Page T2.2 . 11 April 2001                     
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  • Free Software for Energy Code Compliance

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    Free Software for Energy Code Compliance


    Approaching Code Compliance

    To use this software, you need to first understand the basic options that these codes offer for demonstrating compliance.

    The most restrictive compliance option is the prescriptive approach, which mandates that individual components of the building envelope or mechanical system meet a set rating value (e.g. percent of glass allowed, U value, R value) given the building site's climate zone.

    For residential architecture, your code may allow all or most of the following compliance methods: 1) the prescriptive approach, 2) the component performance approach in which tradeoffs are allowed between envelope components and HVAC equipment, 3) MECcheck software, 4) the systems approach, or 5) the renewable energy resources approach.

    Realistically speaking for most architects (and perhaps even many engineers) without advanced degrees in engineering, math, and code deciphering, the prescriptive approach or using MECcheck software are the most feasible alternatives.

    For commercial and high-rise residential, you can similarly comply via 1) the prescriptive approach, 2) system performance, which allows limited tradeoffs within code sections, and 3) whole-building performance, which allows tradeoffs more freely based on "bottom line" building performance. COMcheck-EZ covers the first two options, while COMcheck-Plus offers the whole-building performance method.

    How MECcheck Works

    Don't be intimidated by the use of this software. Once you work through even a sample project once, you should quickly be able to get the hang of it.

    You might think of this software as both a "smart" and a "dumb" spreadsheet program at the same time. It is smart enough to know what the degree-days are for a given location (i.e. climate ) in your state and to know what the component tradeoff values are, but it is not smart enough to know when your building envelope is complete.

    Consider the entire building envelope of your project. Multiply the surface area of each exposed component of that envelope by its "U" (1/R or coefficient of thermal transmittance) value to get its "UA" value. Add up all the UA values to get a total building UA value.

    The software compares that total UA with one you would get if you multiplied each component area by the prescriptive U value (e.g. the ceiling requires R-38) found in the code. If your total UA is less than or equal to the UA calculated by the prescriptive method, your building passes.

    This method allows tradeoffs between components that the prescriptive method does not. As examples, you can have more glass area if you have more insulation in the walls; you can have less insulation in the ceilings if you have a more efficiently rated furnace.

    To get the hang of using the software, you first need to understand typical R (thermal resistance) values for insulation and typical U values for glazing. You should also note that once you pick the construction type for your component, all the software wants to know is the R value of the insulation because the value for the construction materials is already factored in.

    For a general guide, check out the prescriptive package for your building type and climate zone to see what you are trying to match. For instance, a house in the 5600 degree-day Boston climate, under the Massachusetts Building Code, could have up to 15 percent glass, with U-0.41 glazing, R-38 ceilings, R-13 walls, R-19 floors, and R-10 basement walls.

    From insulation manufacturers' charts, you will note that 3-1/2" wall insulation only goes up to R-15, while 5 -1/2" goes up to R-21. Similarly for ceiling insulation, 6-1/4" insulation goes up to R-19, 9-1/2" goes up to R-30, and 12" to R-38. One inch of rigid insulation will get you R-4.3, and 1-1/2" will get you R-6.5. Most modern windows have a U value of around 0.30.

    Testing a Design

    Once you have your schematic plans ready, you can immediately do some quick energy studies with this software. Using CAD, it is easy enough to do the takeoffs and get the perimeter surface areas for your exterior walls, glazing, ceiling/roof, and basement.

    By clicking on the component (walls, glazing, etc.) buttons, a new spreadsheet item is added to your building list. If you pick walls, you are then given a pull-down list of common construction types, and you simply pick the closest fit, such as 2x4 wood stud walls.

    You type in the exposed surface area, the R value of the insulation, or the U value for glazing. You can get "credit" for upgrading the furnace efficiency rating.

    This is where the software becomes very useful for the architect. By swapping different R values, you can improve performance by changing to 2x6 stud walls with R-21 insulation.

    Alternatively, you could increase the ceiling insulation and eliminate one skylight to improve your score. Obviously, these energy decisions are now tangible design decisions. At this early stage of schematics, to change to 2x6 exterior stud walls is not difficult and it gives you much more latitude to add windows and skylights later on.

    Imagine how much harder redesign would be if the construction drawings were nearing completion when you finally decided to do an energy code check.

    When your construction documents are done, you update your final values in the software and print a report of the project. This serves as both your compliance document and a checklist for the building inspector to use during construction.

    Optional Details

    With the commercial versions, you need to specify lighting and mechanical systems in addition to the building envelope. But for all the versions, the principles are the same. Pull-down menus give you choices among standard construction types or fixtures or equipment.

    If you don't know what you are going to use, you can make an educated guess or just pick a default choice for material or fixtures that can serve as place-holder values until you get closer to the actual specifications. If you have any custom items, you can pick the closest choice, and then do some adjustments at the end.

    What I like about this software is that it is relatively easy to use, intuitive, and best of all, a designer's tool. If you have your basic building component areas, and an idea of insulation values, you can juggle the components to come up with a "game plan" for meeting your project's energy code compliance.

    It is a game that many architects are bound to enjoy, because it will help inform the design process to understand how building construction details, lighting, and mechanical systems all interrelate to produce energy-efficient (well, at least energy code-compliant!) architecture.

    Evan H. Shu, FAIA, is an architect with Shu Associates Inc. in Melrose, Massachusetts. He is a frequent contributor to Architectural Record and publisher and editor of "Cheap Tricks," a monthly newsletter for DataCAD users and computer-using architects.

    This article was reprinted from the October 2000 issue of "Cheap Tricks" Shu Associates Inc. with permission of the publisher.



    ArchWeek Photo

    With an R-13 wall, the overall insulating value of the house fails to meet compliance.
    Image: U.S. Department of Energy

    ArchWeek Photo

    When the walls are changed to 2x6 studs with R-21 insulation, the UA drops from 481 to 423 and passes the compliance check.
    Image: U.S. Department of Energy

    ArchWeek Photo

    The building components are organized and displayed in a hierarchical format.
    Image: U.S. Department of Energy

    ArchWeek Photo

    COMcheck deals also with lighting and mechanical systems, but the principles are the same as in MECcheck.
    Image: U.S. Department of Energy


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