The costs and risks of damper-based controls in kitchen ventilation
Lastly, there is the concern that all these moving dampers will only cause hood air imbalance problems. In other words, if hood 1 suddenly sees cooking activity, and then hood 5 sees cooking activity 3 seconds later while hood 2 no longer sees cooking activity and hood 7 starts seeing a lot of heat but no cooking, the dampers and VFD would be in a constant hunting mode. The variables are too many and happen too fast for the dampers and single VFD to be able to respond appropriately and reliably for all hoods. Moreover, most manufacturers of damper-based controls have only one setting between open and closed, making the real-time hood-air balance far less precise and energy-efficient than a fan per hood design with VFDs capable of modulating the fans speeds infinitely in the 30%-100% range.
Of course, if optimal—not just minimal—energy savings can be validated through independent research, proven case studies, and customer testimonials, then let objective data be your final guide. But performance must be proven over time and not just upon initial start-up. Wear and tear over the months and years will reveal the truth.
Engineers should think in terms of total safety and optimal energy efficiency when designing kitchen ventilation systems of the future. Design-in a level of critical redundancy with at least two and possibly more exhaust fans so that no single fan can “bring down” an entire kitchen. A fan has several moving parts—motor, fan, and belt—not to mention any modulating dampers inside the duct, and one of these will inevitably fail at some point. Don’t let a catastrophic failure happen as a result of your design with only one fan, or with a broken modulating damper over a char-broiler. The last thing you want is a call at midnight from an angry customer—or worse, from its attorney. Possible smoke and fire inside a large public space with lots of people is not a good combination. Multiple fans without maintenance-prone modulating dampers help minimize this risk.
Engineers should also design-in optimal energy efficiency by controlling each hood/fan independently of the others. A fan per hood design minimizes duct runs, eliminates multiple 90-deg turns, and minimizes the temptation to install modulating dampers—all three of which reduce static pressure losses and ensure superior energy savings. This also allows more infinite fan speed control such that the fans can modulate between 30% and 100% rather than just between 80% and 100%. Combined, these factors can provide thousands of dollars of additional energy savings per year.
In the end, great design is about maximizing long-term savings and minimizing long-term costs and risks.
Stephen K. Melink is founder and president of Melink Corp. He is a NEBB certified professional, and the inventor of demand ventilation controls for commercial kitchens.