Experimental performance evaluation of solid concrete and dry insulation materials for passive buildings in hot and humid climatic conditions

It is known that enhancement of building energy efficiency can help in reducing energy consumption. The use of the solar insulating materials are the most efficient and cost effective passive methods for reducing the cooling requirements of the buildings. Apart from theoretical studies, no detailed experimental studies were performed in the UAE on energy savings by using solar insulation materials on buildings. Four (3. m. ×. 3. m. ×. 3. m) solar calorimeters were built in RAK, UAE in order to perform an open air outdoor test for energy savings obtained with solar insulating materials. The design is aimed to determine the heat flux reduction and the energy savings achieved with and without different solar insulating materials, mounted at the south wall of solar calorimeters with similar indoor and ambient conditions. Experimental results are discussed to evaluate the thermal performance during high temperature conditions in summer's period when cooling demand of the building is at its peak and also in winterswhen there is no cooling demand. The test is from 2012 to 2014. The controlled-temperature experimental study at a set point of 24. °C showed that if the standard building material, i.e. solid concrete, is retrofitted with polyisocyanurate (PIR) and reflective coatings or completely replaced with energy-efficient dry insulation material walls such as exterior insulation finishing system (EIFS), energy savings up to an average of 7.6-25.3% can be achieved. This is due to the reduction of heat flux by an average of 22-75% at south wall during summer. Similarly, free floating analysis was done during winter and the measurements showed the behaviour of the heat flux flow and the variations in room temperature due to the variation of thermal mass caused by the difference in heat capacities of the façade with and without insulation. Heat flux and temperature variations were minimal in cases of insulated buildings when compared against a reference building in the winter free flow tests. The temperature variation islimited to 2. °C in case of insulated buildings compared to 6. °C in the reference case caused by high thermal inertia. Thus, insulation is essential in summer as well as in winter for the buildings in Middle East and North Africa (MENA). Overall, this paper provides a novel view on the most significant contributors to the thermal behaviour of the structure, and presents a methodology on the outdoor tests with various materials, that can significantly improve the thermal behaviour of the buildings in the extremely hot climate.Peer reviewe

Influence of technical failures on the performance of an optimized community-size solar heating system in Nordic conditions

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.Peer reviewe

Performance comparison between optimized design of a centralized and semi-decentralized community size solar district heating system

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 semi-decentralized 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 (Multi-objective 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.Peer reviewe

Techno-economic optimization and analysis of a high latitude solar district heating system with seasonal storage, considering different community sizes

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 providednoticeable 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.Peer reviewe

A long-term performance analysis of three different configurations for community-sized solar heating systems in high latitudes

This paper proposes various community-sized solar heating systems configurations for cold climate. Three configurations were proposed, (I)a heat pump connected to two tanks in parallel, using charged borehole storage, (II)a heat pump connected between two tanks, using charged borehole storage to directly charge the lower temperature tank, and (III)two heat pumps used in series, one between the tanks and the other between the lower temperature tank and ground. In configurations (I) and (II) the vertical borehole field is used as a seasonal storage, in (III) it is used to extract heat only. The studied energy flows are heat and electricity. The border consists of energy production systems, heating grid and buildings. The impact of the considered system solutions on the heating renewable energy fraction, on-site electrical energy fraction, purchased energy and full cost as a function of the demand, solar thermal and photovoltaic areas, tanks and borehole volumes has been evaluated. The dynamic simulations results shows that an average renewable energy fraction of 53–81% can be achieved, depending upon the energy systems’ configuration. Furthermore, Energy System II utilizes less energy compared to other systems. In all three systems medium-sized solar thermal area is more beneficial instead of large area.Peer reviewe

Design and optimization of a De-centralized community sized solar heating system for Nordic Region

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 solar-charged low temperature tank and smaller de-centralized 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/m2/yr-25 kWh/m2/yr and renewable energy fraction 75%-91%.Peer reviewe

Design of a Simple Control Strategy for a Community-size Solar Heating System with a Seasonal Storage

The presented paper focuses on the design of different control strategies of a cold climate community-size solar thermal system located in Finland. The system was designed on TRNSYS software in order to perform dynamic simulation. A solar thermal system operating with various control strategies has been designed with an integrated ground source heat pump and a seasonal borehole storage to provide domestic hot water (DHW) and space heating (SH) for community-size demand. The system has two short term storage tanks, a hot tank and a warm tank. The impact of the considered system solutions on electricity consumption has been evaluated and compared as a function of the different collector control modes and different tank configurations (short term tanks sizes). Results have shown that the proposed system was able to provide a 78-83% renewable energy fraction. Total electricity consumption of the heating system varied by 20% between the best and the worst cases. Furthermore, system performance was better when solar energy was mainly stored in the warm tank. During a 5-year simulation, the annual seasonal storage efficiency improved from 0.23 to 0.31, whereas the heat pump electricity consumption reduced from 57.17 MWh to 45.93 MWh. The demand in winter was met mainly through ground heat and the rest was provided by the heat pump compressor. However, the demand in summer was met almost completely by solar energy.Peer reviewe

Computational comparison of a novel decentralized photovoltaic district heating system against three optimized solar district systems

Climate change is one of the biggest challenges at the present time, and to tackle such issue, solar energy and efficient buildings, in general, can be used. The goal is to design and optimize photovoltaic based decentralized district heating system and later compare it—economically and technically—against three different optimized typologies of solar district heating system in Nordic conditions. The photovoltaic based decentralized system consists of one centralized low temperature tank charged by photovoltaic and air-water heat pumps and a borehole thermal energy storage, while the decentralized high temperature tank charged by an individual water-water heat pump in each house. The centralized warm tank charges the borehole thermal energy storage. The other three systems are photovoltaic based centralized, roof-mounted solar thermal based centralized and roof-mounted solar thermal based decentralized district heating systems. In solar thermal based systems, collectors are used to directly charge the short-term storage tanks instead of the photovoltaics/heat pump combination. The proposed system is simulated using TRNSYS software. Lastly, purchased electricity and life cycle costs of the system are minimized using multi-objective optimization and the genetic algorithm. The results indicated that the decentralized photovoltaic based system outdoes all the other systems in terms of techno-economic performance. The purchased electricity can be reduced by 22% while at the same time life cycle cost can be reduced up to 40%, compared to the worst optimized system (solar thermal based centralized system). Moreover, the decentralized photovoltaic based energy system has a payback period of 9–27 years, compared to the solar thermal based system and the conventional single building-heat pump system, i.e. around 17–58 years and 15 years, respectively. The highest renewable energy fraction for heating can be close to 99% for this system. The decentralization and electrical based district systems are better in terms of life cycle cost, payback period and in terms of technical performance, compared to traditional single house and solar thermal based district heating systems.Peer reviewe