**3.3. Heat recovery from exhausted waste gas flows**

Heat recovery from exhausted waste gas flows is used to heat fresh air for air-conditioning or process air use. During the last 30 years, no remarkable success has been achieved in the efficiency of the various types of heat recovery equipment applicable to air-conditioning.

Recovery of process exhausts is more demanding because of corrosive substances and particles. For these applications, new types of heat recovery have been developed as well as new materials tested. Although in the past success on the equipment level has been rather limited and it does not seem that it is going to be much better by 2020, there have been improvements due to advanced control systems that help to better run the systems than in the past.

Heat recovery is meant to decrease heat consumption. Heat recovery equipment causes pressure losses in gas flows, which means that the fans and pumps must produce higher pressure and, therefore, more electricity is consumed. However, if they are well designed, the increase in electricity consumption is clearly less than the decrease in heat consumption.
