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USE OM - JANUARY 2017
7.3.3
Fan power, when measured, shall be taken with an instrument having accuracy of 2.0% or better of
the fan motor power being measured.
7.4
Airflow Rate/Air Properties
7.4.1
Airflow rate shall be measured using a code tester per the latest edition of ASHRAE Standard 37,
Section 6.2.
7.4.2
Any code tester used must have completed Section 5.1 of the Laboratory Evaluation and Adjustment
Plan, in AHRI USE OM for calibration.
7.4.2.1
7.4.2 shall be recorded on the final test report.
7.4.3
Air properties shall be calculated per the latest edition of ASHRAE Fundamentals Handbook, using
measurements of properties as specified in this appendix.
7.5
Ductwork
7.5.1
For units that discharge air completely vertically or completely horizontally: the inside dimensions of
the duct shall be at least six (6) inches total greater than the discharge air opening of the unit and centered over
the opening.
7.5.1.1
minimum is not required.
7.5.1.2
minimum is not required.
7.5.1.3
7.5.2
For units that discharge air partially horizontally: the outside dimensions of the duct shall be at least 2
feet greater than the air opening of the unit.
7.5.3
Rectangular ducts may be used on units with round openings, and round ducts may be used on units
with rectangular openings. In either case, the 6 inch minimum applies to the smallest dimension and the ducts
shall be centered over the opening.
7.5.4
For rectangular ducts, one (1) pressure tap per side shall be applied to the center of each duct face
For round ducts, four (4) pressure taps shall be applied at 90° spacing at a distance of 1 length of the greatest
outlet dimension downstream of the unit discharge connection.
7.6
Outdoor air enthalpy calculation procedure requirements
7.6.1
Operational mode is identified as either cooling mode or heating mode, with additional modes in either
cooling mode or heating mode in which the outdoor airflow rate changes. The most common operational mode is:
7.6.1.1
7.6.1.2
72
Any correction factors used from the LEAP evaluation process as noted in Section
Exception #1 is units that have air outlet next to air inlet. In these cases the 6"
Exception #2 Units that have air outlets next to the ground. In these cases the 6"
Exception #3 Units with flanges, the duct shall be the same size as the duct flanges.
For single stage product with single speed outdoor fan:
Cooling mode
Heating mode
For two stage product with two speed outdoor fan:
Cooling mode high stage
Cooling mode low stage
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