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Large Single Story Building HVAC Systems

asked 2023-02-08 09:34:56 -0500

updated 2023-02-08 09:35:22 -0500

We have a 450,000 ft2 single story mental health hospital that we are energy modeling. The building size and climate zone means that we should use System 7. Our confusion is how many HVAC systems we should use with our Baseline.

From ASHRAE 90.1 G.3.1.1

For systems 5, 6, 7, and 8 each floor shall be modeled with a separate HVAC system.

In our case we only have one floor though and one HVAC serving 450,000 ft2 doesn't seem realistic either.

Exception 2 says to use System 3 or 4 when there are sufficiently different occupancy, process, or schedules. In our model though that would create a lot of System 3.

Our gut tells us we should be conservatively match the HVAC system groups in the Proposed to the Baseline. We would like to find language in ASHRAE 90.1 or LEED that some direction though.

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answered 2023-02-08 20:16:03 -0500

Keigo's avatar

You should follow ASHRAE 90.1 G.3.1.1, but in my understanding, this is a minimum requirement (i.e. VAV systems on two or more floors should not be combined), and the VAV system on one floor should be further separated according to other requirements.

For example, if some zones in the proposed case have MERV13 Filter and other zones does not have it, the VAV systems in the Baseline case should be separated because the Fan Power Limitation Pressure Drop Adjustment is different as per Table

If some zones in the Proposed case include humidification and other zones does not include it, the VAV systems in the Baseline case should be separated into those with humidification and those wihtout humidification as per Table G3.1 10.HVAC Systems.

Please also refer to other requirements in Appendix G.

By the way, I think you don't need to worry about whether the Baseline case is realistic or not. There are many requirements in the Baseline case that are not realistic, such as fixed pump head, no matter how large the building is.

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Asked: 2023-02-08 09:34:56 -0500

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Last updated: Feb 08 '23