A long-term performance analysis of three different configurations for community-sized solar heating systems in high latitudes (original) (raw)
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An integrated model for designing a solar community heating system with borehole thermal storage
Energy for Sustainable Development, 2017
Borehole thermal energy storage (BTES) is found to be a favorable method for storing a large amount of thermal energy, and suitable for seasonal solar thermal storage, especially for large communities. Drake Landing Solar Community (DLSC), built in 2006, is the first such solar community in Canada. DLSC has achieved a 97% solar fraction after five years of operation. Although the DLSC project has been a success technically, the cost of the system is not attractive. In this study, an alternative design approach for a similar community is presented. The primary goal is to develop a system that not only achieves similar or better performance but also costs less. TRNSYS 17, along with a novel custom BTES component, is used for the system design and simulation. With the alternative design, the annual community thermal load of 2350 GJ is mostly met by solar thermal collectors via BTES and after five years of operation a 96% solar fraction is predicted. The simulation results are compared with published results for DLSC. It is estimated that the proposed system offers a 19% saving in initial cost in addition to reductions of BTES area of 38% and solar panel area of 25%.
Solar Energy, 2018
A solar community meets a significant amount of its energy demand through solar energy. In a high latitude country like Finland, the seasonal mismatch of solar availability makes it very difficult to achieve high renewable energy fractions without seasonal storage. In this study, a solar community located in Finland was optimized with respect to energy demand and life cycle cost. To gain better understanding of both technical and economical scaling effects, the optimization was done separately for four cases with 50, 100, 200 and 500 buildings. The study was performed for Finnish conditions using dynamic TRNSYS simulations and optimized with a genetic algorithm, using the MOBO optimization tool. The modeled energy system had solar thermal collectors and solar electric panels for energy generation, two centralized short-term storage tanks and a seasonal borehole thermal energy storage system (BTES) for energy storage, and a ground source heat pump for additional heat generation. The larger communities provided noticeable cost-benefits when aiming for high performance. Larger seasonal storages allowed more direct utilization of seasonally stored heat, lowering the need for the heat pump and reducing electricity demand. Comparing the best and worst performing optimal energy system, annual demand for heating electricity was reduced by 80%. Renewable energy fractions close to 90% for heating were possible for all community sizes, but the large communities could obtain them with about 20% lower costs.
Design and Optimization of a De-Centralized Community Sized Solar Heating System for Nordic Region
Proceedings of SWC2017/SHC2017, 2017
There is a need to accelerate the application of advanced clean energy technologies to resolve the challenges of climate change. Solar heating is a feasible solution among clean energy technologies. These technologies are not yet highly used in high latitudes due to various challenges. This paper focuses on the community sized solar district heating system configuration for cold climates. The proposed configuration consists of a partially decentralized heating system. Each individual house heat pump was connected between large centralized solarcharged low temperature tank and smaller decentralized individual high temperature tank in each house. Additionally, the large centralized tank was directly charged by solar-charged borehole storage during winters. Dynamic simulation approach was used through TRNSYS software coupled with MOBO (multi-objective building optimizer) for NSGA-II optimization algorithm. The purchased electricity and investments were two objectives minimized. The impact of the energy system on the renewable energy fraction, purchased electricity and investments as a function of the building heating demand, collectors and photovoltaic areas, short-term tanks storages and boreholes volumes were evaluated. Results showed that purchased electricity varied 47 kWh/m 2 /yr-25 kWh/m 2 /yr and renewable energy fraction 75%-91%.
Renewable Energy, 2018
Solar energy use in Nordic countries suffers from a high seasonal mismatch of generation and demand. However, given a large enough community, seasonal thermal storage could be utilized to store summertime heat gains for use in winter. This simulation study examined a Finnish case of fully electric solar heating, where heat pumps (HP) powered by photovoltaic (PV) panels were used for generating heat for both immediate use and for seasonal storage through a borehole thermal energy storage (BTES) system. Multi-objective optimization of LCC and energy use was performed by a genetic algorithm and TRNSYS simulations. Comparison was done between communities of a 100 and 500 buildings. The need for purchased electricity was between 40 and 26 kWh/m 2 per year for the optimal configurations. For the same cases the life cycle cost was between 220 and 340 V/m 2. Up to 98% renewable energy fraction was obtained for heating, showing that even in Finland it is possible to provide practically all heating by solar energy. The PV-type heating system was also compared to a solar thermal heating system from a previous study and it was found that the new design had as much as 36% lower life cycle cost.
Solar Heating Systems with Aquifer Seasonal Storage and Heat Pumps
2000
In the Netherlands two central solar heating systems with seasonal heat storage have been realised in the past. Due to recent interest in the development of innovative energy infrastructures with seasonal storage of solar energy for new housing developments, a study has been conducted of different system concepts combining active solar energy, heat pumps and aquifer seasonal storage. The study was commissioned by NOVEM. The concepts vary in the temperatures used for heat storage and in the application of centralised or individual heating systems. Energy and cost calculations have been carried out with the goal to optimise the concept lay-out on cost effectiveness with respect to CO2 reduction. A system lay-out with individual solar/heat pump systems attached to a collective aquifer seasonal storage system at low temperatures combines a large primary energy saving (56%) with a good cost-effectivity when compared to a high temperature seasonal storage system. The key factors enabling ...
Energy, 2020
The multi-family residential building sector is the least energy efficient in the United States, thus allowing for ample opportunities for significant cost-effective energy and carbon savings. In the present study, we propose a district solar borehole thermal solar energy storage (BTES) system for both retrofit and new construction for a multi-family residence in the Midwestern United States, where the climate is moderately cold with very warm summers. Actual apartment interval power and water demand data was mined and used to estimate unit level hourly space and water heating demands, which was subsequently used to design a cost-optimal BTES system. Using a dynamic simulation model to predict the system performance over a 25-year period, a parametric study was conducted that varied the sizes of the BTES system and the solar collector array. A life-cycle cost analysis concluded that is it possible for an optimally-sized system to achieve an internal rate of return (IRR) of 11%, while reducing apartment-wide energy and carbon consumption by 46%. Both a stand-alone and solar-assisted ground-source heat pump system were designed and simulated for comparison to the BTES system, and found to be less economically favorable than the solar BTES system. Thus, the promise for district-scale adoption of BTES in multi-family residences is established, particularly for new buildings.
Applied Energy, 2018
Solar thermal energy is widely recognized as one of the most important renewable energy resources. However, in high latitudes, due to various climatic and mismatch challenges, such solar district heating networks are difficult to implement. The objective of the paper is to optimize and compare two different design layouts and control strategies for solar district heating systems in Finnish conditions. The two different designs proposed are a centralized and a semidecentralized solar district heating system. The centralized system consists of two centralized short-term tanks operating at different temperature levels charged by a solar collector and heat pumps. Borehole thermal energy storage is also charged via these two centralized tanks. In contrast, the semi-decentralized system consists of one centralized low temperature tank charged by a solar collector and a borehole thermal energy storage and decentralized high temperature tank charged by an individual heat pump in each house. In this case, borehole thermal energy storage is charged only by the centralized warm tank. These systems are designed using the dynamic simulation software TRNSYS for Finnish conditions. Later on, multi-objective optimization is carried out with a genetic algorithm using the MOBO (Multiobjective building optimizer) optimization tool, where two objectives, i.e. purchased electricity and life cycle costs, are minimized. Various design variables are considered, which included both component sizes and control parameters as inputs to the optimization. The optimization results show that in terms of life cycle cost and purchased electricity, the decentralized system clearly outperforms the centralized system. With a similar energy performance, the reduction in life cycle cost is up to 35% for the decentralized system. Both systems can achieve close to 90% renewable energy fraction. These systems are also sensitive to the prices. Furthermore, the results show that the solar thermal collector area and seasonal storage volume can be reduced in a decentralized system to reduce the cost compared to a centralized system. The losses in the centralized system are 40-12% higher compared to the decentralized system. The results also show that in both systems, high performance is achieved when the borehole storage is wider with less depth, as it allows better direct utilization of seasonally stored heat. The system layout and controls varied the performance and life cycle cost; therefore it is essential to consider these when implementing such systems.
Renewable Energy, 2018
A hybrid installation that includes solar collectors and a ground source heat pump was developed and tested. There are many studies in the field of combined heat pump systems describing relatively large installations, designed for climatic conditions and soil thermal properties different from those in Bulgaria, where the experimental data are limited. The paper presents the construction of a small size hybrid installation containing diurnal and seasonal storages and supporting five different modes of operation with emphasis on the charging of borehole heat exchanger (BHE), heating mode with ground source heat pump (GSHP) and the followed natural relaxation. The paper also proposes a methodology for determination of different system energy efficiencies. High quality data for the different system operation modes in terms of soil and weather conditions typical of the Plovdiv region were obtained. The study proves the necessity of BHE charging with thermal energy from the sun during the summer mainly to avoid the ground thermal depletion. The comparison of the three heating modes investigated shows evident advantage of the ground source heat pump heating (GSHPH). The installation must be tested in the future for a longer time period.
Journal of Cleaner Production
There is a substantial need to accelerate the advancement and implementation of clean energy technologies in order to solve the challenges of the energy crisis and climate change. Solar heating technology is a feasible solution among clean energy technologies. In real conditions such complex systems often suffer from different kinds of technical failures and deviations reducing the system performance. This paper focuses on the challenges of a solar district heating system at high latitudes, proposes an optimized solution and investigates the influence of possible failures in planning, implementation and operation phase. The configuration proposed is a heat pump connected between two tanks, using solar-charged borehole storage to directly charge the lower temperature tank. Dynamic simulations were performed and a multi-objective optimization was carried out. The impact of the considered system solutions on the renewable energy fraction, purchased electricity and investment cost as a function of demand, solar thermal and photovoltaic areas, tanks and borehole volumes have been evaluated. The influence of 10 different technical failures was investigated. The study showed that in the optimized system, the most serious faults were i) de-stratification of the storage tanks (23-35% increase in annual purchased electricity) ii) on-off instead of variable speed control of the solar circulation pump (1-22% increase) and iii) reduction in heat pump performance (7-21%). These numbers of course depend on the initial assumptions, but still they show the magnitude of performance reduction some failures can achieve. Therefore, these parameters need to be considered during the implementation of such a system.
ANALYSES OF GROUND-SOURCE HEAT PUMPS COMBINED WITH SOLAR COLLECTORS IN DWELLINGS
In order to analyze different systems with combinations of solar collectors and ground source heat pumps, computer simulations have been carried out with the simulation program TRNSYS. The advantage of using solar heat was studied and compared for different systems with varied depths of the borehole for a single family dwelling in Sweden.