Monday, August 20, 2007

Energy Modeling, Part 1

With increasing energy awareness and green building momentum, the venerated task of energy modeling has enjoyed some resurgence of notoriety recently, due in part to a higher emphasis placed on building energy performance by state codes, increasing utility rates and rebates, and a groundswell of LEED certifications.

Fundamentally, energy (and its derivative, sustainability) modeling is an art and science that has evolved over decades of continuous improvement by a dedicated cadre of engineering professionals. One of those professionals is Association of Energy Engineers cofounder James P. Waltz.

Mr. Waltz is founder and president of his own building engineering consulting firm, a noted speaker, author, and member of the HPAC Editorial Advisory Board. As an author, Mr. Waltz has written a number of books over the course of his distinguished career, including the one we'll be focusing on in this series of articles entitled Computerized Building Energy Simulation Handbook.

Mr. Waltz's company, Energy Resource Associates Inc., does not engage in new design work nor do they work for architects, focusing exclusively on energy and automation engineering of existing facilities for owners. His perspective as a result is a pragmatic one, based on 30 years of critically assessing and retro-commissioning countless building systems.

What I like most about the CBESH, and why I think it should be on the bookshelf of anyone who is doing computerized building simulations and getting paid for it, is that it's not about the software. It's about dispelling building simulation myths, defining precision levels and selecting the correct tool for the job, field assessing existing conditions, building a library of representative case studies, model construction checklists, analyzing output and model calibration, practicalities of energy conservation modeling, and the role of building simulation in performance contracting, to paraphrase the chapter titles.

Building simulation programs are like standards, the problem is we have so many to choose from... each with their own idiosyncrasies requiring multiple volumes to document and a discussion board to troubleshoot. On the other hand the fundamental ideas presented in CBESH are universal, or as they might say in the software business, "platform-independent" to the application of energy modeling.

Originally I had to planned to review this book as the basis for the first article in a series of energy modeling articles I have been asked to submit for this year's Punchlist. However I believe now that skimming over the multitude of essential concepts presented in CBESH wouldn't best answer the needs of the readership. Which brings me to the second thing I really like about this book, namely that it contains nine chapters, and there are nine newsletters in a Puget Sound ASHRAE Chapter year.

This month we have looked at the Preface and first chapter, entitled "Introduction", about three quarters of which have been summarized so far. The last item I'd like to comment about in the introduction is answering the question that every energy consultant must be ready to unhesitatingly answer, namely 'Why Do We Do Building Simulations?'

The CBESH suggests the following four justifications (in quotations), to which I have editorialized a consultant's perspective addressing new construction:
  • "To obtain funding for retrofit improvements", or to justify new high-performance systems over what may otherwise meet code compliance with minimal efficiency and limited functionality.
  • "To justify taking a risk as a third-party, such as an Esco" or utility company in the form of rebates or incentives. While not financial in nature, LEED certification may also be characterized as a form of third-party risk.
  • "To raise the level of confidence". Manual calculations are useful, and can provide valuable boundary conditions, or 'reality checks' on elements of computer simulations. However computer simulations excel in providing the detailed accounting required to justify individual energy efficiency measures in the context of complex systems interdependencies.
  • "To verify that the homework has been done. Proof that homework has been done is far more valuable than a guarantee." There's simply no substitute for the due diligence required to construct an accurate energy simulation. In the case of new construction, where we do not have existing buildings nor utility bills to help calibrate the model, careful homework tempered with sound judgment based on experience become our only guideposts.
In summary, the first chapter has defined where we are going, why anyone would want to go there, and why we should have some confidence in this fellow who has offered to be our tour guide.

Next month: Dispelling common building simulation myths.

Disclaimer: The views and opinions expressed in this article are those of the author, and do not constitute an endorsement by ASHRAE.

Brandon Nichols, PE, LEED® AP of Hargis Engineers has over 20 years experience in facilities systems engineering and project management for consultants and owners from design through long-term sustaining operations. He is the author of the ELCCA Exchange blog, which compiles information on topics relevant to completing State of Washington Energy Lifecycle Cost Analysis reports.

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