1、15.1CHAPTER 15RETAIL FOOD STORE REFRIGERATION AND EQUIPMENTDisplay Refrigerators. 15.1Refrigerated Storage Rooms 15.11Refrigeration Systems 15.12Condensing Methods 15.16Heat Recovery Strategies . 15.18Liquid Subcooling Strategies . 15.19Methods of Defrost. 15.19Supermarket Air-Conditioning Systems .
2、 15.20N the United States, almost 200,000 retail food stores operateI their refrigeration systems around the clock to ensure propermerchandising and safety of their food products. Figure 1 showsthat supermarkets and convenience stores make the largest contri-bution to this total (Food Marketing Inst
3、itute 2004). In U.S. retailfood stores, refrigeration consumes about 2.3% of the total electric-ity consumed by all commercial buildings (EIA 2003). As shown inFigure 2, refrigeration accounts for roughly 50% of the electricenergy consumption of a typical supermarket (Arthur D. Little1996). Supermar
4、kets and grocery stores have one of the highestelectric usage intensities in commercial buildings, at 43 kWh/ft2peryear. Use for larger supermarkets with long operating hours hasbeen measured at 70 kWh/ft2per year (Komor et al. 1998).The modern retail food store is a high-volume sales outlet withmax
5、imum inventory turnover. The Food Marketing Institute (2004)defines a supermarket as any full-line self-service grocery storewith an annual sales volume of at least $2 million (Food MarketingInstitute 2004). These stores typically occupy approximately50,000 ft2and offer a variety of meat, produce, a
6、nd groceries. A newcategory of supermarkets, called supercenters, incorporates asupermarket section and a general merchandise/dry goods section inone building. Almost half of retail food sales are of perishable orsemiperishable foods requiring refrigeration, including fresh meats,dairy products, per
7、ishable produce, frozen foods, ice cream and fro-zen desserts, and various specialty items such as bakery and deliproducts and prepared meals. These foods are displayed in highlyspecialized and flexible storage, handling, and display apparatus.Many supermarkets also incorporate food service operatio
8、ns thatprepare the food.These food products must be kept at safe temperatures duringtransportation, storage, and processing, as well as during display. Theback room of a food store is both a processing plant and a warehousedistribution point that includes specialized refrigerated rooms. Allrefrigera
9、tion-related areas must be coordinated during constructionplanning because of the interaction between the stores environmentand its refrigeration equipment. Chapter 2 of the 2007 ASHRAEHandbookHVAC Applications also covers the importance of coor-dination.Refrigeration equipment used in retail food s
10、tores may bebroadly grouped into display refrigerators, storage refrigerators,processing refrigerators, and mechanical refrigeration machines.Chapter 16 presents food service and general commercial refriger-ation equipment. Equipment may also be categorized by tempera-ture: medium-temperature refrig
11、eration equipment maintains anevaporator temperature between 0 and 40F and product tempera-tures above freezing; low-temperature refrigeration equipmentmaintains an evaporator temperature between 40 and 0F andproduct temperatures below freezing.DISPLAY REFRIGERATORSEach category of perishable food h
12、as its own physical characteris-tics, handling logistics, and display requirements that dictate special-ized display shapes and flexibility required for merchandising. Also,the same food product requires different display treatment in differentlocations, depending on local preferences, local income
13、level, storesize, sales volume, and local availability of food items by type. Dis-play refrigerators provide easy product access and viewing, and typ-ically include additional lighting to highlight the product for sale.Open display refrigerators for medium and low temperatures arewidely used in food
14、 markets. However, glass-door multideck mod-els have also gained popularity. Decks are shelves, pans, or racksthat support the displayed product.Medium- and low-temperature display refrigerator lineups ac-count for roughly 68 and 32%, respectively, of a typical supermar-kets total display refrigerat
15、ors (Figure 3). In addition, open verticalmeat, deli, and dairy refrigerators comprise about 46% of the totaldisplay refrigerators (Faramarzi 2000).Many operators combine single- and multideck models in mostdepartments where perishables are displayed and sold. Closed-service refrigerators are used t
16、o display unwrapped fresh meat,The preparation of this chapter is assigned to TC 10.7, Commercial Foodand Beverage Cooling, Display, and Storage.Fig. 1 Distribution of Stores in Retail Food SectorFig. 1 Distribution of Stores in Retail Food SectorFig. 2 Percentage of Electric Energy Consumption,by U
17、se Category, of a Typical Large SupermarketFig. 2 Percentage of Electric Energy Consumption, by Use Category, of Typical Large Supermarket15.2 2010 ASHRAE HandbookRefrigerationdelicatessen food, and, frequently, fish on crushed ice supplementedby mechanical refrigeration. A store employee assists th
18、e customerby obtaining product out of the service-type refrigerator. More com-plex layouts of display refrigerators have been developed as new orremodeled stores strive to be distinctive and more attractive. Refrig-erators are allocated in relation to expected sales volume in eachdepartment. Thus, f
19、loor space is allocated to provide balancedstocking of merchandise and smooth flow of traffic in relation toexpected peak volume periods.Small stores accommodate a wide variety of merchandise in lim-ited floor space. Thus, managers of these stores want to display morequantity and variety of merchand
20、ise in the available floor space. Theconcentration of large refrigeration loads in a small space makesyear-round space temperature and humidity control essential.Product TemperaturesDisplay refrigerators are designed to merchandise food to maxi-mum advantage while providing short-term storage. Prope
21、r mainte-nance of product temperature plays a critical role in food safety. Anestimated 24 to 81 million people annually become ill from micro-organisms in food, resulting in an estimated 10,000 needless deathsevery year. As a result, in 1995 the Food and Drug Administration(FDA) Food Code recommend
22、ed a lower storage temperature forcertain refrigerated food products for further prevention of food-borne diseases. The FDA 2001 Food Code requires that the coretemperature of meat, poultry, fish, dairy, deli, and cut produce notexceed 41F throughout packaging, shipping, receiving, loading,and stori
23、ng (FDA 2001).Proper maintenance of product temperature relies heavily on thetemperature of air discharged into the refrigerator. Table 1 lists dis-charge air temperatures in various display refrigerators, althoughcompliance with FDA requirements may require different refriger-ator air temperatures.
24、 Figure 4 depicts a relationship between dis-charge air, return air, and average product temperatures for an openvertical meat display refrigerator. These profiles were obtainedfrom controlled tests conducted over a 24 h period. Discharge andreturn air temperatures were measured at the air grille. A
25、s shown, alltemperatures reach their peak at the end of each of four defrosts(Faramarzi et al. 2001).Product temperatures inside a display refrigerator may also vary,depending on the location of the product. Figure 5 depicts producttemperature profiles and variations for an open vertical meat displa
26、yrefrigerator over a period of 24 h. As shown, the lowest product tem-peratures are observed at the top shelf near the discharge air grille,and the highest product temperatures are at the bottom shelf near thereturn air grille (Gas Research Institute 2000).Display refrigerators are not designed to c
27、ool the product; theyare designed to maintain product temperature. When put into therefrigerator, merchandise should be at or near the proper temper-ature. Food placed directly into the refrigerator or into anotheradequately refrigerated storage space on delivery to the store shouldcome from properl
28、y refrigerated trucks. Little or no delay in trans-ferring perishables from storage or trucks to the display refrigeratoror storage space should be allowed.Display refrigerators should be loaded properly. Most manufac-turers provide indicators of physical load limits that define therefrigerated zone
29、. The product on display should never be loaded sothat it is out of the load limit zone or be stacked so that circulationof refrigerated air is blocked. The load line recommendations of themanufacturer must be followed to obtain good refrigeration perfor-mance. Proper refrigerator design and loading
30、 minimize energy use,Fig. 3 Percentage Distribution of Display Refrigerators, byType,in a Typical SupermarketFig. 3 Percentage Distribution of Display Refrigerators, by Type, in Typical SupermarketFig. 4 Selected Temperatures in an Open Vertical Meat Dis-play RefrigeratorFig. 4 Selected Temperatures
31、 in Open Vertical Meat Display RefrigeratorTable 1 Air Temperatures in Display RefrigeratorsType of FixtureAir Discharge Temperatures, FaMinimum MaximumDairyMultideck 34 38Produce, packagedSingle-deck 35 38Multideck 35 38Meat, unwrapped (closed display)Display area 36b38bDeli smoked meatMultideck 32
32、 36Meat, wrapped (open display)Single-deck 24 26Multideck 24 26Frozen foodSingle-deckc13cMultideck, openc10cGlass door reach-inc5cIce creamSingle-deckc24cGlass door reach-inc13caAir temperatures measured with thermometer in outlet of refrigerated airstream andnot in contact with displayed product.bU
33、nwrapped fresh meat should only be displayed in a closed, service-type displayrefrigerator. Meat should be cooled to 36F internal temperature before placing ondisplay. Refrigerator air temperature should be adjusted to keep internal meat temper-ature at 36F or lower for minimum dehydration and optim
34、um display life. Displayrefrigerator air temperature varies with manufacturer.cMinimum temperatures for frozen foods and ice cream are not critical (except for energyconservation); maximum temperature is important for proper preservation of productquality. Differences in display temperatures among t
35、he three different styles of frozenfood and ice cream display refrigerators are caused by orientation of refrigeration aircurtain and size and style of opening. Single-deck refrigerators have a horizontal air cur-tain and opening of approximately 30 to 42 in. Multideck, open refrigerators have a ver
36、-tical air curtain and an opening of about 42 to 50 in. Glass door reach-in refrigeratorshave a vertical air curtain protected by a multiple-pane insulated glass door.Retail Food Store Refrigeration and Equipment 15.3maximize efficiency of the refrigeration equipment, maximize foodsafety, and minimi
37、ze product loss.In actual applications, however, products may not always beloaded properly. Survey results (Faramarzi 2003) reveal thatimproper loading of products inside display refrigerators may fallinto the following categories:Blocked return air (products block the return air grille)Overloading
38、(products loaded beyond the load limit zones)Cavities (products loaded nonuniformly, leaving empty spots orvoids on the shelves)Blocked air curtain (products suspended in the path of air curtain)Extreme (combination of blocked return air, blocked air curtain,and overloading)Improper loading of the p
39、roducts can significantly affect maxi-mum product temperatures, which adversely affects food safety andproduct loss. Figure 6 depicts the consequences of various improperproduct-loading scenarios on maximum product temperature of anopen vertical meat display refrigerator (Faramarzi 2003).Additionall
40、y, packaging may also affect food temperatures. Thesurface temperature of a loosely wrapped package of meat with anair space between the film and surface may be 2 to 4F higher thanthe surrounding air inside the display refrigerator.Store Ambient EffectDisplay fixture performance is affected signific
41、antly by the tem-perature, humidity, and movement of surrounding air. Displayrefrigerators are designed primarily for supermarkets, virtually allof which are air conditioned.Table 2 summarizes a study of ambient conditions in retail foodstores. Individual store ambient readings showed that only 5% o
42、f allreadings (including those when the air conditioning was not operat-ing) exceeded 75F db or 0.0102 lb of moisture per pound of dryair. Based on these data, the industry chose 75F db and 64F wb(55% rh, 57.5F dew point) as summer design conditions. This isthe ambient condition at which refrigerati
43、on load for food store dis-play refrigerators is normally rated.Store humidity is one of the most critical variables that can affectperformance of display refrigerators and refrigeration systems. Storerelative humidity may depend on climatic location, seasonalchanges, and, most importantly, on the s
44、tore dehumidification orHVAC system.Figure 7 shows an example of the relationship between refrig-erator condensate and relative humidity. The increase in frostaccumulation on the evaporator coils, and consequent increase inFig. 5 Product Temperature Profiles at Four Different Locations Inside a Mult
45、ideck Meat Refrigerator(Average Discharge Air Temperature of 29F)Fig. 5 Product Temperature Profiles at Four Different Locations Inside Multideck Meat Refrigerator(Average Discharge Air Temperature of 29F)Fig. 6 Comparison of Maximum Product Temperature Varia-tions Under Different Improper Product L
46、oading Scenarios inan Open Vertical Meat Display RefrigeratorFig. 6 Comparison of Maximum Product Temperature Variations Under Different Improper Product Loading Scenarios in Open Vertical Meat Display RefrigeratorTable 2 Average Store Conditions in United StatesSeasonDry-BulbTemperature,FWet-BulbTe
47、mperature,FPoundsMoisture per Pound Dry Airrh,%Winter 69 54 0.0054 36Spring 70 58 0.0079 50Summer 71 61 0.0091 56Fall 70 58 0.0079 50Store Conditions Survey conducted by Commercial Refrigerator Manufacturers Asso-ciation from December 1965 to March 1967. About 2000 store readings in all parts ofthe
48、country, in all types of stores, during all months of the year reflected the aboveambient store conditions.15.4 2010 ASHRAE HandbookRefrigerationcondensate weight, is more drastic for open vertical display re-frigerators. In other words, open vertical fixtures demonstratemore vulnerability to humidi
49、ty variations and remove more mois-ture from the ambient (or store) air than other types of display re-frigerators (Gas Research Institute 2000).Increased frost formation from higher relative humidities in-creases latent load, which the refrigeration system must remove(Figure 8). Additional defrosts may be needed to maintain the prod-uct at its desired temperature.When store ambient relative humidity is different from that atwhich the refrigerators were rated, the energy requirements forrefrigerator operation will vary. Howell (1993a, 1993b) concludesthat, compared
