ACHRNEWS

Design Guide: Making Homes Cool and Efficient

August 7, 2006

Though tools and methods are available for the design of energy-efficient HVAC systems, they are not often used when it comes to production homes. That's partly because builders of production homes are unaware that these tools exist. In addition, the existing design methodologies are often hard to find, as they are buried inside various code documents that also include large amounts of unrelated information.

The California Residential New Construction HVAC Design Guide, produced by the consulting firm ConSol, was created to address these problems by consolidating the relevant information for the HVAC design process into an easy-to-use reference and training tool. The guide presents a start-to-finish breakdown of the HVAC design process and discusses how each step can help lead to an energy-efficient system.

The guide also highlights how some elements of HVAC system design fit into the overall construction process, and it discusses specific measures that can be used to reduce HVAC energy use in production homes. In addition, it identifies which personnel need to be involved with the different components of the HVAC design to ensure that it is energy efficient.

FEATURES AND BENEFITS

The design guide breaks down the HVAC design process into seven high-level steps to guide the development of an energy-efficient system including: determine zone, calculate room-by-room loads, select/size equipment, lay out duct system, determine operating conditions, size ducts, and apply final touches.

The guide also includes specific recommendations for special design topics, such as the following:

  • Create a list of all building orientations for a production home development (to the nearest 45 degrees), using a site/plot map of the development. Then calculate loads for only these orientations and assess the potential to downsize equipment and duct sizes for certain plots from the worst-case orientation, which requires the largest capacity equipment and ducts.

  • Calculate room-by-room loads, in addition to those for the whole house, for each house plan. This will allow one to accurately determine how to distribute airflow.

  • Use in-line manual dampers in ducts to allow for different balancing needs due to different building orientations.

  • Place supply registers on a high wall facing a window or exterior wall. According to information in the guide, this location produces the best air mixing without short-circuiting the supply air into the return air stream and without directly heating or cooling the window.

  • In two-story houses, install air returns on both floors to reduce system cycling.

  • Place furnaces in the attic instead of the garage. According to the guide, this typically allows for shorter ducts, which results in less conductive heat loss/gain and less resistance to airflow.

    The guide also provides a table that lists HVAC, building design, and construction personnel and describes how they are affected by HVAC system design components. This was designed to make it easy to identify the key personnel who need to be involved with design decisions.

    In addition, the guide provides a checklist of HVAC-related items to be discussed with stakeholders early in the design process. Example items for discussion include where to locate the condenser, refrigerant lines, ducts, and the thermostat.

    APPLICATIONS

    The California Residential New Construction HVAC Design Guide is written for HVAC designers, architects, and builders. It is particularly suited for production homes in California and areas with similar climates. The HVAC systems discussed in the guide are split or single-packaged air conditioners or heat pumps, with a cooling capacity of 5 tons or less, that are used in residential applications.

    The guide highlights California building codes that are relevant to air conditioning design. For instance, the 2001 California Mechanical Code requires that all residential duct systems be sized according to the Air Conditioning Contractors of America (ACCA) Manual D, which requires ACCA Manual J. According to the California Energy Commission (CEC), an update is scheduled for this code at the end of 2006, which may alter the Manual D requirement so that it applies only to homes needing outdoor air.

    Also, the 2001 Residential Manual of Title 24 dictates how heat loss and gain calculations are to be performed and establishes the temperatures to be used for sizing equipment. The 2005 Residential Manual, which went into effect Oct. 1, 2005, changes the design temperatures to be used and also offers an alternate sizing method. ConSol said it will update the guide as these codes or other changes dictate.

    ConSol said it would use the design guide to train builders, planners, and others involved with production homes. Although the California Mechanical Code requires the use of ACCA Manual D, many jurisdictions are unaware of this requirement, and it is often not enforced, said the CEC. By educating production-home builders and others, this guide should help to ensure compliance with the code, according to the CEC.

    This project was conducted by the California Energy Commission's Public Interest Energy Research (PIER) program. PIER said it supports public-interest energy research and development designed "to help improve the quality of life in California by bringing environmentally safe, affordable, and reliable energy services and products to the marketplace."

    The Building Industry Institute, ConSol, and Fluent Inc. collaborated on this guide project. Detailed reports on this project can be downloaded at www.energy.ca.gov/pier/final_project_reports/CEC-500-2005-118.html. To view technical briefs on other topics, visit www.esource.com/public/products/cec_form.asp. For more concerning the guide, contact Rob Hammon at ConSol, 209-473-5000 or rob@consol.ws; or contact Martha Brook at California Energy Commission, 916-654-4086 or mbrook@energy.state.ca.us.

    Publication date: 08/07/2006