Modeling a humidifier in the baseline case

I have deleted my original comment after digging into this a bit more. Humidification is considered a process load. As such not only must the process be modeled identically but the energy use must also be identical (i.e. energy neutral). Claiming this savings would violate that requirement. Based on the prescriptive requirements within Section 6.5.1 it appears that exception c applies to your situation. Because of this exception and the fact that the process must be identical you should not be modeling economizer in the areas with humidification in the Baseline.

I have a similar situation in that I will model the humidifier the same in both proposed and baseline systems but in our proposed system we have a DOAS unit with energy recovery which will offer some benefit over the baseline system which is not using an economizer. How would you approach this? Thanks, Mike Edit: mine is not a data center but a museum which has humidification for a few spaces.

Technically you should follow the exceptional calculation method to show process load savings related to humidification. If the savings are relatively small you could probably forego this formality and provide a narrative explanation for the savings and how it was modeled. Some small level of savings related to the systems install and in the baseline should be OK. if the savings are large you should probably do the exceptional calculation. To do so run the models with and without the humidification and show the savings as the difference.

That is a pretty clear statement requiring you to model the economizer so I will make another set of suggestions. Obviously ignore my previous advice. You have two choices I think - try to claim the savings for humidification or not try to claim them. If you wish to try and claim them I would suggest that you do it as an exceptional calculation and justify them based on the Appendix G requirements. Doing it this way gives the reviewer a clear picture of what is happening. Personally I think it is a loophole and these savings are not legitimate to claim. The other option is to model the economizer and then just post-process the results. When entering the modeling results in Table EAp2-4 and EAp2-5 enter the proposed energy use for humidification in the baseline so that they are identical. This is the conservative approach and should be accepted.

I had a similar situation which was a computer center/office near Las Vegas which uses a DOAS system and VRF system. The baseline was modeled with an economizer and the required humidity setpoint with autosizing for the humidifier. The proposed was modeled as shown in the contract document with humidity setpoint and the size of the humidifier. It showed a 87% saving in humidifier energy endues. I entered the baseline energy use for the humidifier as shown in the proposed model. I documented the exceptional calculation credit for the remaining energy savings. They rejected the exceptional calculation on the bases for not referencing recently published documents. They also came up with new numbers for the baseline and propose simulation models which I cannot explain. My next project with a humidifier, I plan to model the humidifier as a plug load.

Thanks Marcus for the comments, I've modeled the humidifiers identically and the difference is significant in terms of the humidifier energy use (difference of 87%) but in terms of the energy use of the building it is around 1%. I think this would be safer to include as an exceptional calculation but as far as the documentation that Curtis alluded to that would support what the energy model is calculating, I'm unsure of what would be required? Any suggestions would be great. thanks, Mike

You should provide a thorough narrative that explains how you have modeled the systems and the level of savings being claimed. Make sure to explain why there are savings related to the modeling of the Baseline system as required. The reviewer may still toss out the savings but if you do an exceptional calculation it will be easy for them to make an adjustment.