Blog Archive

Wednesday, April 20, 2011

Utilizing Balancing Dampers to Reduce Night Air Infiltration from Exhaust Hoods

It is generally accepted that the cost of energy will continue to rise and some forecasters see no end in site. With this bleak forecast in mind, we have to take an extremely hard look at how we do business and our operating costs in order to make any profit. This holds true for any business, whether it is a school, a hospital, a country club or any B&I operation. One of the ways to reduce operating costs in new construction is with the LEED (Leadership in Energy and Environmental Design) program that builds more energy efficient buildings thus lowering energy usage (i.e. operating costs). Even though the buildings are more efficient, one of the weakest areas in this program has been the kitchen.

Kitchens use 5 times more energy than any other part of the building. Kitchens use more electric on demand, more gas on demand, more water, and more sewage. Kitchens affect waste management and overall HVAC costs of the building. More and more effort is being applied at evaluating these costs through such organizations as Foodservice Technology Center ( and Energy Star. However, there is still more work that needs to be done. There has to be focus on the high-energy consumers, improve their efficiency and incorporate those improvements in the design specs. One of the biggest consumers of energy is still the exhaust hood. Even with the advancements of demand ventilation, total kitchen ventilation and displacement ventilation there is still a great big hole in the building roof that is being left unattended. It’s like leaving a window open in your home 24 hrs/day and 360days/yr. What is it? It’s the exhaust duct.

There are 960,000 foodservice kitchen operations in the United States (National Restaurant Association, 2011 ¹). It is estimated, that of those kitchens 17% (CBECS, 2003 ²) operated 24 hours a day and the remaining 83% turn off their exhaust hoods and shut down during the unoccupied hours at night. Why is this important? Because in 83% of the operations, outside air is infiltrating the buildings down through the exhaust duct and into the kitchens conditioned space. This is creating an additional load on the cooling and heating systems which requires them to run at night resulting in increased energy costs and an uncomfortable kitchen climate. During the winter and in northern climates where the temperatures drop well below 0° degrees at night the kitchens are freezing in the mornings and in the southern climates the kitchens are humid and musty. Until just recently nothing could be done about this dilemma, since fire codes for Type 1 grease hood applications prevent any type of fire dampers and back draft dampers from being installed in the exhaust duct work (NFPA 96).

In the middle of a difficult economy, the City of Akron, Ohio, home of the Inventor’s Hall of Fame, continues to reinvent itself. Nowhere is this more evident than in the string of new public schools that have been popping up all over town. These beautiful, state of the art, structures are the result of collaboration between the Akron Public School Board, Child Nutrition, and a group of talented Architectural Designers and engineers. While these new structures are striking on the outside, it is the cutting edge technology on the inside that makes these new schools a true testament to this innovative city.

On one of these projects Blasco Associates LLC, who is the foodservice consultant of the Akron Schools, was presented with an interesting design problem. The two Life Skills areas had six exhaust hoods each that needed to be ventilated and due to the building locations and restrictions each area had to operate on just one exhaust fan per area. The normal and accepted design criteria would be to throw a switch and all six hoods would come on regardless of how many hoods needed to be in use. The consultant, realizing that this was an inefficient design method, assembled the Halton design team headed by Matt Lewis of Thermal Products to assess the situation. The two worked together to enable the hoods to operate independently of one another. The hoods were fitted with UL710 listed automatic balancing dampers allowing each hood to function by itself. The dampers closed off the hoods not in use and a logic panel communicated to a variable frequency drive motor telling the exhaust fan how much air to exhaust. This design enabled the teachers to turn on any exhaust hood they desired for instruction, reduced the exhaust volume in the area, and eliminated the night infiltration of cold air in the rooms. Realizing that night infiltration is a serious problem in all kitchen projects, the consultant applied the UL710 automatic balancing dampers to the rest of the project.

The bottom line is that these motor driven dampers should be applied to the following exhaust hood applications, all Type 1, and hybrid Type 2 (Type 2 hoods with Type 1 ducting and fan). The energy savings are significant and quantifiable. Using the Akron, Ohio electric rates of 10¢/kWh with electric heat pumps, Akron Schools will be saving $9,619.00 dollars a year on energy costs with a return on investment of only 3.95 years and most importantly a comfortable working space.

According to Bill Blasco- “As far as I am concerned the School Board just hit the ventilation lotto! This is what we as consultants are supposed to do. Take new technology and apply it where it is needed. Doing things the same old way just doesn’t cut it anymore.”

Note: For supporting Data on the project please contact the writer.