Since the publication of ASHRAE 90.1-2013, more than 25 amendments have been approved by the ASHRAE Standards committee for inclusion in the next version of the Standard to be published in 2016. Of most interest to high performance building design is Addendum BM, which now provides a stable baseline for determining above code performance in all future versions of the Standard. This helps software developers and enforcement authorities to use baseline building energy modeling rules that are consistent, easy to understand, and can be used for both code compliance and above code performance assessments.
This addendum uses ASHRAE 90.1-2004 prescriptive requirements for envelope, lighting, and mechanical systems for developing the baseline building model. The compliance determination and above code performance is assessed by calculating the proposed building “Performance Cost Index (PCI)” and comparing it with a target PCI for the baseline building performance. The target PCI separates the regulated and unregulated annual energy cost of the baseline building and uses a “Building Performance Factor (BPF)” defined for various building types by climate zone. The intent is to define the target PCI as a function of BPF which can be modified in the future without having to modify the baseline building modeling rules in the rating method. This all sounds too complicated, but in reality this approach is easier to implement in software tools and quite likely will bring more consistency in creating the baseline building model in all tools. If you have created 90.1-2004 baseline building models previously, it may be worth keeping them around and it may save you some valuable time when using 90.1-2016 Performance Rating Method.
I am currently participating in the ASHRAE 90.1 Energy Cost Budget subcommittee and plan to provide periodic updates on the 90.1 development. Please let us know if this is useful information that you would like to see in the future and have any questions or comments related to the standard.