The hybrid cooling system of vapor compression system and naturally circulating coolin system using R-410a for indoor mobil tele-communication center(IMTC) is developed and its performance is experimentally studied. Its results are summarized as follows. First, cooling capacity of naturally circulating cooling system is proportional to indoor and outdoor temperature difference and it has max. 4,550 kcal/h at indoor and outdoor air temperature difference 15℃. Second, heat exchangers of evaporator and condenser should be designed and constructed to be able to get maximum refrigerant capacity by naturally circulating force and to enhance heat transfer by refrigerant. Third, cooling capacity of hybrid cooling system has optimum operating point according to refrigerant charging capacity and refrigerant charging capacity of naturally circulating cooling system is 30~50% more than vapor compression refrigeration system.

A temperature control system was developed to save energy in freeze dryer. The objective part in the freeze dryer was a shelf with an electrical heater and cooling compressor. The shelf was a fluid circulation heat exchanger. The temperature control of the shelf is generally a feedback control by present and set values of the shelf temperature only, whereas in new control algorithm the circulating fluid temperature and fluid circulating speed were included as well. The control algorithm was based on a concept of refraining the heater and cooler from being in operation if unnecessary. Actuators in use were mainly thyristor for heater, relay for cooling compressor, inverter for fluid circulating pump, etc. Type of Interfaces were RS232C, and digital-analog converter and digital-output converter. Program language was Visual Basic 6.0. Finally, control performance by the new algorithm could be improved in terms of energy saving and accuracy.