As natural refrigerant, carbon dioxide has excellent thermo physics, safe, nontoxic and cheap. This reason causes the CO2 becomes the best refrigerant alternatives. However, CO2 refrigeration system still has relatively low performance when operate in hot environment temperature. This study aims is to investigate the performance of CO2 trans critical refrigeration system using Internal Heat Exchanger (IHX) in tropical outdoor temperature and will compare with standard CO2 refrigeration system which has been studied previously. The research will be carried out by theoretical study and numerical analysis of the refrigeration system using the EES (Engineering Equation Solver) program. Data input and simulation validation are obtained from experimental and secondary data. The result shows that the simulation has good agreement with the experimental results. Errors only as much as 1% up to 2 % so it can be argued that the simulation valid for CO2 refrigeration system with IHX combination analysis especially when the system is operated in tropical climate i.e. Indonesia.

Post-harvest cold chain of horticulture product in tropical country such as is very urgent to keep the product quality. In this country, the environment temperature and humidity are relatively high, so that the horticultural products are deterioration very fast. On the other hand, this condition can be used naturally for increase the room humidity. This study is aimed to investigate the medium temperature refrigerator performance when apply humidifier to keep the humidity of the system. This research was carried out by experimental investigation. The rig has been built with complete with measurement and instrumentation in order to get a precision control of temperature and humidity. The results show that the system reach good enough of COP which approximately 3.5. However the humidifier contributed a cooling load that can affect of 1 – 1.5 °C temperature increasing. Further studies will be examined optimisation humidifier system with low electricity consumption and eco operation condition with the best combination temperature and humidity to keep the products still has good quality under long time storage.