## 1 Introduction
He estimated that the conversion to an indirect solution would avoid 90% of refrigerant charge but would incur a 3% increment in energy consumption. He also performed an estimation of the total emissions of the system to the atmosphere. For the case of Sweden, for an indirect emission factor of 0.04 kg-CO\({}_{2}\):kWh\({}^{-1}\) emissions would be reduced by 74.0%, but considering the average indirect emission factor for Europe (0.51 kg-CO\({}_{2}\):kWh\({}^{-1}\)) the cut would be only 20.7% due to the increment of energy consumption of the indirect solution. Finally, [PERSON] et al. [13] simulated an R-404A multiplexed direct expansion system for MT and LT, the same system with N40A as the main refrigerant and a split system with N40 in direct expansion for LT and L40 with a loop of propylene-glycol/water mixture for MT. The use of the indirect solution, under a scenario of annual leakage rate of 10%, resulted in an 89% reduction of direct emissions regarding the R-404A system and of 65% using N40. They stated that the indirect solution would offer a good balance between indirect emissions and energy consumption for cold climates, with an average annual leakage rate of 10%, and for all climates if the annual leakage rate were 2% or below [13]. Regarding experimental comparisons, few research works have been found in the literature, mainly because of the cost and complexity of experimentation. You [14] analysed an experimental R-404A direct expansion system against an R-404A with a subcooler indirect system using Temper 40\({}^{\text{\textregistered}}\) as the secondary fluid. The system allowed for 88% charge reduction and 16.6% energy consumption reduction, but it must be highlighted that the primary system was different because the indirect solution incorporated a subcooling system. In addition, those systems operated with electric defrosting, measuring similar energy consumption in both solutions. [PERSON] and [PERSON] [15] presented the results of performance of a 3900 m\({}^{2}\) supermarket using an R-507A multiplexed direct expansion system against the same primary plant but with secondary fluid loops for MT and LT. In that plant, in which heat rejection was performed with an evaporative condenser, they measured a 4.9% energy consumption reduction with only 10% of refrigerant charge. They highlighted that the indirect solution could not be compatible with hot gas defrosting as electrical resistors were needed. [PERSON] et al. [16], under laboratory conditions, evaluated the energy impact of an R-134a/CO\({}_{2}\) direct cascade system against an R-134a-SF/CO\({}_{2}\) indirect cascade system. They measured an energy consumption increment between 7.6% and 14.0% when using a MT secondary loop with a propylene-glycol/water mixture and between \(-\)0.3% and 11.1% when using Temper \(-\)20\({}^{\text{\textregistered}}\). The other experimental works devoted to commercial indirect systems only focused on the performance of the system and not on the energy impact against a multiplexed solution [17; 18; 19; 20; 21]. As can be observed from the literature review, indirect system solutions always offer large reductions in refrigerant charge and thus direct emissions; however, depending on the system, the energy impact can be positive or negative. A possible way to adapt multiplexed direct expansion systems to the F-Gas Regulation is to reconvert those systems into indirect solutions; however, it is not clear what the real impact would be. Accordingly, this work aims to provide accurate information about the conversion process from a direct to an indirect system using the most used refrigerants in existing plants and to establish a reference to evaluate different options to adapt commercial systems to the new regulations. Here, the experimental results of conversion of an R-134a and R-507A direct expansion system to an R-134a-SF and R-507A-SF refrigeration system for MT application are presented.