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What should the fuel source for the ASHRAE Baseline Model be when the proposed has a VRF System?

asked 2016-06-06 18:35:06 -0500

Brian C's avatar

updated 2016-10-18 14:09:58 -0500

I have currently modeled a VRF system for LEED v3-2009 for a facility in CO, USA under the following tariff structures: Xcel SG & CG-S. While the energy savings are great (~45%), the energy cost savings are not so great (~4%). My baseline currently adheres to System 5 (VAV with DX & HW Fossil Fuel Boiler). I have heard from other's in the industry that for Ground Source Heat Pumps jobs they have seen energy models using electricity as the source energy for heating in their baseline model to avoid "fuel-switching" in the proposed model.

What fuel source should be in the baseline energy model for heating if you are modeling VRF/Ground Source (electricity or natural gas)? I am unable to find any mention of how to address "fuel-switching" in ASHRAE 90.1 -2007 and would like to be certain before making a change.

Also, if you have modeled a VRF system, feel free to provide your energy/cost savings results!


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answered 2016-06-06 22:52:32 -0500

updated 2016-06-06 22:54:18 -0500

If you are delivering outside air to your VRF spaces with a gas-fired DOAS, then you have a gas baseline in the eyes of LEED, period.

If you have no gas heating serving those spaces, then you might be able to use the electric baseline:

  • If you have no gas heating anywhere in the building, easy peasy, use the electric baseline. (system 6 instead of 5)
  • If you have no gas in your VRF spaces, but you do have gas heating in other spaces, work very hard to see if those other spaces would qualify for a separate baseline system under G3.1.1 exceptions. Then you can make a case to have multiple baseline systems. If you do use multiple baseline systems, be sure to write a short narrative explaining which exception you are applying and why.

Good luck!

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If I may suggest changing the "eyes of LEED" with "eyes of 90.1 Appendix G", and maybe explicitly quote Table G3.1.1A Baseline HVAC System Types where the categories of fuel are "Electric and Other" and "Fossil Fuel, Fossil/Electric Hybrid, and Purchased Heat". In the case of a gas DOAS + VRF, it falls into the Fossil/Electric Hybrid category.

Julien Marrec's avatar Julien Marrec  ( 2016-06-07 02:34:56 -0500 )edit

Thanks Julien, sorry that was my attempt to differentiate from Xcel's policies on fuel switching in the baseline, which I suspect Brian may also be dealing with. Xcel's modeling protocols often lead us to a different interpretation of Appendix G baselines when there is a mix of fuels.

egillmor's avatar egillmor  ( 2016-06-07 08:49:35 -0500 )edit

@egillmor thanks for the response and clarification. In my case I do have gas-fired DOAS, so I will stick with System 5. Also thank you @Julien Marrec for the script for VRF system works well and is what I will use for my model when submitting for LEED.

Brian C's avatar Brian C  ( 2016-06-07 10:28:47 -0500 )edit

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Asked: 2016-06-06 18:35:06 -0500

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Last updated: Jan 29 '21