Engineered Systems - April 2008 - (Page 28)

BuildingAutomation BY PAUL EHRLICH, P.E., AND IRA GOLDSCHMIDT, P.E. WRITING CONTROL SPECS – One Of Life’s Great Challenges And even then, there are more critical elements of a good design. Several years ago, we had the unique experience to be members of an ASHRAE committee that was charged with developing a guideline for specifying DDC systems. Committee work is often frustrating, involving volunteers with different perspectives and levels of involvement, and this project was no exception. We met twice a year for over ten years, struggling to define the purpose, then to create a guide spec, and finally, to write a guideline that explained how to use the document. While this was often frustrating, it was also fascinating to be involved in the conversation that went on between committee members who represented owners, consultants, contractors, and suppliers. We had productive, spirited discussions about what went into a specification, how they where interpreted, and what was necessary to ensure a successful project. In the end, we completed what is now ASHRAE Guideline 13. Spending this much time and effort focused on this topic resulted in several key lessons learned which are still very relevant today. We learned a lot about not only the end result but also the process that goes into the development of a good controls design. So what where the key lessons? THE CONTROLS DESIGN IS MUCH MORE THAN JUST THE SPECIFICATION Often, we think of the design of the controls system as being reflected in the controls specification. This is rarely the case. In fact, a good controls system design will have four key elements, which include: • Detailed sequences of operations; • Listing of all required hardware and software points/objects; • System diagrams/cartoons; • The written specification which provides details on methods, products, and performance. Of these elements, the first two are the most critical for the successful design of a control system. Yet surprisingly, we are hearing more and more about projects where these are either not properly completed, or in some cases, omitted altogether, instead suggesting that the contractor should determine the proper sequences and/or points. It is also important that these elements be properly coordinated so that they don’t contradict or overlap with each other. THE DESIGN NEEDS TO FIT THE PROJECT Often, we are asked for “the controls spec”! In reality, the design of the controls system really starts with the selections made for the mechanical and electrical systems and a good understanding of how the building will be operated. Standalone buildings will need a different solution than those that are part of a larger enterprise. Systems need to be properly selected and designed. More and more often, we are designing sophisticated control systems with a high We like to see the key elements y specified specified so that the key parameters that the key parameters are clearly specified are clearly specified in a generic generic fashi fashion. B using a performance hion By si ing rformance f perspective we allow the contractor perspective, we allow the contractor to be more creative, have key be more creati ive, have key element th can elements that can readily be l ts hat adil be dily enforced and end enforced, and end up with a more with more strea st eamlined specificat on. e spec catio degree of integration. But while these may be the right solution for a sophisticated owner, they aren’t right for simpler, more basic projects. KNOW WHEN TO BE PERFORMANCE-BASED Ideally, we like to see the key elements of a controls system specified so that the system can be competitively bid and the performance can be verified. Ideally, this means that the key performance parameters are clearly specified in a generic fashion (building automation technology does not lend itself to the practice of “basis of design” specifications that works well for mechanical equipment). By using a performance perspective, we allow the contractor to be more creative, have key elements that can readily be enforced, and end up with a more streamlined specification. ES Paul and Ira first worked together on a series of ASHRAE projects including BACnet committee and “Guideline 13 – Specifying DDC Controls.” The formation of Building Intelligence Group provided them the ability to work together professionally providing assistance to owners with the planning, design and development of Intelligent Building Systems. Building Intelligence Group provides services for clients worldwide including leading Universities, Corporations, and Developers. More information can be found at www.buildingintelligencegroup.com. We also invite you to contact us directly at Paul@buildingintelligencegroup. com or ira@buildingintelligencegroup.com. 28 En gi neer ed S y stem s April 2008 http://www.buildingintelligencegroup.com http://www.buildingintelligencegroup.com http://www.buildingintelligencegroup.com

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Engineered Systems - April 2008 Contents Editor’s Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Energy Wiz HVACR Designer Tips This Time, Water Cooled Was All Wet Cleanroom Design In 10 Easy Steps It's Not The Heat, It's The Humidity Issues & Events Computers and Software Products Glossary Classifieds Advertiser Index Tomorrow’s Engineer

Engineered Systems - April 2008

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