EXHAUST AIR HEAT RECOVERY TECHNIQUE USING A RECUPERATIVE HEAT EXCHANGER
At present the industrial pig-breeding enterprises are focused on growing animals with a high concentration of livestock, which implies the release of corresponding volumes of waste products (water vapor, carbon dioxide, ammonia, hydrogen sulphide, etc.). The assimilation of waste products requires high air exchange, which is an energy-intensive process primarily due to the need to preheat the supplied air. The recovery of exhaust air heat can be realized in a recuperative air-to-air heat exchanger. This raises the problem of freezing of the condensate in the exhaust duct of the recuperator, which prevents the device from operating. The peculiarity of the proposed technique consists in a system of dynamic regulation of the supply air flow with constant output of the exhaust duct. Regulation is performed through the condition of maintaining the temperature of the heat exchange wall above zero, which eliminates the freezing of the condensate being formed. In order to implement the described technique it is proposed to retrofit the recuperator with the system for regulating the rotation speed of the supply fan and to equip the exhaust duct with an electric powered shutter, which ensures the separation of exhaust air flow and its partial reflux into the room. Thus, the atmospheric pressure is maintained in the room, which minimizes infiltration. The author provides the graphs of the efficiency of heat recovery depending on the recuperator performance with and without the account of performance imbalance. On the basis of experimental data the author has obtained the approximating dependence of heat recovery efficiency on the supply air flow rate. The proposed technique of heat recovery helps to eliminate the icing of the exhaust duct of the heat exchanger and ensures a continuous process of ventilation with the required air exchange and recovery of the exhaust air heat without retrofitting the device with expensive air preheating systems.