• Energy Research

This paper presents the development and application of a super performance dew point cooling technology for data centres. The novel super performance dew point cooler showed considerably improved energy saving and carbon reduction for data centre cooling. The innovations of this technology are built upon a series of technological breakthroughs including, a novel hybrid flat/corrugated heat and mass exchanging sheets, an innovative highly water absorptive and diffusive wet-material for the sheets which enable an intermittent water supply with well-tuned water pressure and flow rate, and the optimised fan configurations. Following a list of fundamental research including theoretical, numerical and lab experimental testing of a small scale prototype system, a specialist 100 kW rated data centre dew point cooling system was dedicated designed, constructed, installed and real life tested in an operational live data centre environment, i.e., Maritime Data Centre at Hull (UK) to investigate its dynamic performance, suitability and stability for application in operational data centre environment conditions. During the testing period, the system showed its reliability and capability to remove a tremendous amount of heat dissipated from the IT equipment and maintain an adequate space temperature in the operational live data centre. The dynamic data collection and analysis during the continuous testing and monitoring period showed the average COP of 29.7 with the maximum COP of 48.3. Compared to the existing traditional vapor compression air conditioning system in the data centre, the energy saving using the super performance dew point cooling system is around 90 %. The work presented in this paper include detailed innovation aspects of the technology and the system operation, as well as the established bridging knowledges, methodology and technical procedure for bringing this new technology into real life operation which involve in data centre survey, optimum design and modularization of the specialist cooling system for ...

This study is pioneered in developing digital twins using Feed-forward Neural Network (FFNN) and multi objective evolutionary optimization (MOEO) using Genetic Algorithm (GA) for a counter-flow Dew Point Cooler with a novel Guideless Irregular Heat and Mass Exchanger (GIDPC). The digital twins, takes the intake air characteristics, i.e., temperature, relative humidity as well as main operating and design parameters, i.e., intake air velocity, working air fraction, height of HMX, channel gap, and number of layers as the inputs. GIDPC’s cooling capacity, coefficient of performance (COP), dew point efficiency, wet-bulb efficiency, supply air temperature and surface area of the layers are selected as outputs. The optimum values of aforementioned operating and design parameters are identified by the MOEO to maximise the cooling capacity, COP, wet-bulb efficiencies and to minimise the surface area of the layers in four identified climates within Koppen-Geiger climate classification, namely: tropical rainforest, arid, Mediterranean hot summer and hot summer continental climates. The system monthly and annual performances in the identified optimum conditions are compared with the base system and the results show the annual improvements of up to 72.75% in COP and 23.57% in surface area. In addition, the annual power consumption is reduced by up to 49.41% when the system is designed and operated optimally. It is concluded that identifying the optimum conditions for the GIDPC can increase the system performance substantially.

An efficient low-carbon system is proposed to meet the heating and cooling demands of rural houses in cold regions. Mini-channel solar panels incorporating a novel multiple-throughout-flowing loop are used for heat collection, whilst a vapour injection air source heat pump (VI-ASHP) is innovatively combined with an underfloor heating and cooling system. To demonstrate the system, a multiple-throughout-flowing mini-channel solar thermal panel array of 36 m2 and a VI-ASHP of 40 kW heating capacity have been built and tested. Subsequently, mathematical models of the solar-assisted VI-ASHP system are established and compared with the experimental data. Based on the validated models, the energetic, economic and environmental performance is investigated under the typical weather conditions for a northern Chinese city (Taiyuan). The results indicate that, for a common rural house employing the proposed novel system, the proportion of the annual heat requirement, cooling load and hot water heating energy provided by solar thermal energy, photovoltaic energy and electricity from the power grid is 74.6%, 6.9%, and 18.5% respectively, thus giving a total energy supply proportion of 81.5% from solar energy. In addition, compared with a coal-powered system, our system has a cost payback period of 6.52 years and a life-cycle net cost saving of 56328.4RMB, thus the proposed system provides a greater economic performance. Furthermore, it can save 5tons of anthracite coal and reduce carbon emissions by 12.1tons annually. The proposed solar-assisted VI-ASHP has the potential to fulfil heating and cooling demands whilst reducing carbon emissions in northern China.

Abstract Thermal management of photovoltaic cells is an essential research objective for increasing the conversion efficiency of the photovoltaic. Flat plate heat pipe is a passive cooling device capable of effectively reducing the solar cell temperature. Therefore, this study presents a numerical investigation of a hybrid photovoltaic-thermoelectric system with and without a flat plate heat pipe. A detailed comparative analysis of the electrical performance of the photovoltaic only, photovoltaic-thermoelectric and photovoltaic-thermoelectric-heat pipe systems is performed. The influence of solar concentration ratio, ambient temperature, wind speed and thermoelectric generator cold side temperature on the efficiency and power output of the photovoltaic only and hybrid photovoltaic-thermoelectric systems are studied using COMSOL 5.4 Multiphysics software. A three-dimensional finite element study is carried out and temperature dependent thermoelectric material properties are considered to increase the simulation accuracy. Results show that the photovoltaic-thermoelectric-heat pipe efficiency is 1.47% and 61.01% higher compared to that of the photovoltaic-thermoelectric and photovoltaic only systems respectively at a concentration ratio of 6. In addition, the photovoltaic-thermoelectric-heat pipe is recommended for highly concentrated systems because of its superior performance. Furthermore, the photovoltaic-thermoelectric system is a better alternative to the photovoltaic only system because of its enhanced performance which is second only to that of the photovoltaic-thermoelectric-heat pipe system. Results also show that ineffective cooling of the thermoelectric generator can adversely affect the performance of the hybrid systems. This study will proper valuable information on the feasibility of hybrid photovoltaic-thermoelectric systems with and without heat pipe. Finally, the three-dimensional nature of this study makes it very useful in understanding the actual temperature distribution in the hybrid systems.

This paper presents a comprehensive review on developments and advances of Solar Assisted Heat Pump technology reported in 21st century. Combination of thermal and photovoltaic solar collectors with heat pumps has been widely used in recent decades for simultaneous heat, hot water and power generation for a broad range of applications, from providing domestic and commercial buildings with heat and power to manufacturing and agricultural applications. This review critically analyses the research reported in past two decades with particular attention to the works with substantial importance for future development of the technology. Four distinctive investigation periods were considered and key developments and dominant technologies at each period were reported. The main novelties and breakthroughs in solar assisted heat pump technology, as identified by this review, are: (1) The ban on R-12 refrigerant which lead to dominance of R-134A refrigerant for a wide range of systems and applications, (2) Increasing interest in Solar-assisted Ground Source Heat Pumps following the technological advances that made the utilization of such systems cost effective, (3) Advances in numerical analysis methods and use of Artificial Intelligence applications in investigating performance and effectiveness of various systems, and (4) Integrating the Photovoltaic/Thermal collectors with heat pumps for simultaneous heat and power generation resulting in improved performance and reliable operation of systems under severe operating conditions.

Abstract Compared with conventional silicon solar cell, concentrating photovoltaic cell has a higher incident illumination intensity and non-uniform illumination intensity distribution. There is a close relationship between the illumination intensity and the resistance and shading losses of front metal fingers. In this paper, according to the non-uniformity of the illumination distribution formed by the concentrator, the effects of different finger numbers and spacing on the performance of low-concentrating photovoltaic cells were studied. First, low-concentrating photovoltaic cell modules with different finger numbers and spacing were established, and efficiency of these modules was compared to determine the optimal finger numbers and spacing of the front metal fingers. Then, effects of the shading losses, finger resistance and lateral spreading resistance on the performance of the low-concentrating photovoltaic cell were analyzed. Results show that for the specific illumination intensity distribution of the low-concentrating photovoltaic cell when the numbers and spacing of the front metal fingers are optimized, efficiency of the low-concentrating photovoltaic cell can be increased from 13.805% to 13.837%. Additionally, it can be concluded that the optimization of the number and spacing of the front metal fingers in the crystalline silicon solar cell is an efficient way to improve the electrical performance of the concentrating photovoltaic cell.

Abstract In the building sector, concerns towards the vast energy consumption has promoted the development of renewable energy technologies. In this regards, the solar concentration devices show a promising concept for building applications. However, the solar concentrators for application in buildings have many restrictions, which are different from the traditional solar concentrators. The main objective of this paper is to present a concise review on the building integrated concentrating devices, that have their own characteristics and multiple functions. This paper made a classification based on device’s functions, i.e. building integrated concentrated photovoltaic systems (BICPV), building integrated concentrating solar thermal (BICST) and building integrated concentrating solar daylighting (BICSD) and the combination of functions, i.e. BICPV/T, BICPV/D, BICST/D and BICPV/T/D. At the same time, this paper presented an elaborate introduction of the demands, types and applications of the building integrated concentrating devices and prospects/ directions/ policies about these technologies around the world. The review would provide important information for the actual engineering of building integrated concentrating devices.

Abstract Annular thermoelectric generators can eliminate the thermal contact resistance formed due to geometry mismatch when flat-plate thermoelectric generators are used with round shaped heat source or heat sink. Therefore, in this study, the numerical simulation of a segmented annular thermoelectric generator (SATEG) is investigated using three-dimensional finite element analysis. The thermoelectric and mechanical performance of the segmented annular thermoelectric generator is studied by considering temperature dependent thermoelectric material properties and elastoplastic behaviour of copper and the welding layer (solder). The influence of segmented pin geometry on the performance of the segmented annular thermoelectric generator is investigated and comparison is made with non-segmented annular thermoelectric generators. COMSOL 5.3 Multiphysics software is used to investigate the effects of heat source temperature, thermoelectric leg length and leg angle on the electrical and mechanical performance of the segmented and non-segmented annular thermoelectric generators. Results show that the segmented annular thermoelectric generator has a greater efficiency compared to the annular thermoelectric generator (ATEG) with Bismuth telluride material when the temperature difference is greater than 100 K. In addition, the efficiency of the SATEG is found to be 21.7% and 82.9% greater than that of the Bismuth telluride ATEG and Skutterudite ATEG respectively at 200 K temperature difference. Finally, the results show that increase in thermoelectric leg length can reduce the thermal stress and electrical performance of the segmented and non-segmented thermoelectric generators. Results obtained from this study would influence the design and optimization of segmented annular thermoelectric generators.