  The aim of this work is to study heat pump cycles, using CO 2 based mixtures
as working fluids. Since adding other chemicals to CO 2 moves the critical
point and generally equilibrium lines, it is expected that lower operating
pressures as well as higher global efficiencies may be reached. A simple stage
pure CO 2 cycle is used as reference, with fixed external conditions. Two
scenarios are considered: water is heated from 10 {\textdegree}C to 65
{\textdegree}C for Domestic Hot Water scenario and from 30 {\textdegree}C to 35
{\textdegree}C for Central Heating scenario. In both cases, water at the
evaporator inlet is set at 7 {\textdegree}C to account for such outdoor
temperature conditions. In order to understand the dynamic behaviour of
thermodynamic cycles with mixtures, it is essential to measure the fluid
circulating composition. To this end, we have developed a non intrusive method.
Online optical flow cells allow the recording of infrared spectra by means of a
Fourier Transform Infra Red spectrometer. A careful calibration is performed by
measuring a statistically significant number of spectra for samples of known
composition. Then, a statistical model is constructed to relate spectra to
compositions. After calibration, compositions are obtained by recording the
spectrum in few seconds, thus allowing for a dynamic analysis. This article
will describe the experimental setup and the composition measurement
techniques. Then a first account of results with pure CO 2 , and with the
addition of propane or R-1234yf will be given.
