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0 TRANE, <br /> Selection Procedure <br /> Cooling Capacity <br /> Step 1. <br /> Calculate the building's total and sensible cooling loads at design conditions. Use the Trane® <br /> calculation methods or any other standard accepted method. <br /> Factors used in unit selection: <br /> • Total Cooling Load: 71 MBh <br /> • Sensible Cooling Load: 450 MBh <br /> • Airflow: 2400 cfm <br /> • Electrical Characteristics:460/60/3 <br /> • Summer Design Conditions: Entering <br /> • Evaporator Coil: 80 DB, 67 WB Outdoor Ambient: 95 <br /> • External Static Pressure: 0.47 in.wg <br /> • Downflow Configuration <br /> • Economizer <br /> Step 2. <br /> As a starting point,a rough determination must be made of the size of the unit.The final selection <br /> will be made after examining the performance atthe given conditions.Divide the total cooling load <br /> by nominal BTUH per ton (12 MBh per ton);then round up to the nearest unit size. <br /> 71 MBh/12 MBh =approx. 6 tons <br /> Step 3. <br /> Table 7, p. 29 shows that a WSC072E4 has a gross cooling capacity of 78.01 MBh and 56.74 MBh <br /> sensible capacity at 2400 cfm and 95 DB outdoor ambient with 80 DB, 67 WB air entering the <br /> evaporator. <br /> To Find Capacity at Intermediate Conditions not in the table. <br /> When the design conditions are between two numbers that are in the capacity table,interpolation <br /> is required to approximate the capacity. <br /> Note: Extrapolation outside of the table conditions is not recommended. <br /> Step 4. <br /> In orderto selectthe correct unitwhich meets the building's requirements,the fan motor heat must <br /> be deducted from the gross cooling capacity.The amount of heat that the fan motor generates is <br /> dependent on the effort by the motor-cfm and static pressure.To determine the total unit static <br /> pressure: <br /> External Static Duct System 0.47 wg <br /> Economizer from Table 29, p. 46(100% Outside Air) 0.11 wg <br /> Electric Heater Size 9 kW from Table 30, p. 47 0.02 wg <br /> (reference"Heating Capacity"section on this page for determination of heater size) <br /> Total Static Pressure 0.60 wg <br /> With 2400 cfm and 0.60 wg.Table 16,p. 38 shows 0.75 bhp for this unit.Note belowthe table gives <br /> a formula to calculate Fan Motor Heat, <br /> 2.829 x bhp+0.4024= MBh <br /> 2.829 x 0.75+0.4024=2.98 MBh <br /> Now subtract the fan motor heat from the gross cooling capacity of the unit: <br /> Net Total Cooling Capacity <br /> =78.0 MBh -2.98=75.02 MBh <br /> Net Sensible Cooling Capacity <br /> =56.74MBh -2.98=53.76 MBh <br /> 18 PKGP-PRC013K-EN <br />