Why is my fan power high relative to the Title 24 Standard Building?

For Nonresidential buildings, the Standard (Budget) building will typically have a Variable Air Volume (VAV) system anytime the building being modeled is greater than 25,000 sqft, more than two stories, or has a cooling capacity > 65,000 Btuh. Your proposed design is likely a Constant Volume system, and thus is going to have significantly higher fan power usage than the Standard building. We have been recommending you choose prescriptive compliance when you have high fan power.

For Multifamily buildings, the Standard building will have fans that run intermittently instead of a continuous running fan for the dwellings and guest rooms.  Check your input at the Central System, Controls tab to see what setting you have for the fan operation and consider if using Zone Ventilation fans (Zone level of the tree, Mechanical Tab) will be possible.

In both cases, review your inputs for the fan BHP to be sure this number is not excessive.  Please also understand that the fan power used in the Performance modeling for the budget does not necessarily align with what is required for Prescriptive, so many times your fan will comply under Prescriptive and not Performance.  If so, take that route.  For VAV systems, review the airflows you have input at the Zone level of the tree, Mechanical tab as well as the VAV turndown ratio indicated on the VAV terminal boxes.

Categories: 8. Nonresidential Mechanical, 9. Nonresidential Title 24 Performance

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