Is Low Flow Operation an Advantage for Solar Heating Systems?

Furbo, Simon; Mikkelsen, Svend Erik

doi:10.1016/b978-0-08-034315-0.50186-5

Cited by 16 publications

(8 citation statements)

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“…Among them, stratification has particularly raised the interest of researchers [27,28,33] for its strong influence on the thermal performance of plants [34,35]. For instance, Van Koppen et al [36] and Furbo and Mikkelsen [37] found that thermal stratification in solar heating systems allows a reduction in temperature at the collector inlet (which increases its efficiency) and leads to a limited operation of the auxiliary energy supply. Accordingly, stratification improves not only the water tank efficiency, but also that of the whole extended system.…”

Section: Literature Reviewmentioning

confidence: 99%

Development and Analysis of a Multi-Node Dynamic Model for the Simulation of Stratified Thermal Energy Storage

et al. 2019

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To overcome non-programmability issues that limit the market penetration of renewable energies, the use of thermal energy storage has become more and more significant in several applications where there is a need for decoupling between energy supply and demand. The aim of this paper is to present a multi-node physics-based model for the simulation of stratified thermal energy storage, which allows the required level of detail in temperature vertical distribution to be varied simply by choosing the number of nodes and their relative dimensions. Thanks to the chosen causality structure, this model can be implemented into a library of components for the dynamic simulation of smart energy systems. Hence, unlike most of the solutions proposed in the literature, thermal energy storage can be considered not only as a stand-alone component, but also as an important part of a more complex system. Moreover, the model behavior has been analyzed with reference to the experimental results from the literature. The results make it possible to conclude that the model is able to accurately predict the temperature distribution within a stratified storage tank typically used in a district heating network with limitations when dealing with small storage volumes and high flow rates.

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Section: Literature Reviewmentioning

confidence: 99%

Development and Analysis of a Multi-Node Dynamic Model for the Simulation of Stratified Thermal Energy Storage

et al. 2019

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“…Stratification is just a natural process: the warmth and density of water are inversely proportional properties. It is found that stratification allows low temperature working fluid to enter at the collector inlet, which increases its efficiency (Koppen, et al, 1979;Furbo & Mikkelsen, 1987). Although stratified TES is inexpensive, there are still problems with low energy density and complexity in designing the storage tanks (ARANER, 2016).…”

Section: Tank Stratificationmentioning

confidence: 99%

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

Rehman

Hirvonen

Sirén

2018

Journal of Cleaner Production

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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.

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“…The overall efficiency of ICS-SWHs is strongly related to their capability to capture solar radiation, store the energy collected as well as to their ability to supply hot water at a constant temperature during the discharging phase (draw-off) [44,62,99]. Several studies on ICS-SWHs have been performed showing the correlation between good collector performance and high levels of stratification within the storage tank when operated with no or infrequent large draw-offs [5,33,[63][64][65][66][67][68][69][70][71][72][73]. However when discharging water following that of domestic use, mixing can occurs within the storage tank [44] resulting in decrease in stratification but a potentially higher overall heat transfer from the collector to storage; and consequently better performance [5].…”

Section: Present Researchmentioning

confidence: 99%

Numerical and empirical evaluation of a novel building integrated collector storage solar water heater

2018

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Integrated collector storage is a long established simple low cost solar water heater configuration combining the solar collector with a storage tank into a single unit. Previous studies have shown the potential of integrated collector storage solar water heaters to significantly reduce domestic energy requirements for water heating, however challenges still remain to integrate them in roof/façades and ensure appropriate domestic hot water demand. In this article, a novel integrated collector storage solar water heaters is being investigated. The configuration and geometry proposed incorporates an embedded heating element to provide a self-contained domestic hot water system and consider roof integration restriction allowing the unit to be embedded within a structural insulated roofing panel system. The proposed system also utilizes an inlet diffuser designed to reduce the disruption to the stratification within the storage during and following draw-off. This article presents a Computational Fluid Dynamic analysis of internal flows and heat transfer regimes within this new collector configuration and compares its performance against previous developed prototypes using empirical testing. The increased aspect ratio of the new design was shown to significantly alter the heating and cooling characteristics of the collector, both gaining and loosing heat at a greater rate than the original prototype. The computational analysis showed that the collector charges effectively with some stratification. Higher draw-off rates however resulted in higher bulk water outlet temperatures, providing better energy delivery efficiency. The inlet diffuser was also shown to improve the thermal efficiency of the unit overall. The empirical testing shows the improvement in performance of this novel integrated collector storage solar water heaters against previous developed prototypes. The study highlights the need to review the effect of draw-off regime upon the performance of such systems in order to identify optimal regime and control strategy.

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Is Low Flow Operation an Advantage for Solar Heating Systems?

Cited by 16 publications

References 0 publications

Development and Analysis of a Multi-Node Dynamic Model for the Simulation of Stratified Thermal Energy Storage

Development and Analysis of a Multi-Node Dynamic Model for the Simulation of Stratified Thermal Energy Storage

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

Numerical and empirical evaluation of a novel building integrated collector storage solar water heater

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