This article was originally published in the July/August 1998 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
Home Energy Magazine Online July/August 1998
Energy Stars Shine on Manufactured Homes
These homes, developed with guidance from the Florida Solar Energy Center (FSEC), are the first manufactured homes to leave the factory certified to be 30% more energy efficient than the Model Energy Code (MEC). Once the home is site-installed, the ducts will be tested to verify that their tightness was not compromised during transit. Emanuel Levy of Levy Partnership, a specialist in manufactured housing and energy efficiency, says PHH and the Department of Energy (DOE) are still working out the protocol for testing homes in the field, but if the homes stand up to travel, they will be Energy Star-certified.
PHH is a major producer of manufactured homes, with 16 plants in six states that build more than 7,000 homes per year. The company's plant engineer, Bert Kessler, first became interested in Energy Star after attending a meeting last year sponsored by the DOE's Energy Efficient Industrialized Housing Project. PHH has long promoted energy efficiency, says Kessler; for years, they have offered an optional upgraded Energy Miser insulation package (typically R-30 ceilings, 2 x 6 R-19 walls, and R-11 floors) and a 12-SEER heat pump.
Kessler subsequently sought out FSEC's help to see how PHH could improve its manufacturing process to build homes that merited Energy Star approval. FSEC inspected two of the upgraded PHH homes on-site and determined that because they were already so efficient, all the factory had to do was improve the duct manufacturing process.
High-end as PHH was, according to FSEC's David Beal, the company still had room for improvement in the duct systems. Manufactured homes in general don't have great distribution systems, Beal said, But with a little bit of help they can become great.
The main problem with PHH's method of making ducts was in how holes were cut in the fiber board plenum to attach an R-4 or R-8 insulated flex duct. Hand-cutting produced irregular holes. This problem was exacerbated by the lack of sealant around the joint, and by improper tension when the flex duct was attached. The total duct leakage ranged between 40 and 100 cubic feet per minute at 25 Pascals (CFM25) in each half of the home.
Lasalle Airsystems, which designed the duct system, came up with a simple tool to solve this problem. It is essentially a bar of flat-stock aluminum with a cutting blade at the end. It has holes along its length into which a sharp center pivot pin is inserted. Previously, PHH employees made the hole by placing the flex duct against the fiber board box and tracing it. Now the tool cuts perfect circles of various radii in the plenum. By also using a mastic sealant on the joint and applying the proper tension (using an industrial strength cable tie) air leakage was cut to less than 10 CFM25 for each half of the home--a 75%-90% improvement.
After these improvements, duct leakage to the outside (including the ground-mounted air handler) was below 30 CFM25, less than 2% of the floor area in ft2. Typically, manufactured homes have a duct leakage to the outside of 4% to 10% of the floor area. To meet Energy Star standards, this figure had to be under 3%. Kessler was so impressed with the improved duct performance that he ordered all of the company's factories to use the new duct manufacturing method, regardless of whether the homes they are building are to be Energy Star compliant.
FSEC also tried to improve the overall envelope airtightness of the homes, without much success. The big holes and recessed can lights were sealed, but requirements in the national building code for manufactured homes made it impossible to seal the plumbing penetrations. The code also requires continuous mechanical ventilation, so the whole house fan exhaust duct and backdraft damper were not disturbed. Although there was a gap around the fireplace chimney penetration, it was not sealed for fear of backdrafting. Despite the addition of a thick foam gasket at the marriage wall (which can respond to outdoor temperature even more than insulated exterior walls if improperly sealed), the whole-house air leakage for the two Energy Star homes was essentially the same as that for the six conventional PHH homes that FSEC tested. The Energy Star units had 5.1-5.5 ACH50, compared to 5.5-7.5 ACH50 for the conventional homes.
Preliminary tests show that the PHH Energy Star home can save about 34% in cooling energy. By the time this article is printed, PHH should be producing only Energy Star homes in its North Carolina and Oregon plants.
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