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and tends to increase heat exchanger size. Zeotropic refrigerants with glide also require special consideration of service practices that avoid composition changes resulting from separation and differential leakage of blend components. Other unique refrigerant parameters that chiller designers must take into account in choosing a refrigerant include heat transfer coefficients especially in large pool boiling evaporators and compressor discharge temperatures, particularly at low suction temperature or high ambient conditions. Heat recovery and heat pumping applications for chillers are increasing. A refrigerant’s performance in these higher-temperature conditions will be important for these applications. Another consideration is operating pressure level and the related need for pressure vessel code redesign Unlike small systems that predominately use coils, refrigerant cost is an additional important factor. Centrifugal chillers of an average size (e.g., 1400 kW) hold a refrigerant charge of the order of 500 kg. Refrigerant cost may be affected favourably by increased production volumes stemming due to higher use in new chillers, retrofits or other applications. 9.3.3 Energy efficiency considerations As noted previously in this report, in order to be acceptable, new refrigerants should result in products with energy efficiencies that are equal to or better than the refrigerants replaced. There are two major reasons. First, chillers are a major user of energy and customer demand for higher performance is ever-present due to the cost of energy. Additionally, there is pressure for higher efficiency products in most regions, including the Middle East, the Asia Pacific Region and many Article 5 countries, stemming from energy standards and government regulation. One example is ASHRAE 90.1-2016, “Energy Standard for Buildings Except Low- Rise Residential Buildings” (ASHRAE 90.1, 2016) widely used by building codes and regulations in the US. Secondly, there is a realization that global warming effect from chillers is dominated by their energy consumption over the life of the product. Total Equivalent Warming Impact (TEWI), Life Cycle Climate Performance (LCCP), and Life-Cycle Warming Impact (LCWI) models typically show that more than 95% of the climate effect is due to energy consumption, not direct emissions (Calm, 2006). As noted in the 2014 report, the direct global warming effects from refrigerant emissions are much smaller since direct emissions have been significantly reduced in recent years through lower charge systems, low-leak designs, manufacturing and testing improvements, and improved service practices. The use of higher performing refrigerants and the chillers that use them is more important to climate change than prematurely changing to another refrigerant with lower efficiency (Calm, 2002, Calm 2006). Additionally, the direct global warming impact from refrigerant emissions are significantly smaller today than 10 years ago, as manufacturers have been reducing direct emissions through low-leak designs coupled with manufacturing and testing improvements, and chillers requiring less refrigerant per unit of capacity. Customers can make confident, intelligent choices when efficiency alternatives are explored, considering the cost of energy and other economic factors that govern a project. Manufacturers typically offer an array of efficiency choices for any application. High confidence in chiller selection is achieved through rating standards and certification programs that exist in most countries. AHRI Standard 550/590 (AHRI 2015) and EN 14825 (EN, 2016 a) are among the rating standards in use when determining full and part-load performance. Chiller performance in many countries is verified by third party agencies who conduct performance tests to the appropriate rating and test standard. Furthermore, the annual energy consumption can be calculated with computer simulation programs using the chiller(s) load profiles, building loads, and weather data. For large and complex chiller systems, extensive modeling can provide systems and chiller solutions that minimize total energy consumption. Arguably the tools available to the 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 177PDF Image | Heat Pumps Technical Options
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