Commercial Outdoor Air Acceptance Testing: What to Expect
The technician measures outdoor airflow at set operating points and passes the system when it is within 10 percent of the ventilation rate on the certificate of compliance and a variable air volume damper settles within 5 minutes. A certified mechanical acceptance test technician records it on NRCA-MCH-02-A, under Section 120.5(a)1 and Appendix NA7.5.1.
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The inspection before the instruments
The technician takes the required outdoor airflow from NRCC-MCH-E or the equipment schedule, then verifies that the sensor controlling outdoor air is factory or field calibrated, with the certificate attached. The method of delivering outside air is written down, and the pre-occupancy purge is confirmed: the lesser of the minimum outdoor air rate or three air changes during the hour before occupancy, under Section 120.1(d)2. The Commission's 2022 quick reference adds a one-year calibration limit on the airflow instrument.
Constant volume units: force the minimum
A constant volume system must be designed for a fixed minimum outdoor air flow, with the minimum position marked on the damper and a way to hold it. The test forces any economizer to that minimum position and stops damper modulation, then measures. The reading must land within 10 percent of the ventilation air called for in the certificate of compliance.
Variable air volume: two flow points
A VAV system must use dynamic damper control, so a fixed minimum damper setpoint fails. With the economizer high limit forced off, the technician reads outdoor air at design or maximum airflow, then at the sum of minimum zone airflows, full heating, or 30 percent of design airflow. Each reading must be within 10 percent and the damper must stabilize within 5 minutes. The system is then restored to as-found settings.
Planning the visit
Economizer and demand control ventilation are disabled for the test, and the controls contractor usually drives the building automation system. On a cold day, reduced supply flow can push the unit toward 100 percent outdoor air, so freeze protection and coil controls must work first. The 2022 quick reference estimates 0.5 to 2 hours of inspection plus 1 to 3 hours of testing for the VAV version.
Which systems need the test is on the mechanical acceptance page, and the signer rules are on who performs testing. Next in the sequence: demand control ventilation and duct leakage testing. Form basics are on the NRCA page, and commercial projects are quoted individually.
Common Title 24 Questions
- When does a commercial project need Title 24?
- Does an office tenant improvement need Title 24?
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- Does a retail tenant improvement need Title 24?
- What plans are needed for a commercial Title 24 report?
- What is an NRCC certificate of compliance?
Frequently Asked Questions
Only if that person is a certified mechanical acceptance test technician. Where Part 1 requires certification, Section 120.5(b) calls for a certified technician, and an employee must work for a certified employer.
The single-zone unit controls test and the demand control ventilation test in Appendix NA7 also disable the economizer, so they can be scheduled together. The 2022 quick reference adds that the supply fan test can share the two VAV airflow conditions.
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