From the reference guide: "Show compliance with the applicable requirement above through measurements taken at the system level (i.e., the air-handling unit). For variable air volume systems, the dampers, fan speeds, etc. must be set during the test to the worst-case system conditions (minimum outside air flow) expected during normal ventilation operations. Each air-handler must be measured; sampling or grouping of air-handlers is prohibited."
The building we are working with has a DOAS - dedicated outdoor air system, that supplies OA to three meeting rooms, the pipes that go to each room have fixed dampers that were regulated during the HVAC test and balance. Is our understanding correct to say that the measurements must be made at the system level even when there are fixed dampers are set near the diffusers?
Thanks in advance,
Julia Weatherby
PresidentWeatherby Design & Co. Engineers
94 thumbs up
April 11, 2014 - 4:14 pm
Because your system is 100% outdoor air (no recirculation), I imagine it would be acceptable to add together the air flows at each supply air register. I assume it is easier for you to make the measurements at the air outlets than at the air handling unit outdoor air inlet. You can include a narrative in the Special Circumstances section or the Alternative Compliance section noting that the ductwork routing was confirmed and that airflow was measured at all outlets of the 100% outdoor air system. Theoretically, the sum of the air outlets should be equal to the outdoor air inlet at the AHU. Even considering duct leakage, the sum of the outlets would be expected to be less than or equal to the OA inlet at the AHU, so demonstrating compliance by measuring the sum of the air outlets should be a valid method in a 100% outdoor air system.