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stored between -26oC and -29oC, and some niche market products such as some types of sushi must be kept significantly colder, even down to -60oC, in order to retain product quality. Chilled produce is typically held between 0oC and 4oC, although fruit, bakery products and vegetables are stored between 8oC and 12oC. Some stores offer long term storage contracts, in order to stock produce until it is “out of season” and therefore more valuable. Stock may be held for months in these warehouses. Other sites provide marshalling facilities in order to restock supermarkets on a daily basis; in these plants the product is not usually in the building for more than 24 hours. The cooling load on such a building is high because of the amount of traffic through the temperature controlled chambers, although product load is typically low because the residence time is not long enough for the air temperature to have any appreciable effect on the product. 5.2.3 Industrial heat pumps and heat recovery Many industrial processes including brewing, dairies, food factories and chemical processes require large amounts of heat in addition to a cooling load. Even if the primary use of heat, for example for cooking food, cannot be achieved by heat pumps or recovery there may be many uses for lower grade heat, such as pre-heating boiler feed water or heating wash water for the production area. When the application is collecting and redirecting waste heat from a refrigerating system it is called heat recovery. When it is performing a non-productive chilling process on a source of heat, whether it is at ambient temperature or is the waste heat stream from another process such as a cooker flue, it is a heat pump. Large heat pumps have also been used for heating public buildings, for example in Gardermoen Airport, Norway (8100 kW heating capacity) and Akershus hospital, Norway (8000 kW heating capacity). These systems are custom-designed, using R-717 as the refrigerant (Stene, 2008). Even larger systems are used for district heating systems, with many examples in Scandinavia. The smallest of these systems are about 5,000 kW. Most installations use HFC-134a in centrifugal compressors, with some (up to 40,000 kW) using R-717. The largest is in Stockholm, with a total capacity of 180,000 kW (180 MW) using HFC-134a in centrifugal compressors. This system takes heat from sea water to provide the thermal source; other similar installations have used waste water from the sewage system (Bailer and Pietrucha, 2006). It is perceived that this market will have a large increase over the coming years as countries turn to low carbon heating, with natural refrigerants having a smaller market share of this market than the main industrial refrigeration market it can lead to an increase in HFO use in the coming years. Steam-fired absorption systems (as described in section 5.3.6) can be used to raise condenser water temperature in power plants to provide heat to district heating networks and some industrial processes. Absorption can also be used to boost the temperature of a proportion of a medium temperature process stream by cooling the remainder of the stream. In this way a small part of a stream at 70°C could be raised to 120°C by cooling the rest of the stream and rejecting its heat to atmosphere at, say, 35°C. 5.2.4 Leisure The principal use of refrigeration in the leisure market is for ice rinks, extended also to indoor ski-slopes, outdoor snow-making for ski slopes (some with water as refrigerant), ice climbing walls and other ice features. Many older ice rink systems used direct CFC-12 or direct R-717. To change to an indirect system would require replacement of the floor slab, which is a considerable capital expenditure. Some CFC-12 systems have been converted to HCFC-22 despite the increased pressure. Similarly, some R-717 systems in Central Europe have been converted to R- 104 2018 TOC Refrigeration, A/C and Heat Pumps Assessment ReportPDF Image | Heat Pumps Technical Options
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