# Use of Phase Change Materials for Food Applications--State of the Art in 2022
## 2 Food Applications of PCM
### Food Storage and Transport
#### 2.2.6 Display/Retail Coolers and Freezers  
Like with any other application for storage of food, display/retail coolers and freezers are a storage compartment which is more or less well insulated, and has for temperature stabilization a cooling device, However, being for display/retail of food products they have different, quite specific conditions of use. First, to display the food the compartment is sometimes left completely open, in most cases however closed by a transparent window, thus not at all or at least not well insulated. Second, to allow a customer to take food out, even if there is a window it can be opened and is so for each product taken out. Finally, regularly a large amount of new product is brought in to fill the gaps, and often has to be cooled down. Consequently, compared to other applications for storage of food, the cooling power needs to be larger, and the frequency and magnitude of variations in the required cooling power also tends to be larger. Display/retail coolers and freezers are constructed in two ways, either to present products vertically, with food placed on shelves and display and food takeout to the front, typical for bottles and cans, or to present products horizontally, with display and food takeout to the top, typical for seafood like fish. These construction types have a large impact on options to integrate PCM and resulting advantages. Generally, like with any other application for storage of food, the use of PCM to store cold promises certain advantages. PCM could reduce temperature variations due to cooler on/off, including power outages and defrost cycles, and specific to display/retail coolers and freezers also during opening to take food out, and loading of new food including its cool down. Related is a reduction of the frequency and magnitude of variations in the required cooling power, and related wear down, sizing of the cooler, and energy consumption. If the amount of PCM is large enough, load shifting to off-peak electricity rates is possible. Altogether, the use of PCM promises significant advantages with regard to food quality, maybe equipment design and maintenance costs, and increasingly important regarding electricity cost. Ref. [50] made a review on R&D on cold TES by PCM in refrigeration systems, including PCM available as well as applications in food transport and packaging, commercial refrigeration, and various other refrigeration systems. Regarding equipment like small plug-in vending machines, display cabinets etc., the paper lists theoretical and experimental R&D, which comprises the PCM used, how the PCM is integrated, and the main resultson the effect the PCM has. The PCM used was mainly water/ice, and additionally some commercial paraffins for transition temperatures only a few \({}^{\circ}\)C above 0 \({}^{\circ}\)C. Integration of the PCM itself was in shelfs where products are placed, in air flow channels, into the cooler circuit or on its evaporator (where the cold produced is delivered). Typical results are that the use of PCM leads to a reduction in energy consumption, reduced compressor on-off, and a reduction in temperature fluctuations, specifically during defrost (even power failure), and peak compressor power reduction. The latter two should be specific to applications where openings to take food out are frequent, and also when new product is supplied uncooled and has to be cool down (for example bottled drinks). Ref. [51] lists several studies on open and closed display cabinets, experimental and numerical, the PCM, and the main observations. The PCM in those studies was water/ice as well as some commercial products, probably water-salt eutectics. The PCM was integrated in the air flow, shelf, or at the evaporator of the cooler, and observations were mainly on maintaining the temperature at times when the cooler is off. Ref. [48] also has a short passage covering R&D in this area. Ref. [52] describe specific experimental investigations on a display cabinet (empty), with water/ice as PCM, and integration in the evaporator of the cooler.