We are working on a high rise multifamily building where the corridors are supplied with 100% semi-conditioned OA. This OA is used both for ventilation (62.1) and conditioning the space. Since this results in excess OA in the corridors than what is required by 62.1, the excess OA is also used as makeup air for the local exhaust in each apartment.
However, 90.1-2010 G3.1.2.6 Exception C, clearly states that any OA air in excess of the minimum for ventilation is penalized in term of energy (where as in 90.1-2007, this might not be the case).
I can understand the penalty for using OA to condition spaces, but shouldn't the baseline model be allowed to include OA as makeup for exhaust?
Thanks
Samuel Gelfand
3 thumbs up
November 24, 2015 - 5:12 pm
Some more to think about:
I think what is pertinent here is that 90.1 requires that ventilation is modeled at the minimum requirement (in this case 62.1-2007) ("G3.1.2.6 Ventilation. Minimum ventilation system outdoor air intake flow shall be the same for the proposed and baseline building designs.")
Minimum OA requirement is not just what is calculated by VRP, but all the requirements of section 4 thru 7. Section 5.10.2 requires that:"For a building, the ventilation system(s) shall be designed to ensure that the minimum outdoor air intake exceeds the maximum exhaust airflow whenever the mechanical air-conditioning systems are dehumidifying." (a later addendum removes the de-humidification language and just requires balance).
Therefore I think that the baseline model should include the OA required by VRP plus the makeup required. We should only be penalized for the OA used as conditioning.
Am I correct in my reasoning?
Thanks for your help.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
November 25, 2015 - 11:08 am
Sounds like this is the result of the nature of that type of system design. There are certainly far more energy efficient ways to design this system (like DOAS) and that apparently is being encouraged. Because you are doing both conditioning and ventilation within the same system, the total OA supply will likely be higher than the minimum and result in an energy penalty relative to the baseline. In our opinion you should pay a penalty for this type of inefficient ventilation system. The baseline model for the corridor systems should include the OA required by the VRP for the corridors but the OA for the apartments should be provided by the units within the apartments (system 1 or 2).
Samuel Gelfand
3 thumbs up
November 25, 2015 - 11:41 am
Thanks for the reply Marcus.
I agree that we should pay a penalty for using conditioned 100% OA to service the corridor. However, the engineer has said that OA brought into the corridor serves 3 functions: 1) ventilation for the corridor (VRP), 2) cooling and heating for the corridor and 3) makeup air to keep the building pressurized due to exhaust (kitchen,bath, dryer) from the residential units.
100% DOAS is being brought into the residential units separately to satisfy the VRP.
The required ventilation portion of the corridor is not penalized in the energy model. The conditioning portion is penalized. The extra outside air for pressurization I am claiming shouldn't be penalized due to the requirements of 5.10.2 ("the ventilation system(s) shall be designed to ensure that the minimum outdoor air intake exceeds the maximum exhaust airflow").
Therefore I think the minimum ventilation for the baseline should be the VRP portion + makeup for exhaust (+ any other requirements of the entire 62.1). Appendix G does not specify that the minimum ventilation is only what is required from the VRP, but rather the entire standard.
Thanks
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
November 25, 2015 - 12:14 pm
Now your question makes more sense knowing that there is a DOAS for the apartments. We agree with your assessment of how it should be modeled in the baseline.