Ductwork Design: A Proper System Fulfills Several Objectives
Optimum performance and efficiency of your cooling and heating system begins with proper ductwork design. This doesn’t happen by guesstimates or a one-size-fits-all approach. An HVAC professional utilizes data derived from Manual J and Manual D — the industry standard software produced by the Air Conditioning Contractors of America — to accurately calculate the heating and cooling load of the home and properly design ductwork to accommodate that load. The result is duct efficiency above 80 percent. Failure to properly execute the ductwork design phase, however, can produce efficiencies as low as 60 percent or less. This can result in hundreds of dollars of wasted energy expense every year simply from design shortfalls. The overall benefits of proper design are optimum interior comfort, proper air distribution and economical operation. In a forced-air system, these goals are best achieved with a design that meets these objectives:
- Conveys cooled or heated airflow at consistent temperatures throughout the home and accommodates loads that have been calculated on a room-by-room basis.
- Is sized using industry standard methods so that the static pressure drop measured across the air handler meets the specifications of the HVAC equipment manufacturer and the calculations of the design.
- Utilizes sealed ductwork to convey the proper volume of airflow and to prevent infiltration of contaminated air into the system.
- Incorporates sufficient return ductwork, properly located to provide adequate return airflow. Where possible, dedicated return ducts should be installed in every room with a supply duct.
- Is balanced so supply ducts deliver airflow at positive pressure and returns convey air at slightly negative pressure. This maintains a condition of neutral air pressure in the rooms.
- Minimizes thermal gain or loss occuring between the air handler and the rooms. Ductwork routed through unconditioned zones of acute temperatures such as attics or crawl spaces should be insulated.