Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
I have some difficulties to understand some chapters of Appendix G.
About "For a baseline system the supply air temperature from the AHU to the space should be a delta T of 20F between the setpoint in the space and the air temperature". I think you are talking about G3.1.3.12... but it is talking about the air temperature for cooling. What about heating?
"The outdoor air should be the same between baseline and design case", perfect as it's written in G3.1.2.5.
"The minimum air provided to each space by the baseline system 8 should be 30% of peak flow rate or outdoor air whichever is larger.", in this case I think you are referring to G3.1.3.14... but it's talking about fan-powered boxes (reheat), not about the AHU in my opinion.
Therefore, if more cooling is required in a zone I need to use recirculation, but this cause a recirculated air also in the zone that do not demand more air: the result would be a low fresh air supply. This is because, if I have a fixed supply temperature I can't provide both ventilation and sensible load with a VAV system.
I do think it's impossible to meet both those requirements with a VAV system. The solutions could be: - use 100% outdoor air; this could make the baseline system use more energy (that's dangerous for baseline) - neglect the decrease of fresh air when sensible load increases - use 2 different VAV systems, one for ventilation and one for sensible load
I hope I've been clear enough... I have been thinking about this quite a lot (and I didn't even talk about dehumidification and humidification) but I can't find out where I am wrong. Thanks!
