ASHRAE Journal - May 2013 - 41

dard, identiﬁed 32 published addenda
that were not accounted for in the performance methodologies. These included such potentially impactful changes
such as single-zone VAV requirements,
skylight requirements and daylight dimming, exterior lighting control, and enhanced economizer requirements. These
omissions create signiﬁcant loopholes
for projects using either of the performance approaches in Standard 90.1.

Baseline Building Becoming Difficult
to Define
In the search for additional savings,
prescriptive requirements are becoming
more complex. This is particularly problematic when a prescriptive requirement
is not included in a proposed building design. Conventional and historic requirements such as wall insulation, lighting
power, or heat recovery are straightforward. But modeling some of the newer requirements when there is no accompanying design has proven to be problematic.
For example, the standard now requires that large, high ceiling spaces have
skylights and a daylight area equal to half
the space area with controls to automatically reduce electric lighting when daylight is available. There are many ways to
meet these criteria, each providing potentially different levels of savings. Do you
model one big skylight or many small
ones? What about skylight spacing? Do
you require a baseline design that optimizes skylight area and layout to maximize lighting savings while minimizing
heat gain and loss? What is the target illumination level in the space? Where are
daylight sensors located and how are the
controls conﬁgured and operated?
Deﬁning the baseline building becomes
a design problem, with many acceptable
solutions. Other prescriptive requirements
that are difﬁcult to incorporate in the baseline building are building orientation, perimeter daylighting, and exterior shading.

ECB Doesn’t Credit Energy Saving
Building Design Choices
The ECB method is designed to track
prescriptive compliance based on whatever form the proposed design takes.
Within the prescriptive path there are
May 2013

good and poor options from an energy
standpoint. A good choice for one building may be a poor choice for another.
ECB doesn’t recognize the difference,
only the variation from the prescriptive
value of each individual component.
The building described previously with
20% window-to-wall ratio, all windows
facing south, served by a water-source
heat pump system will have no “tradeoff credit” when compared to a similar
building with 40% window-to-wall-ratio, all windows facing west, and electric resistance heating. How does that
make sense when the latter building will
almost certainly have a much higher energy cost?

Addendum bm Improvements
Recently proposed Addendum bm to
Standard 90.1 creates a new approach
to performance-based code compliance,
which addresses many of the issues and
problems discussed earlier. The following
highlights the principle beneﬁts and risks.

One Procedure for Both Compliance
and Beyond-Code
Performance analysis using the PRM
of Appendix G could be used for compliance. Prescriptive compliance and the
ECB would still be available. The main
beneﬁts of a PRM compliance path are:
• A single model can be used for both
code compliance and beyond-code programs such as LEED or utility and tax incentives. It would no longer be necessary
to create different baselines for different
uses. However, when using the PRM for
code compliance, only regulated energy
use is considered (credit is not allowed
for improvements in unregulated plug and
process loads). Note that as the scope of
Standard 90.1 increases to address more
currently unregulated loads (as has recently been the case for elevators, computer
room air conditioners, and commercial
refrigeration equipment), this difference
will be reduced.
• Using the PRM for code compliance
allows greater recognition of good design
choices such as optimized orientation and
building massing, improved mechanical
equipment type selection, right-sizing of
mechanical equipment, efﬁcient use of

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ASHRAE Journal - May 2013

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