Energy Efficient Roof Exhaust Fans

EC or Electronically Commutated Motors

With increased attention on energy efficiency, our industry is evolving to more efficient motors with reduced energy consumption. It is important that the (electronically commutated) motors are of high quality standards. Typically, the EC motor is manufactured here in the USA. You will find that these high efficiency motors are used in many downblast roof exhaust fans, upblast roof fans, square inline duct fans, and sidewall propeller fans to allow engineers to utilize the advantages of demand based ventilation without the disadvantages of extensive controls and high energy costs offered by PSC (permanent split capacitor motors). An EC motor is approximately 80 percent efficient vs a traditional PSC motor which is around 60 percent efficient.  


There are several advantages to demand-based ventilation, but the clearest one is the ability to create a constant pressure system to more closely match the way a multi-family building or office building actually functions. In a multi-family building, a downblast fan is mainly used for bathroom and dryer ventilation, whereas an upblast fan is primarily used for kitchen exhaust. Since dryers, kitchen hoods, and bathroom fans are usually not running at the same time, single speed PSC powered fans are not the most efficient option. These exhaust systems only operate a fraction of each day, so having the central exhaust systems running at 100% for 24/hours per day wastes energy. In an office building these fans are used for the individual office spaces, lavatories, kitchens, etc… In this case, the fans are being utilized on a much more regular basis since businesses are typically open Monday – Friday, 8 hours per day or so. Again, energy efficiency can be a key factor in building maintenance and energy costs.

Prior to the EC motors (which accept milliamp signals), complex control strategies and additional external electrical components, such as VFD’s (variable frequency drive), were employed to vary the volume of air.

Now, with the advent of EC motors and a constant pressure controller, a single probe in each shaft is all that is required to maintain the constant pressure in the shaft when all of the fans are not in operation. This has made demand-based ventilation a more effective solution on multi-family projects.