Solar Domestic Hot Water Research Articles

Test method for evaluating and predicting thermal performance of thermosyphon solar domestic hot water system

A test method for evaluating and predicting the thermal performance of thermosyphon Solar Domestic Hot Water (SDHW) system was proposed. The evaluating mathematical model of SDHW system was developed based on the two-node theory – a SDHW system was divided into the solid part and the fluid part. By combining the dynamic energy conservation equations of the solid part and the fluid part, the evaluating mathematical model of SDHW system was derived. The model parameters have clear physical meaning which can be used to evaluate the SDHW systems. The evaluating mathematical model was further processed by using the Laplace transformation technique and the predicting mathematical model was then derived. The predicting model can be used to predict the thermal performance of SDHW system for short and long term period with flexible draw off load conditions. The experimental method was designed and experiments were carried out to validate the test method. The measured mean fluid temperature in the storage tank was compared to the predicted mean fluid temperature. The annual thermal performance prediction of the system with two draw off load conditions at different daily hot water consumptions was also carried out.

Techno-economical analysis of building envelope and renewable energy technology retrofits to single family homes

In recent years, the popularity of single family homes, which have higher energy intensity than multi-family homes, has increased steadily in Turkey. This trend can be contributed to the interest of middle and high-income families towards living in larger homes, which also offer more privacy. Since multi-family homes are prevalent in Turkey, various studies are conducted to investigate the application of energy efficiency measures to these type of homes. Due to the increase in the number of single family homes and lack of research conducted to reduce the energy consumption for these type of dwellings, determining the feasibility of energy efficiency measures for the Turkish single family housing stock is an important concern. In this study, the techno-economic feasibility of applying a wide range of energy efficiency measures and renewable energy technologies to existing single family homes is investigated using monitored energy consumption data and building energy simulation program. The findings are extrapolated to the existing single family housing stock in three major cities of Turkey, namely Ankara, Istanbul, and Izmir, to estimate the potential for energy and emission reductions in Turkey. The results indicate that applying window glazing, roof, and a combination of window, wall, and roof improvements reduce heating energy demand by 21%, 34%, and 50%, respectively, with favorable payback periods. Among the renewable energy technologies analyzed, solar domestic hot water system results in the highest energy savings with the shortest payback period. Applying the combination of wall, window, and roof improvements and the retrofit of solar domestic water heating systems to existing single family homes in Ankara, Istanbul, and Izmir result in reductions of about 14 million, 8 million, and 15 million m3/year natural gas consumption in Ankara, Istanbul, and Izmir, respectively. These results can be used to develop policies for building insulation and equipment standards towards achieving low energy and emission national housing stock.

100% 에너지자립 제로에너지주택을 위한 비용효과적 신재생 설비시스템 최적구성에 관한 연구

Purpose: The domestic thermal insulation standard value has significantly increased to realize the Zero Energy House and many passive houses or zero energy houses are being built recently. Passive technology, which is represented by high thermal insulation and high density, shows relatively stable implementation by development of building materials and accumulated construction experience. On the other hand, there are not matured technologies for heating and cooling, hot water supply and ventilation including new and renewable energy. This study investigated the possibility of constructing optimal renewable energy and facilities system in terms of cost and effectiveness for zero energy houses that can achieve 100% of energy independence rate at current level. Method: The target building is a single story house with a floor area of 100 ㎡ located in Gyeonggi-do. Outer wall and roof floor are composed of 200mm SIP (Structural Insulation Panel) structure and window is vacuum window with U = 0.5 w/㎡℃. As a building equipment, this study considered following systems: ground source heat pump (GSHP), air source heat pump (ASHP), electric heating boiler (EHB), electric cable heating (ECH), electric air conditioner (EAC), solar domestic hot water system (DHWS), and solar PV. Finally, this study selected four combinations of systems (GSHP, ASHP+EAC, EHB+EAC, ECH+EAC) for the investigation. Result: This study assumed that all the loads in the building are covered by electric energy, and the calculation of the annual energy cost was based on the current electric charge system. Therefore, all loads are supplied by domestic electricity except GSHP. In addition, this study assumed that all renewable energy facilities for 100% energy self-reliance are supplied by solar power and then calculated the capacity to cover all household electricity with PV to derive the range of required PV capacity. Finally, this study calculated the initial investment cost range for each system configuration and the investment payback period, and determined the cost effective system configuration.

Thermal performance assessment and improvement of a solar domestic hot water tank with PCM in the mantle

To develop an appropriate solar DHW (Domestic Hot Water) tank for residential dwellings and put it into the European solar thermal market for promotion, thermal performance tests of PCM (Phase Change Material) hot water storage tanks of both a prototype and an improved version with a water volume of 148 l and 35 kg PCM in the mantle has been carried out. The tank was designed to provide DHW for residential dwellings through a combination of solar and auxiliary heating, concurrently using PCM on the basis of cheap SAT (Sodium Acetate Trihydrate) as a thermal battery to shave off peak auxiliary power or to work under power outage. Heat transfer matching properties of the bottom and the top spirals separately for solar charge and auxiliary charge of the prototype DHW tank were ascertained in terms of heat exchanger capacity rate (HXCR) and the rule of thumb of boiler powers, respectively. Moreover, heat content of the PCM was estimated via a series of test cycles in order to infer its capacity and stability. It was found that there were some technical problems for the prototype tank module, such as mismatching property of the heat exchanger spirals, heat mixing phenomena during hot water draw-off. Thus, an improved tank was manufactured based on the test results of the prototype. Further tests indicated that the matching property of the top heat exchanger spiral was ameliorated for auxiliary charge and the heat mixing between hot water supply pipe and water tank was restrained during discharge, except that the length of the bottom spiral should be further reduced. Regarding the PCM in the mantle, it was inferred that the PCM heat content was somewhat lower than that of ideally working SAT. The PCM tended to perform stably under 16 test cycles with more than 3-month consecutive tests, implying no phase segregation occurred as that would degraded its performance.

Experimental investigation and comparative performance analysis of a compact finned-tube heat exchanger uniformly filled with a phase change material for thermal energy storage

In the present paper, a latent heat storage system using a heat-transfer enhancement technique has been built and tested. The potential of using a natural phase change material of Moroccan provenance for energy storage was studied by experimental analysis. The enhanced heat transfer surface of the compact finned-tube heat exchanger presents geometric complications. Therefore, a new method based on equivalent circular fin efficiency for the calculation of the effective heat transfer surface area was developed and applied to the system under study. In order to carry out the performance analysis for this innovative system, charging and discharging experiments were conducted for different heat transfer fluid flow rates. It was found that increasing the flow rate from 0.2 to 1 l/min divides melting time by 2.5 and solidification time by four. The average effectiveness was calculated for each flow rate and was proven to decrease during charging from 0.95 for a flow rate of 0.2 l/min to 0.63 for 1 l/min. Likewise, increasing flow rate from 0.2 to 1 l/min for discharging process decreases heat exchanger effectiveness from 0.99 to 0.7. The combination of the effectiveness-number of transfer units method with the procedure that was developed to compute the effective heat transfer area lead to derive an empirical correlation. This equation was used to compare the finned-tube compact storage system with other heat and cold storage units. The comparison showed that the present system displayed satisfactory results. The second use of the correlation was to design, through a case study, a heat storage system suitable for solar domestic hot water production in a residential building.

Taguchi optimization of solar thermal and heat pump combisystems under five distinct climatic conditions

Solar domestic hot water systems worldwide generally combine solar collectors and heat pumps. The utilization of heat pump as the auxiliary heat generator of solar combisystem is a common solution of the last decade. Atmospheric factors such as solar radiation, ambient temperature, and relative humidity influence the performance of such systems; therefore, optimizing the flow rates in the solar and heat pump loops, as well as the volume of the water tanks, is essential to obtain maximum heating performance. In this study, the Taguchi method was applied to determine the optimal operating parameters for two solar combisystems (single- and dual-tank) by determining the higher-the-better characteristics of the signal-to-noise ratio. Moreover, five metropolitan areas were selected to investigate the effect of divergent climatic conditions on the Taguchi optimizations. The results demonstrated that the predominant parameter affecting performance varied for the two hydraulic layouts, but was identical across the five cities. In addition, the payback periods of the solar combisystems in the five cities were investigated. The combined results provide practical guidelines for choosing the best type of solar combisystem to implement under varying climatic and economic conditions.

The Optimization of Solar Water Heating System Using Hybrid Algorithm (PSO/HJ) for Different Locations of Turkey

In this study, optimum dimensions of Solar Domestic Hot Water System (SDHWS) were determined according to initial capital cost and energy consumption cost in different locations of Turkey. Typical Meteorological Year (TMY) data of 12 different locations which represent climatic characteristics of Turkey were used. Analysis was performed by using Particle Swarm Optimization / Hooke-Jeeves (PSO/HJ) hybrid algorithm which is a part of EnergyPlus®-GenOpt® programs. For each location, optimum number of solar collectors and hot water storage tank volume was determined. Initial investment and energy consumption costs decreased 6.1% for Gaziantep whereas solar fraction increased 42.8% for Ankara. In average, 4.5% decrease in initial investment and energy costs and 35.4% increase in solar fraction were obtained.

Introduction of organic-organic eutectic PCM in mesoporous N-doped carbons for enhanced thermal conductivity and energy storage capacity

A systematic mesoporous N-doped carbons/myristic acid-stearic acid composite materials with improved thermal conductivity, energy storage density and shape stable performance were prepared by encapsulating myristic acid-stearic acids (MA-SA) eutectic mixture into porous carbon matrixes derived from two synthesis strategies. The effect of synthesis strategies and the N species present in porous carbons on the microstructure and thermal energy storage properties of composite phase change materials were studied by various characterization techniques. The results indicated that N-doped porous carbons derived from in situ (NPC) had maximum of up to 88 wt% PCM loading with a melting latent heat of 164.33 ± 0.29 kJ/kg, which was up to 45.69% higher than that of composite PCMs by post synthesis route (MGC/MA-SA). Factors, like pore characteristics, capillary force, surface tension and additional interaction with N species present in carbon matrix played vital roles for encapsulation of MA-SA to the pores of supporting materials. Notably, NPC/MA-SA composite materials exhibited excellent thermal conductivity, 117.65% higher than pristine PCM, while 74.59% for MGC/MA-SA. The content, homogeneous distribution and graphitic nature of N as well as the interconnected porous carbons improves the heat transfer pathways in the composite PCMs during phase change process. All the prepared samples were thermally and chemically compatible even after 100 times thermal cycling, confirming that the prepared composite materials were a promising candidates for thermal management system in a medium phase transition temperatures like domestic solar hot water supply and air-conditioning purposes.

Inorganic Salt Hydrate for Thermal Energy Storage

Using phase change materials (PCMs) for thermal energy storage has always been a hot topic within the research community due to their excellent performance on energy conservation such as energy efficiency in buildings, solar domestic hot water systems, textile industry, biomedical and food agroindustry. Several literatures have reported phase change materials concerning various aspects. Among these materials, salt hydrates are worthy of exploring due to their high-energy storage density, rational price, multiple sources and relatively good thermal conductivity. This paper reviews the present state of salt hydrates PCMs targeting classification, properties, defects, possible solutions as well as their idiographic features which are suitable for applications. In addition, new trends of future research are also indicated.

Multi-objective optimization methodology for net zero energy buildings

The challenge in Net Zero Energy Building (NZEB) design is to find the best combination of design strategies that will face the energy performance problems of a particular building. This paper presents a methodology for the simulation-based multi-criteria optimization of NZEBs. Its main features include four steps: building simulation, optimization process, multi-criteria decision making (MCDM) and testing solution's robustness. The methodology is applied to investigate the cost-effectiveness potential for optimizing the design of NZEBs in different case studies taken as diverse climatic zones in Lebanon and France. The investigated design parameters include: external walls and roof insulation thickness, windows glazing type, cooling and heating set points, and window to wall ratio. Furthermore, the inspected RE systems include: solar domestic hot water (SDHW) and photovoltaic (PV) array. The proposed methodology is a useful tool to enhance NZEBs design and to facilitate decision making in early phases of building design. Specifically, the non-dominated sorting genetic algorithm (NSGA-II) is chosen in order to minimize thermal, electrical demands and life cycle cost (LCC) while reaching the net zero energy balance; thus getting the Pareto-front. A ranking decision making technique Elimination and Choice Expressing the Reality (ELECTRE III) is applied to the Pareto-front so as to obtain one optimal solution.

Potential of cascaded phase change materials in enhancing the performance of solar domestic hot water systems

The current paper explores a multi-tank thermal storage system for multi-residential solar domestic hot water applications. The thermal storage system includes phase change materials (PCMs) of different melting temperatures incorporated in the tanks. The PCMs are introduced as vertical cylindrical modules and water flowing along the length of tank is used as the heat transfer fluid. An enthalpy porosity model was developed to solve for the phase change process within the PCM modules. The model was validated and verified with previous work and predictions were in good agreement (less than 5% deviation). The hybrid tank model was linked with the collector performance. Typical Canadian weather data and a dispersed demand profile for a multi-residential building were considered. The performance of the hybrid system was judged based on the maximum possible storage volume reduction compared to the water only system with the same benefit to the end user. PCM maintains cooler water temperature entering the collector which results in a reduction of collector losses and extension of pump activation time. This increases the delivered energy to the load and hence increases the solar fraction. It was found that cascading four 75 L tanks containing PCMs of melting temperatures 54 °C, 42 °C, 32 °C and 16 °C gives a similar solar fraction to that for a 630 L water only tank. The multi-tank hybrid system thus allowed for over 50% reduction in the required storage volume.

Energy saving concept development for the MORE-CONNECT pilot energy renovation of apartment blocks in Denmark

The European Horizon2020 project MORE-CONNECT on prefabricated deep energy renovation of residential dwellings also covers pilot demonstration projects, which are to be carried out in six of the participating countries. For each country a unique, climate specific concept development analysis is carried out. The concept development follows the MORE-CONNECT methodology and thus aims towards a Zero Energy Building (ZEB) level or if cost limitations require nearly Zero Energy Building (nZEB). For the Danish situation, this means that the energy requirement for heating purpose is to be brought down from around 100 kWh/m² to below 20 kWh/m². As the pilot project has not yet been identified, concept development calculations has been conducted for a generic building. The technologies to be considered for this energy renovation are: Insulation of the façade, insulation of the roof, low-energy windows, heat-recovery ventilation, solar domestic hot water and a PV-system. Within the MORE-CONNECT two technologies are under development in Denmark. The first is a new PV-roof solution in which the PV-cells are fully integrated in the roofing elements. This PV-roof can be fitted into any roof surface shape. It can also be constructed as a PVT-roof connected to a heat pump for heating purposes. The second technology under development is 3-D finishing of a new layer of façade insulation by an industry robot. When an insulation layer has been placed on any given façade a finishing layer of plaster can be added and finished with any desired patterns or painting.The paper presents the present stage of the concept development work and is a continuation of the first concept development analysis presented at the SBE conference in Tallinn in 2016.

An alternative approach for assessing the benefit of phase change materials in solar domestic hot water systems

Phase change materials (PCM) for thermal energy storage in solar energy systems have been the subject of a great deal of research in the literature. Despite this, the research results pertaining to the efficacy of PCMs in enhancing system solar fraction are mixed. The current paper explores this issue numerically within a systems context. A typical solar domestic hot water system is considered. The PCMs are introduced as vertical cylindrical modules contained within the water tank, thus forming a hybrid PCM/water thermal storage. Water flowing along the length of tank is used as the heat transfer fluid. A model was developed based on the enthalpy-porosity method to solve for the phase change process within the PCM modules. The model was thoroughly validated and verified and predictions were in good agreement (less than 5% deviation) with results from the literature. The hybrid tank model was linked with the collector performance and the system was tested for typical days of Canadian weather with a dispersed demand profile. The solar fraction of the hybrid system was compared to that for an identical system using water-only as the thermal storage medium. The system analysis explores the impact of storage volume on solar fraction for systems with and without PCMs included. The systems approach is critical since it allows for the coupled effects of the thermal storage, solar collector, and household load to be incorporated. The analysis clearly shows that incorporation of PCMs into the thermal storage results in enhanced solar fraction at undersized tank volumes relative to the demand. In contrast, as the tank volume is increased, the benefit of the PCMs diminishes and identical performance is obtained between the two systems at large volumes. An energy balance of the system shows that, despite marginally increased heat losses from the hybrid tank, the benefits of the hybrid storage at small storage volumes are due to the reduction in the collector fluid inlet temperature which increases the pump run time and thus the solar energy collected and reduction of collector losses.

Small Changes Yield Large Results at NIST's Net-Zero Energy Residential Test Facility.

The Net-Zero Energy Residential Test Facility (NZERTF) was designed to be approximately 60 % more energy efficient than homes meeting the 2012 International Energy Conservation Code (IECC) requirements. The thermal envelope minimizes heat loss/gain through the use of advanced framing and enhanced insulation. A continuous air/moisture barrier resulted in an air exchange rate of 0.6 air changes per hour at 50 Pa. The home incorporates a vast array of extensively monitored renewable and energy efficient technologies including an air-to-air heat pump system with a dedicated dehumidification cycle; a ducted heat-recovery ventilation system; a whole house dehumidifier; a photovoltaic system; and a solar domestic hot water system. During its first year of operation the NZERTF produced an energy surplus of 1023 kWh. Based on observations during the first year, changes were made to determine if further improvements in energy performance could be obtained. The changes consisted of installing a thermostat that incorporated control logic to minimize the use of auxiliary heat, using a whole house dehumidifier in lieu of the heat pump's dedicated dehumidification cycle, and reducing the ventilation rate to a value that met but did not exceed code requirements. During the second year of operation the NZERTF produced an energy surplus of 2241 kWh. This paper describes the facility, compares the performance data for the two years, and quantifies the energy impact of the weather conditions and operational changes.

Case study for experimental validation of a new presizing tool for solar heating, cooling and domestic hot water closed systems

This paper presents a case study experimental validation of PISTACHE which is a new presizing tool intended for designers and planners. It facilitates pre-design and allows the evaluation of annual performance and the integration potential of solar heating, cooling and domestic hot water closed systems. This new tool has been performed in order to standardize the sizing methodology and the comparison of the SHC&DHW closed systems. The comparison framework used in PISTACHE has been performed using seasonal performance indicators that were issued and gathered from experimental data provided by several operating plants. Thus, PISTACHE is an easy graphical user interface and free downloadable tool. In order to check the reliability of the new developed tool, two configuration modes are investigated in this experimental study: a simple cooling mode (RAFSOL plant) and a double cooling and heating mode (SONNENKRAFT installation). The whole validation process is performed using the GenOpt optimization program to determine the optimum set of internal parameters for PISTACHE tool.

Performance analysis and economic assessment of solar thermal and heat pump combisystems for subtropical and tropical region

In the present research, combinations of solar collectors and air-source heat pumps for domestic hot water (DHW) are addressed in terms of hydraulic layout and climate conditions. TRaNsient SYstems Simulation (TRNSYS) software was implemented to simulate and examine the heating capacities of various DHW systems. For validating the numerical results, a demonstration site featuring a solar collector and heat pump combisystem with real-time monitoring sensors was established in Tainan, Taiwan. The corresponding parameters of TRNSYS modules were also tested and validated using experimental data. For comparison with the electrical heating water system, three common DHW systems—a conventional solar DHW system, a single-tank solar combisystem, and a dual-tank solar combisystem—were selected, and their technical and economical aspects were assessed. To determine the effect of climate conditions, two metropolitan cities in Taiwan were simulated: Taipei represented subtropical cities and Kaohsiung represented tropical cities. Results for both Taipei and Kaohsiung showed that the dual-tank solar combisystems had the lowest electrical consumption levels and operating costs. The incremental capital costs of the solar combisystems were considered, and realistic payback periods were calculated to determine economic feasibility.

A comparative survey of the energy performances of dwellings across Cyprus

Cyprus, due to a long-lasting political conflict, has been divided for nearly 50 years, Greek Cypriot community living in the southern and Turkish Cypriot community living in the northern part of the island. Research has been carried out on both sides of the island separately, to meet the requirements of the Directive 2002/91/EC on energy performance of buildings. In the present study, an attempt was made to characterize the energy performances of dwellings across Cyprus since the negotiations to settle the problem between the two communities are still in progress. The methodology and the results of a recent survey conducted in the northern part are presented together with an earlier data reported for the residential building stock in the southern part of the island. It is noted that the dwellings in the northern part had relatively smaller mean floor area and lower electricity consumptions. The utilization of central heating systems and double glazed windows were more common in the southern part. Nevertheless, similar house types with often poor external wall insulations, extensive use of solar domestic hot water systems, significant cooling energy consumptions and almost the same primary energy demand per total area appear to be the common features of most dwellings in both parts of the island.

Inclusive analysis and performance evaluation of solar domestic hot water system (a case study)

In recent years Solar Domestic Hot Water systems have increased significantly their market share. In order to better understand the real-life performance of SDHW systems, a single detached house was selected for extensive monitoring. Two solar panels were installed on the house roof to provide thermal energy to the Domestic Hot Water (DHW) system. The house was equipped with data logging system and remotely monitored with performance data collected and analyzed over one year. The paper presents the inclusive analysis and performance evaluation of SDHW system, including DHW recirculation loop, under Canadian weather conditions for average family occupancy (two adults and two kids) with daily average DHW, draws of 246L. Moreover, the study is carried out a significant recommendation to improve the SDHW performance, decrease the gas energy consumption and reduce greenhouse gas (GHG) emissions. The SDHW performance depends mainly on DHW flow rate, draw time and duration, city water temperature, DHW recirculation loop control strategy and system layout. The performance analysis results show that 91.5% of the collected solar energy is transferred to the DHW heating load through the solar tank. The contribution to DHW heating load is about 69.4% from natural gas and 30.6% from solar. The recirculation loop is responsible for close to 34.9%, of DHW total energy.

Control strategy and thermal inertia influence on evacuated tube solar water heating systems

The main objective of this article is to investigate the effect of a control scheme on the behavior of a solar domestic hot water system, consisting of two evacuated tubes with compound-parabolic concentrator (CPC) collectors and a storage tank. In this regard, a transient thermal analysis of the system was performed using an original mathematical model. The developed model was validated by comparing the results with the data provided by the manufacturer. Simulations were conducted during a 48-h period in the meteorological conditions of Bucharest, Romania (latitude 44°24′N, longitude 26°05′E). The second objective of the present work relates to the working fluid thermal inertia. An analysis was made to determine whether the solar collectors’ fluid thermal inertia has an impact on the storage tank water temperature. Three different working fluids have been considered. The results showed that for the entire 2-day period in which simulations have been conducted, differences between the useful energy delivered to the storage tank water in the case with mass flow rate adjusted depending on the incident solar radiation and the cases with constant mass flow rate were approximately 1 kWh in summer and 0.72 kWh in winter. In addition, it has been concluded that the time required to heat the storage tank water from 30 to 60 degrees centigrade is approximately an hour less when the system is working with water compared to the propylene glycol case.

Energy efficiency of a solar domestic hot water system

The solar domestic hot water (SDHW) system located on the campus of Bialystok University of Technology is the object of the research described in the current paper. The solar thermal system is composed of 35 flat plate collectors, 21 evacuated tube collectors and eight hot water tanks with the capacity of 1 m 3 of each. Solar facility is equipped with hardware for automatic data collection. Additionally, the weather station located on the roof of the building provides measurements of basic parameters of ambient air and solar radiation. The main objective of Regional Operational Program was the assessment of the effectiveness of this solar energy technology in the climatic conditions of the north-eastern Poland. Energy efficiency of SDHW system was defined in this research as the ratio between the useful heat energy supplied to the domestic hot water system and solar energy incident on the surface of solar panels. Heat loss from water storage tanks, and from the pipe network to the surrounding air, as well as the electrical energy consumed by the pumps have been included in the calculations. The paper presents the detailed results and conclusions obtained from this energy analysis.