• Energy Research

This paper presents an innovative finned-plate latent heat thermal energy storage system for its integration in cogeneration systems. For optimization purposes it is very important to maximize the efficiency of the computational calculations. Therefore, three approaches are presented for the simulation of the same storage system: a numerical model, a simplified analytical one and a simplified numerical model.These three models are applied to the simulation of a prototype which has been tested experimentally by means of a test benchmark for storage systems. The simplified analytical and simplified numerical models are implemented by the definition of an effective heat transfer coefficient. From the comparison of the results it was concluded that the three approaches gives rise to a good agreement with the test results. However, the simplified analytical model fails to predict long configurations. On the other hand, the simplified numerical model presents very good results for every configuration, reducing the computational cost of the numerical model from several hours to minutes. The authors want to acknowledge the Spanish's Ministry of Economy and Competitiveness for the financial support through the project microTES (ENE2012-38633). Many thanks also to the Laboratory for the Quality Control in Buildings (LCCE) of the Basque Government. Gonzalo Diarce and Iker González-Pino acknowledge the financial support of the Basque Government, through the Department of Education, Universities and Research’s Personnel Research Training Program. Finally, the authors acknowledge DIKOIN for their technical support in the design and construction of the prototype, especially Alberto Cuadrado for his commitment.

In this paper an economic analysis of a 1 kWe Stirling engine-based micro-CHP (combined heat and power) residential plant is developed, approaching the case of a Spanish detached house sited in a cold climatic zone. The work focuses on analysing how the latest modifications in the Spanish micro-CHP and renewable energies regulation affect viability of this technology, as well as predicting what results could be achieved if policy support mechanisms in Spain were like those in two other European countries, Germany and United Kingdom, where this kind of equipment has good acceptance. For that purpose, once defined the reference dwelling, with the consequent consumption patterns, an installation for covering heating and DHW (domestic hot water) demands of the building, as well as part of the electric load, is designed and simulated in TRNSYS 17, getting results of those performance parameters necessary for applying the economic analysis. A condensing boiler supported by solar thermal collectors is taken as the reference installation. Results show that pay-back conditions of this kind of installations have turned hardly achievable with new remunerative conditions, getting widely better results with economic frameworks of other European countries. Iker González-Pino acknowledges the financial support of the Basque Government, through the Department of Education, Universities and Research’s Personnel Research Training Program (BFI-2011-153). Many thanks also to the Laboratory for the Quality Control in Buildings (LCCE) of the Basque Government. Finally, the authors want to acknowledge Centro Stirling for kindly supplying information about the maintenance requirements of the micro-CHP device.

In this paper, potential energy savings by implementing different energy saving methods to enhance the building envelope are presented and calculated through transient simulations using TRNSYS software. To do that, a reference building was selected. In order to develop an accurate model, a dwelling of that building was monitored during 3 months, and data obtained in that monitoring study was used to calibrate and adjust the simulation model. The monitoring study as well as the definition of the building model and the different assumed hypothesis are presented in this paper. Then, different energy saving measures (ESM) are defined for roof, façade and windows, and 64 combinations are simulated. Those results, which are evaluated under economic and energy criteria, are assessed using as reference thermal requirements fixed by Spanish regulation (both for new buildings and for building renovations). These results show how energy renovations in buildings involve important benefits not only under an energy or environmental approach, but also considering economic issues. Moreover, they evidence how the Spanish thermal regulation can be still toughened in order to meet European goals led to the mitigation of CO2 emissions. Many thanks are due to the Laboratory for the Quality Control in Buildings (LCCE) of the Basque Government, and to Bilbao Social Housing. Iker González-Pino also wants to acknowledge the financial support of the Basque Government, through the Department of Education, Universities and Research's Personnel Research Training Program BFI-2011-153.

This paper presents a comprehensive analysis of the energetic, economic and environmental performance of a micro-combined heat and power (CHP) system that comprises 29.5 m2 of hybrid photovoltaic-thermal (PVT) collectors, a 1-kWe Stirling engine (SE) and energy storage. First, a model for the solar micro-CHP system, which includes a validated transient model for the SE micro-CHP unit, is developed. Parametric analyses are performed throughout a year to evaluate the effects of key component sizes and operating parameters, including collector flow rate, storage tank size, SE micro-CHP flow rate, and battery capacity, on the energetic, economic and environmental performance of the proposed system using real hourly weather data, and thermal and electrical energy demand profiles of a detached house located in London (UK). The optimum component sizes and operating parameters are determined accordingly. The daily and monthly operating characteristics of the system are evaluated, and its annual performance is compared to those of a reference system (gas boiler plus grid electricity), as well as of other alternative solar-CHP systems including a PVT-assisted heat pump system and a standalone PVT system. The results indicate that the installation of such a system can achieve an annual electricity self-sufficiency of 87% and an annual thermal energy demand coverage of 99%, along with annual primary energy savings and carbon emission reduction rate of 35% and 37% relative to the reference system. Over 30 years of operation, the net present value (NPV) of the proposed system is £1990 and the discounted payback period is 28 years. The economics of the proposed system is very sensitive to utility prices, especially the electricity purchase price. Relative to the alternative solar systems, the proposed system offers greater environmental benefits but has a longer payback period. This implies that although the energy saving and emission reduction potential of the proposed system is significant, the initial/capital investment, especially of the SE CHP unit and the PVT collector array, are currently high, so efforts should focus on the cost reduction of these technologies. This work was supported by the International Postdoctoral Exchange Fellowship Program of the Office of China Postdoc Council (Grant No. 2020051). This work was also supported by the UK Engineering and Physical Sciences Research Council (EPSRC) [grant numbers EP/M025012/1, and EP/R045518/1], and by the Royal Society via an International Collaboration Award 2020 [grant number ICA\R1\201302]. The authors would like to thank UK company Solar Flow Ltd. (www.solar-flow.co.uk). Data supporting this publication can be obtained on request from cep-lab@imperial.ac.uk. For the purpose of Open Access, the authors have applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission.

Micro-cogeneration has been recognized as an efficient technology that can contribute to European Union's energy and climate objectives with respect to delivering low-carbon heat and power to citizens and small businesses. For improving the performance of this technology and so take as much advantage as possible of its potential, thermal energy storage plays a key role. This paper presents a techno-economic evaluation and optimization procedure focused on properly sizing and designing a micro-cogeneration residential installation, emphasizing how thermal energy storage is arranged and the different thermal loads prioritized within the plant. Therefore, the proposed methodology can be easily applied to buildings with different conditions and constraints. The methodology is then applied to a representative case study that consists of a detached house with a 1 kWe micro-cogeneration plant. Results of the case study show that in small installations DHW accumulation does not provide any significant improvement but a worsening of efficiency. Additionally, it is also proved that the layout of the distribution loop has an importance on the final performance of the plant that must be kept in mind. Moreover, results show that TES systems coupled with micro-cogeneration engines are traditionally highly oversized, thus worsening economic viability of these facilities This work was supported by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund through the MONITHERM project ‘Investigation of monitoring techniques of occupied buildings for their thermal characterization and methodology to identify their key performance indicators’, project reference: RTI2018-096296-B-C22 (MCIU/AEI/FEDER, UE)

This paper explores the effects of multi-zone heating systems in residential buildings in different Mediterranean climates. The aim is to evaluate their potential in residential sectors to provide a general basis from the results (from the energy and economic point of view). In addition, if feasible, a further detailed evaluation of this management strategy for optimising the energy use in residential buildings would also be carried out. To do so, the effects of two different zoning controls in different types of apartment, occupancy patterns, building characteristics and locations in Spain, have been assessed. Different combinations of these parameters have resulted in 336 different scenarios that have been dynamically simulated using Design Builder software. The obtained energy results have been analysed in detail. Moreover, an economic analysis of these results has also been carried out to evaluate the economic feasibility of these systems in residential buildings located in temperate climates. This has been calculated by evaluating the maximum investment that can be assumed in each scenario to achieve different payback periods (namely 10 and 20 years). The results obtained show that these systems could be a cost-effective strategy aimed at reducing the energy consumption in residential buildings, not only in cold climates, such as is shown in the literature (the majority of the studies found are located in the UK and northern countries), but also in more temperate climates, such as that of Spain. Savings of around 20% were obtained in the most usual scenarios in Spain (coherent with results obtained in previous studies in the UK found in the literature), showing that in several cases, the initial investment in zone-controlled systems could be paid off in less than ten years, especially in large apartments and the coldest weather conditions This work was supported by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund through the MONITHERM project ‘Investigation of monitoring techniques of occupied buildings for their thermal characterization and methodology to identify their key performance indicators’, project reference: RTI2018-096296-B-C22 (MCIU/AEI/FEDER, UE)

In this study, a hybrid cogeneration system that combines photovoltaic-thermal (PV-T) collectors with a Stirling engine, and a battery-pack-based energy option is proposed for residential applications. The system’s purpose is to fulfil the electrical and heating requirements of different types of houses in the United Kingdom, including detached, semi-detached and mid-terraced houses. This study includes a comprehensive assessment of the techno-economic feasibility and environmental impact of the proposed integrated energy system, after determining the appropriate sizing of the system’s components for the three different house types. The exergy efficiency of the integrated system for detached houses (with a 1 kWe-Stirling engine plus 28 m2 of PV-T collector array) is found to be higher compared to that for the semi-detached and mid-terraced house configurations, with the highest efficiency of 22 %. In terms of economic performance, detached houses have the lowest levelized cost of electricity (0.622 £/kWh), levelized cost of heat (0.147 £/kWh), and levelized cost of total energy (0.205 £/kWh). Furthermore, the system demonstrates the maximum potential reduction in CO2 emissions in detached houses. The achieved CO2 emissions reduction rates for different house configurations fall within the range of 30 % to 45 %. The proposed hybrid cogeneration system shows promise as an effective and sustainable solution to meet the energy demands of various residential house types in the United Kingdom, offering improved efficiency, cost-effectiveness, and substantial reductions in carbon emissions for detached houses. This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) [grant numbers EP/T022949/1, EP/M025012/1, and EP/R045518/1], and by the Royal Society via an International Collaboration Award 2020 [grant number ICA\R1\201302].

Individual metering and charging of heat and domestic hot water is one of the possibilities for reducing the energy consumption in existing multifamily buildings and, with this aim in mind, the EU-directive 2012/27/EU enforced the installation of individual heat consumption meters. Even though some experimental evaluation of energy savings that may be achieved in multifamily buildings with individual metering & charging systems can be found in the literature, the majority of these research pieces are focused on case studies or taking into consideration conditions related to cold climates, and there is still a lack of studies focused on evaluating its effects in more temperate climates that can be also found in Europe. Thus, in this paper, the potential of individual metering and charging of heat and hot water for saving energy in residential buildings in temperate climates is evaluated and quantified. To do so, a literature review on implementation of this system is carried out and presented firstly to get a better understanding of its implications on energy consumption in buildings. Afterwards, heating and hot water consumption data collected in a multifamily building where individual metering and charging system was implemented is evaluated in detail. With the aim of quantifying its effect on heating and hot water consumption, data corresponding to four complete heating seasons (two heating seasons prior to its implementation, and the two first heating seasons after implementing it) have been evaluated in detail, following a specific method described in the paper. Results show that individual metering and charging has brought a reduction of normalized energy consumption of 15–20% during the first two years after implementing it, and simple payback periods are around 10 years. These results confirm that individual metering and charging affects directly on user behaviour encouraging inhabitants to change their habits to reduce their energy consumption, and this effect is significant even in European temperate climates, such as the evaluated case study shows The authors acknowledge financial support by Basque Government, through the Environment, Territorial Planning and Housing Department’s ERAIKAL Programme (2015), as well as the financial support from the project ENE2015-65999-C2-2-R, by the Spanish Government (Economy and Competitiveness Ministry)