Den energieffektiva kyldisken Monica Axell SP Per Fahlén CTH God morning ladies and gentleman. The title of my thesis is Vertical diplay cabinets in supermarkets Energy efficiency and the influence of the air flows

Försäljningen av kylda matvaror ökar Vanligt förekommande Stora kvantiteter mat på en liten butiksyta Stor öppen front är viktig för försäljningen

Energianvändning 5 m kyldisk använder lika mycket elektrisk energi som en eluppvärmd villa 100.000 m kyldisk i Sverige

Matvarornas kvalité Investigations of the temperature quality of chilled foods have shown that display cabinets are a weak link inthe chill chain. On the right side you see a display cabinet with cheeses, The highest permissible temperature is +8 °C. On the left side you see the same display cabinet. It is the result from measurement performed with an infrared camera. The temperature scale at the right side show that low temperatures are blue with increasing temperature the colour change to violet, red and so on. It is only the cheeses in the bottom shelf which have a correct storage temperature.

Mål Analysera kyldiskens energiflöden för att minska energianvändningen i vertikala kyldiskar med bibehållen eller förbättrad prestanda. Ta fram en laboratoriedisk med en ny typ av luftströmning som har en lägre energianvändning och en mindre temperaturskillnad mellan kallaste och varmaste matvara

System gräns These boundaries represent the interaction interfaces between the cabinet and the following two systems in the shop. The shop´s heating and ventilation system The shop´s refrigeration system The large open area at the display cabinet means that there will be a transport of heat and mass between the cabinet and its surroundings, despitethe presence of the air curtain in order to reduce this transport. An open vertical display cabinet is influenced by persons in the shop, the shop lighting the design of the HVAC system and the outdoor climate. The deisgn and operating conditions of the rerigeration compressor and the evaporator temperature depend on the cooling power requirement and the required incoming brine temperature. In turn the cooling power requirement depends on the design of the display cabinet, ambient conditions in the shop and the required storage temperature. In aother words the design of the refrigeration system is decided of the display cabinets connected to the system and it is the cabinet with lowest required inlet temperature of the brine which decide the evaporation temperature. The efficiency of the compressor increases with an increase in evaporation temperature.

Kyldiskens kylbehov Beror på följande parametrar: Kyldiskens konstruktion Omgivnings klimatet Högsta tillåtna varutemperatur The heat extraction is defined as the steady state coil capacity in balance with the cooling requirement of the cabinet. It is measured using the temperature difference of the brine and the flow rate of the brine. The heat extraction rate depends on following parameters: The design of the particular cabinet The ambient climate condition The highest permissible storage temperature

Energi balans The heat input as a result of conduction through the back is somewhat greater than the radiation heat input. However heat input as a result of radiation exchange with tha ambient, together with internal and external lighting, is aggreagated and acts on a small local area at the front of the cabinet where cooling is poorest. It can therefore be said that heat input from radiation , lighting has a relatively greater effect on the cooling requirement as they act on the warmest fooodstuffs in the cabinet. Therefore I have illustrated tihis by showing the sum of infiltration, radiation and lighting in the yellow bar with the red lines. Together they stands for more than 75 % of the total heat inputs to the cabinet.

Inverkan av omgivningsluftens entalpi på kylbehovet This figure shows the heat extraction for different specific enthaply in the ambient. The blue bar is daytime operation and the yellow bar is with open front covered. The necessary heat extraction rate is considerable lower during the nightoperation. The figure also indicates that there is a connection between the specific enthalpy and the cooling power requirement. But you shall note that cooling requirement is higher for the case with dry air and a temperature of 20 °C in the ambient than it is with a 15 dgress and a higher humidity even if the specific enthalpy is higher in this case.

Kylbehov som funktion av entalpiskillnad It is not until the necessary heat extraction rate is expressed with the enthalpy difference between the warm ambient and the cold air inside the cabinetthat a liear relationship is obtained. This is due to the fact that the thermal conditions in the cabinet must be changed in response to changes inthe ambient climate conditions.

Relativ inverkan av infiltrationen som funktion av omgivningsluftens entalpi T have performed energy balances for different climate conditions. A comparison of heat input due to infiltration with the heat extraction rate with the specific enthalpy in the ambinet air shows a linearly relationship. Also the growth of frost vary with the ambient condition. It is interesting note that the growth of frost has a relatively substantial effect on the efficiency of the air curtain.

Kyldiskens energiflöden: Slutsatser Infiltration → 65 % av det totala kylbehovet Infiltrationens relativa inverkan sjunker med sjunkande entalpi Effektiva luftridåer är viktiga för att minska inverkan av infiltrationen Strålning och belysning har också en relativt stor inverkan på kylbehovet Nattgardin minskar kylbehovet Sum conclusions from the analyze of the energy flows Infiltration accounts for 65 % The degree of infiltration falls with falling enthalpy The build-up of frost on the cooling coil is reduced if the dry bulb temperature falls while the moisture content is constant The build up of frost, therefore, is affected both by the moisture content of the surrounding air and by the surface temperature Both effective air curtains and efficient cooling coils are important in minimising the build-up of frost and the degree of infiltration

Inverkan av lastning

Målsättning för det nya konceptet Vertikal kyldisk Försäljningsapparat för att lagra matvaror vid rätt temperatur med minsta möjliga tillsats av energi Målsättning för det nya konceptet Klara temperaturkrav med minsta möjliga tillsats av energi Opåverkad funktion med varierad varumängd inne I kyldisken Opåverkad funktion när kunder plockar matvaror Undvika frosttillväxt i kylbatteri Maximal exponering av matvaror

Luftflöde och luftridåer: Syfte Analys av luftflödet i kyldiskar och luftridån för att beskriva de parametrar som påverkar: Värmetransporten från matvarorna Luftridåns stabilitet Luftridåns effektivitet

Värmeöverföring från matvarorna This figure illustrates the position of the warmest and the coldest item in a vertical display cabinet. The warmest packages is usually found in the front of some of bottom shelves.

Krafter som verkar på luftridån The vertical position where the air curtain tends to deflectinward depends on the momentum of the air being blown into the air curtain and the temperature difference between the cold interior and the ambient.

Luftridåns effektivitet Effektiviteten påverkas av: Luftridåns bredd vid inblåset Luftridåns höjd Hastigheten vid inblåset Turbulensintensiteten Luftridåns vinkel vid inblåset The efficency of the air curtain depends on The width of the supply opening The height The supply velocity The turbulence intensity The air curtain angle at the inlet The width, heigth and supply velocity has the greatest influence

Visualisering av temperaturfördelning The phenomena can be illustrated with this picture. The direction of the velocity from shelves is directed more and more outwards from the food from top to bottom. And it is in the lowermost shelves the cooling requirements are greatest.

Inverkan av höjd, bredd och inblåsningshastighet på luftridåns effektivitet H=800 mm H=535 mm H=300 mm The heigth, width and supply velocity has the greatest influence on the air curtain efficiency. For this reason I have performed a parameter study using three different two dimensional CFD model there I have varied the width of the air curtain and the supply velocity. The ambient temperature is 25 °C in order to create horizontal forces acting on the air curtain. The food is inactive blocks and the surface inside the cabinet is 0 in order to acieve a cold interior. The inlet is moved out from the shelf in order to study the ability of the air curtain to maintain the centerline. I have shown that air curtains in display cabinets today are sensitive for load varitions. The deflection modulus is low which means that the air curtain is flowing at front of the load. But it also means that it is a risk that the air curtain deflects inside the shelves if the lod is missing on the shelf and it is a risk that the function of air curtain is deteriorated.

Syftet med parameterstudien Undersöka vilka parametrar som påverkar: Kylningen av matvarorna Luftridåns stabilitet Lägsta kylbehov  Mest effektiva kombinationen

Luftflöde och luftridå: Slutsatser Det finns inget behov att tillföra kall luft i kyldiskens ryggparti där kylbehovet är minst Lastningen av matvaror i kyldisken påverkar såväl kylbehovet som temperaturen i matvarorna Luftridån måste sluta tätt och kyla matvarorna längst fram på hyllplanen En tjockare luftridå är mer effektiv än en tunn luftridå

Resultat Doktorsavhandling Nytt koncept för en kyldisk Luftridå Luftströmning Nattgardin Belysning Kylbatteri Fläktar

Finansiering Svensk Fjärrvärme Wica Cold AB FRICO AB REFCON AB AIA AB SP - Sveriges Provnings- och Forskningsinstitut This work has been performed financed by a Swedish national research programme effsys which is an abbrevation energy efficient refrigeration and heat pump systems. Swedish National Energy Agency Swedish District Heating Association FORMAS Wica Cold AB FRICO AB REFCON AB AIA AB And finally thank you for your attention