Four Steps to Success
To succeed in today’s ultra-competitive quick-serve restaurant landscape, it’s vitally important that brands provide an inviting atmosphere for their customers. The primary focus is of course on the food, but customers also expect an exceptional experience from the moment they walk in the door. Restaurant designers have responded with updated lighting and quality finishes in the dining room, but research has shown that physical comfort is a key component as well. In fact, a 2014 Harvard Business Review article made the case that customers are willing to pay more when they’re comfortable. Comfort is also critically important for the team in the kitchen. It’s not surprising that studies have shown that a 10-degree rise in room temperature can drive productivity down 30%. The good news is that designing an HVAC system that provides a comfortable space is very straightforward and can be done without breaking the bank.
STEP 1 – Understanding the internal loads
To provide a comfortable environment for customers and team members, many designers target a temperature of 75oF (24oC) and 55% relative humidity. To achieve this target, you need to understand the internal heat loads in the restaurant – derived from the equipment, lighting, people, and the envelope. Once these are known, the designer can then calculate the capacity of the HVAC (Heating, Ventilation, and Air Conditioning) equipment required. It’s interesting to note that in most QSR’s the primary load in the dining room is from the occupants and in the kitchen from all the equipment. Having this understanding establishes the baseline for your HVAC and a starting point for your design.
STEP 2 – Optimize Outdoor Air
Fresh outdoor air is vitally important to a safe and healthy HVAC design and is a key component of CDC and ASHRAE guidance for COVID mitigation. All retail establishments need outdoor air to meet ASHRAE ventilation requirements. What makes restaurants unique is that they also need outdoor air to balance the air exhausted from cooking. In a typical QSR, the amount of outdoor air needed to balance the cooking exhaust far exceeds the ASHRAE requirements and may exceed the COVID mitigation recommendations too. This is a good thing from a health perspective but can compromise comfort and result in a significant energy penalty. The goal, therefore, is to provide the proper amount of outdoor air but not to go overboard.
Comfort for customers and team members is critically important and outdoor air is the biggest source of comfort issues in the kitchen. It’s often believed that outdoor air provided in a plenum near the exhaust hood will immediately be sucked out of the hood and, therefore, doesn’t need to be conditioned. Unfortunately, models and field demonstrations have shown this is not the case. While a portion of this air is immediately exhausted, a significant amount mixes with the air in the space and creates a hot, humid kitchen. Additionally, this outdoor air behaves differently during the winter versus the summer. For this reason, it’s recommended that all outdoor air be conditioned to space-neutral conditions before being introduced into the kitchen.
In addition to causing comfort issues, excess outdoor air also drives up energy costs. The HVAC system is typically the second largest user of energy in a QSR behind only the kitchen cooking equipment. It routinely accounts for 25% – 40% of a restaurant’s total energy bill. If not properly managed, conditioning the outdoor air can account for up to 40% of the total HVAC energy usage.
To improve comfort and minimize energy cost, it’s obvious that the most important goal of any restaurant HVAC design is to optimize the amount of outdoor air required. And the best way is to specify a high-efficiency exhaust hood system – because every bit of air that is reduced from the exhaust is also reduced from the outdoor air. The techniques to optimize a hood design are well documented. They include but are not limited to, using a backshelf hood when possible, adding side panels on each end of the hood, and increasing the front overhang. Other proprietary hood technologies are available that have been demonstrated to reduce exhaust flow rate. Before choosing a hood supplier, ensure they provide third-party validation of any technologies they propose.
It’s also important that your hood supplier sizes the exhaust flow based on the heat load of your cooking appliances rather than simply using a rule of thumb such as cfm/ft. Sophisticated modeling software is available to properly size and minimizes exhaust requirements.
STEP 3 – Utilize RTU’s For Outdoor Air
Once the outdoor air volume has been optimized, the next step is to determine the most efficient way to introduce it into the restaurant. For QSR’s the ideal solution is to first bring as much outdoor air as possible through the existing RTU’s (Roof Top Unit) since they’re already there and available. Most RTU manufacturers recommend a maximum of 25% outdoor air as a percentage of supply air. The outdoor air introduced in the dining room can be transferred to the kitchen and exhausted out the hood. This not only utilizes the capacity of the RTU but also provides comfortable air for your customers and team.
In some cases, the RTU’s can provide all the outdoor air required. When that’s not the case, the remainder of the outdoor air needed to balance the restaurant can be provided through a small makeup air unit that conditions the outdoor air to space-neutral conditions.
Once all the sources for outdoor air have been designed, it’s important to keep air velocity near the hood at a minimum. High-velocity air from diffusers or a makeup air plenum can create a vacuum that pulls the heat plume and grease out of the hood. Therefore, it’s critically important to control the airflow and drafts around the cooking area.
STEP 4 – Properly Balance the Restaurant
A QSR should be designed so that the total amount of outdoor air exceeds the total amount of exhaust air by approximately 5%. This helps keep outdoor contaminants from being pulled into the restaurant. Additionally, to keep the odors and other kitchen contaminants from affecting the dining room, the kitchen should be designed to be negatively pressurized relative to the dining room. The outdoor air provided into the dining room will then be transferred into the kitchen.
HVAC systems or air handlers are not often at the top of the list in helping build a QSR’s brand image. However, providing a comfortable, inviting environment can be a tool for differentiating your brand for today’s customers and team members. Following these four steps can provide this inviting atmosphere at a price that you can afford.
Director of Chain Development, Halton Group
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Our recommended next article would be: It’s not the heat, it’s the humidity! Addressing comfort, space conditioning and make up air in commercial kitchens.
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