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I 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.

I 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. though.