Trane TRG-TRC013-EN manual Effect of Actual Conditions, Air Density Ratio =, Densityactual

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Effect of Actual Conditions

1) Air Density Ratio =

Densityactual

Densitystandard

SPactual

2) SPstandard = Air Density Ratio

3) Use Airflowactual and SPstandard to select fan

4) RPMstandard = RPMactual

5) Poweractual = Air Density Ratio ⋅ Powerstandard

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basically sea level elevation and 70°F [21°C]. If the airflow requirement for a given application is stated at nonstandard conditions, a density correction must be made prior to selecting a fan.

The procedure for selecting a fan at actual elevations and/or temperatures is:

1)Determine the actual air density and calculate the air density ratio (density at actual conditions divided by density at standard conditions)

2)Divide the design static pressure at actual conditions by this air density ratio

3)Use the actual design airflow and static pressure, corrected for standard conditions, to select the fan from the performance tables/charts and to determine the speed (rpm) and input power requirement of the fan at standard conditions

4)The fan speed (rpm) is the same at both standard and actual conditions

5)Multiply the input power requirement by the air density ratio to determine the actual input power required

It is important to note that most pressure-loss charts for other system components, such as ducts, filters, coils, etc. are also based on standard air conditions.

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