Chilled refrigerated display cabinets with open fronts rely on a fan-driven air curtain. This technology enables easy access for customers, while forming a barrier to the exchange of air. The aim of using the front air curtain is to minimise entrainment of the warm “moist” room air and protect the temperature of the products that are located at the front of the shelves. The air curtain is not perfect and causes entrainment into the chilled area mainly through turbulent mixing (Stribling, 1997). As the length of the air curtain increases, so does its temperature and its ability to keep product cold at the bottom of the cabinet. A longer air curtain requires a higher flow rate to reduce this problem. Short air curtains for open, vertical refrigerated display cabinets have been investigated by Hammond et al (2016) and Pitchers et al (2018), who reported a 36 and 25 % reduction in total energy consumption, respectively, compared to a display cabinet with a conventional curtain.
The work in demonstrator 10 is focusing on optimizing an advanced display cabinet based on best available technologies (BAT). These technologies include doors, short air curtains, proximity sensors, reflective packaging.
Figure 1: Future retail display (Short air curtain concept) at LSBU’s facilities).
A cabinet was adapted to incorporate short air curtain technology. This technology has been used for open fronted cabinets, however, there was still a considered potential for reducing energy consumption on cabinets with doors. Therefore, this cabinet had high efficiency doors fitted. Proximity sensors during door opening were simulated and reflective packages were tested. All tests were to the ISO/EN23593 test standard, which is used for Ecodesign energy labelling.
The cabinet used CO2 (R744) refrigerant (GWP=1) reducing GHG emissions from refrigerant leakage. This cabinet was optimised at the LSBU facilities such that it was within the M0 temperature classification (temperature range of only 4.2°C) at climate class 3 (25°C/60%RH). The EEI of 17.3 (Energy Class B) is class leading for a 2.5 m supermarket refrigerated display cabinet. The cabinet operated at a very warm evaporating temperature for an M0 cabinet (-2.8°C) limiting the need for defrosts.
Reflective packaging was simulated by covering the test packs in aluminium foil tape. Energy benefits were within experimental error (+/1%) when the cabinet was open fronted and therefore would be even less when the doors were applied. There were however benefits of approximately 1 K reduction in temperature of the warmest pack.
Proximity sensors which only turned the light on during the door opening time were found to decrease the EEI by 0.4.
Figure 2: Air flow in short air curtain concept.
