Feasibility of solar thermal collectors usage in dwelling apartments in Mashhad, the second megacity of Iran

Today, the concept of net zero-energy buildings has become a major concern regarding fossil fuels combustion side effects, such as air pollution or global warming. Nonetheless, NG (natural gas) is a kind of fossil fuels which is widely combusted in Iran to meet various buildings heating demand. However, the objective of this study is mitigating NG flaring by substituting solar energy as an auxiliary energy source in dwelling buildings. To promote this idea a solar thermal collector is designed. This application is installed on the roof and is responsible to preheat either water circulates in radiators loop, to provide space heating, or domestic hot water to supply washing demand in residential apartments. Indeed, in case of utilizing this application fewer NG will be combusted for rising input water temperature to required value. This approach, consequently leads to decline CO2 emission eventually. Also a dwelling complex including 136 flat apartments is taken into account to perform this research. This complex is situated in Mashhad, the second megacity in Iran. Besides, to evaluate this potential four steps have been taking into account. In the first step annual DHW (domestic hot water) load is computed. Second, heating load is achieved according to actual NG consumption (the sole energy source in case study). In the third step the net annual energy which can be gain by solar absorber is calculated. Finally, annual NG economy, invest return time of solar collector and CO2 avoided are evaluated 203,000 m3, 4 yr and 380 t/yr, respectively.