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TRENDS

Home Energy Magazine Online November/December 1997

TRENDS

Improving Ducts in Southern California

When Robert Johnson, director of community development for the Southern California city of Irvine, attended an HVAC conference in 1995, he was appalled to discover how poorly designed and poorly installed many residential duct systems were. Even in new construction, ducts can leak 20%-40% of their conditioned air, costing homeowners needless expense while compromising the comfort of their new home. Johnson decided to develop a program for Irvine to improve the performance of HVAC duct systems.

As a result of that meeting, Irvine's voluntary, performance-based residential energy conservation program was officially launched in April 1997. Called Irvine Quality Plus, or simply, IQ+, it encourages residential builders to install high-quality HVAC duct systems and take special building envelope measures that ensure energy efficiency. The city is helping to market the program to prospective home buyers by supplying promotional literature, videotapes, and certificates of compliance for participating builders.

How IQ+ Works

In the planned community of Irvine, virtually all homes are built by eight to ten production home builders. To participate in the voluntary energy-efficiency program, these contractors must first send the city a letter of intent. Once enrolled in IQ+, they become eligible to receive refunds of the city's mandatory energy plan check and inspection fees. Based on floor area, these fees amount to approximately $140 for a 2,500 ft² home.

To collect the refunds, builders must have a city-certified, third-party inspector sign a certificate of compliance with the program's protocols. The builder selects from a list of applicants who have passed a city-run exam.

Joe Farber, with the City of Irvine, listens to building scientist Iain Walker explain how to use energy testing equipment.

Iain Walker of Lawrence Berkeley National Laboratory demonstrates a smoke test on a flex duct to the developers, energy engineers, and HVAC contractors who attended the Irvine Quality Plus program launch.

Program Requirements

The program requires that all wall and ceiling insulation be carefully installed to completely fill each bay, without compression or gaps. Thermal bypasses must be mitigated by providing the equivalent of fire-stops to prevent undesirable internal air movement within building cavities. All return air must be ducted; building cavities themselves may not be used as ducts.

A mechanical drawing showing the layout of the duct system (including register locations and types, duct lengths, and connections) must be prepared by a mechanical engineer or a contractor possessing a C20 license and submitted to the city. To ensure room-by-room design, the air flow in CFM (cubic feet per minute) at each register must be detailed on the plans, using the ACCA's (Air Conditioning Contractors of America) Manual D, or estimated according to the floor area weighted method. Total HVAC system design static pressure and air flow must also be shown and must conform with the equipment manufacturer's performance data.

A mechanical engineer or C20 contractor must verify that the proposed system, as designed, will meet the minimum heating and cooling load requirements. Furnace and air conditioning equipment must be specified on the drawings.

If a home has two stories (as most do in Irvine), it must have at least one return air inlet on each story and at least one second-floor return air grille located within 3 ft of the first floor.

All tape and mastic sealants must comply with UL-181, or must be aluminum-backed butyl adhesive tape, or must be approved by the city's chief building official. All HVAC system joints must be made with a mechanical connector. All connections must be sealed with mastic or UL-181-compliant tape (standard gray duct tape can't be used).

All model homes have to be tested for duct leakage and air flow and must pass these tests before testing of production homes can begin. A formula for the number of homes tested specifies pass/fail requirements, allowing builders to test a percentage of homes built in lieu of testing every home. Tests must be made using a duct leakage measuring device such as a Duct Blaster^TM. Measurements are to be taken at a pressure of 25 Pascals (Pa). Total leakage cannot exceed 50 CFM per 1,000 ft² of conditioned floor area.

Air flows must be tested at each supply air register, using an approved device such as a flow hood, and cannot be less than 80% of the calculated flow, with the total flow required to be at least 90% of the total calculated air flow.

To help develop the requirements for IQ+, Johnson initially relied upon the in-house staffs of both of Irvine's planning and building divisions, and the mechanical engineering and energy consulting firm of Richard A. Palmer and Associates. Final design of the program was overseen by Principal Engineer Shawn Thompson, of the Irvine Planning Division. It was accomplished with help from the Lawrence Berkeley National Laboratory, Southern California Air Conditioning Distributors, the energy consulting firm ConSol, Incorporated, local Irvine builders and HVAC subcontractors, and the staff of the California Energy Commission in Sacramento.

The Impact of IQ+

To date, only two of the eight to ten builders in Irvine have officially signed up to participate in the program. One of the two is California Pacific Homes, the largest builder in the city. The projects in the IQ+ program represent 20% of Irvine's recent housing starts.

"By emphasizing quality control, IQ+ will help builders avoid construction defects and costly callbacks in new home construction," said Sheri Vander Dusen, who replaced Johnson as director of community development in 1996. "By refunding energy fees, the city is helping to absorb the cost of making buildings more energy efficient, providing consumers with more comfortable and cost-saving homes."

--John Eash

John Eash is a licensed architect and an associate energy specialist at the California Energy Commission.

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