Don Fisher

Comfort and air quality can’t be overlooked in today’s hotel kitchen. Just as guests want to be happy and healthy, so do the employees in your foodservice operation. Think of it another way: the exhaust hoods and makeup air system are the “lungs” of your kitchen. They exhale contaminated air from cooking equipment, while simultaneously inhaling a fresh supply of outdoor air. But when the exhaust hood fails to remove the heat and smoke generated by appliances, or when the replacement (makeup) air is not adequately conditioned, your kitchen may be suffocating.

No piece of equipment generates more controversy within the foodservice equipment and design community than the exhaust hood. In hotel kitchens, exhaust hoods come in sizes large, xlarge, and xx-large. Exhaust rates can be as high as 50,000 cfm (cubic feet per minute) in foodservice facilities supporting a convention center or casino. That’s a lot of air being sucked out of the building. The challenge of heating or cooling replacement air makes the exhaust ventilation system the largest energy-using system in a foodservice operation.

In our world of automated control, the hotel kitchen ventilation system is operating in the dark ages. You turn it on, turn it off, and in between it operates at full speed. Meanwhile, the makeup air (MUA) unit replacing the air removed by the exhaust hood heats outdoor air completely independent of the kitchen temperature where this air is delivered—a control dinosaur.

A large hotel in San Francisco installed a state-of-the-art energy management system for its lighting and HVAC systems. But it stopped short of the kitchens. During a foodservice audit, it was observed that 35,000 cfm of the MUA required by the exhaust hoods was being heated to 70°F, while the other 15,000 cfm of MUA was being simultaneously cooled to 55°F. By simply lowering the temperature setting on the MUA units, the operating engineer saved the foodservice operation $50,000 in annual energy costs.

Short-circuit MUA hoods were developed as a strategy to reduce the amount of conditioned air required by an exhaust system. By introducing a portion of the required MUA in an “untempered” condition directly into the exhaust hood reservoir, the net quantity of conditioned air exhausted from the kitchen is reduced (with an assumption that energy costs will be reduced accordingly). Research demonstrates that internal MUA can’t be introduced at a rate more than 15 percent of the exhaust rate without causing spillage (despite the 80 percent shown on the air balance schedule or marketing literature).

Simply stated, short-circuit hoods are not recommended. If you have a short-circuit hood in your operation, consider converting it to an exhaust-only hood with conventional makeup air.

DEMAND-VENTILATION CONTROL
By controlling the speed of kitchen ventilation fans based on the “need for exhaust” created by the cooking equipment under the hood, energy consumption can be reduced. The application of demand-ventilation controls is particularly attractive for hotel kitchens where exhaust hoods often operate on a 24/7 basis and cooking equipment spends a lot of time in standby. While this technology currently is led by one manufacturer, it is anticipated that other strategies of variable speed control will emerge and that its specification in hotel kitchens will become mainstream.

A case study conducted by the Pacific Gas and Electric (PG&E) Food Service Technology Center evaluated the cost/benefit of the Melink Intelli-Hood Controls, a demand-ventilation control package www.melinkcorp.com that had been installed on the kitchen ventilation system at the InterContinental Mark Hopkins Hotel in San Francisco.

The Melink Intelli-Hood Controls modulate the speed of the exhaust and makeup air fan motors with variable frequency drives (VFDs). These VFDs receive commands from a central controller, which receives its input from two sources: an infrared (IR) beam that spans the length of the exhaust hood and a temperature sensor mounted in the exhaust duct. A disturbance in the IR beam or an increase in the exhaust duct temperature signals the controller to increase the exhaust system fan speed as necessary.

The annual savings for the Mark Hopkins Hotel was $19,370. With an installed cost for the Melink Intelli-Hood Controls of $15,000, the payback was less than a year. And the bonus for staff was a much quieter kitchen when the fans were running on low speed.

EMISSION CONTROL
When the “lungs” of the kitchen blow cooking odors across someone’s balcony or the swimming pool, your foodservice operation is on the hook. But what are the solutions for effective grease and odor control? Ultraviolet (UV) light is a technology featured by several hood manufacturers as one solution. Although I believe this technology has a legitimate role in mitigating grease loading in ductwork, there is limited experience in the United States with its performance. Some manufacturers acknowledge that a UV system won’t completely remove smoke or odors. Complementary technologies such as two-stage filters, electrostatic precipitators (ESP), waterbased scrubbers, high-efficiency HEPA filters, along with activated charcoal or potassium permanganate modules, may be necessary components of a total grease and odor control system. So be prepared. An effective control package comes with a hefty price tag and maintenance is ongoing.

The future is now. If “greening” your hotel kitchen is one of your new business goals, tuning up the exhaust system may a great place to start.

Don Fisher, president/CEO of Fisher-Nickel, Inc., manages the Food Service Technology Center in San Ramon, California. This center collaborates with the Commercial Kitchen Ventilation Laboratory in Wood Dale, Illinois, to develop and apply standard test methods for evaluating the performance of food service equipment. The program is funded by California utility customers and administered by the Pacific Gas and Electric Company under the | auspices of the California Public Utilities Commission.