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High consumption of fossil fuel resources has always been associated with large amounts of pollutants' production. Due to this, Tehran weather condition reaches emergency state every year and causes a health threat to residents. Residential sector consumes over 40% of the total energy in Iran and causes a high amount of emission. In this article, the amount of loss reduction is calculated when new insulations are used (instead of stone-wool) in a building located in district 3 of Tehran. Innovative insulations involve the use of expanded polystyrene (EPS) and hollow silica nanospheres (HSN). To validate the previous part and observe the wall condition in detail, walls with current and new insulations are modelled by ANSYS FLUENT. Results indicate that EPS and HSN reduce total energy demand in the studied apartment by 1.2% and 5.1%, respectively. Finally, Tehran's under-construction buildings during 2015 are assumed to utilize mentioned insulations to observe their effects. The annual amount of reduced six air pollutants (CO2, SPM, CO, SO2, CH4 and NOx) by using EPS and HSN are 16,681 and 60,712 tonnes, respectively. It is found out that by using EPS and HSN, CO2 external costs can be decreased by 4,376,846$ and 15,929,919$ per year. [ABSTRACT FROM AUTHOR]

• A new CPVT model is provided using a photovoltaic module and pulsating heat pipe in its collector. • Different HTFs including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture experimentally tested. • Enhancing heat pipe performance, a variety of working fluids were tested. • The provided cooling system recycles 47.3% of the thermal energy, resulting in a 48.8% efficiency increase. In this paper, the experimental investigation of the performance of a concentrated hybrid photovoltaic thermal solar system is sought. Accordingly, there is a parabolic trough concentrator receiver that consists of three components: a triangular duct, photovoltaic cells covering the duct, and a three-turn PHP. The PHP cools down the photovoltaic cells efficiently and regenerates waste heat. The duct is filled with a heat transfer fluid surrounding the PHP's evaporator. The condensation section of the PHP is located outside the solar concentrator. Using a one-axis polar mechanism, the concentrator tracks the sun from east to west. The system experiment setup was fabricated and tested outdoors in Tehran's climate. Different heat transfer fluids, including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture, were tested. Given the enhancement of PHP performance, a variety of working fluids were tested, including graphene oxide nanofluid/water, acetone, and pure water. The experiments showed that graphene oxide nanofluid/water mixture provided the highest thermal performance. With the use of graphene oxide nanofluid/water (as a working fluid) and glycerine (as heat transfer fluid), experiment results showed a decrease of 7.84 °C in PV temperature and a consequent increase of 21.85% in electrical efficiency in best condition. Furthermore, the provided cooling system recycles a maximum of is 190.4 kJ of thermal energy equivalent 52.5% thermal efficiency, increasing overall efficiency by 74.35%. Lastly, the IRR of 65.41%, PBT of 1.04 years, and LCOE of 1.84 $/kWh demonstrate appropriate financial profitability. [ABSTRACT FROM AUTHOR]