Air Conditioning Design Advice For Homebuilders In The New Orleans Area

Energy Efficiency Begins With Home Design
We are seeing renewed interest in the new home market.  If you are considering building, work with your contractor to plan energy efficiency into the home location and design before construction begins.  Surgi's offers free consulting for your new home.

Best-practice measures
Over the past decade, our understanding of the best building practices for hot climates has been significantly advanced by researchers working at the Florida Solar Energy Center. Useful hot-climate research has also been conducted by engineers from the Building Science Corporation; much of this research has been funded by the Department of Energy’s Building America program. The following advice represent a distillation of researchers’ findings:

  • Orient the house with the long axis east-west.
  • A slab foundation should have perimeter insulation (unless termite concerns preclude it) but no sub-slab insulation. Uninsulated slabs can actually reduce a home’s cooling load.
  • Shade is good. Roofs should have wide overhangs, ideally 3 feet wide or wider. Hurricanes like to grab onto roof overhangs, though, so be sure to secure roof trusses or rafters to top plates with adequate hurricane clips. Since a hipped roof can shade all four sides of a house, hipped roofs are preferable to gable roofs.
  • Most windows should face north or south. Because they are harder to shade, east- and west-facing windows contribute much more to overheating than north- or south-facing windows; so east- and west-facing windows should be minimized.
  • Every effort should be made to shade every window. Windows can be recessed into thick walls or protected by projecting architectural elements. On the east and west elevations, it’s often best to protect any windows with a wide porch.
  • It is critical for a home’s air handler and all ductwork to be within the home’s thermal envelope. One way to do this is to “cathedralize” the attic by spraying closed-cell foam insulation against the underside of the roof sheathing. Of course, duct seams should always be carefully sealed; slightly oversized ducts are better than undersized ducts.
  • Ceilings or roofs should be insulated to at least R-30.
  • If the house has an unconditioned attic, specify radiant-barrier roof sheathing.
  • Use highly reflective roofing — ideally, white metal roofing or white concrete tile roofing.
  • Wall insulation is much less crucial down south than it is up north; 2 inches of rigid foam (R-10) is probably plenty. If the house has concrete-block walls, install the insulation on the exterior, not the interior.
  • Specify windows with a solar heat-gain coefficient (SHGC) below 0.32; if possible, aim for 0.28 or 0.29.
  • The home’s thermal envelope should be carefully air sealed.
  • While high internal loads — that is, waste heat from lights and appliances — benefit cold-climate houses in winter, such loads hurt the performance of hot-climate houses in summer. So in Florida and Texas, it’s particularly important to install CFLs rather than incandescent bulbs and to specify the most efficient available appliances, including refrigerators and televisions.
  • Ceramic tile floors are best. Avoid carpeting.
Reprinted from GreenBuildingAdvisor.Com posted on Oct 9, 2009 by Martin Holladay, GBA Advisor

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