• Energy Research

Employing green energies for building energy sector decarbonization has captured the world’s attention in the current century. However, the imbalance between energy demand and availability necessitates designing reliable and cost-effective energy storage systems. The present study aims to propose an innovative building-integrated solar thermal storage method using insulated concrete form (ICF) foundation walls for residential buildings in cold climates such as that of Canada. Surplus solar thermal energy is stored inside the ICF wall, which has a high thermal capacity and mass and is integrated into the building envelope. The ICF wall and solar thermal collectors are coupled with a water-to-water heat pump to meet building space heating load and domestic hot water demand. Different configurations integrating the ICF wall are modeled and simulated in TRNSYS software to perform a yearly transient analysis. It is shown that a system with ICF walls has an 11% higher solar fraction (SF) than a similar system with a large water thermal storage tank. By replacing the solar thermal collector with a hybrid photovoltaic/thermal collector, the overall system solar fraction can increase to 20% above that of a similar system with a large water thermal storage tank system. An ICF-based system with a 16 m2 solar collector can completely cover nine months of space heating and domestic hot water load for a single-family house in London, Ontario. A detailed sensitivity analysis shows that the proposed ICF-based systems achieve an optimum solar fraction at high tilt angles (65-70°), unlike a similar design with an extensive water thermal storage tank system. Because of their ability to achieve a high SF at high tilt angles, ICF systems are suitable for vertically mounted solar systems typically required by high-rise buildings due to limited roof area. As part of the building envelope, ICF foundation walls have no additional cost and can be considered a feasible strategy for reducing the residential sector’s carbon footprint..

A twisted-fin array as an innovative structure for intensifying the charging response of a phase-change material (PCM) within a shell-and-tube storage system is introduced in this work. A three-dimensional model describing the thermal management with charging phase change process in PCM was developed and numerically analyzed by the enthalpy-porosity method using commercial CFD software. Efficacy of the proposed structure of fins for performing better heat communication between the active heating surface and the adjacent layers of PCM was verified via comparing with conventional longitudinal fins within the same design limitations of fin material and volume usage. Optimization of the fin geometric parameters including the pitch, number, thickness, and the height of the twisted fins for superior performance of the proposed fin structure, was also introduced via the Taguchi method. The results show that a faster charging rate, higher storage rate, and better uniformity in temperature distribution could be achieved in the PCMs with Twisted fins. Based on the design of twisted fins, it was found that the energy charging time could be reduced by up to 42%, and the energy storage rate could be enhanced up to 63% compared to the reference case of straight longitudinal fins within the same PCM mass limitations.

Abstract Supplying the ever-increasing energy demand both economically viable and environmentally friendly is among the primary challenges of the present century. In this regard, the current research suggests a resilient smart hybrid renewable energy system to supply the electricity and heat demand of Eram Campus, Shiraz University. Pre-assessments are carried out to realize the energy demand, primary energy potentials, and geographical constraints of the Campus. In the present work, simulations, optimizations, and sensitivity analyses are performed to explore the feasibility of utilizing a unique integrated energy system to meet the load demand of the case study. The results indicate that the suggested energy system consists of a micro gas turbine with combined heat and power module, thermal boilers, converters, photovoltaic panels, pumped hydro storage units, and a predictive controller. To make use of the proposed power plant, $15 M is needed for initial capital cost. Levelized cost of electricity and net present cost of the system are 0.09$/kWh and $42.5 M, respectively. Based on the findings, using the suggested energy system reduces the annual carbon dioxide production of the Campus by 8000 megatonnes compared when using the national energy grid. Furthermore, the calculations reflected that the impacts of variations in financial parameters, carbon penalty, energy demand increase, and allowable capacity shortage on the characteristics of the energy system are considerable. In the most economical strategy, the capacities of the gas turbine, thermal boiler, photovoltaic panel, converter, and pumped hydro storage should be 2650 kW, 17 MW, 13754 kW, 4995 kW, and 70 units, respectively, to meet the increase of 50% in energy demand. By reducing the energy consumption in specific time steps by 1% of the total load, the net present cost and levelized cost of electricity significantly decline by 6% and 15%, respectively. The results of this study concern whatever the policymakers need to ensure the feasibility of implementing a smart integrated energy system to reach the first renewable-powered University Campus in Iran.

The melting process of a multi-tube’s thermal energy storage system in the existence of free convection effects is a non-linear and important problem. The placement of heated tubes could change the convective thermal circulation. In the present study, the impact of the position of seven heat exchanger tubes was systematically investigated. The energy charging process was numerically studied utilizing liquid fraction and stored energy with exhaustive temperature outlines. The tubes of heat transfer fluid were presumed in the unit with different locations. The unit’s heat transfer behavior was assessed by studying the liquid fraction graphs, streamlines, and isotherm contours. Each of the design factors was divided into four levels. To better investigate the design space for the accounted five variables and four levels, an L16 orthogonal table was considered. Changing the location of tubes could change the melting rate by 28%. The best melting rate was 94% after four hours of charging. It was found that the tubes with close distance could overheat each other and reduce the total heat transfer. The study of isotherms and streamlines showed the general circulation of natural convection flows at the final stage of melting was the most crucial factor in the melting of top regions of the unit and reduces the charging time. Thus, particular attention to the tubes’ placement should be made so that the phase change material could be quickly melted at both ends of a unit.

This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mass. Moreover, the melting time for the case of using four straight fins was 8.3% lower than that compared with the no-fins case. By raising the fins’ number from two to four and six, the heat storage rate rose 14.2% and 25.4%, respectively. This study presents the effects of novel configurations of fins in PCM-based thermal energy storage to deliver innovative products toward commercialization, which can be manufactured with additive manufacturing.

Abstract To obtain maximum exergy and energy efficiencies of photovoltaic-thermal (PV-T) systems, innovative configurations of coolant tubes are proposed and simulated numerically. The tubes’ configuration is modified using non-uniform wavy tube concept, which forms different styles, including ascending and descending amplitude of coolant tubes. Besides, the influences of geometrical parameters, extending PV panel length, sensitivity analysis on the operating conditions and a comprehensive investigation of different types of heat transfer fluids are analysed for the innovative systems. The results demonstrate that the PV-T performance develops in terms of electrical, thermal, and exergy efficiencies using ascending wavy tubes compared with straight, uniform wavy and descending wavy tubes. The electrical and thermal efficiencies are promoted from 10.94% to 61.04% for the straight tubes to 11.32% and 65.21%, respectively, for the system in which ascending wavy tubes are utilised. A comprehensive study of different coolant fluids proves that when SiC and MPCM-28 are simultaneously employed, the best cooling fluid is achieved, leading to a 0.4% higher electrical efficiency than the case in which water is used.

Abstract To develop a more efficient water-cooled photovoltaic-thermal system, energy and exergy analysis of a photovoltaic-thermal system with wavy tubes are investigated numerically using different coolant fluids. A comparison between the straight tube and wavy tubes is conducted for various wavelengths and wave amplitudes. The geometrical parameters of the wavy tubes as well as the velocity of the coolant fluid are examined. Besides, the consequences of coolant fluid including water, Ag/water nanofluid, microencapsulated phase change material slurry, and also a new type of cooling fluid called microencapsulated phase change material nano-slurry are studied. The results show that the electrical, thermal, and exergy efficiencies of the photovoltaic-thermal module enhance by using the wavy tubes compared with the corresponding straight tubes. By declining wavelength in a constant wavelength/amplitude, the heat absorbed by the heat transfer fluid raises. For the best configuration, the primary and exergy efficiencies of the module increase by 6.06% and 4.25%, respectively, for the wavy tubes system compared with those for the straight unit. Furthermore, in both configurations, by increasing the inlet velocity, the overall performance of the photovoltaic-thermal module increases due to a higher heat transfer rate. The results also reveal that among different types of cooling fluids, the microencapsulated phase change material nano-slurry has higher performance in terms of both energy and exergy efficiencies due to having higher thermal conductivity and heat capacity. By employing the wavy tube and the novel proposed coolant fluid, the primary and exergy efficiencies increase in comparison with a typical photovoltaic-thermal module.