Exam 2020 07 03 Exercises solutions

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Department of Energy Politecnico di Milano Author Emanuela Colombo Pag.1 of 12 Date 11/07/2020 Milan, 24th June 2020 Exam – Advanced Thermodynamic and Thermoeconomics 03-07-2020 Total score: 21 points (exercise 1 roughly 2/3 of the total) Exercise 1. Let’s consider a domestic hot water (DHW) system based on renewable energy. The system consists of three main components. The first one is the solar thermal panel that collects the solar incident power and warms up a mixture of water glycol. Then, there is a heat exchanger that conveys the heat collected by the water -glycol mixture to the water of a secondary circuit that flows in a hot water storage. The storage component has an inlet directly from the main aqueduct and an outlet that is the delivery of hot water to the end- uses. End-uses are in general shower, bath tub and sinks. The system is supposed to work in a steady condition, storage level and mass flow rates are constant. Exergy values related to each stream are reported in Table 1. Consider that the overall costs are charged to each component according to the shares reported in Table 2. Recommendation: keep second digit accuracy when dealing with exergy streams. Consider that T0 and P0 are respectively: 288 K and 1 atm. Additional data: Solar thermal panel Heat Exchanger Storage 0 1 2 3 4 5 6 Table 1 State Exergy [kW] 0 Solar Irradiance 15.00 1 Water-Glycol Inlet 916.06 2 Water-Glycol Outlet 918.21 3 Storage Inlet 1.33 4 Storage Outlet 0.16 5 Water from aqueduct 0 6 Hot water to end-use 0.64 Table 2 Total Cost of Investments [€] 15000 Total cost of Operation & maintenance [€/y] 300 Solar thermal panel [%] 55 Heat Exchanger [%] 15 Storage [%] 30 Interest rate on capital [%] 3 Plant operative lifetime [years] 15 Load factor [-] 0.4 FIGURE 1. PLANT CONFIGURATION…