Solar Domestic Hot Water Research Articles

Uncertainty in estimating the performance of solar thermal systems

The scope of this article is to present a methodology for the estimation of the uncertainty characterizing the energy performance of solar domestic hot water systems. The work concentrates on the uncertainty characterizing the expected annual energy output, as calculated through tests implemented according to the valid international standards. In order to cope with difficulties related to the algorithmic character of the measurement model, which cannot be explicitly formulated, Monte-Carlo simulation techniques are implemented. The component of uncertainty associated with measurement errors is estimated, on the basis of the metrological quality anticipated by the relevant testing standards. Errors due to imperfections of the energy model used through the test are also counted in, as well as uncertainties attributed to the variability of meteorological conditions. The proposed uncertainty analysis allows the realistic assessment of the actual energy provided to the user by a solar domestic hot water system. Implementation of the proposed methodology for a typical system leads to an expanded uncertainty in the order of 9% for the expected annual energy output.

Study on the Low Temperature Hot Water Heating System by Solar Energy

In this paper, we combine villa in comparing low temperature solar water for floor heating with regular heating sources. In the end, this paper analysis the economization and conservation benefit of solar heating system and domestic hot water. The best scheme of villa is solar system combining centralizing hearing.

Development of a stratified tank storage component for ESP-r with embedded phase change material modules

Solar domestic hot water systems are very common and are considered an efficient system for exploiting the renewable energy source of the sun, for instance national Italian regulations require the adoption of solar domestic hot water systems in new buildings. Water tanks are typical components for such systems, but have a serious drawback since they require a great amount of space in buildings. In this article, a new water tank model with embedded phase change material modules for the ESP-r code is presented in order to assess the possibility of using reduced size water tanks with additional latent storage. This article describes the numerical model used to deal with phase change phenomena and the incorporation of the method into ESP-r source code. To validate the model, the results of a test case have been compared with the literature data. A typical solar domestic hot water system has been simulated in order to study the impact of the phase change material modules inside tanks on the energy performance of the system. The results are reported using a global parameter that represents the fractional primary energy saved using the solar system. Water temperature plots with and without phase change material have been reported as well.

MEASUREMENT OF THE EFFICIENCY OF EVACUATED TUBE SOLAR COLLECTORS UNDER VARIOUS OPERATING CONDITIONS

The operating efficiency of evacuated tubes themselves under varying environmental conditions and installation scenarios, independent of water and space heating auxiliary equipment, are not readily available values. Further, Manitoba specific data has not been established. The purpose of this research program was to measure the efficiency of evacuated tube solar collectors under various operating conditions including: the angle of inclination towards the incident solar radiation, heat transfer fluid flow rate, glazing installation, and number of evacuated tubes. The operating conditions and configurations were chosen to represent realistic or probable installation scenarios and environmental conditions. Furthermore, the research aimed to identify the suitability of evacuated tube solar collectors to each of the scenarios. These design values are of use for appropriate sizing of water or space heating systems, system configuration and optimization, and calculation of return on investment. The scope of the research project was limited to the efficiency of various configurations of a 32-tube panel, not the entire solar domestic hot water or space heating system. Thus, factors such as heat loss in the tubing, solar storage tank, and heat exchanger efficiency were not investigated. The findings indicated that efficiency varied by approximately 5% between the different collector configurations, as observed from the overlay graph of results. When the efficiency of a collector is considered within a system it is proposed that effectiveness may be a better measure of overall performance.

A storage domestic solar hot water system with a back layer of phase change material

Phase Change Materials (PCMs) may be incorporated in solar thermal energy systems to act as latent heat storage media offering a high storage capacity compared to sensible heat storage. In this work, a storage solar collector that consists of six 80-mm diameter copper pipes connected in series is integrated with a back container of paraffin wax as a PCM thermal storage media. Outdoor experiments are carried out to demonstrate the potential of the storage solar system for water heating. The performance of the system is evaluated by calculating the various performance factors of the collector. The plate temperature is found to increase up to a distance of 2.5m from entrance, after which an almost steady temperature is noticed. Such trend was in contrast to the increasing trend previously noticed for a similar system without the PCM back layer. During off-sunshine hours, the liquid PCM transferred heat to the absorber, part of which was conducted as a useful heat in the circulating water. Therefore, the water continued to get heated after sunset, as the PCM acted as a heat source.

Application of Adaptive Resonance Theory neural networks to monitor solar hot water systems and detect existing or developing faults

Reliability is the Achilles’ heel of domestic solar hot water (SHW) systems, which otherwise offer a cost-effective way of reducing energy consumption and related emissions. Using a solar hot water system reliability testbed developed for this purpose, novel neural-network-based monitoring and fault detection methods were developed. It is argued that these methods could easily be incorporated in control or supervisory software, thereby allowing rapid detection and correction of faults. This would in turn prevent further damage, and ensure continued energy savings. In particular, the Adaptive Resonance Theory (ART) class of neural networks was used to detect and classify anomalies. Compared with other network types, ART networks are fast, efficient learners and retain memory while learning new patterns. Various ART networks were trained using simulation, and tested in the field using the testbed. The results show that simulation-based training is representative of real-life operating conditions, and that faults are correctly detected in the field. Using this technology, it will be possible to improve the reliability of SHW systems with little or no additional sensing equipment compared to typical installations.

Thermal Energy Storage using PCM for Solar Domestic Hot Water Systems: A Review

Thermal energy storage using phase chase materials (PCM) has received considerable attention in the past two decades for time dependent energy source such as solar energy. From several experimental and theoretical analyses that have been made to assess the performance of thermal energy storage systems, it has been demonstrated that PCM-based systems are reliable and viable options. This paper covers such information on PCMs and PCM-based systems developed for the application of solar domestic hot water system. In addition, economic analysis of thermal storage system using PCM in comparison with conventional storage system helps to validate its commercial possibility. From the economic analysis, it is found that, PCM based solar domestic hot water system (SWHS) provides 23 % more cumulative and life cycle savings than conventional SWHS and will continue to perform efficiently even after 15 years due to application of non-metallic tank. Payback period of PCM-based system is also less compared to conventional system. In conclusion, PCM based solar water heating systems can meet the requirements of Indian climatic situation in a cost effective and reliable manner.

Assessing the technical and economic viability of low-cost domestic solar hot water systems (DSHWS) in low-income residential dwellings in Brazil

Abstract Domestic solar hot water systems (DSHWS) have been used worldwide for many decades. Activities in this area are usually targeting middle- or upper-class residential dwellings, and solar collector design and sizing is carried out aiming at this market. In developing countries of the sunbelt, however, there is a huge potential for low-cost DSHWS in low-income residential dwellings. We have assessed the technical and economic viability of this technology, both from the electric utility's perspective, and from the standpoint of low-income residential consumers. We have analysed data of 12 months of continuous monitoring of a statistically representative sample of consumers at a low-income residential building in Florianopolis – Brazil (27°S, 1550 kWh/m 2 /year solar irradiation average). We have studied the power consumption of 60 residential units equipped with a commercially available, low-cost DSHWS, and a 30 units control group, where hot water was supplied with the electronic showerhead typical of Brazilian dwellings. Annual electricity savings averaged 38%, and peak-time electricity demand was reduced by 42%. For discount rates of up to 9.5%, this technology is attractive from a utility's perspective for large-scale deployment. The financial benefit from avoided CO 2 emissions has limited economic attractiveness, and can only be justified under a large-scale deployment program.

A Simulation Model for Predicting the Performance of Solar Domestic Hot Water System

The article deals with the modeling and simulation aspects of the performance improvement of a solar domestic hot water system. A mathematical model of this system is carried out to predict its operating performance under specified weather conditions of Jeju Island, Korea. The optimum mass flow rate through collector based on the relationship between the useful heat gain of solar collector and the electricity consumption of solar pump is investigated. Besides, the effect of various parameters such as solar collector area, initial water temperature and volume of storage tank is analyzed. The result of the simulation shows that the optimum mass flow rate was determined at kg/s with the new coefficient . At this value, the amount of useful heat gain slightly decreased about 84.3 (Wh) corresponds to 0.16% but the amount of electricity consumption strongly decreased about 227.8 (Wh) corresponds to 48.8% compares with kg/s ( ) was proposed by . Furthermore, the system performance is affected strongly by the change of collector area, initial water temperature and volume of storage tank.

Calculation of Performance Indicators for Solar Cooling, Heating and Domestic Hot Water Systems

In the framework of the French R&D project MeGaPICS (Method towards Guarantee of Performances for Solar Cooling and Heating applications – funded by Agence Nationale de la Recherche), a selected number of indicators are defined. The final goal is to find the right indicators to guarantee the performance of solar cooling, heating and Domestic Hot Water (DHW) systems. The selection process consists in several steps, which are presented in this article. First part sets up the best practice of configuration schemes for both packaged small size installation and large-scale units. Second part deals with annual and seasonal performance indicators. Then they are applied to different existing installations (French and European units), using monitoring data. Finally, some boundaries are defined for those indicators.

Environmental Life-Cycle Analysis of Hybrid Solar Photovoltaic/Thermal Systems for Use in Hong Kong

While sheet-and-tube absorber is generally recommended for flat-plate photovoltaic/thermal (PV/T) collector design because of the simplicity and promising performance, the use of rectangular-channel absorber is also tested to be a good alternative. Before a new energy technology, like PV/T, is fully implemented, its environmental superiority over the competing options should be assessed, for instance, by evaluating its consumption levels throughout its production and service life. Although there have been a plenty of environmental life-cycle assessments on the domestic solar hot water systems and PV systems, the related works on hybrid solar PV/T systems have been very few. So far there is no reported work on the assessment of PV/T collector with channel-type absorber design. This paper reports an evaluation of the energy payback time and the greenhouse gas payback time of free-standing and building-integrated PV/T systems in Hong Kong. This is based on two case studies of PV/T collectors with modular channel-type aluminium absorbers. The results confirm the long-term environmental benefits of PV/T applications.

Innovative and Energy Efficient Concept for Solar Cooling (DHW/Cooling Hybrid Strategy): Practical First Results

Within the framework of the French program called Emergence aimed at financing high quality solar heating and cooling demonstration projects, a first solar cooling installation was designed in 2011, and then installed on the beginning of 2012. This installation is based on an innovative and energy efficient concept to optimize solar energy valorization all year long: hybrid solar Domestic Hot Water and cooling strategy. The actual monitoring data won’t be shown on this document since the implementation of the system is still not over at the time of the paper redaction, but simulation data will be shown. This document will also give a feedback about implementing such systems and will show the high interest of such strategy to combine long term quality, simplicity of use and economical efficiency.

The Performance of a High Solar Fraction Seasonal Storage District Heating System – Five Years of Operation

The Drake Landing Solar Community in Okotoks, Alberta, Canada utilizes a solar thermal system with borehole seasonal storage to supply space heating to 52 detached energy-efficient homes through a district heating network. Systems of similar size and configuration have been constructed in Europe, however, this is the first system of this type designed to supply more than 90% of the space heating with solar energy and the first operating in such a cold climate (5200 degree C-days). Solar heat captured in 2293 m2 of flat-plate collectors, mounted on the roofs of detached garages, is stored in soil underground and later when needed for space heating, is extracted and distributed through a district system to each home in the subdivision. Independent solar domestic hot water systems installed on every house are designed to supply more than 50% of the water heating load. Annual greenhouse gas emission reductions from energy efficiency improvements and solar energy supply exceed 5 tonnes per house.The seasonal storage utilizes approximately 34,000 m3 of earth and a grid of 144 boreholes with single u-tube heat exchangers. The system is configured to maintain the centre of the field at the highest temperature to maximize heating capacity and the outer edges at the lowest temperature to minimize losses. A short -term thermal storage consisting of 240 m3 of water is used to interconnect the collection, distribution and seasonal heat storage subsystems.The system has undergone detailed monitoring since it was brought into service in July 2007 to characterize its performance and to improve the TRNSYS model employed in its design. A solar fraction of 97% in its fifth year of operation, convincingly confirms the design target, a solar fraction of more than 90% in year five, has been met. This paper describes the system and its operation, presents 5 years of measured performance and compares those results against the TRNSYS predicted performance for the same period.

The Effect of Discharge Configurations on the Thermal Behaviour of a Multi-tank Storage System

This paper presents the results of an experimental study conducted on a multi-tank thermal storage. The purpose of the study was to investigate the thermal behaviour of the stratified tank system when subjected to standard draw profiles. The experimental set up consisted of a charge loop to simulate a solar collector input, three commercially available 270 L domestic hot water tanks and three side-arm, natural convection heat exchangers. The system was charged using two 3kW electric heaters which produced a variable input power to simulate the variation in output of a typical fixed orientation solar collector. Realistic hot water draws were conducted according to the specifications of the Canadian Standard Association, CSA-F379.1, for Solar Domestic Hot Water Systems. Tests were performed over 2 days for three different plumbing configurations, and compared with simulated results produced in the TRNSYS simulation environment. Comparisons between system configurations were based on stratification levels and hot water delivery temperatures.

High performance storage composite for the enhancement of solar domestic hot water systems

The overall objective of this work is to evaluate the potential of compressed expanded natural graphite (CENG) and phase change material (PCM) composites to improve the performance of solar domestic hot water (SDHW) systems. To achieve this target, an original approach has been chosen. Comparatively to other studies, in which the storage material is usually placed on top of the water tank, the proposed approach was to place the composite directly inside a flat plate solar collector in substitution to the traditional copper-based solar absorber.

Performance evaluation of evacuated tube solar domestic hot water systems in Hong Kong

Evacuated tube solar water heaters are increasingly in use in Hong Kong because of their good thermal efficiency and high water temperature achievable as compared to the flat-plate solar water heaters. But so far their thermal performance has not been systematically evaluated and therefore not well known to the users. This paper reports our experimental and numerical works on evaluating the performance of the two common types of evacuated tube solar water heaters for domestic hot-water applications. These are the single-phase open thermosyphon system and the two-phase closed thermosyphon system. Our results show that the daily and annual thermal performance of the two-phase closed thermosyphon solar collector is slightly better than the single-phase open thermosyphon design. But the payback periods of the two are relatively the same because of the higher initial costs of the two-phase closed thermosyphon collector system. Although economically they are less attractive than the flat-plate type collector system, they are suitable for applications in advanced systems with higher temperature demands.

Experimental investigation of forced and wind assisted domestic solar hot water systems

This paper investigates a proposal to replace the electrically operated pump of a forced circulation solar hot water system with a windmill-driven pump. A two-stage centrifugal pump driven by a vertical axis windmill with a Savonius type rotor is added to the fluid loop. Tests on the forced circulation system (FCS) mode, with two different pump speeds, driven by an electrically operated pump or in wind-assisted system (WAS) mode were carried out during January, April, July, and October 2009. Test results obtained on clear days are reported. A daily average thermal efficiency level of between 30 and 37 per cent was obtained in FCS mode and it was between 31 and 36 per cent in WAS mode. With higher wind velocities, higher collector flow rates and higher efficiencies are obtained. In general, the performance of a domestic hot water system operating in WAS mode is on a par with that obtained in FCS mode. The WAS mode is a viable alternative to FCS mode in remote areas where the supply of electricity is problematic.

Enhancement of natural circulation type domestic solar hot water system performance by using a wind turbine

Performance improvement of existing 200 litres capacity natural convection type domestic solar hot water system is attempted. A two-stage centrifugal pump driven by a vertical axis windmill having Savonius type rotor is added to the fluid loop. The windmill driven pump circulates the water through the collector. The system with necessary instrumentation is tested over a day. Tests on Natural Circulation System (NCS) mode and Wind Assisted System (WAS) mode are carried out during January, April, July and October, 2009. Test results of a clear day are reported. Daily average efficiency of 25–28 % during NCS mode and 33–37 % during WAS mode are obtained. With higher wind velocities, higher collector flow rates and hence higher efficiencies are obtained. In general, WAS mode provides improvements in efficiency when compared to NCS mode.

Feasibility analysis of an indirect heat pump assisted solar domestic hot water system

It is well understood that a typical solar domestic hot water system can greatly reduce a building’s reliance on electrical consumption. The system may be further improved by including a heat pump as part of the design. In theory, a heat pump would result in colder fluid temperatures entering the collector thereby resulting in higher collector efficiencies and longer operation periods.One Indirect-style Solar Assisted Heat Pump (i-SAHP) design was modeled using the TRNSYS software and compared to a traditional solar domestic hot water (SDHW) system and an electric domestic hot water (DHW) system. All of the systems had the same load profile and delivered domestic hot water at a constant temperature. This insured that each system delivered the same amount of energy for the entire modeling period thereby creating a common basis for comparison. It is important to note that each system considered in this study was used for domestic water heating only. It was found that the electrical consumption and operating cost were the lowest with the i-SAHP system. Other i-SAHP configurations need to be modeled to determine which configurations work best under the local design constraints. Further, the incremental cost of the i-SAHP needs to be determined in order to estimate realistic payback periods and to gauge economic feasibility.This work was done as a preliminary stage and was meant to roughly gauge the feasibility of the specific i-SAHP system in the study. Therefore, generic inputs were consistently used with all of the TRNSYS components and the trends of the results were considered more important than the actual numerical values obtained.

Experimental and numerical study of a directly PV-assisted domestic hot water system

► PV-assisted Solar Domestic Hot Water system. ► The different control mode of the SDHW systems. ► The start-up characteristics of the solar pump optimized through various electronic devices. ► The evaluation of the yearly energy performance of the PV-SDHW system. The solar domestic hot water (SDHW) system is the most highly developed system for use of solar energy. The developments for the thermal regulation of buildings should reinforce this trend given the significant reduction of heating needs. Currently, the design of these SDHW installations is well controlled and the system performance is reasonably good. The annual average solar fraction is consistent with expected level (between 60% and 70%) according to a report of CSTB by evaluating 120 SDHW installations ( Buscarlet and Caccavelli, 2006 ). However, the control mode of conventional SDHWs induces additional costs related to the consumption of auxiliaries and other risks of dysfunction of the circulation pump due to the temperature probes and controller setup which induces low annual productivity of solar collector (200 instead of 400 kW h/m 2 expected). From this point of view, the photovoltaic pumped system seems suitable since it eliminates the controller and temperature sensors. This paper focuses on an experimental and numerical study of the behavior of a PV-SDHW system, focusing on the start-up phase optimized through various electronic devices. A detailed model of a circulation pump was developed by considering a direct current (DC) circulation pump coupled with various electronic devices (linear current booster and maximum power point tracker). The developed models were then validated experimentally, to reveal the influence of the threshold solar radiation on the circulation pump start-up and the pump flow rate as a function of the solar radiation, and its effects on the annual energy performance of PV-SDHW systems.