National Oilheat Research Alliance 7 a PSC motor rated at 60% efficiency could be operating at as low as 40% efficiency when on low speed, whereas the ECM will maintain its electrical efficiency across its entire operating range. Indoor blower motor applications benefit greatly from lower continuous fan speeds where the ECM is quieter and uses up to 200% less energy than a PSC motor. Many ECMs are also built with internal protection features such as surge protection, water resistance and speed limits, which help improve motor life and reduce nuisance failures due to overheating. Most ECMs are built with permanently lubricated ball bearings designed for long life at the wide range of operating speeds ECMs are capable of achieving. Most OEM ECMs are uniquely programmed and must be replaced with an OEM-only part. There is a growing market for retrofit/replacement ECMs for upgrading PSC or shaded pole motors and even for replacing OEM Constant Torque applications. Some of these retrofit ECMs can also reduce truck stock with dual rotation, dual voltage and multi-horsepower features. The initial investment of an ECM driven system or retrofit may seem high, but more and more consumers are looking for energy saving alternatives, as well as comfort and health features, and that will lead you to ECMs as a logical choice. Fan Laws The performance of all fans and blowers is governed by three rules, commonly known as the FAN LAWS. The fan laws describe the relationships between cubic feet per minute (cfm), revolutions per minute (rpm), static pressure (s.p.) and horsepower (hp). For example, when the CFM changes, the rpm, s.p., and the hp will also change. A fan’s performance varies depending upon the conditions under which it operates. A fan that moves 400cfm of air under one condition might only move 300cfm under another condition. The amount of air a fan moves, the speed of the fan and the motor horsepower are all related. This can be proven by the fan laws: Fan Law 1 states that the amount of air delivered by a fan varies directly with the speed of the fan. Stated mathematically, New CFM = (new rpm x existing cfm) divided by existing rpm or New rpm = (new CFM x existing rpm) divided by existing cfm Fan Law 2 states that the static pressure (resistance) of a system varies directly with the square of the ratio of the fan speeds. Stated mathematically, New s.p. = existing s.p. x (new rpm divided by existing rpm)2 Fan Law 3 states that the horsepower varies directly with the cube of the ratio of the fan speeds, or New hp = existing hp x (new rpm divided by existing rpm)3 Example: Assume an existing system with the following conditions: 1000cfm, 825rpm, and 0.5 in. w.c. with a fan hp of 1/3hp. With an increase in airflow to 1200cfm, what are the new rpm, s.p. and hp? Fan Law 1 calculates the new rpm: New rpm = (1200 x 825)/1000 New rpm = 990,000/1000 New rpm = 990 Fan Law 2 calculates the static pressure: New s.p. = .5 x (990/825)2 New s.p. = .5 x 1.44 New s.p. = .72 Fan Law 3 calculates the horsepower: New hp = .33 x (990/825)3 New hp = .33 x 1.728 New hp = .57
NORA Advanced Air Flow
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