Air reversing R744 conditioning system

Over the last years there has been a growing interest in air conditioning (AC) systems which apply the natural working fluid carbon dioxide (CO₂) as the refrigerant (R744). Experiments on prototype systems have demonstrated the competitiveness of R744 systems, and the automotive industry is now doing a commercial introduction. There is an increasing interest for different AC systems that can be reversed for heat pump (HP) operation. There are two possible ways of reversing the mode of such units, either the refrigerant flow is redirected or the air flow is reversed. The second choice will be the focus of this work. The performance of a small capacity prototype unit was measured in the climate chamber / HVAC test facility at SINTEF/NTNU Refrigeration and AC laboratories.Focus of the study is the system performance of the unit, including extreme operating conditions, i.e. from -20 °C to +52 °C ambient temperature. The system design and components is presented along with experimental results applied in a Life Cycle Climate Performance (LCCP) analysis; this analysis has been performed for different climate regions of the world.