Energy, Usability, and Exhaust Fans

Exhaust fans use a lot of energy. The fan motor consumes electricity and draws potentially dangerous air out of the building. It is a health and safety requirement in order to maintain a good working environment. But that dirty air that needs to be blown outside has already been heated to make the workplace comfortable, and now the clean, fresh air is cold and needs to be heated again. The combination of the fan motor and the waste heat means it is important that exhaust fans are operated efficiently to reduce the long term energy costs.

Since the primary purpose of exhaust fans is safety, often the rule is to turn them on when people enter the workplace, and leave them on while people are there. Safety is a clear priority, and no one will buy the claim that turning of the fans to save energy is worth making workers sick. The challenge is to make sure the exhaust fans fulfill their safety role, without simply running constantly and wasting energy.

It is necessary to look at the workplace system and devise a solution that meets the priorities of safety for workers, production for the business, and energy efficiency to reduce costs. Just putting ups signs that tell people to turn off the fans when not needed isn’t going to work. Usability means designing systems that work properly with the minimum of fuss, so that people can concentrate on their jobs.

Paul McDunphy is the manager of the DIT Kevin Street building. In the effort to reduce energy use, he found that the chemistry lab consumed a high amount of electricity. The Kevin Street building houses the Chemistry department and the laboratory contains fume hoods with exhaust fans that extract dangerous gases during experiments. The fume hoods consume 50 Kw of electricity while running. They also extract the heated air from the lab along with the gases, meaning additional energy had to be used to compensate and heat the room again.

Through observation, McDunphy found that fume hoods were being left running when they were not needed. The problem was to find a method to reduce energy use while still ensuring the critical safety function of the equipment.

The solution was to install sensors to detect current when the fume hood was in use. That switch then turned on the fans, and when the user finished their work the fans switched off automatically after a short period of time. This method reduced the power use from the fume hoods by 50%, with no loss in safety or functionality. While one might complain that the students and staff should be able to take responsibility and turn off equipment when not in use, in this case the users are focused on the education process. They know that having the fans working is necessary for their safety and successful training, while saving energy is not a requirement of their course. In this case, it was more effective to install technical measures to achieve the goal of energy savings than to put up signs telling the students to turn the fans on and off as necessary.

Good application of usability principles means creating a system that works properly and takes into account the realities of how people manage their priorities.

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