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Software Correctly Sizes HVAC for Concrete Homes
John Gajda
Insulated concrete walls have unique energy-saving properties that until now have been largely ignored when it comes to heating and cooling systems. HVAC systems are routinely sized based on information developed for wood-frame houses and in some cases are sized based on methods such as Manual J and the ASHRAE Handbook of Fundamentals. These methods can be cumbersome and do not account for the unique properties of concrete walls — their thermal mass, high level of insulation and their low air leakage and infiltration. In other cases, the sizing of HVAC systems is based on an old rule of thumb that approximates equipment size from the floor area of living space. In either case, the result is an inefficient HVAC system — one that is often greatly oversized.
Oversized systems may adequately heat or cool the house during the most extreme conditions that occur only briefly during a typical year. But most of the time an oversized HVAC system will use more energy than a properly-sized system. An oversized system also has a shortened “on time,” which can lead to wide temperature swings and reduced thermal comfort. More importantly, air conditioning systems with short "on times" do not remove enough moisture from the indoor environment, which can result in mold growth and damage to building materials.
Thanks to Portland Cement Association (PCA) and the U.S. Department of Housing and Urban Development (HUD), there is now software available to correctly size heating and cooling equipment for single-family concrete homes with insulated concrete walls. The software is intuitive and was designed to be easily used by residential contractors and HVAC installers.
The software is applicable to the majority of homes being constructed today. All types of insulated concrete walls are considered, including: insulating concrete form (ICF), removable-form, precast concrete, autoclaved aerated concrete (AAC) and concrete masonry (CMU). For comparison, the software will also provide results for wood-frame walls. The information required by the software includes the overall dimensions of the house, the wall areas, windows (area, type and orientation), house orientation and geographical location. The software also accounts for foundation type (basements, crawlspaces and slabs), roof construction (cathedral or attic) and other typical construction details.
The current software contains information for almost 250 locations across the United States and Canada, and an upcoming enhancement will add locations in Canada and Mexico. The enhancement will also incorporate new features, such as the ability to use metric units.
The software has been on the market for more than a year, and more than 500 copies have been sold.
For more information on the software, click here.
John Gajda is a licensed professional engineer with CTLGroup in Skokie, Ill. He has managed several Portland Cement Association (PCA)-sponsored practical research projects on insulated concrete walls, including studies on sustainability, concrete consolidation use, HVAC sizing, moisture susceptibility and cold-weather construction. CTLGroup is a structural/architectural engineering and materials consulting firm that is an independent subsidiary of PCA. In conjunction with PCA, CTLGroup has developed much of current knowledge related to the thermal performance of all types of insulated concrete walls.
 ‘HVAC Sizing Software for Concrete Homes’ Available at BuilderBooks.com
“HVAC Sizing Software for Concrete Homes,” available through BuilderBooks.com, provides an alternative means of estimating heating and cooling system capacities for single-family concrete homes. The software calculates the system capacities based on the house dimensions, construction materials, location and thermostat set point. To view or purchase this publication set online, click here, or call 800-223-2665.
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