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The objectives of the present work is to theoretically and experimentally demonstrate the advantages of a two-stage cycle equipped with an economizer and single variable speed compressor for heat pumps using air as cold source. Furthermore, an efficient deicing device based on the two-stage concept is discussed in this paper. A two-stage cycle numerical model has also been developed allowing fast determination of the heat pump’s steady-state operating range as a function of the principal design variables. The experimental validation has been carried out using two successive heat pump biPAC1 uses a two-stage cycle with an economizer and a variable speed compressor with a mid-stage casing pressure (two scroll compressors, the first one with a 30 to 110 Hz frequency range). The second heat pump biPAC2 uses a two-stage cycle with a two-phase injection (limitation of the distillation effect of the non-azeotropic refrigerant in the economizer) for further optimization. Furthermore, another first stage compressor type has been used (piston compressor with a frequency range of 45 to 65 Hz) as well as a new evaporator with an enhanced tube surface and a new plat condenser. The experiments using the biPAC2 have resulted in a 70% increase of the condenser’s power and a 14% increase of the performance coefficient for an operating regime L-7/W50 with the HCFC 22 refrigerant. The good performances of the biPAC2 have been confirmed through further testing using HFC407C, the de-icing cycle and following the normalized test case EN255. These results have been compared to the three best commercial heat pumps. Two-stage cycle results show an excellent exergetic efficiency for the extreme temperatures (50% at L-10/W60). The simulations based on the experimental results are given for a temperature range between L-8/W50 and L-12/35 for typical household requirements (degrees-day of Zurich). the numerical simulations lead to an average annual performance coefficient (with de-icing) of 3.9 in a monovalent operation.