HVAC Economizers 101 Section #9 Determining the TRUE % of ...

HVAC Economizers 101 Section #9

Determining the TRUE % of Outside Air

Using Charts and Formulas

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Section #9-Determining the TRUE % of OSA Using Charts and Formulas

? The TRUE percent (%) of outside air entering into the building via the air handling unit is found by using percentage charts or formulas. The next couple of slides will demonstrate both.

OA Percentage Formula

OA Percentage Chart

% OA =

Tra - Tma Tra -Toa

X

100

Or to find Temp of Mixed Air

Tma=Tra x (%Tra)+Tosa x (%Tosa)

Note Tma =Temp Mixed Air Tra = Temp Return Air Tosa = Temp Outside Air

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Outside Air Percentage Chart

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Using the Outside Air Percentage Chart

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Exercise to Determine % OSA Using the Chart (Plot out the Answer)

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The Answer to % OSA on the Chart

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Formulas to Determine % OSA and Minimum Position Control

Formula for Calculating the Percentage of Outside Air in an Air Handler from Measured Temperature

% Return Air = (100 - % Outside Air)

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Exercise to Determine Actual % Outside Air Supply using the Formula

Return Air (RA) is 80?F

EA Exhaust Air

RA Return Air

Outside Air (OA) is 40?F

Mixed Air Temp (MA) is 55?F

OA Outside Air

SA Supply Air

MA Mixed Air

Use Outside Air Equation to determine % of OA

% OA =

Tra - Tma Tra -Toa

X 100

Temperature Sensor

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