According to the International Energy Agency, buildings are the largest energy-consuming sector globally, producing over one-third of greenhouse gas emissions in 2013. Renewable energies such as solar can be harnessed to fully or partially meet the energy demands of buildings. In this study, solar thermal collectors are used in a building to provide the hot water required for an underfloor heating system. Three cities in Iran, namely Tabriz, Tehran and Kish island, with distinctive climatic conditions are considered to gain a better understanding of the performance of solar-powered underfloor heating systems in different climates. Moreover, an economic analysis is conducted to assess the feasibility of the proposed system. DesignBuilder software is applied to simulate the energy performance of the building. The results indicate that the annual fuel consumption of the building with a solar collector located in Tehran, Tabriz and Kish island is reduced by 125.39, 303.58 and 1.41 MWh compared to that of without collector, respectively. The payback period of the system for Tehran, Tabriz and Kish Island is found to be 8.2, 9.4 and 12.1 years, respectively.
Depletion of fossil resources, global warming, industrialization and growing population pose challenges to the energy sector [1e3]. The building sector presently accounts for approximately 40% of global energy consumption, producing 30% of annual greenhouse gas (GHG) emissions in 2013 [4,5]. Renewable energies such as solar can be harnessed to meet the electricity, heating and cooling demands of buildings using photovoltaic (PV) or solar thermal collectors, with a reduced carbon footprint . Solar thermal systems have been widely used throughout the world for heating and cooling purposes [7e10]. The global installed capacity of solar thermal systems reached 456 GW by the end of 2016 .
Heating, ventilation and air conditioning (HVAC) systems are the primary energy consumers in buildings [12,13]. PV and solar thermal systems can be implemented in buildings, to meet some or all of the electrical, heating and cooling demands. However; prior to installation of these systems, the feasibility needs to be assessed in both technical and economic terms to avoid investment risks as well as to ensure the reliability and sustainability of the system.
Much research has been reported on the technical, economic and environmental aspects of buildings integrated with PV and solar thermal systems. A dynamic approach was adopted to investigate domestic hot water (DHW) production using solar thermal collectors . That study showed that the solar coverage factor correlates closely with daily water consumption. The application of phase change materials (PCMs) in evacuated tube solar collectors was examined to enhance the performance of the collectors . The charging efficiency of PCM integrated collectors varies from 30 to 70%, depending on PCM temperature and solar radiation level. The annual solar fraction of these collectors increases by 20.5% compared with conventional solar collectors. To improve the design accuracy of solar water heating systems, Nogueira et al. developed a program in MATLAB that enables users to model different types of solar collectors with auxiliary equipment . The thermal performance of a 4 m2 solar flat plate collector for water heating was experimentally studied over a oneyear period in Dublin, Ireland . The annual mean daily energy, pipe losses and solar fraction were found to be 19.6 MJ/d, 3.2 MJ/ d and 32.2%, respectively. The effects of mass flow rate, inlet water and ambient temperature and solar insolation on thermal performance of open and closed loop solar water heating systems was examined . That study showed that the efficiency of the system improves with increasing mass flow rate in the solar collectors, ambient temperature and solar insolation.
In this study, the feasibility of solar-assisted underfloor heating systems was assessed for three cities of Iran with distinctive climates. A building with and without solar thermal collectors was simulated in DesignBuilder software. Then, an economic assessment was carried out to assess the feasibility of utilization of the aforementioned systems. The following conclusion can be drawn from the findings:
- The indoor air temperature of the building integrated with solar collectors located in Tehran and Tabriz, is liable to fluctuations. However, for Kish island, the temperature remains constant.
- The utilization of solar-powered underfloor floor heating can reduce the annual fuel consumption by 125 MWh in Tehran, 300 MWh in Tabriz and 1.4 MWh in Kish island.
- During the lifespans of the building systems, over 570 tonnes in Tehran, 1400 tonnes in Tabriz and 6.5 tonnes in Kish island of GHG emissions can be avoided by using solar collectors.
- The payback periods of the solar-powered system for Tehran, Tabriz and Kish island are 8.2, 9.4 and 12.1 years, respectively.
Overall, it can be concluded that the solar-powered heating system outperforms the conventional one since it requires less fuel and reduces GHG emissions. However, the system performs better in cold climates, when considering the economic, technical and environmental aspects. Future studies appear to be merited that consider different types of solar thermal collectors, the possibility of incorporating solar cooling in the building, and the use of PVT systems in the building to simultaneously meet the heating and electrical demands.