• Energy Research

Abstract To reduce the stress on the electrical grids during peak periods, pre-charging the building envelops with high thermal mass during off-peak periods and utilizing the stored energy during peak periods is an effective approach. However, most of the residential buildings in North America are generally built with lightweight materials, and the concrete slabs in the basement are the only option for energy storage. This means, heat storage is possible only in the basement, and achieving the peak shifting in the entire house is a challenge. To extend the peak shifting to the entire building, an automated heat extraction system (HES) that transfers the stored heat from the basement to the other parts of the house is desirable. Accordingly, this study developed two advanced controllers, which controls both electrically heated floor (EHF) (for energy storage in the basement) and HES (for transferring the stored heat to other parts of the house), to achieve peak shifting and heating cost-saving while guaranteeing the occupants’ thermal comfort. The performance of the developed controllers was compared with other control strategies (i.e., constant set-point control, rule-based control and self-learning predictive control). The results showed that the developed advanced controllers effectively shift the energy consumption from the peak period (97 % for the basement and ~87 % for the second floor) and decrease the heating cost by ~33 %.

Abstract To reduce the stress on the electrical grids during peak periods, pre-charging the building envelops with high thermal mass during off-peak periods and utilizing the stored energy during peak periods is an effective approach. However, most of the residential buildings in North America are generally built with lightweight materials, and the concrete slabs in the basement are the only option for energy storage. This means, heat storage is possible only in the basement, and achieving the peak shifting in the entire house is a challenge. To extend the peak shifting to the entire building, an automated heat extraction system (HES) that transfers the stored heat from the basement to the other parts of the house is desirable. Accordingly, this study developed two advanced controllers, which controls both electrically heated floor (EHF) (for energy storage in the basement) and HES (for transferring the stored heat to other parts of the house), to achieve peak shifting and heating cost-saving while guaranteeing the occupants’ thermal comfort. The performance of the developed controllers was compared with other control strategies (i.e., constant set-point control, rule-based control and self-learning predictive control). The results showed that the developed advanced controllers effectively shift the energy consumption from the peak period (97 % for the basement and ~87 % for the second floor) and decrease the heating cost by ~33 %.

Abstract The present review provides an overview and critical analysis of recently published simulation approaches and experimental studies addressing the phase change hysteresis (PCH) and supercooling (SC) of phase change materials (PCMs). In terms of the enthalpy-temperature h(T) relationships for the solid-liquid phase changes, the PCH is a temperature delay of the h(T) curves between the melting and solidification process, while SC means that solidification does not start at the nominal solidification temperature and a lower temperature is needed for the nucleation to start. However, the PCH and SC are often neglected in the studies dealing with thermal energy storage in PCMs. Several studies indicate that experimental techniques and conditions can significantly influence the behaviour of PCMs, including the PCH and SC. Another issue is the difference in the behaviour of small samples, such as those used in the differential scanning calorimetry (DSC), and the behaviour of bulk PCM. As the DSC results are often used as inputs in simulations of systems with the bulk PCM, this issue is of high importance. Further, the entire amount of PCM does not always fully melt and solidify, and thus partial phase transitions are common in many real-life applications. Several modelling approaches have been proposed to address the PCH and SC of PCM. While simulations of complete phase change cycles are rather straightforward even with the PCH and SC involved, incomplete phase change cycles with partial phase transitions are much more challenging, and this issue has not yet been satisfactorily solved. The simulation techniques identified in the literature search were analysed, assessed, and compared to each other. The results indicate that there are only a few modelling approaches for partial phase transitions, and only some of them are reasonably validated with experimental data.

Abstract The present review provides an overview and critical analysis of recently published simulation approaches and experimental studies addressing the phase change hysteresis (PCH) and supercooling (SC) of phase change materials (PCMs). In terms of the enthalpy-temperature h(T) relationships for the solid-liquid phase changes, the PCH is a temperature delay of the h(T) curves between the melting and solidification process, while SC means that solidification does not start at the nominal solidification temperature and a lower temperature is needed for the nucleation to start. However, the PCH and SC are often neglected in the studies dealing with thermal energy storage in PCMs. Several studies indicate that experimental techniques and conditions can significantly influence the behaviour of PCMs, including the PCH and SC. Another issue is the difference in the behaviour of small samples, such as those used in the differential scanning calorimetry (DSC), and the behaviour of bulk PCM. As the DSC results are often used as inputs in simulations of systems with the bulk PCM, this issue is of high importance. Further, the entire amount of PCM does not always fully melt and solidify, and thus partial phase transitions are common in many real-life applications. Several modelling approaches have been proposed to address the PCH and SC of PCM. While simulations of complete phase change cycles are rather straightforward even with the PCH and SC involved, incomplete phase change cycles with partial phase transitions are much more challenging, and this issue has not yet been satisfactorily solved. The simulation techniques identified in the literature search were analysed, assessed, and compared to each other. The results indicate that there are only a few modelling approaches for partial phase transitions, and only some of them are reasonably validated with experimental data.

Abstract Occupant’s schedules and their energy-use behavior are substantial inputs for building energy simulations and energy management in buildings. In practice, most of the research studies consider default occupant schedules from the standards. Subsequently, the temporal variations associated with occupancy is often missed out, leading to uncertainties in simulation results. This study aims to address two research problems in terms of occupancy: 1) upon the availability of the data, how to systematically extract the different occupant schedules, 2) when the occupancy data is not available, what are the other commonly logged parameters (such as plug load, lighting energy consumption, indoor carbon dioxide (CO2) concentration, and indoor relative humidity data) that shall be used to represent the occupancy in buildings. Regarding the first objective, a generic data-driven framework with the combination of shape-based clustering and change-point detection method is proposed to extract the distinct occupancy in residential buildings in terms of occupant activity schedule and presence probability. To demonstrate the outcomes of the framework, it was applied to the dataset collected from eight apartments located in Lyon, France. The results show the existence of different occupant patterns in buildings with respect to day of the week and season of the year. To achieve the second objective, linear and logistic regression models were developed to represent the occupant activity level and occupant presence/absence state, respectively. The linear regression model results show that among the examined variables, the lighting, and plug load consumption data along with the hour of the day show better prediction results in terms of adjusted R2 and mean absolute percentage error. For the occupant presence/absence state, the logistic regression model developed using CO2 concentration and plug load energy consumption dataset shows better results in misclassification error, confusion matrix, and receiver operating characteristic curve.

Abstract Occupant’s schedules and their energy-use behavior are substantial inputs for building energy simulations and energy management in buildings. In practice, most of the research studies consider default occupant schedules from the standards. Subsequently, the temporal variations associated with occupancy is often missed out, leading to uncertainties in simulation results. This study aims to address two research problems in terms of occupancy: 1) upon the availability of the data, how to systematically extract the different occupant schedules, 2) when the occupancy data is not available, what are the other commonly logged parameters (such as plug load, lighting energy consumption, indoor carbon dioxide (CO2) concentration, and indoor relative humidity data) that shall be used to represent the occupancy in buildings. Regarding the first objective, a generic data-driven framework with the combination of shape-based clustering and change-point detection method is proposed to extract the distinct occupancy in residential buildings in terms of occupant activity schedule and presence probability. To demonstrate the outcomes of the framework, it was applied to the dataset collected from eight apartments located in Lyon, France. The results show the existence of different occupant patterns in buildings with respect to day of the week and season of the year. To achieve the second objective, linear and logistic regression models were developed to represent the occupant activity level and occupant presence/absence state, respectively. The linear regression model results show that among the examined variables, the lighting, and plug load consumption data along with the hour of the day show better prediction results in terms of adjusted R2 and mean absolute percentage error. For the occupant presence/absence state, the logistic regression model developed using CO2 concentration and plug load energy consumption dataset shows better results in misclassification error, confusion matrix, and receiver operating characteristic curve.

Abstract Direct Evaporative Cooling (DEC) is a passive cooling technology widely adopted in places with hot-dry weather conditions to achieve indoor thermal comfort. The major drawbacks of the conventional DEC system are water stagnation in the sump where the water is stored and the continuous pump operation for the water circulation. In this study, vermicompost – a material with high porosity and water retention capacity is used to replace the pad, pump and sump of conventional air-cooler. The effect of velocity on the performance of a vermicompost based cooling system is compared with conventional air-cooler and the results are presented. The results show that vermicompost based cooling system operated at 2.7 ms−1 provides a cooling effect similar to a conventional air-cooler with 10 % deviation. The energy savings of this cooling system due to the elimination of the pump is about 21.7 %. This proposed cooling technology could be an energy-efficient method to provide passive thermal comfort in residential, commercial building sectors and further paves the way for sustainable cooling for applications like poultry, greenhouse and flower bouquet shop where cooled air with higher humidity is of great importance.

Abstract Direct Evaporative Cooling (DEC) is a passive cooling technology widely adopted in places with hot-dry weather conditions to achieve indoor thermal comfort. The major drawbacks of the conventional DEC system are water stagnation in the sump where the water is stored and the continuous pump operation for the water circulation. In this study, vermicompost – a material with high porosity and water retention capacity is used to replace the pad, pump and sump of conventional air-cooler. The effect of velocity on the performance of a vermicompost based cooling system is compared with conventional air-cooler and the results are presented. The results show that vermicompost based cooling system operated at 2.7 ms−1 provides a cooling effect similar to a conventional air-cooler with 10 % deviation. The energy savings of this cooling system due to the elimination of the pump is about 21.7 %. This proposed cooling technology could be an energy-efficient method to provide passive thermal comfort in residential, commercial building sectors and further paves the way for sustainable cooling for applications like poultry, greenhouse and flower bouquet shop where cooled air with higher humidity is of great importance.

Abstract The adoption of phase change material (PCM) based free cooling technology in all the climatic conditions is challenging because of its site-specific nature. In order to support the implementation of free cooling concept in unfavorable climatic condition, a novel hybrid system with the combination of evaporative cooling and PCM based free cooling is proposed herewith. The present experimental work aims to compare and analyze the charging behavior of the PCM-based free cooling system without and with the integration of direct evaporative cooling (DEC) unit during the summer month (April) in an Indian city possessing hot–dry climate. By considering the local ambient conditions, PCM with a phase change temperature of 27–29 °C is opted for the present study. The time-temperature history of PCM, instantaneous heat transfer rate, charging efficiency, heat exchange between the storage tank and ambient were analyzed and the respective results are presented. It is inferred from the experiments conducted without the integration of DEC unit that PCMs did not undergo phase transition and remained in the liquid phase even after 8 h of the experimentation due to unfavorable local ambient conditions. However, in the case of experiments conducted with the integration of DEC unit, PCMs at all locations in the thermal energy storage (TES) tank got solidified irrespective of local ambient temperature and reached its freezing temperature. This is due to the reduction in heat transfer fluid (HTF) temperature and the additional temperature driving potential achieved through DEC. Better results in terms of charging duration was obtained for the experiments conducted with higher temperature driving potential than the higher HTF velocities. The main inference from the present study is that it is much possible to store the useful energy in PCM even during the summer season in the hot and dry climatic zone irrespective of local ambient temperature through the integration of DEC unit with the PCM based free cooling system.