Chilled and frozen retail display 235 Increased energy consumption of the refrigeration compressor. About 60% of electricity consumed in modern supermarkets is used by display cabinets for frozen and chilled foodstuffs, Decreased temperature in the store next to the cabinet. This is described Is thecold feet effectand can lead to temperatures as low as 10C ir he centre of refrigerated aisles. The are many variables affecting the efficiency of the air curtain, for The temperature difference between the chilled air and the store air The velocity of the air curtain The thickness of the air curtain The pressures either side of the curtain Obstructions in the path of the air curtain. Some cabinets use a dual air curtain which has an extra jet of air parallel to the first jet but on the store side. This jet has the same velocity as the first jet but the air is not refrigerated as it is taken from the store and is therefore at store temperature. The idea behind the dual air curtain is that there will be little entrain- ment between the two air jets as they are travelling at the same speed Therefore there will be little heat gain through the barrier between the two air curtains. The entrainment will take place at the interface between the second curtain and the store, and because there is no temperature differ ence between this jet and the store there will be no heat infiltration One of the difficulties of dual air curtains is getting them to stay together all the way down the front of the cabinet. As the first curtain is chilled will be forced downwards due to natural convection but this will not happen to the second curtain because it is not colder than the surroundings. 11.1.4 Cabinet development Getting the air curtain to work properly is critical to the correct operation of the cabinet. Temperatures of the food simulants inside the cabinet can be monitored within specified store conditions to see if the cabinets meet the required specifications. British Standard methods of test for commer- cial refrigerated cabinets are contained in parts 1-8 of BS 6148 with part 3 covering the determination of temperature. The determinations are carried out in a controlled environment corresponding to the climatic class of inter est. Temperatures are measured in M-packages, 50 x 100 x 100 mm pack- ages of a meat simulant, positioned at defined positions in the cabinet. Set positions are 150mm from the centre line and within 150mm of one end ith additional positions for large cabinets. The standard also states 'In ddition to these M-packages, two extra M-packages shall be located within he useful net volume so that the maximum and minimum test package• Increased energy consumption of the refrigeration compressor. About 60% of electricity consumed in modern supermarkets is used by display cabinets for frozen and chilled foodstuffs, • Decreased temperature in the store next to the cabinet.This is described as the ‘cold feet effect’ and can lead to temperatures as low as 10°C in the centre of refrigerated aisles. The are many variables affecting the efficiency of the air curtain, for example: • The temperature difference between the chilled air and the store air, • The velocity of the air curtain, • The thickness of the air curtain, • The pressures either side of the curtain, • Obstructions in the path of the air curtain. Some cabinets use a dual air curtain which has an extra jet of air parallel to the first jet but on the store side. This jet has the same velocity as the first jet but the air is not refrigerated as it is taken from the store and is therefore at store temperature. The idea behind the dual air curtain is that there will be little entrain￾ment between the two air jets as they are travelling at the same speed. Therefore there will be little heat gain through the barrier between the two air curtains. The entrainment will take place at the interface between the second curtain and the store, and because there is no temperature differ￾ence between this jet and the store there will be no heat infiltration. One of the difficulties of dual air curtains is getting them to stay together all the way down the front of the cabinet. As the first curtain is chilled it will be forced downwards due to natural convection but this will not happen to the second curtain because it is not colder than the surroundings. 11.1.4 Cabinet development Getting the air curtain to work properly is critical to the correct operation of the cabinet. Temperatures of the food simulants inside the cabinet can be monitored within specified store conditions to see if the cabinets meet the required specifications. British Standard methods of test for commer￾cial refrigerated cabinets are contained in parts 1–8 of BS 6148 with part 3 covering the determination of temperature. The determinations are carried out in a controlled environment corresponding to the climatic class of inter￾est. Temperatures are measured in M-packages, 50 ¥ 100 ¥ 100 mm pack￾ages of a meat simulant, positioned at defined positions in the cabinet. Set positions are 150 mm from the centre line and within 150 mm of one end with additional positions for large cabinets. The standard also states ‘In addition to these M-packages, two extra M-packages shall be located within the useful net volume so that the maximum and minimum test package Chilled and frozen retail display 235