Heating and Cooling Distribution
Summary
Each year about ten thousand new factory built homes are sold in California. Over ninety-four percent of these typically highly affordable homes are built in factories as two or more fully finished modules that are shipped to and finished at the site. Nearly all factory built homes provide heating and cooling through ducts connecting a central air handler with the living spaces of the home. The design of the air distribution system (ADS) has changed little in the past three decades and varies little among companies. ADS improvements offer the single greatest potential for energy use reduction and at the lowest possible cost.
The goal of this project was to reduce energy use in California homes by improving the ADS inter-module connection (crossover) in factory built homes by curing three common system defects: air leaks to the exterior due to poor field connections; inefficient airflow due to bends and constrictions in the duct; and thermal losses due to contact with the ground and resulting deterioration of insulation. These defects can result in immediate and dramatic problems requiring expensive service calls or can go undetected for years eroding energy and overall building performance.
Objective
The main project objectives were as follows:
Characterize whole system performance for air distribution designs typically used in factory built homes.
Calculate costs of current practices.
Understand the factors that result in variations from this average.
Develop two preliminary ADS crossover designs that compete on cost with current designs but promise superior performance.
Complete mock-ups and evaluations of the two designs.
Compare and evaluate the concepts based on performance, cost, manufacturability and other criteria.
Modify the design approaches for further testing.
Prototype the modified designs.
Performance-test the prototypes.
Demonstrate that, under typical conditions, the proposed crossover systems can achieve leakage and energy loss of less than 3 percent and installed costs are comparable to existing systems.
Demonstrate that, under typical conditions, thermal comfort and air quality are superior or comparable to existing systems.
Write a report documenting the development process, testing and evaluation results, design specifications, and recommended fabrication, manufacturing and site assembly procedures.
Provide the report to all manufacturers selling homes in California. 14. Write a report that includes a market transformation strategy.
Conclusion
The major project conclusions indicate that manufactured home air distribution performance varies significantly, with new homes often performing well while older homes may suffer due to outdated duct construction methods and deterioration. Current system costs are very low, and although several alternative designs are possible, meeting cost criteria is challenging. Rigid ducts offer superior air distribution and greater installation reliability and durability compared to flex crossovers. In-floor through-the-rim crossover ducts can perform well if properly installed. Despite being more expensive, the proposed technology offers a superior solution, particularly for higher-end plants and a large existing home segment, suggesting a market transformation strategy in the Recommendations section of the report.