From Baseline to Proposed model, or from Proposed to Baseline?

I'm curious as to the pros and cons of building either the Baseline first of the Proposed Model first, when using ASHRAE 90.1 Appendix G for New Construction projects.

What makes more sense? Why?

I'll accept both software-agnostic and software-specific reasons.

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Julien Marrec

asked 2015-02-24 02:51:09 -0500

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__AmirRoth__

updated 2015-07-11 20:04:30 -0500

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Reasons to start with Baseline model:

If you are modeling for a program that takes credit for beyond-code buildings and the program requires you to document the impact of each measure individually, it is often easier to start with the baseline and add each measure stepwise, documenting the savings at each step. This is a common requirement of utility design assistance programs.
If you get involved with the design process before major design decisions are made, you can model individual design choices as they are being considered, and hopefully help guide the decisions. Having a neutral baseline can help the design team avoid biases involved with picking one of their designs as the baseline and judging everything compared to that.

Reasons to start with Proposed model:

If the plans are already done and you can't have any impact on the design, start with the Proposed and hopefully you can use one of the things @Amir Roth mentioned in his answer to automatically generate the Baseline model from the Proposed model. IMO, this is misses the point of energy modeling as a design tool, but it happens all the time for LEED.

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aparker

answered 2015-02-24 09:08:39 -0500

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Well, one (I think strong) case for building the proposed model first is that there are tools like CBECC-Com (http://bees.archenergy.com/software.html) that will automatically generate the baseline model given the proposed model. Obviously, it would be more difficult to automate the reverse path! CBECC-Com works with OpenStudio and with VirtualEnvironment. Maybe other tools too.

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__AmirRoth__

answered 2015-02-24 07:32:42 -0500

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In Appendix G you will notice that many items that describe the baseline are shown as "same as proposed" which implies that starting with the proposed and modifying it to achieve the baseline. Without a firm description of the proposed building, it is difficult to construct a model of the baseline.

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JasonGlazer

answered 2015-02-24 09:33:47 -0500

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I'll give the first "it depends" answer. For early design I think it makes sense to build the baseline first, whereas for construction phase compliance modeling I think building the proposed model and then auto-generating the baseline makes more sense and is more efficient.

In OpenStudio, my preferred tool, auto-generating a baseline requires writing and running several measures (scripts) so in my opinion it's not quite as efficient as other tools for consulting.