Air conditioning represents one of the main energy loads in buildings submitted to a tropical climate. In La Reunion, a French overseas territory located in the Indian Ocean close to Madagascar and Mauritius, it accounts for 40 % of the whole electricity consumption of the Island. Evaluating the latter as well as the amount of the refrigeration capacity is not straightforward, especially during the early design phase. Generally, and for bad safety reasons, oversizing HVAC system (compressors, heat exchangers, pumps fans, …) is very common. It results in operating conditions far from the optimum and leads to unexpected high electricity consumptions. Moreover, nominal working conditions provided by manufacturers are not always representatives of real conditions, often depending on climate, building thermal inertia and building use. To face these challenges, Building Energy Modelling (BEM) is widely used in consultancies but suffers from requiring a quite good and accurate description of the intended chiller or split which is generally not selected at that step. What is aimed in this work is to present a simple phenomenological model suitable for any manufactured air conditioning machine and able to accurately evaluate refrigeration capacity and electricity consumption thanks to a very few numbers of parameters relative to the heat exchangers and to the compressor.