Trane PKGP-PRC001-EN manual Selection Procedures, Cooling Capacity, Heating Capacity

Selection Procedures

Cooling Capacity

Step 1

Calculate the building’s total and sensible cooling loads at design conditions. Use theTranecalculation form or any other standard accepted method.

Step 2

Given the following building requirements:

A

Electrical Characteristics: 460/60/3

B

Summer Design Conditions:

Entering Evaporator Coil: 80 DB/ 67WB

Outdoor Ambient: 95 DB

C

Total Cooling Load: 172 MBh

D

Sensible Cooling Load: 122 MBh

E

Airflow: 6000 cfm

F

External Static Pressure: .50 in. w.g.

G

Rooftop - downflow configuration.

H Accessories Economizer Supplementary Electric Heat

I

Heating Capacity 88 MBh

460 volt/3 phase Electric Supplemental Heat - at 6000 cfm

Size the equipment usingTable PD-3.

As a starting point, a rough determination of the size of the unit must be made.This selection will then be confirmed after examining the performance at the given conditions. Divide the total cooling load by nominal BTUH per ton (12 MBh per ton); then round up to the nearest unit size.

172 MBh/12 MBh = 14.33 (approx. 15 tons.)

Step 3

Table PD-3 shows that a WCD180B4 has a gross cooling capacity of 183.0 MBh and 129.0 MBh sensible capacity at 95 degree ambient and 6000 cfm with 80 DB/67 WB air entering the evaporator.

To Find Capacity at Intermediate Conditions

When the design conditions are between two numbers that are in the capacity table, interpolation is required to approximate the capacity.

Note: Extrapolation outside of the table conditions is not recommended.

Step 4

Verify that there will be enough capacity by determining net capacity. In order to select the correct unit which meets the building’s requirements, the fan motor heat must be deducted from the gross cooling capacity.The amount of heat that the fan motor generates is dependent on the effort by the motor cfm and static pressure.To determine the total unit static pressure, add the following:

External Static: 0.50 in.

Standard Filter 1 in: 0.11 in. (from table PD-13)

Economizer Return Air: 0.04 in. (from table PD-13)

Electric Heater Size 18 kW: .06 in.

Total Static Pressure: .71 in.

Note:The Evaporator Fan Performance Table PD-7 has already accounted for the pressure drop for standard filters and wet coils.

Therefore, the actual Total Static Pressure is .71 - .11 = .60.

With 6000 cfm and .60 inches,Table PD-7 shows 2.66 Bhp.

The note below Table PD-7 gives a formula to calculate Fan Motor Heat:

3.15x bhp = MBh

3.15x 2.66 = 8.38 MBh

Now subtracting the fan motor heat from the gross cooling capacity of the unit:

NetTotal Cooling Capacity =

183-8.38=170.62

Net Sensible Cooling Capacity=

129-8.38=120.62

Step 5

If the performance will not meet the required load of the building, try a selection at the next higher size unit.

Heating Capacity

Step 1

Calculate the building heating load using theTrane calculation form or other standard accepted method.

Step 2

Size the equipment usingTable PD-16 to match the heating loads at design conditions.

A

Total Heating Load: 88 MBh

B

Outdoor Ambient (Winter) 17 DB

C

Indoor ReturnTemperature: 70 DB

D

Airflow: 6000 Cfm

Use the integrated portion of Table PD-16 for the WCD180B4 to determine capacity at winter design conditions.The mechanical heating portion of the heat pump will provide 45 MBh.

Step 3

Because 45 MBh is less than the building’s required heating capacity at winter design conditions, a supplementary heater must be selected.

88 MBh - 45 MBh = 43 MBh

FromTable PD-20, at 480 volts, the 18 kW Heater will be adequate to do the job.

18 kW 61 MBh

FromTable ED-3 select heater AYDHTRK418A (18 kW 460/60/3).

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