1、2011 ASHRAE 847This paper is based on findings resulting from ASHRAE Research Project RP-1402.ABSTRACT The objective of this project was to compare a typical openrefrigerated display case line-up to a typical glass-dooredrefrigerated display case line-up with the aim of quantifyingthe difference in
2、overall energy consumption and the differencein food product sales for each case type. For this research proj-ect, two supermarkets were identified as test sites: one super-market received a new, open refrigerated display case line-upand the other supermarket received a new, doored refrigerateddispl
3、ay case line-up. Per unit length of case line-up, the opendisplay case line-up consumed approximately 1.3 times moreenergy than the doored display case line-up. Comparison ofproduct sales between the open and doored display case line-ups showed that “doored versus open” had no effect on productsales
4、. Finally, the door opening duration data collected in thisstudy from the doored display case line-up validate the dooropening procedure used in the method of test described inANSI/ASHRAE Standard 72-2005 (ASHRAE 2005).INTRODUCTIONRefrigerated display cases are utilized by retail foodstores to store
5、 and display food products in a manner thatextends food shelf life and ensures food safety. Retail foodstores and supermarkets operate their refrigeration systemscontinuously to maintain proper food storage conditions, andthe continual operation of this equipment accounts for approx-imately 50% of t
6、he total electrical energy consumption of atypical supermarket (Westphalen et al. 1996). Clearly, anincrease in the energy efficiency of refrigerated display caseswill result in significantly reduced energy consumption andoperating cost of supermarkets.Infiltration accounts for over 70% of the refri
7、gerationload in open refrigerated display cases (Faramarzi 1999).Other contributions to the refrigeration load are minor incomparison and include radiation and conduction heat gain aswell as heat gain from lighting, fans, defrost, and anti-sweatheaters. Thus, reducing the infiltration into open disp
8、lay caseswill lead to a significant reduction in the overall refrigerationload, thereby reducing the overall energy consumption.One technique to reduce infiltration is to utilize refriger-ated display cases with glass doors. Under controlled labora-tory conditions, Faramarzi et al. (2002) found that
9、 installingglass doors on an open vertical refrigerated display casereduced the refrigeration load by 68%, resulting in an 87%reduction in compressor power demand. Furthermore, theaverage temperature of the food products was reduced by 6F.Thus, energy savings from doors may be achieved both fromthe
10、smaller cooling loads and from the ability to use higherevaporating temperatures to achieve the same product temper-ature. Therefore, a significantly large-scale reduction innational annual energy usage could be realized if the nationssupermarkets adopted the use of glass-doored refrigerateddisplay
11、cases. On a nationwide scale, DOE (2002) estimatestotal supermarket refrigeration energy usage is about 0.33quads/yr. Assuming that 80% of the nations supermarketsadopted the use of glass-doored refrigerated display cases, thesavings would be about 0.04 quads/yr. This savings would bea significant c
12、ontribution toward ASHRAEs goal of reducingsupermarket energy use by 30%.In addition to the infiltration energy savings, glass-dooredrefrigerated display cases offer several other advantages. Dueto their design, glass-doored vertical cases allow for moreComparison of Vertical Display Cases: Energy a
13、nd Productivity Impacts of Glass Doors Versus Open Vertical Display CasesB.A. Fricke, PhD B.R. Becker, PhD, PEMember ASHRAE Fellow ASHRAEB.A. Fricke is an assistant professor and B.R. Becker is a professor in the Civil and Mechanical Engineering Department, University ofMissouriKansas City, Kansas C
14、ity, MO.LV-11-018 (RP-1402)2011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is no
15、t permitted without ASHRAES prior written permission.848 ASHRAE Transactionsproduct facings using less floor space. Another benefit is that,due to the reduced refrigeration load of glass-doored cases, themedium temperature compressor rack size can be reduced byabout 15%, resulting in a lower first c
16、ost to the supermarket;however, doored cases are more expensive than open multi-deck cases. Glass-doored cases also improve food safety byreducing the wide variations in product temperatures that areobserved in open cases. Reduced product temperature rangescan bring about easier compliance with the
17、41F (5C) producttemperature requirements of ANSI/NSF Standard 7-2001(NSF 2001) and the FDA Food Code (FDA 2009). Doors alsoreduce cold air spillage into shopping aisles, resulting inincreased shopper comfort, which may translate into increasedsales. Furthermore, doors will prevent partial cooling an
18、ddehumidification of the store by the refrigeration system, thusallowing the HVAC system, which operates at a higher evap-orator temperature and COP, to cool and dehumidify the storemore efficiently. On the other hand, the capacity of the HVACsystem may have to be increased if the case credits for t
19、he opendisplay cases are eliminated.However, in spite of these advantages, the fear of a possi-ble reduction in product sales prevents supermarkets fromimplementing glass-doored cases (Walker et al. 2004). Unfor-tunately, the available information regarding the merchandis-ing productivity of display
20、 cases is vague and anecdotal.Thus, there is clearly a need to compare a typical openrefrigerated display case to a typical glass-doored refrigerateddisplay case. The objectives of this project were to quantify thedifference in overall energy consumption for each case typeunder actual operating cond
21、itions and to quantify the differ-ence in food product sales for each case type. By comparingthe advantages and disadvantages of medium-temperaturerefrigerated cases with and without doors, ASHRAE willencourage the supermarket industry to shift toward moresustainable options.Furthermore, the results
22、 of this study will be used to vali-date testing procedures given in ANSI/ASHRAE Standard 72-2005, Method of Testing Commercial Refrigerators and Freez-ers (ASHRAE 2005).TEST PLANThe following test plan was developed in an effort tocompare a typical glass-doored refrigerated display case line-up to
23、a typical open refrigerated display case line-up with theaim of quantifying the difference in overall energy consump-tion for each case type and the difference in food product salesfor each case type. For this research project, two supermarketswere identified as test sites: one supermarket received
24、a newdoored refrigerated display case line-up, and the other super-market received a new open refrigerated display case line-up.The general test plan for this project included a “before-and-after” comparison of selected product sales. An existingdisplay case line-up was identified in each store, and
25、 the salesdata of the products from that display case line-up werecollected for a period of approximately two months. The exist-ing display case line-up in each store was then replaced witha new display case line-up. Each new case line-up was thenstocked with the same products in the same location w
26、ithin thenew case, as they appeared in the old case line-up. The salesdata of these products from each new display case line-up werethen collected for a period of approximately two months.Thus, a comparison between sales data was made before andafter installation of the new display case line-ups to
27、determinethe effect that new case line-ups had on product sales.The products studied in the two supermarkets were differ-ent. In order to account for random and uncontrolled effects inproduct sales, sales data for all the test products were collectedfrom both supermarkets. Thus, sales data from one
28、supermar-ket were used as a control to adjust the sales data of productsstudied in the other supermarket (and vice versa).In addition, the energy usage of each new display caseline-up was monitored. Thus, comparisons could be madebetween the energy usage of a new open display case line-upversus that
29、 of a new doored display case line-up.Outline of the Test ProcedureA detailed outline of the test procedure used in this projectis given as follows:For Store #1:1. An old open case was replaced with a new glass-dooredcase.2. The new case was in the same location as the old case.3. The new case was s
30、tocked with the same product as theold case.4. The sales of the product were studied before and after thecase was replaced.For Store #2:1. An old open case was replaced with a new open case.2. The new case was in the same location as the old case. 3. The new case was stocked with the same product as
31、 theold case. 4. The sales of the product were studied before and after thecase was replaced. In both stores:1. The product studied in Store #1 was different than theproduct studied in Store #2, although sales data fromStore #1 were used to adjust the sales data of productsstudied in Store #2 (and v
32、ice versa).2. The arrangement of the product in the new case was asidentical as possible to the product arrangement in the oldcase, and both the old and new product arrangementswere recorded so that anomalies in sales data could becompared to any differences in the arrangements.3. The studied produc
33、ts were not duplicated elsewhere inthe store.4. The location of the case in Store #1 was different than thelocation of the case in Store #2. 2011 ASHRAE 8495. Energy consumption of the new cases was measured. 6. The “before-and-after” test in Store #1 occurred simulta-neously to the “before-and-afte
34、r” test in Store #2.Instrumentation PlanThe following detailed instrumentation plan was used todetermine the energy use and thermal performance of the newrefrigerated display case line-ups in each supermarket.Two pressure transducers and two thermocouples wereused to monitor the pressures and temper
35、atures of the refrig-erant entering and exiting the refrigerated display cases. Thepressure and temperature sensors were installed in the inletand outlet refrigeration lines as close as possible to the displaycase line-ups in an effort to comply with the specificationsgiven in ANSI/ASHRAE Standard 7
36、2-2005 (ASHRAE 2005),which states that the pressure and temperature sensors shouldbe no more than 6.1 in. (155 mm) from the refrigerated displaycase. A coriolis mass flowmeter was installed in the refrigerantline entering each display case to determine the refrigerantmass flow rate.Air discharge and
37、 return temperatures within the displaycase line-ups were measured with thermocouples. In addition,the surface temperatures of the evaporators within the displaycase line-ups were measured with a thermocouple mounted ona return bend of the evaporators and insulated from the airaround it.Electrical e
38、nergy consumption of the refrigerated caseswas determined through the use of kWh transducers. SeparatekWh transducers and current transformers were installed inthe electrical lines leading to the fans, lighting, and anti-sweatheaters to determine the individual electrical loads producedby these comp
39、onents.Shopper traffic at the new doored refrigerated displaycase line-up in Store #1 was estimated by the number of dooropenings. The number of door openings and duration weredetermined from the open/shorted status of contact switchesinstalled on each door. Customer traffic at the new, opendisplay
40、case line-up at Store #2 was monitored and recordedvia a surveillance video camera and a time-lapse videocassette recorder. The number of “reach-in” events, or thenumber of times a person reached into the case through the aircurtain to make contact with product in the case, was deter-mined by viewin
41、g the surveillance video.Store ambient dry-bulb temperature and relative humiditywere measured with a thermocouple and a humidity sensor.The temperature/humidity sensors were located near therefrigerated display case line-ups, sufficiently far from heatand cold sources, at an elevation of approximat
42、ely 10 ft (3 m),so as to measure the representative ambient conditions of thestore.Local outdoor dry-bulb temperature and relative humiditywere measured with a thermocouple and a humidity sensor.The temperature/humidity and sensors were located in such amanner as to minimize the effects of radiation
43、 from directsunlight.All measurements discussed above were recorded using aone-minute sample rate.Product sales for each refrigerated display case, as well astotal store product sales, were tracked with the aid of stockkeeping units (SKUs). For each week of the study, the follow-ing data were obtain
44、ed from the electronic point-of-salessystem in each supermarket, and exported to a file in commaseparated values (CSV) file format: the universal product code(UPC) of the product, a description of the product, the quantityof product sold, the actual sales price of the product, and theregular sales p
45、rice of the product.IDENTIFY AND SECURE TEST SITESFor this research project, two supermarkets were identi-fied as test sites: one supermarket received a new, dooredrefrigerated display case line-up and the other supermarketreceived a new, open refrigerated display case line-up. Thesetwo test sites w
46、ere large public supermarkets with footprints ofapproximately 25,000 ft2(2300 m2), located in the Midwest-ern United States. The two supermarkets were similarly situ-ated to ensure that climate, weather, time of year, andeconomic conditions of the shoppers were comparable. Test-ing was performed at
47、both stores simultaneously.Store #1Store #1 is located in Osawatomie, KS, a community of4600 people, which is located approximately 50 miles (80 km)south west of Kansas City, MO. Store #1 has average retailsales of $80,000 per week, and the store size is 23,000 ft2(2140 m2).Store #2Store #2 is locat
48、ed in Wamego, KS, a community ofapproximately 4000 people, which is about 10 miles (16 km)east of Manhattan, KS (pop. 50,000), and approximately 100miles (160 km) west of Kansas City, MO. Store #2 has averageretail sales of $140,000 per week and the store size is30,200 ft2(2810 m2).DISPLAY CASES AND
49、 PRODUCTS TO BE STUDIEDAt Store #1, it was agreed that dairy products, includingyogurt, prepackaged cheese, butter, and sour cream, would beused in this study. The dairy products initially resided in a 44 ft(13.4 m) open, multi-deck case line-up, shown in Figure 1a.This case was replaced with a new, medium-temperature, 20-doored case line-up, nominally 48 ft (14.6 m) in length, shownin Figure 1b.During the test period, sales of the selected dairy productswere monitored for a period of two months in the original caseline-up. The original open case line-up was then replaced with850 AS
