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

For Nonresidential buildings, starting with the 2013 modeling rules, the Standard (Budget) building will typically have a Variable Air Volume (VAV) system anytime the building being modeled is greater than 10,000 sqft or more than one story. 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 High-rise Residential buildings, the Standard building will have fans that run intermittently instead of a continuous running fan for the 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 Natural Ventilation (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 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: 7. Nonresidential Mechanical, 8. Nonresidential Title 24 Performance

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