Hello,

We are currently working on a LEED assessment regarding a Laboratory Building. The proposed design includes a number of labs that are separated from corridors/transition areas by airlocks which are kept at positive pressure (pressurized). Additionally, the AHU's serving this spaces are 100% fresh air AHU's per national code. 

In this scenario for the baseline model, addendum cn to 90.1-2010 adds exception d.: "For baseline systems serving only laboratory spaces that are prohibited from recirculating return air by code or accreditation standards, the baseline system shall be modeled as 100% outdoor air". 

My questions are:

1 – In the proposed design, the airlocks are receiving large amounts of fresh air in order to keep the positive pressure. I am currently considering the airlock as a laboratory (ASHRAE 62.1-2010) to determine the minimum amount of outdoor air that must be provided in the baseline case (Unoccupied -> 0 + 0.9*Floor Area [L/s]). By doing this way, fresh air rates for airlocks are 25-35 times higher in the proposed, when compared to the baseline. How should this be treated for the baseline building? In this case am I allowed to implement into the baseline the same air flow rates as in the proposed design (for pressurized zones only)?

2 – Another question is related to the fact that in the proposed design there are many Fume Hoods (hottes) in various laboratory areas. These fume hoods have very high extraction/exhaust rates. In order to compensate the air that is being removed by the fume hoods from that zones, high amounts of air (outdoor air in this case since there is no recirculation) is being provided. Again, this result in minimum outdoor air rates 6-8 times higher in the proposed, when compared to the baseline case, for which the OA rates were determined based on ASHRAE 62.1-2010 ventilation rate procedure. How should I treat the baseline in this case?

Thank you in advance and I am sorry for the long text.