I'm modelling a European Industrial project where nearly a 5th of the floor area is a specialist process area, similar to a clean room or laboratory, however used for industrial processes, in use 24/7 with an air-change rate of 15ACH supplied by many AHUs. Of this volume, 1/48th is fresh air for occupants, the remainder is recirc for maintaining a close temperature, humidity and filtration band.

Due to the large floor area and the fuel type, the baseline system must be #7 VAV w/ Reheat.

We previously submitted a CIR about discounting the 15 ACH as process, however the reply was the baseline should model the 15ACH also, provided documentation proves this rate is standard.

The problem we encounter, or at least from my understanding, is we are comparing this against a VAV system, which with the same air change rate of 15ACH means a massive baseline heating load is created, and as the local conditions are cool the #7 baseline system our software automatically creates dumps a lot of the air, draws in cool air (and because of the supply air to room air temperature difference of 11˚C (as well as having to control the humidity), cools a lot of this air, and then re heats it to the room condition. Giving us a large baseline heating load.

Are we correct in using system #7? - Section G3.1.1 makes exceptions to the system use - point c states you may use system 3 or 4 depending on cross-contamination requirements, while point d states use system (5 or) 7 for laboratories. Which of these takes precedence in this case?

And if we are correct in using #7 does this method sound acceptable? It seems comparing against a VAV system doesn’t give the baseline system a chance compared with out system