Design/Sizing Methodology and Economic Evaluation of Central-FanIntegrated Supply Ventilation Systems

Ventilation systems for residential buildings can be generally categorized as supply, exhaust, or balanced systems. Subcategories include: integration into central air distribution ducts, or single- or multi-point air distribution. This effort focused on establishing a design methodology for central-fan-integrated supply ventilation systems using an outside air duct to the return side of a central air distribution fan, with a specialized fan recycling control. A measurement protocol was developed, and air flow measurements were taken for 25 ' lengths of 5" through 9 " diameter flexible ducts, with a 6 " wall-cap, at duct pressures of-10 Pa to-120 Pa. Using these measurements, a five-step method was developed as a guide for correctly designing, sizing, and installing the components of the ventilation system. An economic evaluation was made by conducting hourly computer simulations to determine the impact on heating, cooling, and fan energy use for four U.S. climates: cold (Chicago), mixed (Charlotte), hot-dry (Las Vegas), and hot-humid (Orlando). It was found that an effective ventilation system can be achieved using a 5 " to 9 " diameter insulated duct from outdoors to the return side of a central air distribution fan, with a specialized fan control that automatically cycles the fan if the fan has been inactive for a period of time. The advent of this specialized fan recycling control has made this type of ventilation system viable and more energy efficient