• Energy Research

Abstract Thermal energy storage in concentrated solar thermal power plants improves the dispatchability and eliminates the miss-match between the energy supply and demand. Recently, considerable attention has been made to latent heat thermal energy storage due to its high energy density per unit mass and volume at nearly constant temperature. This paper presents a computational fluid dynamics (CFD) model using ANSYS FLUENT 15.0 for phase change material (PCM) in a vertical triplex tube thermal energy storage system and its validation through experimental results. To enhance the heat transfer inside the PCM, eight fins have been incorporated between the internal and external tubes. Experiments were conducted for both freezing and melting processes. The CFD model endeavoured to simulate both the freezing and melting processes of the PCM. The inlet and outlet temperatures of the heat transfer fluid (HTF) as well as six temperature locations in the PCM were compared with the CFD results. The average effectiveness as well as the duration of the phase change process at each experimental point were compared with results from the CFD model and found to be in good agreement. The variation between the experimental and CFD for the phase change duration are within an average of 5.8% for freezing and 1.6% for melting.

Abstract Thermal energy storage in concentrated solar thermal power plants improves the dispatchability and eliminates the miss-match between the energy supply and demand. Recently, considerable attention has been made to latent heat thermal energy storage due to its high energy density per unit mass and volume at nearly constant temperature. This paper presents a computational fluid dynamics (CFD) model using ANSYS FLUENT 15.0 for phase change material (PCM) in a vertical triplex tube thermal energy storage system and its validation through experimental results. To enhance the heat transfer inside the PCM, eight fins have been incorporated between the internal and external tubes. Experiments were conducted for both freezing and melting processes. The CFD model endeavoured to simulate both the freezing and melting processes of the PCM. The inlet and outlet temperatures of the heat transfer fluid (HTF) as well as six temperature locations in the PCM were compared with the CFD results. The average effectiveness as well as the duration of the phase change process at each experimental point were compared with results from the CFD model and found to be in good agreement. The variation between the experimental and CFD for the phase change duration are within an average of 5.8% for freezing and 1.6% for melting.

Abstract An experimental investigation was undertaken in which the thermal resistance for the heat flow through a typical timber framed pitched roofing system was measured under outdoor conditions for heat flow up. The measured thermal resistance of low resistance systems such as an uninsulated attic space and a reflective attic space compared well with published data. However, with higher thermal resistance systems containing bulk insulation within the timber frame, the measured result for a typical installation was as low as 50% of the thermal resistance determined considering two dimensional thermal bridging using the parallel path method. This result was attributed to three dimensional heat flow and insulation installation defects, resulting from the design and construction method used. Translating these results to a typical house with a 200 m 2 floor area, the overall thermal resistance of the roof was at least 23% lower than the overall calculated thermal resistance including two dimensional thermal bridging. When a continuous layer of bulk insulation was applied to the roofing system, the measured values were in agreement with calculated resistances representing a more reliable solution.

Abstract An experimental investigation was undertaken in which the thermal resistance for the heat flow through a typical timber framed pitched roofing system was measured under outdoor conditions for heat flow up. The measured thermal resistance of low resistance systems such as an uninsulated attic space and a reflective attic space compared well with published data. However, with higher thermal resistance systems containing bulk insulation within the timber frame, the measured result for a typical installation was as low as 50% of the thermal resistance determined considering two dimensional thermal bridging using the parallel path method. This result was attributed to three dimensional heat flow and insulation installation defects, resulting from the design and construction method used. Translating these results to a typical house with a 200 m 2 floor area, the overall thermal resistance of the roof was at least 23% lower than the overall calculated thermal resistance including two dimensional thermal bridging. When a continuous layer of bulk insulation was applied to the roofing system, the measured values were in agreement with calculated resistances representing a more reliable solution.

Abstract Climate change has been shown to significantly alter the heating and cooling needed to maintain thermal comfort within a home. However, limited studies have investigated the impact on the design philosophy associated with achieving an energy efficient building envelope with the onset of climate change. Applying robust future TMY for 2070 the change in heating and cooling demand has been studied in this paper for various combinations of external and internal wall insulation, roof insulation, reflective foil, thermally reflective roofs and different floor coverings. A building thermal model was used for the mild temperate climate of Adelaide, Australia, which requires both heating and cooling, but is dominated by heating. Climate change was found to increase and shift this demand to cooling dominated. It was determined that with climate change, heating becomes significantly less important in better insulated buildings and therefore measures which reduce cooling load are more critical. It is concluded that in this climate zone, climate change design approaches need to dramatically change to focus on cooling, contrary to present strategies.

Abstract Climate change has been shown to significantly alter the heating and cooling needed to maintain thermal comfort within a home. However, limited studies have investigated the impact on the design philosophy associated with achieving an energy efficient building envelope with the onset of climate change. Applying robust future TMY for 2070 the change in heating and cooling demand has been studied in this paper for various combinations of external and internal wall insulation, roof insulation, reflective foil, thermally reflective roofs and different floor coverings. A building thermal model was used for the mild temperate climate of Adelaide, Australia, which requires both heating and cooling, but is dominated by heating. Climate change was found to increase and shift this demand to cooling dominated. It was determined that with climate change, heating becomes significantly less important in better insulated buildings and therefore measures which reduce cooling load are more critical. It is concluded that in this climate zone, climate change design approaches need to dramatically change to focus on cooling, contrary to present strategies.

Abstract Phase change materials (PCMs) can store large amounts of heat or cooling in a small amount of material, they potentially have less weight and volume compared with other thermal energy storage materials. Thermal energy storage applications such as solar hot water systems and off peak refrigeration systems are able to use PCMs to store heat or cooling. However, research has shown that the effectiveness of these systems heavily depends on the arrangement of the PCM system, which affects both the storage density and the thermal resistance to heat transfer. However, specifying as well as determining an effective PCM system has been difficult in the past because it involves using numerical modelling which is time consuming. This paper presents the results of an experimental investigation carried out on a tube-in-tank design filled with PCM for cold storage applications. The PCMs used are salt hydrate with phase change temperature of −27 °C and water. From the experimental measurements, the average heat exchange effectiveness of the storage tank was determined and a characteristic design curve has been developed as a function of the measured average NTU.

Abstract Phase change materials (PCMs) can store large amounts of heat or cooling in a small amount of material, they potentially have less weight and volume compared with other thermal energy storage materials. Thermal energy storage applications such as solar hot water systems and off peak refrigeration systems are able to use PCMs to store heat or cooling. However, research has shown that the effectiveness of these systems heavily depends on the arrangement of the PCM system, which affects both the storage density and the thermal resistance to heat transfer. However, specifying as well as determining an effective PCM system has been difficult in the past because it involves using numerical modelling which is time consuming. This paper presents the results of an experimental investigation carried out on a tube-in-tank design filled with PCM for cold storage applications. The PCMs used are salt hydrate with phase change temperature of −27 °C and water. From the experimental measurements, the average heat exchange effectiveness of the storage tank was determined and a characteristic design curve has been developed as a function of the measured average NTU.

The applicability of the effectiveness–NTU method for characterising a PCM thermal energy storage system was experimentally investigated. The system consisted of PCM encapsulated in spheres with a liquid heat transfer fluid. Freezing and melting tests have been carried out for a variety of conditions on a tank filled with 60 spheres. The investigation demonstrated that a correlation existed between the effectiveness of heat transfer and the mass flow rate in accordance with the effectiveness–NTU relationship for condensers and boilers. It has been proven experimentally that the effectiveness–NTU method is applicable for PCM encapsulated in spheres in a tank.