x 1.01 = 43.94 MBh
14.5 x 1.39 = 20.16 GPM
Refer to Table PD-1 to determine
approximate brake horsepower and fan
rpm:
1035 rpm and 0.66 bhp.
Determine net capacities by subtracting
fan motor heat from gross capacities:
2.8 x 0.66 bph = 1.85 MBh
Net total capacity =
61.21 - 1.85 = 59.36 MBh
Net sensible capacity =
43.94 - 1.85 = 42.09 MBh
Supply air temperature DB
Q
s
= 1.085 x CFM x (T
r
-T
S
)
42,090 = 1.085 x 1950 x (80-T
S
)
T
S
= 80 - 42,090
(1.085) (1950)
T
S
= 60.1°F
Air-Cooled
Design Conditions
— 80 F/67 F DB/WB return air
temperature
— 95 F Ambient
— 109300 BTUH Total Net
— 76500 BTUH Sensible Net
— 0.380 External Static Pressure
(evaporator fan)
— 4200 CFM
— 0.25 External static pressure
(condenser fan)
Required
1. Select unit
2. Fan speed and BHP for
a) Evaporator fan
b) Condenser fan
3. Supply air temperature DB
Solution
1. Select Unit
Initially Select a 10-Ton Unit
From Table PD-13
80/67 EAT
95 F AMB = 118.7 MBh Total Gross
4200 CFM 86.6 MBh Sensible
2. Fan speed and BHP determination
Total Static Pressure
Evaporator
0.380 esp
From Table PD-3
Evaporator
10-ton unit
4200 CFM = 1107 RPM
0.5 ESP = 1.63 BHP
Note: If values fall between cfm’s or
esp’s it is proper to interpolate between
values. Do not extrapolate beyond
values in catalog. Contact Trane
marketing department for assistance.
Fan Motor Heat Equation
Fan motor heat = 2.8 x 1.63 = 4.56 MBh
Net total capacity = 118.7 - 4.50
= 114.14 MBh
Net sensible capacity = 86.6 - 4.56
= 82.04 MBh
Conclusion:
Required — 109300 BTUH Total Net
76500 BTUH Total
Sensible Net
Provided — 114140 BTUH Total Net
82040 BTUH Total Net
The 10-ton unit is the proper choice for
this application.