Selecting baseline HVAC system (ASHRAE 90.1 2010)

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According to your description, it seems that only the outdoor air is heated by TFA (Treated Fresh Air Unit) and there is no thermostat and no circulating air in the corridors for indoor air temperature control. If that's the case, I think the corridors are regarded unocnditioned zones with preheat coil.

• Fans for unconditioned zones are regarded process loads, and they shall be modelled identical to the Proposed case.
• G3.1.2.4 Preheat Coils. If the HVAC system in the proposed design has a preheat coil and a preheat coil can be modeled in the baseline system, the baseline system shall be modeled with a preheat coil controlled in the same manner as the proposed design.

That is, the same system as the Proposed case (i.e., TFA) should be modeled in the corridors in the Baseline case.

...That's my opinion. It would be better to wait for other opinions.

Supplement

ASHRAE90.1-2010 Performance Rating Method Reference Manual states that "The baseline will be modeled with preheat coil in the mixed air stream controlled to a fixed setpoint 20°F less than the design room heating temperature setpoint."

However, there is no design room heating temperature setpoint in the corridors, right? That's the problem. I think ASHRAE 90.1 does not specify how to model such zones in detail.