[Bldg-sim] New Report: Review & Comparison of Web- and Disk-based Tools for Residential Energy Analysis
Jason Glazer
jglazer at gard.com
Wed Sep 18 06:50:57 PDT 2002
An interesting report was recently posted by LBL titled:
Review & Comparison of Web- and Disk-based Tools
for Residential Energy Analysis
It can be downloaded at:
http://eetd.lbl.gov/emills/PUBS/SoftwareReview.html
Here is the abstract:
There exist hundreds of web- and disk-based building energy
software tools. These tools exhibit considerable range in
approach and creativity, with some being highly specialized
and others able to consider the building as a whole.
However, users are faced with a dizzying array of choices
and, often, conflicting results. The fragmentation of
development and deployment efforts has hampered tool
quality and market penetration. The purpose of this review
is to provide information for defining the desired
characteristics of residential energy tools, and to
encourage future tool development that improves on current
practice. We evaluated 50 web-based residential
calculators, and 15 disk-based calculators. The comparison
shows that some tools require a relatively small number of
well-considered inputs while others ask a myriad of
questions and still miss key issues. The value of detail
has a lot to do with the type of question(s) being asked by
the user (e.g., the availability of dozens of miscellaneous
appliances is immaterial for a user attempting to evaluate
the potential for space-heating savings by installing a new
furnace). More detail does not, according to our
evaluation, automatically translate into a better or
more accurate tool. Efforts to quantify and compare the
"accuracy" of these tools are difficult at best, and prior
tool-comparison studies have not undertaken this in a
meaningful way. The ability to evaluate accuracy is
inherently limited by the availability of measured data.
Furthermore, certain tool outputs can only be measured
against actual values that are themselves calculated
(e.g., HVAC sizing), while others are rarely if ever
available (e.g., measured energy use or savings for
specific measures). Similarly challenging is to understand
the sources of inaccuracies. Many factors conspire to
confound performance comparisons among tools. Differences
in inputs can range from weather city, to types of HVAC
systems, to appliance characteristics, to occupant-driven
effects such as thermostat management. Differences in
results would thus no doubt emerge from an extensive
comparative exercise, but the sources or implications of
these differences for the purposes of accuracy evaluation
or tool development would remain largely unidentifiable.
For the tools that we tested, the predicted energy bills
for a single test building ranged widely (by nearly a
factor of three), and far more so at the end-use level.
Most tools over-predicted energy bills and all over-
predicted consumption. The deviations (over-predictions) we
observed from actual bills corresponded to up to $1400 per
year (approx. 250% of the actual bills). Energy savings
estimates automatically generated by the web-based tools
varied from $46/year (5% of predicted use) to $625/year
(52% of predicted use). The estimates reflect widely
different packages of measures proposed by the tools, and
thus a diversity of messages sent to users about the
opportunities for saving energy. Based on spot checks, we
also discovered a remarkable number of results that suggest
errors in programming or algorithm accuracy. There are
numerous potential avenues for improvement of residential
energy tools. Various important building science issues and
energy efficiency features cannot be sufficiently well
evaluated using existing tools. Synthesizing the
information gathered, we developed best-practice guidelines
that may be useful to developers of residential-energy
tools.
=========================================================
Jason Glazer, P.E. mailto:jglazer at gard.com 847 698 5686
GARD Analytics - http://www.gard.com/
1028 Busse Highway, Park Ridge, IL 60068
Building Energy Simulation and Analysis
Admin of BLDG-SIM list for building simulation users
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