In this research sustainable refrigerants are tested as filler gases in Transparent Thermal Insulation (TTI) for the first time. These are compared with pig fat, a readily available material with good thermal inertia that is proposed as an organic phase change material (PCM). The aim of this paper is to compare the thermal behaviour of a Hybrid Air Conditioning System (HACS) with TTI filled with R134a, R1233zd and a pig-fat-based PCM. Numerical simulations using the OPAQUE 3 program and two online platforms are used to evaluate the possible application of TTI and PCM as passive systems. Additionally, three TTI models are used to simulate the heat transfer processes of TTI, PCM and R134a. The velocity of the flow in the air gap is also analysed numerically in both laminar and turbulent states. For the assessment, infrared thermographic imagery is used to measure the temperatures in the HACS, giving values of 46.17 °C by day and 38.05 °C at night. The results show that the heat loss and heat gain in the combination TTI filled with refrigerants and pig-fat-based PCM are between 2.22 and 1.51 W/m2. In addition, the HACS was able to keep a small box warm during the night. The flow in the air gap of the HACS can be controlled by installing Ni-Ti wire actuators with a cooling temperature of 23 °C and a heating temperature of 70 °C. The Ni-Ti wire actuators can open and close the dampers at 23 °C and 51 °C, respectively. By installing a 5-watt solar-power fan, the velocity of the flow in the air gap in the HACS can be increased, thus improving the efficiency of the system. In all the experiments, the pig fat proved to be suitable for use in building applications as a non-flammable organic material.
