15 Minute Blog: Fan Efficiencies

Recently I had to select some small and some medium sized fans for a sustainable project.

The small fans were a breeze: it was a light commercial building, so I went with residential quality exhaust fans. I selected them from the Energy Star excel list of qualified fans:

http://downloads.energystar.gov/bi/qplist/vent_fan_prod_list.xls

These lists are available for all Energy Star certified equipment, and are great tools for selecting them: find a good performance index (for fans, I used CFM/watt) and then select one of the better performing, reputable manufacturers.

I put the CFM/watt effectiveness requirement right on the drawing, so that I would be guaranteed the performance I wanted from what was installed. I could also provide a good list of alternate suppliers who also meet the efficiency standard right from the Energy Star list.

The larger fans were much harder. I used a fan selection program from a major manufacturer to determine which kind of fan they sold would be in the right range for efficiency and price-point, given the parameters I needed, but the program listed a variety of different efficiencies, none quite as easy-to-understand as a CFM/watt. ASHRAE lists motor efficiency requirements, and BHP requirements, but these aren't typically provided by the equipment selection program. Without some calculations and work on my part, it was difficult to even tell if the selected fans met our standard minimum efficiency requirements. I'm not allergic to work, but if energy efficiency were considered as important as other performance indicators, our industry would have standardized ratings - the EER of the fan industry.

This problem is endemic in medium-sized HVAC products. Very small, consumer goods are being provided with clear information about operation, and are benefiting from good engineering practise to reduce energy use. Very large equipment is subject to rigorous examination by engineers for energy efficiency, and is the focus of large manufacturers for efficiency increases.

Medium sized equipment -- fans in the 400cfm - 5000cfm range, for example -- seem to be left behind by today's practises, even through the majority of Noth American commercial buildings are full of them.