Hello all,
I currently modeling a project for LEED NC v2009 submission for a corporate office building that's roughly 125,000 SF. The proposed design's primary HVAC system are AHUs + VAVs w/Electric Reheat supplemented with electric baseboard along hot water preheat generated from gas boilers. This system also uses chilled water with very efficient chillers from a DES. The baseboard is suppose to take care of the envelope loads and the VAV electric reheat coils will take care of the rest. Based on the size of the building, the baseline HVAC system shall be System #6: Packaged VAV with PFP Boxes.
I'm pretty down the road on the models and for some reason cannot get savings between the 2 models. The heating energy use on electrical consumption overrides any savings attributed from lighting, site lighting, cooling energy use, etc. Also, I know that in 90.1-2007, preheat must be model identical on the proposed and baseline models. I am having a hard time modeling both to be the same (inputs for preheat capacity are the same but the energy use is different). The gas consumption is significantly higher on the baseline model.
I double checked the loads from both models and the heating/cooling requirements are roughly the same so there's nothing wrong with the building shell/internal load inputs. Any guidance on how to reduce the consumption on the heating use for electrical consumption would be great! I am confused why the baseline model wouldn't require similar, if not more, heating requirements and isn't using more heating use for electrical consumption. Also, guidance to ensure that the preheat is model identical would help too!
Thanks!
Cliffnotes:
Proposed System: AHUs w/VAV Electric Reheat + Electric Baseboard//Chilled Water from DES//Hot Water Preheat
Baseline System: Packaged VAV with PFP Boxes
Issue #1: Heating electrical consumption is super high on proposed model despite similar loads for both models.
Issue #2: Preheat is not being model identical as required from 90.1-2007. Capacity and design inputs are same for building but baseline building is using significantly more gas.
William Mak, LEED Green Associate
