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 1650 MJ/m2per year. Use for larger supermarkets with long operating hours hasbeen measured at 2710 MJ/m2per year (Komor et al. 1998).The modern retail food store is a high-volume sales outlet withma
5、ximum 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 approximately4650 m2and offer a variety of meat, produce, and
6、 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, peris
7、hable 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 operations
8、 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. Allrefrigerati
9、on-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 sto
10、res 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 refriger
11、ation equipment maintains anevaporator temperature between 18 and 4.5C and product temper-atures above freezing; low-temperature refrigeration equipmentmaintains an evaporator temperature between 40 and 18C andproduct temperatures below freezing.DISPLAY REFRIGERATORSEach category of perishable food
12、has 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 foo
14、d 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 refrigera
15、tors (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
16、to 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
17、Use Category, of a Typical Large SupermarketFig. 2 Percentage of Electric Energy Consumption, by Use Category, of Typical Large Supermarket15.2 2010 ASHRAE HandbookRefrigeration (SI)delicatessen food, and, frequently, fish on crushed ice supplementedby mechanical refrigeration. A store employee assi
18、sts the 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. T
19、hus, floor 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 me
20、rchandise 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.
21、 Proper 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 rec
22、ommended 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 5C throughout packaging, shipping, receiving, loading, and
23、storing (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 temperat
24、ures. 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 gril
25、le. As 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 d
26、isplayrefrigerator 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
27、 to cool 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 pr
28、operly 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
29、 zone. 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 lo
30、ading 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 Tempera
31、tures in Open Vertical Meat Display RefrigeratorTable 1 Air Temperatures in Display RefrigeratorsType of FixtureAir Discharge Temperatures, CaMinimum MaximumDairyMultideck 1.1 3.3Produce, packagedSingle-deck 1.7 3.3Multideck 1.7 3.3Meat, unwrapped (closed display)Display area 2.2b3.3bDeli smoked mea
32、tMultideck 0 2.2Meat, wrapped (open display)Single-deck 4.5 3.3Multideck 4.5 3.3Frozen foodSingle-deckc25cMultideck, openc23cGlass door reach-inc20cIce creamSingle-deckc31cGlass door reach-inc25caAir temperatures measured with thermometer in outlet of refrigerated airstream andnot in contact with di
33、splayed product.bUnwrapped fresh meat should only be displayed in a closed, service-type displayrefrigerator. Meat should be cooled to 2.2C internal temperature before placing ondisplay. Refrigerator air temperature should be adjusted to keep internal meat temper-ature at 2.2C or lower for minimum d
34、ehydration and optimum display life. Displayrefrigerator air temperature varies with manufacturer.cMinimum temperatures for frozen foods and ice cream are not critical (except forenergy conservation); maximum temperature is important for proper preservation ofproduct quality. Differences in display
35、temperatures among the three different styles offrozen food and ice cream display refrigerators are caused by orientation of refrigera-tion air curtain and size and style of opening. Single-deck refrigerators have a horizon-tal air curtain and opening of approximately 760 to 1070 mm. Multideck, open
36、refrigerators have a vertical air curtain and an opening of about 1070 to 1270 mm.Glass door reach-in refrigerators have 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, maxi
37、mize foodsafety, and minimize 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 ret
38、urn air grille)Overloading (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 overloadin
39、g)Improper loading of the products 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 (
40、Faramarzi 2003).Additionally, 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 1 to 2 K higher thanthe surrounding air inside the display refrigerator.Store Ambient EffectDisplay fixture perf
41、ormance is affected significantly 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 re
42、adings showed that only 5% of allreadings (including those when the air conditioning was not operat-ing) exceeded 24C db or 10.2 g of moisture per kilogram of dryair. Based on these data, the industry chose 24C db and 18C wb(55% rh, 14.2C dew point) as summer design conditions. This isthe ambient co
43、ndition at which refrigeration 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
44、, most importantly, on the store 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 Diffe
45、rent Locations Inside a Multideck Meat Refrigerator(Average Discharge Air Temperature of )Fig. 5 Product Temperature Profiles at Four Different Locations Inside Multideck Meat Refrigerator(Average Discharge Air Temperature of 2C)Fig. 6 Comparison of Maximum Product Temperature Varia-tions Under Diff
46、erent Improper Product Loading 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-Bul
47、bTemperature,CWet-BulbTemperature,CGramsMoisture perKilogram Dry Airrh,%Winter 20.6 12.2 5.4 36Spring 21.1 14.4 7.9 50Summer 21.7 16.1 9.1 56Fall 21.1 14.4 7.9 50Store Conditions Survey conducted by Commercial Refrigerator Manufacturers Asso-ciation from December 1965 to March 1967. About 2000 store
48、 readings in all parts ofthe country, in all types of stores, during all months of the year reflected the aboveambient store conditions.15.4 2010 ASHRAE HandbookRefrigeration (SI)condensate weight, is more drastic for open vertical display re-frigerators. In other words, open vertical fixtures demon
49、stratemore vulnerability to humidity 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. Howel
