Modelling DOAS in eQUEST is always a bit tricky. Some things to keep in mind about OA-FROM-SYSTEM:
- For the borrowing systems, this keyword will set the incoming OA temperature to the return temperature for the DOAS. If the corridors have a set point of 70ºF, the return temperature will be 70ºF, even in cooling mode when the DOAS supply temperature is 55ºF.
- The OA required by the borrowing systems is NOT automatically added to the OA requirement for the DOAS. The DOAS calculates its OA requirement from the zones listed under it (the corridors). If this OA requirement is lower than the OA required by the borrowing systems, the DOAS OA requirement is set to be equal to the OA required by the borrowing systems, NOT to the sum of the OA for the corridors and the OA for the borrowing systems.
With those points in mind, I will try to answer your questions.
- the corridors can safely stay under the DOAS as you have modelled it. You may get high unmet load hours in the corridors. One possible workaround is to relax the zone set points (say to 60ºF in heating and 80ºF in cooling) to allow the corridors to fluctuate in temperature. Another is to model the corridors as unconditioned.
- If you want the DOAS to supply 4000 cfm of OA, set the supply flow to 4000 cfm (System Parameters -> Fans -> Flow Parameters). Then set the Minimum OA Sizing Method (System Parameters -> Outdoor Air -> Outside Air and Economizer) to "Set by Critical Zone". Then, for one of the corridor zones, specify the design flow rate (Air Flow tab of the Zone parameters window) and the outdoor air flow rate to be equal to the same number. This should enforce an outdoor air ratio of 1.0. Another approach is to add enough OA to each corridor zone that the sum adds up to 4000 cfm.
You might want to look up the OA-FROM-SYSTEM keyword in the DOE2.2 Dictionary (http://doe2.com/download/DOE-22/DOE22Vol2-Dictionary_48r.pdf)
Hope that helps.
