Commercial kitchens are one of the most challenging designs a plumbing engineer will ever face. The design of the plumbing systems in a commercial kitchen is almost as complex as a hospital, but without the critical life support systems. Commercial kitchens come in many sizes and shapes from small restaurant or deli kitchens to large commercial kitchens preparing thousands of meals at a time. Large kitchens are typically found in casinos, hospitals, prisons, large schools, corporate headquarter dining facilities or other large buildings serving a number of people. These large kitchens typically have a head chef or dietician that prepares a menu and orchestrates the production of many meals.
Buried water pipe to island fixtures detail.
Food Service Consultants
When looking at the plumbing drawings for a large commercial kitchen, it is an impressive sight to see all of the plumbing and piping routing around the kitchen. The design portion of the project can be made much easier if a food service consultant is involved in the project from the beginning. It is not unusual to work on projects where the food service consultant was going to be part of a tenant finish-out package after the building was constructed, and we had to provide utility stubs to the kitchen for the future food service contract by a yet-to-be-named franchisee. In these cases, you need to plan and size the piping equipment for the worst-case scenario. Drains need to be deep enough for piping grease waste sloped at a 1/4" per foot slope to keep the velocity up in the grease waste pipes. When the drain locations are not confirmed, plan on the piping coming from the farthest corner of the space at a slope of 1/4" per foot. Sometimes the slab is not poured in the kitchen area when a tenant has not laid out equipment and associated drains. Water piping needs to be stubbed into the space with isolation valves and sized generously. Often when the hot water demands for a tenant finish space are not known, the water heater can be located in a mechanical space or janitor's closet within the kitchen space.
When a food service consultant is able to work on the project from the very beginning, they usually provide food service equipment layout drawings at the schematic and design development stages of the project. These drawings should give the plumbing engineer enough information to lay out the piping and size the water heater and grease interceptors.
The final submittal from the food service consultant usually has a food service equipment plan with all of the equipment identified with equipment tags. In addition to the equipment layout drawing, there are typically utility connection drawings for plumbing, ventilation and electrical connection to the kitchen equipment. Some food service consultants provide an equipment schedule on the drawings showing all the utilities and rough-in connection sizes to each piece of equipment. This will be included in the food service cut-sheet book, a binder containing all the manufacturer's catalog information, usually with a cover sheet for each item that lists the equipment identification number, utility connection information, capacities, physical dimensions and manufacturer model number information.
Concrete grease interceptor detail from a specific job. Intended only for reference.
I'll Have One Model Code, Please!
The one thing that is constant for all commercial kitchens is the fact that the requirements are different depending on where you are. I've worked on the plumbing design for many hyper-marts for several major retailers that had grocery stores attached to large retail stores. They had thousands of stores all across the country and were just entering the grocery market with their new super centers. We helped the owner develop criteria drawings that were the basis for all site-adapted stores, and then we site adapted stores for specific sites around the country. The stores were different sizes based on the local market, and they were oriented with left-handed and right-handed floor plan layouts. They had lease spaces across the front for small businesses like restaurants, banks, barbershops, optical stores, etc. The interesting thing we found was that when we crossed state lines, county lines, and even city limits, the health department requirements and plumbing code requirements were different from one jurisdiction to another. This caused significant revisions to the plans, depending on the jurisdiction. Some of the different requirements included:
- Venting requirements for sanitary drainage.
- Indirect waste requirements from food preparation and dishwashing sinks.
- Grease interceptor sizing requirements and location.
- What was allowed to, or required to, route to the grease interceptor.
- The height of the floor sink above the floor. (Some jurisdictions want floor sinks flush with the floor; others want them as much as four inches above the floor.)
- Some state health departments had water heater sizing requirements for food service establishments that greatly increased the storage and energy input requirements for water heaters.
- Food waste grinder discharge requirements (through the interceptor via a solids interceptor or bypass the interceptor).
- The number of hand wash sinks or the travel distance to hand wash sinks.
- The location of employee restroom facilities.
- Backflow prevention requirements for various pieces of food service equipment.
- Floor drain requirements.
- Water temperature requirements.
- The location of adjacent site utilities, including the domestic water size and pressure, and sewer size and invert elevations.
The electrical code requirements for the hyper-marts were the same for the whole country because the National Electrical Code is widely accepted. This made the electrical engineers' work a lot easier. The plumbing engineers needed a couple of weeks extra to do the health code and plumbing code research, make site utility revisions, adapt for code changes and issue drawings.
Probably one of the most elaborate kitchens I've worked on was for a major casino. Many of the new casinos feature numerous upscale restaurants in addition to large buffets or food courts. The amount of food service equipment for these facilities is impressive. They have practically every piece of food service equipment you could think of-steam kettles of all sizes, grills, ranges, fryers, Chinese ranges, tilting skillets, refrigerated equipment, serving lines, etc. At one casino, the facility engineer sent a sketch of a large concrete passive-type grease interceptor located outside of the building. It was larger than a boxcar! The sizing calculations used on that unit were based on past experience, which showed that a large interceptor was required due to the large quantities of greasy foods in the casino and the amount of time between pumping the interceptors. One casino even required a mechanical exhaust system with underground ducts connected to the grease interceptor and a flexible hose for the truck's pump exhaust. There was a switch on the wall of the loading dock that allowed the grease waste hauler to turn on the exhaust before opening the manholes to the interceptor. The exhaust system removed the odors when the lid was removed and the interceptor was being pumped. Apparently, they'd had an incident where the interceptor was located in a loading dock near the service doors, and when the interceptor was being pumped, it emitted such an odor that several customers at slot machines near the service doors became ill.
The one thing that is very inconsistent from jurisdiction to jurisdiction is the interceptor sizing and location. There are areas of the country where the interceptor must be outside because of the obvious concerns about the odor from cleaning an interior passive-type interceptor. Many of the jurisdictions require the exterior grease interceptor to be a minimum size of 750 gallons. There are no consensus standards for the concrete grease interceptors, so the designs vary greatly. Most are simply a concrete septic tank. It is important to note that concrete is a porous material that may degrade when exposed to grease and oils, so any time a concrete interceptor is used, it should be lined with epoxy paint or an asphalt coating. There are jurisdictions that do not allow exterior grease interceptors because they have had a lot of problems with grease coagulating in the piping before it gets to the grease interceptor outside. Still other areas require even larger exterior grease interceptors. Some locations require every fixture in the kitchen to drain through the grease interceptor, while other jurisdictions exempt the food waste grinder from the grease interceptor, and some require the interceptor to discharge through an interceptor after passing through a solids interceptor. Several jurisdictions have required that only the wash compartment on a three-compartment sink route through the interceptor. Some of the problems stem from the maximum size limitation in the ASME standard of 100 gpm flow rate for grease interceptors. Larger grease interceptors have been rejected in some jurisdictions because the larger units are not listed to the ASME standard.
I recently worked on a kitchen renovation for a large college where the floor sinks, trench drains and other kitchen area floor drains needed to flow through a grease interceptor. The kitchen was located in the interior of a building that was almost a half-mile long and a quarter-mile wide. The invert elevation of an adjacent existing sewer inside the building and the extremely long distance to any exterior wall did not allow for a remotely located grease interceptor. The solution was to use a large grease interceptor with a GRD (grease removal device) located in a pit under a nearby storage room. The GRD automatically removes the grease from the interceptor, thus reducing the maintenance on the individual unit. In this installation, the grease and oil went into a small holding sump inside the pit where it was pumped through an underground heated hose inside a pipe sleeve to a remote barrel at the loading dock. The grease interceptor pit had a solids interceptor prior to the interceptor that removed the solids from the waste stream, ground them up through a grinder pump and discharged them to the outlet of the interceptor. This was a system requiring little maintenance besides changing the grease barrel at the loading dock at proper intervals, and periodic inspection and maintenance of the grease removal device.
Flexible gas connection schematic.
Kitchen Exhaust Hoods
Another area requiring additional plumbing engineering design considerations is the kitchen exhaust hood wash down system. These systems typically require a domestic hot water connection to the wash down system control panel where detergent is injected into the hot water. The hot water mixed with detergent is then piped to a series of spray nozzles in the kitchen exhaust hood and the associated exhaust duct. These systems require a significant hot water load, but they are usually used during off-peak hours. The hood typically has a drain that is piped down to a floor sink near one end of the hood. The water supply to the wash down panel needs backflow prevention in accordance with the local codes. This is typically a reduced pressure backflow preventer when a detergent injection pump is used.
A fabricated grease interceptor detail supplied by Josam Co.
Check with the local codes for specific backflow preventer requirements. Many manufacturers leave it up to the plumbing engineer to design a system with proper backflow prevention for a given application. Special consideration should be given to dishwashers, potato peelers, food waste grinders with a water supply connection, hose connections and ice machines.
There are local codes that require additional backflow prevention for various pieces of equipment. For carbonated beverage dispensers, for instance, all of the codes recognize the internal ASSE 1022 backflow preventer as an acceptable means of backflow protection. These backflow preventers are now included in all new carbonated beverage dispensers or dispensing systems.
Most codes prohibit a reduced pressure backflow preventer from being installed in a ceiling space. However, when a reduced pressure backflow preventer or vacuum breaker is used above a ceiling, a drain pan should be installed to catch any spilled water with indirect drainage to a nearby floor sink or drain.
Sizing the water heaters for a restaurant can be very challenging. There are numerous references for sizing water heaters serving food service equipment. The ASPE Domestic Hot Water Design Manual, the ASPE Databook, manufacturers' catalog sizing guidelines and some state health codes all have hot water sizing criteria. It should be noted that the model plumbing codes do not give sizing criteria for water heaters.
Be careful when sizing systems with hot and cold water hose stations for clean up. Experience shows that it takes approximately one tank of hot water to wash down the floors. In similar large facilities with different-sized water heaters, a study was done to determine how much hot water is used for washing down the cooking and food prep areas. Meters were installed on the water lines to the water heater, and the staff was not told of the study. It seems they washed down the floor until the hot water ran out. Where there was more hot water, they used more. Most food service equipment manufacturers list the hot water demands for their equipment. Large hot water users are dishwashers (especially conveyor type), hood wash down systems, hot and cold water hose stations and large pot sinks. Remember to research all of the hot water demands for your project and include them in your hot water load calculations. And be sure to retain your calculations in the project file folder. That folder may be the only thing that keeps you out of hot water.