Dehumidification + reheat

ASHRAE 90.1 Appendix G is unclear in how to appropriately account for humidity (both humidification and de-humidification). As stated in ASHRAE 90.1 Table G3.1.1 (b), all conditioned spaces shall be modeled with temperature and humidity control setpoints the same for the Proposed and Baseline Case, however there is no other guidance/requirement for modeling humidity. Humidification should therefore be modeled the same in the Baseline and Proposed Case unless an Exceptional Calculation Method is used. The Exceptional Calculation should justify the use of the Baseline (including evidence for what is standard practice in the project location for the type of application). It is not always possible to model identical forms of humidity control. In that case, it is recommended that the same fuel source for humidity control be modeled in the Baseline and Proposed Case. For example, if electric reheat is used, that would be modeled in both cases. If fossil fuel is used for humidity control, that would be modeled in both cases. You should provide additional justification if including reheat in the baseline.

This is a great thought provoking question. Comfort vs. energy savings. Which is more important?! I think the incentive to save energy is already well established. If ASHRAE in this case would refuse to make the baseline reheat, it is saying that user comfort should be degraded to save energy! I don't think that is a good approach. In the LEED system we will punish the design for bad comfort, but do we punish the baseline also? In the spirit of LEED I would make the baseline reheat and make my case to the reviewers. Perhaps, this is something for the 90.1 commitee to consider that as much as you may want to seperate 55 and 90.1 to do their respective jobs, sometimes you just can't.

Yip. Try and see if you can "cut it off" onto a seperate system using one of the exceptions. So like if a zone sees very different occupation schedules, but hangs onto the same system, you could have the baseline serve it with a different system. Similary, there are exceptions for schedules regarding loads, outdoor air requirements, and so on.