A small-scale trial system for energy saving is installed in a food processing factory in Vietnam. The system utilizes unused coldness of wastewater released from a poultry factory in Hanoi. The installed system is “pre-cool system” with a polyethylene made heat exchange system called “G-HEX”. As G-Hex is made of polyethylene, which is strong against chemical reaction, the system can be used in a bad water quality. The food processing factory in Vietnam generates a cold water (0 ℃) from an industrial water (30 ℃) by an electrical chiller system for their operation. As the electricity cost for the current cooling system is expensive, 45,000 US dollars per year, the pre-cool “G-Hex” system is expected to lower the electricity cost. After installation of the system, the water temperature and flow rate at the inlet and outlet of each component were closely monitored. The temperature and the flowrate have fluctuated slightly during the operation. Energy savings are calculated based on the monitored data. The existing chiller system on the left in Fig.4 required “64.9 kW” of energy to cool water to 0 ℃. In contrast, for the chiller with the pre-cooled G-Hex system on the right, “53.6 kW” was consumed reducing electricity consumption by 18% in total. Same system is applicable for a hot wastewater, too. There is a possibility of introducing the system to companies in the fisheries and textile industries with appropriate pretreatment and adjustment in the operation. Consequently, the pre-cool G-Hex system was successfully installed to reduce for saving electricity by 18% in the trial study in Vietnam. As the system can be used for hot condition and is strong against the chemical reaction, the system is applicable for a wide variety of industries, such as fisheries or textile industry etc.