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Session: Poster session
Session starts: Tuesday 13 October, 13:30

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Violette Mounier (EPFL)
Jürg Schiffmann (EPFL)

Abstract:
Vapor compression cycle heat pumps driven by thermal engines such as organic Rankine cycles (HP-ORC) are able to provide both heating and cooling for domestic applications for a large set of heat sources. Recently, an oil-free Compressor-Turbine Unit (CTU) in a HP-ORC has been investigated in which both the radial ORC turbine [1] and the radial heat pump compressor are running on the same gas bearing supported shaft [2]. The radial compressor and the radial inflow turbine have tip diameters of the order of 20 mm. The CTU has been tested at rotor speeds in excess of 200 krpm with shaft powers up to 2.4 kW. The compressor and the turbine were operated at pressure ratios of up to 2.8 and 4.4, while reaching isentropic efficiencies in excess of 70%, thus validating the concept based on small-scale turbomachinery[3]. Based on reduced order models, a study has been conducted to investigate the feasibility of the HP ORC system using an optimized CTU running with different working fluids and with different operating conditions. The effect of a regenerator and of the turbine inlet pressure has been investigated. The results reveal that HP-ORC systems can achieve a theoretical COP up to 2.11 and exergetic efficiencies up to 80% with R134a working fluid for an heating capacity of 40 kW, a sink temperature of 35 °C, an inlet turbine temperature of 180 °C and an evaporation temperature of 7 °C while preliminary experimental results [4] show COP up to 1.55 and exergetic efficiency up to 41%. It turns out that these cycles are of great interest since they are highly flexible, offer a wide operation range and can run on low GWP, hazard less fluids. Since heating power has a direct impact on the CTU-unit the scaling effects on the turbomachinery design and on rotor speed are investigated and presented in this article.