This study aims to rationalize the consumption of thermal energy in residential buildings by recovering heat from wastewater inside the building before entering the central sewage network outside the building, by conducting an analytical study for a residential tower in Syria to find out the coverage percentage of the heat energy recovered from wastewater for the heating and domestic hot water loads needed for the tower, and calculating the percentage of reduction in carbon dioxide (CO2) gases.

It is a simple technology as the thermal recovery system consists of three main components, which are in order: a wastewater tank, heat exchangers, and a heat pump. The research begins with an introduction that consists of the importance of wastewater and the waste heat energy it carries. After that, there are some case studies, research problem, its importance, the aim of the research, and finally the research methodology.

In the first chapter, we talked about the concept of heat recovery from wastewater in general, methods of heat recovery, and the most important advantages and disadvantages of this process. It also includes an identification of the main parts used in this technology and how it works, especially the exchangers and the heat pump. This chapter also addresses the problem of forming a layer of biofilms on the surface of heat exchangers from the wastewater side and the most important methods used to treat it.

We move on to the second chapter, in which we review the most important facilities for heat recovery from wastewater that have been viewed. Then comes the third chapter in which the heat recovery process was conducted for a nine storey residential tower in Syria, each floor has four apartments, where we first calculated the rate of wastewater flow for the entire tower, and we proposed a heat recovery system (physical model) inside the tower. Then the mathematical equations for heat recovery and the solution of these equations were developed based on some necessary assumptions needed in the solution process to know the most important results desired in this field. It also included the calculation of the coverage ratio of the heat energy recovered from the wastewater for the domestic hot water and heating loads, as well as the calculation of the mass and percentage of the reduction of carbon emitted to the atmosphere. Then simple economic feasibility was also conducted in this chapter to know the daily financial savings as a result of using this technology.

The research ends with the most important conclusions and future research that have been reached and the conclusion of the research. The most important results show that the average coverage percentage of heat energy recovered from wastewater for heating load in residential buildings ranges between [30-56%]. It was also found that the average coverage percentage of heat energy recovered from wastewater for domestic hot water load ranges between [65-100%].