Experimental investigation of a direct driven radial compressor for domestic heat pumps J. Schiffmann a, *, D. Favrat b a Fischer Engineering Solutions AG, Birkenweg 3, CH-3360 Herzogenbuchsee, Switzerland b Ecole Polytechnique Fe ´de ´rale de Lausanne, EPFL STI IGM LENI, Station 9, CH-1015 Lausanne, Switzerland article info Article history: Received 13 April 2009 Received in revised form 1 July 2009 Accepted 16 July 2009 Published online 25 July 2009 Keywords: Heat pump Domestic application Centrifugal compressor R134a Design Compressor Simulation Performance abstract The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on two- stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept proto- type with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a. ª 2009 Elsevier Ltd and IIR. All rights reserved. Etude expe ´ rimentale sur un compresseur radial entraı ˆne ´ directement pour les pompes a ` chaleur re ´ sidentielles Mots cle ´s : Pompe a ` chaleur ; Application domestique ; Compresseur centrifuge ; R134a ; Conception ; Compresseur ; Simulation ; Performance 1. Introduction According to the IEA (2007) the worldwide energy fraction consumed by the residential sector accounts for 35% of the total energy consumption, out of which 75% are used for space and tap water heating, showing that domestic heating repre- sents a considerable share in the overall energy consumption. This share is considerably larger for colder climatic zones. * Corresponding author. Tel.: þ41 (0) 62 956 88 50; fax: þ41 (0) 62 956 22 00. E-mail address: juerg.schiffmann@fischerprecise.ch (J. Schiffmann). www.iifiir.org available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ijrefrig 0140-7007/$ – see front matter ª 2009 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2009.07.006 international journal of refrigeration 32 (2009) 1918–1928