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Serving up Change in School Cafeterias (with related video)

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This isn’t your grandfather’s cafeteria. No sterile white walls, institutional smell or Sloppy Joes in sight. Instead, today’s education institution kitchens are colorful and inviting, designed with curvature and stainless steel to compete with local restaurants, offering more variety and efficiency to the demanding health-conscious "Generation Me" consumer who is short on time and big on selection. In short, campus eateries are less "cafeteria" and more "cafe."

Unlike their predecessors, these cafes imitate a mall food court and are in business for business’ sake; multiple food stations include different ethnic cuisines and offer transparency. The food is made in front of the consumer, and the kitchen is in the middle of the space instead of being placed in the back of the house.

These cafes have become meeting places where students gather to study and eat. They often close as late as midnight and open as early as 5 a.m., and some even service their students 24-7. To accommodate these new demands and still meet rising energy efficiency and operational budget requirements, cafeteria HVAC systems have gotten a facelift, too.

With more efficient equipment and controls, the mechanical support for university kitchens now can meet comfort, safety, energy conservation and budget demands. Innovations in technology and engineering have transformed the challenges of yesterday’s school kitchens into the solutions of today’s sustainable and economical college cafes.

Taking the challenge

The top five challenges and solutions to kitchen upgrades in education institutions:

1. Comfort Considerations.

-Challenge: Yesterday’s cafeterias were designed to deliver conditioned air only to the dining hall space, then repurpose it as makeup air to be transferred into the kitchen through ceiling vents. This transfer air could be as hot as 80°F when entering the kitchen. As a result, air temperatures as high as 100ºF may be seen at the hoods where workers operate. As temperatures elevate within the kitchen, worker productivity plummets. According to a 1996 study, "Enhancing Productivity While Reducing Energy Use in Buildings" by David P. Wyon, International Centre for Indoor Environment & Energy, Technical University of Denmark, thermal comfort and worker productivity are linked; productivity may decrease as much as 30 percent in rooms with air temperatures of 90ºF and above.

-Solution: Conditioned supply air between 55º and 65ºF should be injected directly into the kitchen, so that the room can maintain average temperatures of 75º to 80ºF. Kitchens are good sites for displacement ventilation, which in this case, will supply low-velocity conditioned air about 5 feet away from the hoods via ceiling perimeter diffusers. As the cool air begins to heat, natural buoyancy will enable the hottest air to occupy the top of the space, causing intentional stratification. This upper level of hot air will then be exhausted through the kitchen hoods.

2. Hood Safety.

-Challenge: Smoke and heat control. Often in cafeterias, hood selection optimization is overlooked. Selecting the proper hood size is crucial to controlling smoke and containing heat. When a grill is not positioned properly under its associated hood, smoke can "roll out" of the hood exhaust area and consequently set off smoke alarms. Exhausting too much or too little air will create less than optimal conditions. Smoke may be visible, but heat is not. Owners often do not realize the harm done by heat rollout, including making occupants quite uncomfortable.

-Solution: Designers should review hood manufacturer information, as well as the American Society of Heating, Refrigerating and Air-Conditioning Engineers handbooks for equipment guidelines (www.ashrae.org). The proper amount of exhaust airflow must match the requirements for the cooking equipment situated under the hood. Airflow verification with a test and balance procedure should be performed during a project’s commissioning process to solidify hood safety.

-Tips: Check in with the kitchen designer periodically throughout design to make sure kitchen equipment needs haven’t changed drastically. Include hood size and exhaust air in the discussion. Hoods should overhang grills by a minimum of 18 inches.

3. Energy Conservation.

-Challenge: Most older kitchens have no way to control makeup-air or exhaust-air volume. Hood exhaust fans continuously operate at full capacity, whether or not they’re being used, and hot makeup air is transferred constantly into the kitchen space.

-Solution: It’s so simple that it works. Turn the hoods down when you’re not using them. Depending on the equipment manufacturer, hoods can operate at as little as 30 to 50 percent when cooking is not being done. This turndown can be achieved by a high-low switch that is adjusted manually by kitchen personnel or through automated controls. Automated systems use smoke and temperature sensors in the ductwork to automatically reduce hood fan speed. Similarly, makeup air also can be controlled to increase or decrease proportionally, further lowering energy usage.

-Tips: Specify smooth radius elbows (as opposed to square radius elbows) and check to make sure that fire protection piping doesn’t block the hood exhaust inlet will optimize fan energy.

4. Cost-Effectiveness.

-Challenge: Constant-volume ventilation systems waste energy and elevate operational expenses unnecessarily. Note: Today, many universities require individual buildings or departments to monitor their own energy consumption. In some cases, these departments must pay said energy bills out of their budgets. This factor has heightened accountability for the kitchen staff and points out the need to educate workers and emphasize conservation.

-Solution: HVAC fan energy costs can be reduced by as much as 50 percent when switching to a variable air volume (VAV) displacement system. This system will enable variable control of air volume to match real demand. More robust equipment such as dual-path air handlers, hood controls and exhaust fans are needed and will increase first cost. However, depending on the systems installed, payback for a VAV system vs. the traditional constant volume system can be as short as just two years.

5. Heat Recovery.

-Challenge: Smoke and heat generated in the kitchen traditionally is exhausted out of the building. Energy is wasted, and an opportunity is lost to conserve environmental resources and cost.

-Solution: Thanks to technology, heat recovery can be employed when using kitchen heat-only hoods. (When using grease hoods, heat recovery is not cost-effective or recommended). As much as 50 percent of the heat leaving the kitchen’s hoods can be recovered via coils and run-around loops or energy recovery wheels to preheat air entering the air handler during the winter. Recycled heat also can be used to preheat the domestic water, which is distributed throughout the facility year-round.

When specifying HVAC systems and equipment for the university kitchen, consider the following factors: life-cycle cost analysis, maintenance complexity, equipment life span, controllability, flexibility and operating cost every step of the way. From occupant comfort to hood safety and energy conservation to cost-effectiveness, today’s HVAC systems design can meet any institution’s kitchen sustainability and budgetary goals.

Related Video

A video from the University of Illinois showcases its newest residence dining hall and its use of sustainable practices.

Sidebar: 21st-Century Campus Cafe

The University of Illinois at Urbana-Champaign served up a big change last year with its Pennsylvania Avenue Residence (PAR) Dining Hall makeover and expansion. With average kitchen temperatures above 100ºF and smoke bellowing out the side of the grease hoods, an HVAC systems renovation of this 1960s dining hall was imperative.

The first HVAC system option the university considered would update existing HVAC equipment, providing a single path air handler, to serve above the ceiling with reheat coils and diffusers, delivering air at 55ºF to the kitchen and dining areas. The kitchen area hoods and associated makeup air would be constant volume and the dining areas variable- air volume. The second option would feature displacement ventilation, delivering low-velocity supply air at 65ºF directly to occupants in the kitchen and dining areas. Low-flow kitchen hoods that have VAV control with smoke and temperature sensors provide the ability to reduce exhaust air volume during high- and low-intensity cooking. The kitchen temperatures rarely exceed 80ºF, and all of the hood exhausts run an average of 50 percent of maximum.

Although the initial cost of these state-of-the-art systems is higher ($1.2 million for Option 1 and $1,512,000 for Option 2), a life-cycle cost analysis revealed an annual operational savings of almost 50 percent ($161,361 for Option 2, compared with $319,906 for Option 1). This reduction translates to a savings of 1.5 million in life-cycle operating costs over 20 years, with a simple payback of just two years.

Opening last year, the dining hall has a new look and feel that appeals to the 21st-century student, and features displacement ventilation with VAV hood design. Smoke and heat sensors are used to reduce exhaust hood flow during lighter operations. The dual-path VAV air handlers serve VAV boxes and diffusers mounted near the floor level and deliver 65ºF air at less than 40 fpm velocity. Measures such as long radius duct elbows and intelligent fan tracking controls save energy while providing optimal thermal comfort for the occupants.

Capalbo is a mechanical engineer at Environmental Systems Design, Inc., Chicago, and serves as a project manager, lead mechanical engineer and designer on various projects in the healthcare, laboratories, education, commercial and government market sectors. He can be reached at mcapalbo@esdglobal.com.

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