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Energies 2021, 14, 4103 14 of 28 and SH are considered during winter mode. While operating in summer mode, only DHW heating and AC cooling loads are included in the COP calculation. 3.5. Environmental Impact Evaluation The total equivalent warming impact (TEWI) assesses both the direct and indirect emissions of greenhouse gases related to the system. Direct emissions are due to refrigerant leaks and is a function of refrigerant GWP [kg CO2-eq·kg−1] and leakage rate, L [kg]. Indirect emissions are a product of annual electric energy consumption at each location, Ee, and the CO2 emissions associated with the process of electricity generation at each location, β [g CO2-eq·kWh−1]. The annual TEWI, TEWIannual, is defined in Equation (4). TEWIannual = TEWIdirect + TEWIindirect (4) TEWIdirect =GWP·L (5) TEWIindirect = Ee · β (6) The following values were applied in the analysis: • GWP of CO2 = 1. GWP of existing R134a AC system = 1430 [47]. • Annual leakage rate is assumed 15% of refrigerant charge for all systems [48]. • The charge of the CO2 systems is assumed to be 300 kg. The charge of the R134a system is assumed to be 2 kg134a·kWAC,max−1 [48]. • Emissions associated with electricity generation at each location is given according to country values (2019) as βStockholm = 12, βCopenhagen = 112, βTromsø = 19, βHelsinki = 89, βMunich = 350, βRome = 233, βAthens = 606 and βMadrid = 210 [49]. 3.6. Economic Evaluation In evaluating the proposed designs’ economic viability as retrofit solutions, both initial capital cost and operational costs are considered. Cost functions were applied for all major system components, i.e., compressors, heat exchangers and valves. Equipment costs were collected from the manufacturer catalogs for specialized components, such as the ejector and the combined air evaporator/gas cooler. Table 4 lists the capital cost functions applied in the economic analysis, which are applied for full load conditions. Table 4. Cost functions of various components [50–52]. Component Compressors with electrical motor Plate HX Fin-and-tube HXs Valves Receiver Ejector Capital Cost Function 10,167.5 × W ̇ 0.46 a 1397 × A0.89 a 119,500 b, * 114.5×m ̇a 1000 b 9000 b, * a Function given in $, b Function given in €, * From manufacturer catalog. Investment costs related to the secondary systems have not been considered, as the necessary components would already be in place during a retrofit. The cost of installation and additional equipment, such as the control system and piping, is assumed to be equal to 15% of the total capital cost of the system [53]. The Chemical Engineering Plant Cost Index is applied to adjust the original cost to the cost at reference year [54]. The annual average cost index (607.5) of 2019 is used as a reference. The cost of the components is adjusted according to the cost index as given by Equation (7) [55]. Cost at reference year = original cost × Index value for reference year (7) Index value for original yearPDF Image | Evaluation of Integrated Concepts with CO2 for Heating
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