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13.2 Definition of high ambient temperature according to Kigali and countries covered Previous TEAP Task Force reports summarised the methods to assess the temperature conditions using the incidence of the number of hours, weather profiles, cooling degree days, or bin weather data. These methods are used for designing air conditioning and refrigeration systems utilising existing tables for most cities around the world, or for specifying components for safe operation at certain conditions (TF-XXVII/4, 2016). Montreal Protocol Parties (at OEWG-37, 2016) agreed to a definition of a “High Ambient Temperature Country” for a country that would have an incidence of at least two months per year over 10 consecutive years of a peak monthly average ambient temperature above 35°C. Countrywide values in the dataset applied (and decided by Parties at OEWG-37) are calculated by taking a spatially weighted average of all weather stations within that country. For the "Peak Monthly Average" temperature, according to the Kigali HAT definition (Decision XVIII/2), the weighted average temperature is derived from the daily highest temperatures, according to the Natural Environmental Council (NEC) of the United Kingdom are used (CED, 2011). These peak monthly average temperatures are checked over 10 years (2005–2014 for the latest available figures). For example, for each country, the peak average temperatures for the month of January during 2005-2014 are averaged to get the peak monthly average temperature for the January month. Exemption for Parties (countries) has been agreed upon where suitable alternatives do not exist for the specific subsector of use. This exemption allows for a delay in the HFC freeze date and initial control obligations by an initial duration of four years. The exemption so far applies to 35 countries (i.e., the following Parties): Algeria, Bahrain, Benin, Burkina Faso, Central African Republic, Chad, Cote d'Ivoire, Djibouti, Egypt, Eritrea, Gambia, Ghana, Guinea, Guinea Bissau, Iran, Iraq, Jordan, Kuwait, Libya, Mali, Mauritania, Niger, Nigeria, Oman, Pakistan, Qatar, Saudi Arabia, Senegal, Sudan, Syria, Togo, Tunisia, Turkmenistan and United Arab Emirates. 13.3 The high ambient issue-impact on capacity, efficiency and refrigerant selection As ambient temperatures increase, the application system heat load increases while the refrigeration system capacity decreases due to higher condensing temperatures. This is a normal thermodynamic issue, but will be much more accentuated with higher ambient temperatures. Similarly, condensing pressure and thus compressor discharge temperatures also increase, leading to higher risk of reliability problems (Li, 2014). This will impact the capacity of the system and reduce the efficiency of the system installed, which will lead to a higher energy consumption for the cooling capacity to be provided. The two key thermodynamic parameters that affect performance, particularly at high ambient temperatures, are the critical temperature and molar heat capacity (Domanski et al, 2000). At higher ambient temperatures and if no mitigation measures are taken some refrigerants will be operating too close to their critical pressure and the prescribed high pressure for good operation. Consequently, mitigation measures are taken to assure good operation if these refrigerants are used. Example: at 67°C corresponding to the maximum allowable pressure prescribed by EN378: • • HCFC-22 corresponding pressure is 2,760 kPa equivalent to 55% of its critical pressure; R-410A corresponding pressure is 4,347 kPa equivalent to 91% of its critical pressure. 256 2018 TOC Refrigeration, A/C and Heat Pumps Assessment ReportPDF Image | Heat Pumps Technical Options
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