Keywords:Modeling Experimental Scroll Screw Piston Roots Volumetric Expander ORC a b s t r a c tThe aim of this paper is to facilitate the selection of the expander for a small-scale organic Rankine cycle based on an experimental comparison of a piston, a screw, a scroll and a roots expander. First, based on a literature review, a comparison between these four technologies of volumetric expansion machines is performed. Afterward, four displacement expanders [2e4 kW] are tested on two similar small-scale ORC unit with fluid R245fa. The maximum effective isentropic efficiencies measured are 53% for the piston expander and the screw expander, 76% for the variable-speed scroll and 48% for the roots machine. However, these performances do not reflect the highest efficiencies achievable by each expander: the test-rig presents experimental limitations in terms of mass flow rate and pressure drop (among others) that restricts the achievable operating conditions. The calibration of semi-empirical models based on the measurements allows to overcome this issue and to predict the isentropic efficiency in optimal conditions despite the limitations of the test-rigs. Based on experimental results, extrapolated prediction of the semi-empirical model and practical considerations, some guidelines are drawn to help the reader to select properly a volumetric expander.

This paper tackles the issue of frost formation in air-to-air heat recovery devices dedicated to single room ventilation by means of both numerical simulations and experimental approaches. In such heat exchangers, it is commonly known that the formation of a frost layer on the surface generates an additional thermal resistance and a flow section reduction, which leads to an overall degradation of the overall unit performance. This paper proposes a three-zone model, considering a dry, a wet and a frost zone, by determining the location of moving boundaries. Each zone is handled independently and the relative proportion of each zone is determined by means of the exchanger wall temperature. Besides this frost model, a defrost model is also envisaged. Once validated with experimental data collected on a U-flow-type heat exchanger, the developed model is used to implement different strategies to reduce or prevent frost formation in the exchanger. Based on three different criteria, these strategies are compared with each other to evaluate their benefits and drawbacks. The criteria give information on the energy efficiency of the ventilation, on the air renewal quality and on the pressure balance between the inside and the outside of the building.

The present paper describes the design improvement of a single-room ventilation unit. This ventilation system presents many advantages, however, several drawbacks exist. The first one is the acoustic disturbance. As the facilities are directly installed within the rooms, the fans' noise may create discomfort. Furthermore, in the cold or temperate climates, condensation or frost may appear. A dedicated management should then be implemented. Finally, as the system is not centralized, communication between the different units is required to ensure the global system efficiency. A team of several industrial partners and research institutes tackles the above-mentioned issues in the frame of the "Silenthalpic" project. The project is split in three major tasks. To correctly reduce the sound emission level (i), a spectral analysis of the noise emitted by an existing unit was undertaken, revealing that frequencies under 1 kHz are mainly responsible for the noise disturbance. From this analysis, active and passive solutions for noise reduction are envisaged, showing encouraging trends. The next research aspect is the exchanger of the ventilation unit (ii). The constituting material is a new porous membrane allowing the humidity transfer (vapor or liquid). This specific exchanger is numerically modelled to predict its performances. The last considered problematic is the optimization of the ventilation and control strategies for the specific case of decentralized units (iii), taking advantage of sensors and recent communication technologies like IOT (Internet Of Things) to establish communication between decentralized units and ensure their consistent control. The association of the three aspects presented here should then lead to versatile and efficient ventilation systems.