A Truly Super Market (May 2000)
Remodeled supermarkets are becoming a very important part of this mature industry as prime locations are updated and expanded to meet increased sales volumes. Typically, remodeling happens every seven or eight years, depending on the supermarket chain. There are many potential advantages that enter into the remodel decision, including improved store sanitation, increased sales volume and product offerings, and improved traffic patterns. Over 1,000 new product offerings become available to the supermarket industry each week, so the competition and need for more shelf space is constant.
The average supermarket contains approximately 35,000 sq ft and can go as large as 260,000 sq ft. The main purpose of these facilities is to merchandise food product, much of which is perishable and must be refrigerated or frozen. The integration of the refrigeration system, store environment, and lighting must be coordinated to ensure maximized energy efficiency and reliability. Supermarkets consume approximately 4% of the total U.S. electric power usage. A typical annual power requirement for a supermarket represents 7% of the total cost of business. For an industry where a typical chain has a 2% to 4% profit income, this is a major expense.
Trends for supermarkets vary by geography, demographics, climate, market affluence, and available technical expertise. The ownership of certain key supermarket chains influenced by ownership from overseas also has a bearing on trends established in our domestic industry. The merchandisers working for supermarket companies are often most influential in selecting display case refrigerators, with very little regard to the energy consumption of these units. The supermarket’s primary responsibility, obviously, is to sell product. They want the best refrigeration display to accomplish this. Supermarket engineers and construction individuals have the responsibility to ensure that the display refrigerator is properly installed and can maintain product at appropriate temperatures. They also have the responsibility to ensure operation as well as reliability of these units.
Major trends that the industry currently faces include:
- Product safety;
- Energy improvement; and
These trends have taken on more importance in recent years. Considerations such as reliability and lowering first cost have been with this industry for quite some time and continue to be important.
New Safety StandardProduct safety has assumed a higher profile in the eyes of many supermarket chains and operators. In this case, product safety refers to product temperature of food in a display refrigerator.
The 1993 Federal Drug Administration Food Code combined vending machines, food service, and retail food stores into one comprehensive recommendation. This food code lowered the cold holding product temperature from 45˚F to 41˚F for a potentially hazardous product. Potentially hazardous products include meat, poultry, dairy, cut produce, etc. that are susceptible to food contamination due to higher temperatures. Although the food code has not been adopted by all state and local agencies, supermarket operators and owners have been following tighter controls to ensure proper product temperature is being maintained.
The 1997 FDA Food Code also included a change that equipment, in order to meet the sanitation requirements of the proposed Food Code, had to be American National Standards Institute (ANSI) approved. As a result of this recommendation, refrigeration display manufacturers began working with the National Sanitation Foundation (NSF) in developing its Standard 7 to include retail food store equipment. This modified NSF-7 standard will include materials, construction, design requirements, and a performance indicator to ensure 41˚ product temperature is maintained. The performance issue of temperature is based on the ASHRAE standard 72 and 117 — standards for testing commercial refrigerator display cases. The NSF-7 modified standard was released in December 1999.
Manufacturers are working diligently to certify their product to this new standard with a completion date of approximately January 2001. It is therefore assumed that many of the store operators will be looking for manufactured equipment that has the NSF-7 modified standard certification approval associated with its product. Typically, when a display case is defrosted, there is also a slight increase in temperature within the display case that may have an effect on product temperatures per ASHRAE test conditions. Manufacturers are working to reduce the impact of that temperature increase, thus ensuring that the product temperatures remain as stable and as consistent as possible throughout the display case. Other efforts to improve temperature distribution throughout the display refrigerator center on heat exchanger design as well as air distribution within the display case.
No Escaping Environmental IssuesAs it has for the past dozen years, the industry continues to spend significant resources in addressing important environmental issues. The issue first surfaced with the ozone depletion theory way back in 1974. The science that was required to support this was overcome by the political issues of the Clean Air Act, which phased out certain CFC refrigerants.
The supermarket industry has successfully phased out CFCs and are now currently using HFCs in the form of 404A as well as 507. HCFC-22 is also used, primarily in medium-temperature applications; however, there are still some supermarkets using this material on low-temperature applications as well.
Concerns over global warming are also putting pressure on choices available to the supermarket operators. With the possible exception of HFC-410A, there are very few refrigerant opportunities left for the supermarket industry. Between increased pressure from the northern European countries and additional purchases of U.S. supermarkets by companies headquartered in these areas, the interest in natural refrigerants is continuing.
Refrigerants such as ammonia and hydrocarbons, as well as carbon dioxide (CO2), are being investigated primarily in universities to determine acceptability in various applications. Ammonia applications (due to their toxicity) and hydrocarbons (due to flammability) will require the development of secondary fluids to keep these materials in a contained area away from the store shopping area. Medium-temperature applications using propylene glycol seem to be well at hand; however, additional work in low-temperature fluids continues to ensure maximum performance at an appropriate cost.
Secondary refrigerant systems are not commercially viable at this time, but many of the equipment manufacturers have, and continue to, supply secondary refrigerant to stores primarily for medium-temperature applications. Advantages of secondary refrigerant systems include better use of the display case refrigerator evaporator coil, keeps product quality high and improved product temperature throughout the display case, and quick and efficient defrost. Reduction in total system refrigerant change is also key.
Disadvantages for this system are higher first costs and decreased energy efficiency. As in any new application of technology, both costs and efficiency are being investigated to drive this possibly in to commercial applications for those that have a strong interest in reducing refrigerant charge. Secondary refrigerant systems can reduce the refrigerant charge by as much as 80%. Work continues on secondary refrigerant systems, supported primarily by the industry, as well as by universities and the federal government.
Other efforts to reduce refrigerant charge include reduced tube diameters on evaporators as well as condensing units associated with refrigerant systems. There are also manufacturers offering proprietary systems that reduce total system refrigerant charge by 25% to 40%. Work continues to reduce refrigerant requirements of supermarkets that in many applications take anywhere from 1,000 to 3,000 lb of refrigerant. Reductions of 20% to 30% refrigerant charge, are therefore, important factors in supermarket decision makers’ equipment selection.
In an effort to eliminate environmental risks, all manufacturers have instituted improved leak checking procedures in their manufacturing operations. Their designs have also eliminated flare fittings which have been notorious in allowing leaks to occur in systems, as well as reduced tubing connections with modifications involving design considerations.
Today large compressor systems utilizing semi-hermetic reciprocating compressors are still the major mechanical refrigeration system of choice. Over 85% of these applications utilize this type of compressor. These large mechanical refrigeration systems typically take the form of one or two systems for low- and medium-temperature applications each. They quite often are located in mezzanine areas in the supermarket where they can be grouped together and monitoring for leak detection is made quite easy. While semi-hermetic reciprocation compressors are used in more systems, screw and scroll compressor applications are increasing.
A system called “distributive systems” takes the form of a few different applications, depending on the manufacturer. One manufacturer offers these distributive units located in the store area close to the display cases, thereby reducing the amount of refrigerant charge by as much as 20%. Other manufacturers offer distributive systems that allow for location close to display cases with five or six of these units located strategically in the area above the display cases that they supply. Also key to these applications are the scroll compressor which allows for reduction in noise, vibration, and physical size.
What’s a TEWI?This is an issue that equipment manufacturers and suppliers have been working on continuously for a number of years. Most equipment manufacturers have redone their display case lighting to include remote electronic ballasts with small fluorescent tubes classified as T8 tubing. This has made dramatic reductions in the display case lighting requirements.
Work on product safety and temperature requirements will continue to improve energy efficiency, particularly in the area of defrost changes as well as better utilization of heat exchangers and improved temperature profile within the display case. The development and application of electronic controls to better hold tighter temperature requirements within a display case have also helped.
With electrical deregulation and the rise of energy service companies (ESCO), additional emphasis on improved efficiency has increased the acceptability of energy improvements with payback periods longer than the previously conventional 18 to 24-month range. With the high concentration of electrical use in supermarkets, this is an ideal target for ESCOs to direct their efforts in improving performance under various contract arrangements. Some applications of this new concept have not become fruitful for either party; however, the ESCO consideration will be constantly reviewed.
Manufacturers are working on proprietary projects to improve energy efficiency of compressor systems as well as display case applications. One major manufacturer offers a reduced head pressure system that has documented energy savings of 20% to 35%, depending on store location.
Many of the decisions involved in the environmental area, such as natural refrigerants, will require analysis regarding energy efficiency. The industry, along with its trade associations and various agencies, is looking at a concept called “Total Equivalent Warming Impact” (TEWI). TEWI is an equation that represents a numeric value for CO2 that includes both the total warming impact of the refrigerant being used as well as the impact of required electrical generation to supply the refrigeration affect.
The TEWI therefore includes a direct CO2 admission from the refrigerant leaking into the atmosphere as well as the direct portion of CO2 admissions required for the electrical generation at the specific energy efficiency of that equipment. There are issues associated with developing the TEWI equation which include the lifetime of the refrigerants in the atmosphere, the leak rate of the equipment over its life, as well as the materials used in generating the electricity whether it be coal, oil, gas, hydroelectric, etc.
The TEWI concept is the best way of determining both environmental and energy efficiency issues. There are store chains in the European market that use TEWI calculation for every store being constructed to ensure all the elements of CO2 generation are understood. A stronger effort to work with and embrace this concept is certainly needed in the United States.
Another area of energy improvement is attributed to the environment in which the refrigerated display cases operate. Manufacturers test and rate their refrigerated display cases per ASHRAE conditions at 75˚, 55% rh. Most stores are maintained at a temperature and rh below these levels. However, in areas of high humidity, conditions above 55% rh will cause increased moisture and frost accumulation inside the display case, thereby decreasing the performance of the unit and requiring increased defrost intervals or time.
In areas of high humidity concentrations, the dehumidification system is of particular importance and should not be overlooked in designing and constructing the supermarket envelope. A rule of thumb is that 1% efficiency gain of the refrigeration equipment can be achieved by a 2% rh reduction. So designing a facility to maintain 40% rh instead of 55% rh can yield a 7% reduction in refrigeration energy used.
The cost of running the dehumidification system is much more economical and cost-effective than having the additional burden on the refrigeration system.
Take-Out is Back InSupermarket owners and operators are looking for more convenience and sales opportunities, particularly in the area of “home meal replacements” or “heat-n-serve.” This requires flexibility in the merchandising aspect of refrigerated display cases, particularly where high-quality and precise product temperature are required, to ensure repeat sales as supermarkets compete with “take-out” restaurant service. The ability to use a display case for applications of product that may change between a noon product offering and a dinner one is of extreme interest to supermarkets. Also tied to these merchandising changes is the flexibility in being able to relocate display cases. A major chain in the Chicago area required a produce case that had previously been self-contained to be tied to a secondary loop system, allowing the display cases to be wheeled from one location to another and allowing flexibility with in-store trafficking as well as product offering.
Another rising concept is the availability of vacuum drain systems that allow supermarkets the flexibility of having refrigeration, electrical, and drain lines piped in from overhead. The challenges of integrating the overhead lines into the store architecture and design are significant, but certainly surmountable. The flexibility associated with overhead lines allows for refrigerated cases to be relocated or realigned in differing configurations. Also, the elimination of trenching in the supermarket, either during construction or remodeling, is a major incentive.
Another paramount trend is the elimination of machine rooms, along with taking the rack systems or the distributive systems with weather covers and enclosures and moving them appropriately either around the perimeter of the store or onto the roof of the store. This eliminates the need of a machine room dedicated to this type of equipment. It also allows for an extreme amount of flexibility in locating packaged and enclosed systems in the most appropriate location to eliminate noise and flexibility in access to and servicing of these units. ES