Energy advantage of cold energy recovery system using water- and air-side free cooling technologies in semiconductor fabrication plant in summer

Abstract

The semiconductor industry requires large amounts of energy. Of the total energy, semiconductor manufacturing facilities consume the most electricity, where 21–29% of the total energy is used to maintain a clean room environment at a constant temperature and humidity. The energy required for constant temperature and humidity has been developed and applied in various ways, e.g., waste heat recovery technology without a boiler. However, it is highly difficult to obtain the energy required for cooling without operating a chiller unless there is a climatic advantage. Therefore, with the perspective of introducing cold energy recovery system into outdoor air-conditioner, this paper suggests the analysis of the energy-saving effect of the recovery system which recovers wasted cold energy of the exhaust gas from the semiconductor fabrication plant located in high-temperature and humid region. Two systems have been proposed: a water-side free cooling system that recovers cold energy by connecting a cooling tower to exhaust gas, and an air-side free cooling system that recovers cold energy by connecting a membrane energy heat exchanger. When applied to the conventional outdoor air-conditioner after cold energy recovery in both systems, the energy-saving effect was estimated by a simulation program (i.e., engineer equation solver) using a theoretical calculation model. The result showed that the cooling load of the outdoor air-conditioner decreased by 10.2–13.1% and 8.5–11.2% when the water-side free cooling system and air-side free cooling system, respectively, were applied at an exhaust gas temperature of 24–28 °C and a humidity ratio of 0.00733 kg/kg’. However, with the consideration of the power consumed by the cold energy recovery system (i.e., water/air-side free cooling system), actual energy-saving rate was low. Consequently, the head and static pressure designs of the fluid transfer equipment (i.e., pumps and fans) of the cold energy recovery system should be considered with caution when the cold energy recovery system is applied.