Since 1985, equipment manufacturers have used ECM motors in residential air conditioners and furnaces. These motors have made it possible to achieve SEER ratings of 12 and higher. Until more recently though, they were only manufactured in 120 and 240 VAC, which precluded their use in commercial applications. Following two years of research and development and the availability of a new 277 VAC version, Engineered Comfort was first to introduce the ECM motors to the commercial HVAC market as an option for use in commercial fan coil unit applications.
What is an ECM Motor?
The ECM (Electronically Commutated Motor) is an ultra high efficiency programmable brushless DC motor utilizing a permanent magnet motor and a built-in inverter. DC motors are significantly more energy efficient than AC motors and much easier to control. The major weakness of commercial fan coil units until now, has been their low fan motor efficiency. The widely used three speed fractional horsepower shaded pole and permanent split capacitor (PSC) induction motor in combination with a 3 speed switch or an electronic SCR speed controller is extremely inefficient at typical operating conditions. Due to acoustical considerations, the fan motor is usually adjusted to operate at considerably less than full load (where PSC motor efficiencies may be as high as 62%). PSC motor efficiency drops off dramatically when turned down; typically by at least half. Installed PSC motor efficiencies are therefore typically in the range of only 12 – 45%. ECM motors in contrast, maintain a high efficiency of 65 – 72% at all speeds.In addition to lower operating costs, ECM motor technology allows Engineered Comfort to pre-set the fan airflow volume at the factory.The graphs shown in our catalog demonstrate the lower watts per cfm (translating into lower operating costs) and wider operating ranges of commercial fan coils employing ECM/EPIC Fan Technology® versus PSC induction motors.
Features and Benefits
Soft starts and slewed speed ramps are programmed into the ECM motor eliminating stress transmitted to the mounting bracket or hardware. They incorporate ball bearings providing permanent lubrication unlike sleeve bearings requiring a minimum rpm operation for oiling. The wider operating range of the ECM motor allows each model to actually replace two models using induction motors. This feature alone provides several benefits: a simpler product line to choose from, little or no equipment changes necessary when tenants change, more similar sized units on the job, decreased spare parts inventory and increased contractor flexibility. The low operating temperature of the ECM motor (essentially ambient) requires very little energy to offset the heat gain from the motor versus PSC motors which run hot (typically around 90 – 150ºF).
ECM/EPIC Fan Technology®
ECM/EPIC Fan Technology® provides an average 90,000 hours of operation (versus 50,000 hours for a typical PSC motor). This translates into about 10 years for a typical fan coil as opposed to 8 for a one using a PSC motor. In addition to these standard features are two primary benefits, energy savings and the ability to pre-set the fan airflow volume at the factory.
Why and How do You Pre-set Fan Airflow?
Pre-setting the fan airflow (cfm) has not been an issue with fan coil manufacturers because these units were either on at full load or off in normal operating conditions. With ECM/EPIC Fan Technology®, the fan coils can now be run as a VAV device with all of the requisite savings that VAV brings to other commercial jobs. (See control sequence in our catalog for further explanation.)AC motors are not synchronous machines and the rpm, and consequently the unit cfm, changes when static pressure changes. The difficulty in pre-setting the fan lies in estimating the motor workload required at the job site in actual working conditions. The fan operated by an AC motor will not produce the same volume of air as it did at the factory without the duct work or loaded filter. Because there is no way to accurately predict the downstream static pressure as it would exist at the job site, it was impossible to pre-set the fan cfm. The ECM motors are DC and inherently synchronous machines. The motors are programmed to calculate the work they are doing and then compare the work accomplished to the cfm requirement. The integral microprocessor based controller automatically adjusts the speed and torque in Engineered Comfort commercial fan coil units Engineered Comfort fan coil units incorporate our own custom EPIC™ fan controller. An electronic PWM volume control device that allows adjustment of airflow volume. Minimum and Maximum airflows can be pre-set on the assembly line. It is field adjustable either manually using a screwdriver and voltmeter locally at the fan coil or with the Engineered Comfort thermostat and controller or remotely using a 0 – 10 VDC analog output from a digital controller via the BAS or Engineered Comfort’s standard thermostat and controllers. A fan volume versus DC volts calibration chart is provided. The importance of this feature is the energy that is saved due to controlling the fan airflow as well as the large reduction in noise generation. This also removes the uncertainty of diffuser flow measurement with hoods. Laboratory tests show the fan cfm to be accurate within +/- 5% of the factory set point. This is a huge benefit to the owner, the occupant, the controls contractor, and the mechanical contractor.