We have an office building designed with DOAS CAV (20degC ) and active chilled beams with induction factor of 4 (at 18.5degC). The fresh air for higenic reasons is 40m3/h*person, however it has been increased to 50m3/h*person in order to make the active chilled beams work to cover peak space cooling load.
The design occupancy is 6m2/person. The designed system with design occupancy provides low summer unmet hours due to high supplied air volume working together with the active chilled beams.
However, for CS LEED compliance, we have been asked to change the occupancy to default values (23m2/person). if we use 50m3/h*person with lower occupancy, the active chilled beams are not able to cover the peak summer gains. Therefore we will need to supply around 150m3/h*person to keep the active chilled beams working in order to cover the cooling loads with high solar gains. This means that even with lower occupancy (23m2/p), the total supplied fresh air is quite similar to the case with 6m2/p.
At the same time, the baseline case is modelled with a VAV system 7. I understand that the baseline case should be modelled with the outdoor fresh air per person as per local regulation and does not have to the same as the proposed case (in our case 40m3/h*person).
In this case, the building performs much worse when using 23m2/person than when using 6m2/person because of the required air with lower to make chilled beams work.
I would like to ask what is the best approach in this case.
- Should we model with 6m2/p as per desing specifications, or with 23m2/p as per CS default occupancy to match other LEED credits?
- if we use 23m2/p, how can we overcome the issue with active chilled beams and worse performance compared to the baseline case than when using 6m2/p?
Thank you in advance.