The fast economic growth worldwide, an expanding population, urbanization, demographics and high standards of living required by people has led to increase in the energy demand. The global energy demand will rise by 35 percent as the world’s population reaches 9 billion people by 2040 (ExxonMobil, 2013). Moreover, the statistics of International Energy Agency show that fossil fuel is leading the energy market of the world with 81% share (IEA, 2016) and it is forecasted to control the world’s primary energy by 2030 (Petroleum, 2010). However, the conventional fossil energy sources are depleting and their usage is related to the emission of harmful gases. Hence, energy resources should be utilized efficiently.
The United Nations Environment Programme (UNEP) estimated that building sector is one of the main consumers of the global energy (40% share) and the biggest greenhouse gas emitter in the world (30% share) (IEA, 2016; Pekka et al., 2009). According to the Intergovernmental Panel report on Climate Change, the building related greenhouse gas (GHG) emissions will double from around 8.6 billion tons CO2 reported in 2004 to 15.6 billion tons CO2 in 2030 (Levine et al., 2007). Furthermore, the energy demand for buildings have increased rapidly in recent years due to various reasons including population growth, high standards of living required by people and improvement of building services and thermal comfort levels (Pérez-Lombard et al., 2008). Therefore, improving the energy consumption of buildings is essential to reduce the environmental impact related to greenhouse gas emissions.
One of the solutions, which has attracted researchers and engineers, is to integrate phase change materials (PCM) into building envelopes to improve buildings energy efficiency and thereby reducing the environmental impact related to energy use (Pasupathy et al., 2008). PCM working is based on the principle that as the temperature rises, the material store energy during phase transition from solid to liquid. Similarly, when the temperature falls, PCM releases heat during phase transition from liquid to solid (Figure 1). The energy efficiency of PCM integrated buildings have been studied for many countries including United States, China, Singapore, Australia, United Kingdom etc. However, due to variation of climate in the studied countries, the results obtained cannot be extended to other parts of the world. Hence, in this research, an innovative approach would be adopted by investigating the thermal performance and energy saving potential of buildings integrated with PCM in different climate zones of the world.
The objectives of the project are as follows:
Thermal energy storage is an effective and environmental friendly solution to reduce heating and cooling loads and thereby improves the energy efficiency of buildings. Among various thermal energy storage techniques, latent heat storage using PCM is the most popular and promising technique because of its high energy storage density with small temperature swing (Memon, 2014). Many researchers performed numerical simulations to evaluate the performance of PCM applied to building envelope. For Singapore, the energy saving performance of cubic model (3 x 3 x 2.8 m) integrated with PCM was evaluated in EnergyPlus (Lei et al., 2016). The parametric study took into account the effect of phase change temperature range (22-32oC) and shape of enthalpy-temperature curve, location (exterior/interior) and amount of PCM. Test results showed that PCM was able to reduce heat gain in 17 to 32% range. In terms of efficiency and economy, the authors concluded that thinner PCM layer is effective in reducing heat gains through building envelope than thicker PCM layer. The energy saving potential and environmental performance of PCM integrated wallboard for a typical residential flat located in Hong Kong was evaluated in Energy Plus (Chan, 2011). The author found that PCM building was economically infeasible; however, environmental analysis showed that PCM contributed in reducing GHG emission over the life span of the building. The impact of climate change was evaluated by considering current and future climate scenarios (2020, 2050 and 2080) on the performance of PCM integrated in two storey detached house located in London (Sajjadian et al., 2015). The detached house was optimized for air gap, effect of PCM thickness as well as melting temperature of PCM by performing simulation in EnergyPlus (summer period only). For the current scenario, an air gap of 25 mm with PCM having melting temperature and thickness of 25oC and 48 mm respectively were found to be optimum. It was concluded that the application of PCM for current weather scenario in London is not feasible. However, for future climate scenario of August 2080, PCM integrated in walls was effective and was able to save cooling loads up to 128 KWh. The energy saving potential of five different PCM ranges in eight different cities of Australia was evaluated by using EnergyPlus software (Alam et al., 2014). The simulations carried out for single room showed that the effectiveness of PCM is dependent on factors such as PCM layer thickness and surface area, local weather etc. The annual energy savings from PCM were in between 17 to 23% except for Darwin city. Based on simulation results, the authors concluded that PCM is a promising candidate and can benefit the field of building energy conservation.
Many researchers also carried out experimental investigations to evaluate the performance of PCM integrated into building walls. The thermal performance of room integrated with PCM wallboards during winter season in Shenyang, China was investigated for the tested period of three consecutive days (Shilei et al., 2006). The authors concluded that PCM gypsum wallboards were effective in reducing indoor temperature fluctuations as well as the related investment cost The thermal performance of full-scale room was evaluated experimentally and numerically for winter condition in Montreal (Athienitis et al., 1997). Test conducted for one day showed that PCM gypsum wallboards are not only effective in reducing daytime temperature but can significantly reduce the heating loads at night. The thermal behavior of full scale test rooms integrated with micro encapsulated PCM in Germany was evaluated over a period of one year (Schossig et al., 2005). Test results showed that the PCM were effective in reducing the cooling demand and increased the comfort of lightweight buildings. Similarly, the thermal performance of micro encapsulated PCM room was investigated in Spain. It was found that the maximum temperature in the walls with PCM appeared about 2 hours later than non-PCM room (Castellón et al., 2007).
From the above literature, it is clear that various researchers investigated the performance of PCM integrated buildings in different cities of the world. However, the results obtained cannot be extended to other parts of the world. In 1900, a German scientist Wladimir Koppen presented the first quantitative classification of world climates (Kottek, 2006). It remains one of the most widely used climate classification systems (Domroes, 2003) and has been successfully applied to climate change, hydrology, greenhouse gas warming, agriculture, physical geography, biology etc. (Kottek, 2006). The climate classification system used monthly temperature and precipitation to define boundaries of different climate zones around the world (Chen and Chen, 2013). In 2006, the updated digitalized version of Koppen-Geiger classification system consisting of 34 possible different climate zones was presented (Kottek, 2006) (Figure 3). However, according to the authors, only 24 climate zones occupy prominent area on the world map. As mentioned earlier, the energy saving potential (with HVAC) of five different PCM ranges in eight different cities of Australia was evaluated and the most efficient PCM for different cities of Australia (Table 1) were identified (Alam et al., 2014). An interesting phenomenon is observed if we assign Koppen Classification code represented by three letters to each city. The Table clearly shows that there may be a possibility of using the PCM with a narrow range for one classification system. Very recently, the thermal performance of PCM (PCM21, PCM24 and PCM26) integrated solar box located in Rome and Palermo (belonging to Csa category), Italy was investigated (Cornaro et al., 2017). In these cities, the thermal performance of PCM21 was the best when compared with PCM24 and PCM26. Hence, in this research, we are going to adopt an innovative approach by investigating the thermal performance and energy saving potential of buildings integrated with PCM in different climate zones of the world. More specifically, we would address the following key issues or clear gap in knowledge.
•What would be the thermal performance and energy saving potential of buildings integrated with PCM in different climate zones of the world? Can we use a suitable PCM melting range for a climate zone as defined by Koppen-Geiger climate classification?
•What would be the economic and environmental benefits of the application of PCM in buildings located in different climate zones of the world?
•Can we develop a ranking system for different climate zones to assess and identify superior PCMs based on technical, economic and environmental criteria?
Research Significance, the impact of the results on the development of science and technology and the expected social and economic effects
•The proposed research is classified as one of research priority areas and specialized fields set by Supreme science and technology commission in Kazakhstan: Section 1. Energy. According to the Organisation for Economic Co-operation and Development within the framework of the EAP Task Force (2012), the building sector of Kazakhstan consumed approximately 60% of total heat and power energy for space heating. Hence, PCM can be used to decrease heating and cooling loads in buildings. Moreover, improving the energy consumption of buildings is essential to reduce the environmental impact related to GHG emissions. Thus, it would contribute to Kyoto-protocol of the United Nations Framework Convention on Climate Change as well as to Policy options for reducing emissions from buildings as highlighted by Building and Climate Change report published by UNEP.
•By knowing the climate regions suitable for the utilization of PCM in buildings as well as climate regions showing maximum energy and economic savings, it would advance the knowledge on how the PCM are performing in different climate regions of the world. In this way, it would help the researchers, scientific community, technologist, architects, and engineers in selecting suitable PCM having maximum impact in terms of energy and economic savings for their selected climate region. The developed system would also be a way forward towards and would contribute to net zero energy buildings.
•The economic evaluation of PCM integrated buildings would give an indication of feasibility of utilizing PCM for building applications. The shifting of heating and cooling loads away from the peak hours can be helpful in reducing the peak demands on gas and power utilities. Hence, energy can be purchased at a lower cost in countries where it is sold at differential pricing system during peak and off peak periods.
•The use of PCM in buildings will reduce energy cost, dependency on fossil fuels and will make the building thermally efficient.