Sanyo Split System Air Conditioner. Wrong Way.

If ductwork sizing is performed incorrectly, homeowners can make simple modifications to the ducts to improve efficiency and comfort. An air damper installed within a duct allows users to regulate airflow, or reduce air pressure in one area to bring more air to other parts of the home. If air is moving too slowly through a duct, a fan or duct blower can be installed within the duct itself. Duct blowers supplement the main furnace or air conditioning blower, and help increase airflow to distant parts of the home.

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The second ASHRAE technique used for ductwork sizing involves measuring static regain. This system is more complex, but also results in improved energy efficiency when used correctly. To size ducts with static regain, engineers use ducts that create equal static pressure at every supply and return outlet in the home. This includes all exhaust vents and supply grills, and is based on a series of charts developed by ASHRAE that are used in conjunction with data taken from the home.

Sanyo Mini Splits.  Equal Friction.

Armed with this information, designers can choose one of two basic systems to determine proper duct sizing. People throughout much of the world rely on systems created by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) to size ductwork. The most widely used ASHRAE system relies on achieving equal friction within the duct network. This means sizing ducts to equalize pressure lost during air supply and air return, which creates a balanced system of heating, cooling and ventilation.

Sanyo Split System Air Conditioner Manual. Amount of pressure.

Based on the size of the central unit, the engineer can determine the initial air pressure within the duct network. He then calculates the distance the air must travel to and from each room, as well as the amount of air volume needed in each area. Engineers must also consider how much air pressure is lost as the air travels through the ducts themselves, either due to distance from the blower or to simple leaks in the duct.