On substances that deplete the ozone layer
Commercial refrigeration 4.1 Introduction
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- 4.2 Applications
4 Commercial refrigeration4.1 IntroductionCommercial refrigeration is characterised by storing and displaying food and beverages at different levels of temperature within commercial stores with sales areas varying in size from approximately 10 m2 to 20,000 m2. The refrigerating capacities of equipment vary from hundreds of Watts to as high as 1.5 MW. Two main levels of temperatures are generated by refrigeration systems from around 0 °C to 8 °C for the conservation of fresh food and beverages, and around -18 °C for frozen food and ice cream. Globally, HCFC-22 continues to represent the largest refrigerant bank in commercial refrigeration and is used at all temperature levels. The most used HFC (blend) is R-404A for all temperature levels. For the past decade, HCs for low refrigerant charge systems, and CO2 for larger supermarket applications are increasingly used in many developed nations. In parallel, progress has been made to improve energy efficiency and leak tightness, especially for centralized systems. The progressive phase-out of HCFC-22 in developing countries requires making informed choices on the best replacement options. AHRI launched a Low GWP Alternative Refrigerant Evaluation Program (AREP) in 2010 (AHRI, 2013). A number of new blends based on HFC-1234yf and HFC-1234ze(E) as well as HFC-32 have been formulated to replace HFC-134a, HCFC-22, and R-404A. So, for the three groups of commercial refrigeration equipment, comparisons are now being made in order to select amongst the most energy efficient options with the smallest environmental impact due to refrigerant emissions. In commercial refrigeration, as in air-conditioning, high ambient applications require special consideration in selecting and designing components and equipment. However, designers of commercial refrigeration equipment choose components to design systems based on delivering the cooling required at the highest ambient condition. For moderate and cold climates it is an important option to recover heat from the refrigeration plant for heating purposes in the cold season. Considering the supermarket as an energy system for which energy use should be minimized may give considerable energy savings. The ozone depleting potential (ODP) and global warming potential (GWP) values of the alternates mentioned in this chapter are given in Chapter 2 of this report. 4.2 ApplicationsStand-alone equipment are self-contained refrigeration systems and comprise a wide variety of applications: ice-cream freezers, ice machines, beverage vending machines, and display cases. These systems are found not only in large commercial stores but also restaurants, convenience stores, mini supermarkets and gas stations. For developing countries, domestic refrigerating equipment, refrigerators, and freezers can be found in small shops and used for commercial purposes. Stand-alone equipment are increasingly used in developed countries in medium-size supermarkets because of ease of maintenance of the fully-welded circuit. In Europe, and lately in other markets, this choice is also often related with the use of hydrocarbons or CO2. Condensing units exhibit refrigerating capacities ranging typically from 1 kW to 20 kW. They are composed of one (or two) compressor(s), one condenser, and one receiver assembled into a so-called “condensing unit”, which is typically located external to the sales area. The cooling equipment consists of one or more display case(s) in the sales area and/or a small cold room. Condensing units are typically installed in specialty shops such as bakeries, butcher shops, and convenience stores. In a number of supermarkets, one can find a large number of condensing units (sometimes up to 20) installed side-by-side in a small machinery room. In most of the A5 countries, the use of systems using condensing units is very extensive. Condensing units are easily found in all countries through refrigeration equipment distributors. The global market of condensing units has a strong consequence in terms of refrigerant choices; they are developed based on the most used refrigerants: HCFC-22, R-404A, and HFC-134a. Centralised and Distributed systems are the preferred options in supermarkets. They operate with racks of compressors installed in a machinery room as in the case of a centralized system or several smaller racks installed in a machinery room or on the roof as in the case of a distributed system. Distributed systems may be thought of as multiple smaller centralized systems which lead to lower charge levels. A number of possible designs exist and will be addressed in Section 4.3 3. Two main design options are used: direct and indirect systems. Direct systems are the most widespread. The refrigerant circulates from the machinery room to the sales area, where it evaporates in display-case heat exchangers, and then returns in vapour phase to the suction headers of the compressor racks. The supermarket cold rooms are cooled similarly. In the machinery room, racks of multiple compressors are installed; these utilise common discharge lines to the air cooled condenser and common suction and liquid lines to the refrigerated fixtures. Specific racks are dedicated to low temperature and others to medium temperature. Each refrigerant circuit of each rack is independent. Supermarket centralised systems with long piping circuits have led to large refrigerant charges (100 to 3,000 kg depending on the size of the supermarket) and consequently to large refrigerant losses when ruptures occur. Studies have been conducted which show that low leak rates are possible to achieve in supermarket applications to less than half the typical values, some as low as 3.5% (EPA). Typical emission rates of small supermarkets vary between 15 and 25% and those of large supermarkets between 20 and 35%. These figures represent, in general, the situation of non-Article 5 countries. The emission rates for most of the Article 5 countries are much higher. Indirect systems are composed of primary heat exchangers where a heat transfer fluid - HTF (also called secondary refrigerant) is cooled and pumped to the display cases where it absorbs heat, and then returned to the primary heat exchanger. HTFs have been receiving interest because indirect systems allow for lower primary refrigerant charge and facilitate the use of flammable or toxic refrigerants when isolated from the sales area.
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