Solar Domestic Hot Water Research Articles

Transparent insulation integration in solar thermal collector: Advancing performance for domestic water heating in oceanic climates of Western Europe

Decarbonizing residential hot water demand requires efficient solar collectors. Conventional flat plate collectors are widely available but experience high heat losses in colder climates. This work investigates the performance of a modified flat plate collector that incorporates honeycomb transparent insulation to reduce convective heat loss, offering a cost-effective alternative to energy-efficient evacuated tube collectors. The thermal performance of the modified flat plate collector was obtained using the finite element method in COMSOL Multiphysics, revealing a significant reduction in convective heat loss. The obtained thermal performance was then incorporated into a transient simulation to assess the year-around performance of the modified flat plate collector in a solar domestic hot water system for Irish climate. The transient simulation accounted for variations in the transparent insulation’s transmission with incidence angle which was overlooked in previous studies. Over a year-long simulation, the modified flat plate collector generated a total useful energy of 532.45 kWh m−2, while requiring 1640 kWh of auxiliary energy to meet the hot water demand of a single-family house in Ireland. An economic analysis of solar domestic hot water system revealed that the modified flat plate collector could yield savings of 443.44 € more than the standard flat plate collector and 3281.03 € more than the evacuated tube collector for homeowners. Consequently, the simple payback period for the solar domestic hot water system decreased from 3.72 years with a standard flat plate collector and 8.37 years with an evacuated tube collectors to 3.56 years with a modified flat plate collector. In addition to its economic viability, the modified flat plate collector could result in a CO2 savings of 901.85 kgCO2 per year. The study concludes with a sensitivity analysis to identify the market conditions that maximize the profitability of the modified flat plate collector based solar domestic hot water system.

Economic Analysis for Performance of Photovoltaic-Direct-Powered Solar Domestic Hot Water Systems Using Experimental Evaluation in Iraq

Economic Analysis for Performance of Photovoltaic-Direct-Powered Solar Domestic Hot Water Systems Using Experimental Evaluation in Iraq

The Renewable Energy course at the Technical Engineering School of Barcelona

A “Renewable Energy Course” has been offered for several years at the Technical Engineering School of Barcelona (EUETIB). This paper reports on our experience as teachers of the “Renewable Energy Course”. The course program and its methodology are also described. The main objectives of the course “Renewable Energy ” are to allow engineering students to learn fundamentals and essentials on Renewable Energy, the present situation on Renewable Energy in Catalonia and what kinds of renewable energy are basically used in Barcelona. Due to “Ordenança Municipal de Medi Ambient Urbà” we decided pay attention especially on Solar Domestic Hot Water Systems (SDHWS). The aim of our paper is to share our experience on: - What kind of knowledge we considered the most reasonable for a course on renewable energy. - What kind of methodology we used during the course.

Achieving Net Zero Carbon Performance in a French Apartment Building?

Containing global warming to 1.5 °C implies staying on a given carbon budget and therefore being able to design net zero carbon buildings by 2050. A case study corresponding to a French residential building is used to assess the feasibility of achieving this target. Starting from an actual construction built in 2016, various improvement measures are studied: lowering heating energy needs, implementing bio-sourced materials and renewable energy systems (geothermal heat pump, solar domestic hot water production, and photovoltaic electricity production). Dynamic thermal simulation is used to evaluate energy consumption and overheating risk in hot periods. Greenhouse gas emissions are quantified using a consequential life cycle assessment approach, considering that during a transition period, exporting electricity avoids impacts corresponding to marginal production on the grid. Avoided impacts decrease and become zero when the grid is ultimately “decarbonized”. From this point, the building should be net zero emissions, but there remain unavoidable emissions. Residual GhG (greenhouse gas) emissions account for 5.6 kgCO2 eq/m2 annually. The possibility of offsetting these emissions is investigated, considering sequestration in forests or vegetation systems. A net zero emission level can be achieved, but on a national level, it would require that the whole sequestration potential of forest growth be devoted to offset emissions of new construction. A circular economy for construction products and equipment and considering water use will be needed to further decrease environmental impacts.

Investigation on the thermal performance and economy of a solar assisted air source heat pump domestic hot water system

In order to increase the utilization of renewable energy and reduce carbon dioxide emissions, a solar assisted - air source heat pump (SA-ASHP) domestic hot water supply system is proposed, designed and built, the thermal performance and economy are numerically simulated and experimentally verified, the optimal design parameters are determined based on the economic optimization analysis. The results show that the coefficient of performance (COP) of air source heat pump (ASHP) varies from 2.62 to 3.93 and the COP of SA-ASHP system varies from 2.76 to 6.26. The solar fraction varies from 8.83% to 45.51%, and varies greatly in different seasons. The simulated heat collection of solar collector, the power consumption and heating capacity of ASHP, and the total power consumption of water pump are in good agreement with the measured results. Compared with the existing SA-ASHP system, the annual cost has decreased by 1998.32USD, annual cost converted from initial investment has decreased by 629.08USD, operating cost has decreased by 1369.25USD and total power consumption has decreased by 16897.79 kWh of the optimized SA-ASHP system. The optimum ratio between the input power of ASHP and the collector area is 0.078 kW/m2. The research results play an important role in guiding the design, operation and heat source selection of domestic hot water (DHW) system in student dormitory.

TRNSYS Simulation of the Use of Solar Collector-based Domestic Hot Water System in Central and Eastern European Countries (CEEC)

With the prevailing energy crisis and the public’s growing environmental awareness, renewable energy sources (sun, wind, water) are playing an increasingly important role in Europe and around the world. Due to its easy availability and relatively high efficiency, it is the solar energy that is attributed with great potential in decarbonizing the energy sector. Among the most popular devices that enable the use of solar radiation are solar collectors. They are used in heating and domestic hot water preparation systems, as well as for heating swimming pool water. However, their efficiency depends on many factors, of which the main one being the climatic conditions. This paper presents the results of energy simulations of a solar collector-based domestic hot water system for the capitals of five selected Central and Eastern European Countries (CEEC) – Riga (Latvia), Warsaw (Poland), Prague (the Czech Republic), Bratislava (Slovakia), and Zagreb (Croatia). The system model was developed using the TRNSYS software, in which dynamic simulations were also performed for an entire year (8760 h). For each location, the efficiency of the flat-plate solar collectors, the amount of useful energy generated by them, as well as the amount of energy needed to meet the load and auxiliary energy requirements were analyzed and compared. The extent to which increasing or decreasing the area of solar collectors affects the operation and efficiency of the system for different locations was also estimated. The results showed that in terms of efficiency, the use of solar collectors is most favorable in Slovakia and placed southernmost-located Croatia, where it also achieved the lowest annual auxiliary energy demand. The least favorable location, on the other hand, turned out to be the capital of Latvia. It is also worth noting that regardless of location, the area of solar collectors has a significant impact on the efficiency of the entire system.

Design of a latent heat thermal energy storage system under simultaneous charging and discharging for solar domestic hot water applications

Latent heat thermal energy storage (LHTES) systems using phase change materials (PCMs) have appeared as promising solutions for energy storage when harnessing renewable energy sources in a wide range of engineering applications. The present study focuses on the design of horizontal shell-and-tube PCM-based LHTES systems capable of simultaneous charging and discharging in solar domestic hot water (SDHW) applications. Two scenarios are investigated: (i) initially fully charged, and (ii) initially fully discharged LHTES systems, in both cases with a 30-min charge/discharge time interval. Configurations with key geometrical design variations are considered to identify the best radial and tangential positions of the heat transfer fluid (HTF) tubes inside the shell that enhance storage performance against the following criteria: (i) gained and released thermal power, and (ii) total gained and released energy per unit mass of PCM. The distance between the hot and cold HTF tubes was maintained constant and an LHTES with horizontally aligned HTF tubes was selected as a baseline case. The findings showed that tangential displacement had a considerable impact on the performance of the system, while the effect of radial displacement was marginal. A design with displacements of ¼ tube diameter and 90° in the radial and tangential positions of the HTF tubes, respectively, had promising performance in both considered scenarios. In comparison to the baseline case, which had the hot and cold tubes positioned horizontally, and symmetrically on the shell's central plane, this configuration demonstrated a 103.02% enhancement in energy delivery in the fully discharged and a 2% enhancement in the fully charged scenario, respectively.

Plus Energy Buildings: A Numerical Case Study

The feasibility of Plus Energy Building for a sample relevant case is investigated. After a literature review aimed to identify key aspects of this type of buildings, a preliminary evaluation of the thermal performance of a building constructed using conventional material is presented together with a parametric analysis of the impact of typical influential parameters. Solar domestic hot water (SDHW) and photovoltaic systems (PV) are considered in the study. Numerical simulations indicate that for the examined sample case (Beirut in Lebanon) the total annual energy need of conventional building is 87.1 kWh/y.m2 . About 49% of energy savings can be achieved by improving the building envelope and installing energy efficient technologies. Moreover, about 90% of energy savings in domestic hot water production can be achieved by installing a SDHW system composed of two solar collectors connected in series. Finally, the addition of a grid connected PV array system can significantly mitigate the energy needs of the building leading to an annual excess of energy.

Mathematical Modelling and Experimentation of Soy Wax 68℃ Encapsulated into Solar Tank (Case Study)

Governments worldwide are attempting to minimise CO2 emissions, and solar energy storage remains the most difficult problem to tackle in the current climate. Typically, domestic hot water is mainly used for heat process services in colder climates when the tank loss is significant. Any design modification can result in a higher solar yield. Since water is a perfect medium for heat storage, this article will examine different Solar Domestic Hot Water (SDHW) systems in cold climates such as Central Europe and hot and dry climates such as the Middle East (Syria). Linear modelling was conducted using R script software using coded values to define the optimal value using the response surface method (RSM). The programming phase uses the least-squares approach to provide a general rationale for the line's best-match position among the data points under consideration. For each variable, the coded values range from [-1, +1]. The number of experiments is determined by the formula 2k , where k is the variable number. Since each variable has two possible values [-1, +1], the total number of experiments was 23= 8. In addition to these experiments, we performed one more experiment for defining second-degree non-linear coefficients. The second-degree factors were checked to evaluate the non-linearity of the system. The experimental work was done in the laboratory; an insulated water tank filled with 5 litres of water was used. A capsulated PCM soy wax 68℃ test was conducted. For the charging phase, the response surface approach with non-linear correlation was used to determine the optimal number of samples and PCM quantity at two temperature levels. The results of temperature, sample numbers, and wax quantity demonstrate a 0.22, 2.3, and -1.12 first-degree magnitude effect, respectively. In addition, each two-factor interaction contour plot is depicted.

The Use of Solar Collectors in Domestic Hot Water Systems in Central and Eastern European Countries: Simulation in TRNSYS

Abstract Solar collectors are devices that enable the use of solar radiation, e.g., for hot water preparation or space heating. They are playing an increasingly important role in Europe and around the world, mainly due to the easy availability of the sun, as an energy source. The advisability of their use depends on a number of factors, of which climatic conditions are an extremely important one. This paper presents the results of energy simulations of a solar collector-based domestic hot water system for the capitals of five selected Central and Eastern European Countries (CEEC): Riga, Warsaw, Prague, Bratislava, and Zagreb. Using TRNSYS software, a theoretical model of the system was developed and dynamic simulations were carried out for the entire year. The amount of useful energy generated by the flat-plate collectors, their efficiency, as well as the auxiliary energy requirements and the amount of energy needed to meet the load were estimated and compared. The extent to which changing the area of solar collector affects the operation and efficiency of the system for different locations was also analysed. The results showed that in terms of efficiency, the use of solar collectors is most favourable in placed southernmost Croatia and in Slovakia, where it was also achieved the lowest annual auxiliary energy demand. The least favourable location turned out to be Riga. It is also worth noting that regardless of location, the area of solar collector has a significant impact on the efficiency of the entire system.

Experimental evaluation of the performance of a domestic water heating system under Baghdad climate conditions

The aim of the current study is to evaluate the performance of a domestic water heating system for residential areas in Baghdad climatic conditions for substituting electric water heaters with solar-powered water heaters using solar collectors. Many countries, such as Iraq, are sluggish with electric power issues while receiving very high solar insolation. Solar energy is a clean, non-depleting and low-cost source that can be used especially in residential areas, which forms a great percentage of energy consumption by replacing electric water heating with solar water heating to reduce electricity usage. Therefore, six flat plate solar collectors with an absorbing area of 1.92×0.85 m with one 4 mm thick glass cover are utilized for experimental investigation under the Baghdad climatic conditions. The collector was tested under steady-state settings, which assumed that sunlight intensity, ambient temperature, and inlet-outdoor temperature difference in each collector in the system were constant throughout the operation. According to the experimental results, during the test months of November, December, January, and February, the time-weighted experimental daily average collector array efficiency is found in the range of 40 % to 60 %. Furthermore, the greater energy gain and performance of the solar collector array attain a peak value at solar noon. Additionally, a solar collector with flat plates can easily achieve relatively high water temperature levels of 70 °C in the winter season. In addition, using a solar domestic hot water system as a water heater in Baghdad climatic conditions by substituting electric water heaters is useful for saving power consumption

Simulation and Optimization of Solar Domestic Hot Water Systems

Energy-efficient building is the only solution to reduce energy costs and greenhouse gas emissions. A solar combi-system is a solar installation that provides both domestic hot water and heating. In this work, the authors evaluated the energy needs of such a system in the case of an F3 type house on a site in Meknes. The technical regulatory document is used to determine the energy demand for heating and to verify the conformity of the buildings to the thermal regulations. The domestic hot water demand is evaluated according to the analytical method. A thermal simulation of the production of domestic hot water under TRNSYS 16 confirms the results obtained by the analytical method.

Adaptation of residential solar systems for domestic hot water (DHW) to hybrid organic Rankine Cycle (ORC) distributed generation

Among the portfolio of energy systems for local power generation, Organic Rankine cycles (ORCs) for residential applications are an opportunity for local cogeneration based on synergies with existing thermal heating and storage systems. They can be highly competitive for isolated installations and the refurbishment of existing solar heating installations based on solar domestic hot water. This article evaluates the potential for hybrid solar ORC integration in residential buildings. The analyses focus on the annual yields of a domestic 1 kW ORC cycle to assess the advantages and disadvantages of the variation of demand and the availability of solar resources. The models are developed, integrating TRNSYS and EES to allow a detailed evolution characterisation. Performance and impact of CHP adaptation are considered based on demand, storage volume-collectors area ratio, and production strategies. The analysis is completed with a thermo-economic analysis under different ranges of thermodynamic parameters. Positive IRR results of 8.61% are obtained for the installation located in Seville, Spain, operating the ORC 15% of the year. It also reduces the overheating associated with the lack of heat demand and excess solar irradiation in the solar system for the warm months by 20%.

Adsorption Cooler Design, Dynamic Modeling, and Performance Analyses

This paper presents an adsorption cooler (AC) driven by the surplus heat of a solar thermal domestic hot water system to provide cooling to residential buildings. A cylindrical tube adsorber using granular silica gel as adsorbent and water as adsorbate was considered. The AC was modelled using a two-dimensional distributed parameter model implemented in previous adsorption heating and cooling studies. The performance coefficients of the resultant thermally driven cooling system were obtained for a broad range of working conditions. The thermally driven AC was found to have coefficient of performance (COP) of 0.5 and a specific cooling power (SCP) of 44 W·kg−1 when considering condenser, evaporator, and regeneration temperatures of 30 °C, 15 °C, and 70 °C, respectively. Moreover, the results showed that the AC could be used for refrigeration purposes at temperatures as low as 2 °C and that it could also operate during hotter days under temperatures of 42 °C.

Domestic hot water production system in a hospital: Energy audit and evaluation of measures to boost the solar contribution

Hospitals consume large quantities of energy to produce hot water and offset the distribution and recirculation thermal losses. This paper analyses a solar thermal system combined with gas boilers for domestic hot water production in a medium-size hospital. The solar contribution to the total demand (27%) is below design expectations (75%), resulting in significant gas consumption. The energy audit conducted in the first part of the paper highlights the vast thermal loss through poorly insulated pipes as the primary cause of the poor solar fraction. This issue is endemic to hot water-intensive buildings. The second part of the paper addresses the techno-economic evaluation of energy retrofit measures to reach a solar fraction of 60%. The simulation results indicate that cost-optimised solutions generally expand the solar caption area by 43–57% and improve insulations to reduce thermal losses by 70%. Depending on carbon taxes, the cost of hot water production would be 31–41 cent-€/kWh, which represents a 15–45% reduction from the current costs. Under stringent climate policies, installing heat pumps may further enhance economic competitiveness. The indicators and charts developed in this work are helpful decision-making tools concerning the energy refurbishment of solar domestic hot water systems.

Unglazed solar thermal collector for building facades

In this paper, a novel concept of an unglazed solar thermal facade collector (USTFC) was developed based on a commercially available metal cladding facade system. A detailed mathematical model of USTFC was developed. To validate the developed mathematical model, five prototypes of the USTFC, different in design, were prepared and experimentally tested. To demonstrate the application potential of the USTFCs for a solar domestic hot water (SDHW) system, a whole year simulation analysis was performed in the TRNSYS simulation software using the validated mathematical model under three different climatic conditions (Stockholm, Prague, and Barcelona). The simulation results showed that the efficiency of the USTFC-based SDHW system is strongly dependent on climatic conditions. The highest SDHW system efficiency of 14.5% was obtained for Prague and the lowest SDHW system efficiency of 11.7% was obtained for Barcelona. The influence of the solar storage volume to the collector field area ratio on the performance parameters of the presented SDHW system was also investigated. It was found that a value of 35–45 l/m2 can be used as the first estimation for the preliminary USTFC-based SDHW system configuration.

Modeling occupant behavior’s influence on the energy efficiency of solar domestic hot water systems

Solar hot water (SHW) systems are widely used to save energy and reduce CO2 emissions. The domestic hot water (DHW) usage behavior of occupants has a significant influence on the energy consumption of SHW systems; the operation of SHW systems also affects the DHW usage of occupants. However, there is a lack of quantitative analysis for coordinating DHW behavior and the design and operation of SHW systems to maximize solar energy utilization and reduce energy consumption. Therefore, an information-driven stochastic DHW usage model that interacts with SHW systems is proposed. The optimal design and control strategies for SHW systems to match user behaviors were explored. Meanwhile, the effects of occupants’ sensitivity to water temperature and their energy-saving awareness on the energy performance of SHW systems were studied. The results showed that optimal design and control strategies based on the actual DHW profile can increase the annual solar energy utilization rate by 11.5%, and the corresponding electricity savings, CO2 emission reduction, and cost saving are 163.10 kWh, 145.52 kg, and 81.06 RMB, per household. The location of the reheater had a significant influence on the energy performance and optimal measures of the SHW systems. Moreover, based on technologies or policies to adjust hot water demand, the water supply capacity of SHW systems can be matched with the hot water demand, which can improve the efficiency of solar energy utilization, save 8.5% of electrical energy for reheating, and lead to a 107.55 kg CO2 reduction and 59.91 RMB cost saving per household per year.

Feasibility Study of Using Solar Thermal Energy for Heating Swimming Pools in Central European Climate (Hungary as a Case Study)

Heating swimming pools using electrical elements is costly and causes environmental impact by producing CO2 emissions. While renewable energy, such as solar energy, proves a viable alternative source for swimming pool heating. This article aims to simulate various Solar Domestic Hot Water (SDHW) systems in cold climates like Central European countries to define the best system for swimming pool heating. Three different systems were compared: a solar heating system without auxiliary heating or heat exchanger (B6), with a heat exchanger (B6.1) and with a heat exchanger and an auxiliary heating source (B6.2). Also, five crucial variables were chosen, along with the variation of the other parameters using the response surface method (RSM). This system optimisation aims to define an optimal system with less financial expenditure. It was found that the best system is B6, represented by Experiment No 25, which indicates the Collector type: flat plate collector (FPC), pool depth: 1 m, pool temperature: 26 ℃, pool covers, and windshield are actively operated. We used the T*SOL Valentine Software-2018 (kWh) to measure the solar contribution for each case. For each vector, our coded values range from [-1, +1]. The formula 2k (25=32 experiments) defines the number of experiments, where k is a vector number. In addition, two more experiments were done to define second-degree non-linear coefficients with a pool depth (B) of 1.5 m and 28 ℃ pool temperature. These two additional experiments, however, had no impact on our results. Finally, the swimming pool heating systems suitable for this weather were compared. This experiment can help the locals to find the optimal swimming pool heating system for their pools.

Experimental and simulation analysis on thermal stratification characteristics in solar storage tanks with phase change materials

Among the various ways to improve energy storage and utilization in solar thermal energy storage systems, the water tank is often considered as an effective heat storage utilization. In this study, sodium acetate trihydrate (SAT) is coupled with a solar domestic hot water (DHW) storage tank as a phase change material (PCM). The thermal stratification of latent heat storage water tanks with different locations of PCM units and inlet flows was researched experimentally and numerically. The results show that in the charging process, as the inlet flow increases, the thickness of the thermocline gradually increases, with the degree of mixing in the tank aggravation. The Richardson number gradually increases as the PCM units are moved closer to the inlet. The RMSE between the experimental and simulated values reached the minimum at a flow rate of 3 L/min. The system has taken as the optimal working condition with better thermal stratification when the PCM units are placed at PCM1, and the flow rate is 3 L/min. This study provides theoretical and experimental guidance for the optimal design of DHW storage systems.

Materials selection criteria weighting method using analytic hierarchy process (AHP) with simplest questionnaire and modifying method of inconsistent pairwise comparison matrix

The analytic hierarchy process has been widely used to determine subjective weights of materials selection criteria in materials selection using multi-criteria decision-making. However, the analytic hierarchy process has some drawbacks: it is difficult to construct a pairwise comparison matrix and meet the consistency requirement. First, we propose a new simplest questionnaire to perform the pairwise comparison without confusion, conventionally and easily. Next, we propose an improved modifying method for inconsistent pairwise comparison matrix according to the following principles: (1) the elements of the reconstructed pairwise comparison matrix should be nine-point scales, (2) the number and modifying the amount of the modified elements should be as small as possible and (3) the deviation between the original and reconstructed pairwise comparison matrixes should be as small as possible. The outline of the proposed modifying method is as follows: (1) calculate the consistency ration decrements of all the pairwise comparison matrixes reconstructed by modifying every element of the original pairwise comparison matrix to the lower and upper adjacent nine-point scales and (2) find the element with the maximum consistency ratio decrement and modify it to the lower or upper adjacent scale. To illustrate the effectiveness, we apply the proposed methods to determine the criteria weights for selecting the best phase change material used in a solar domestic hot water system, and apply the proposed modifying method to some examples from the published papers, and compare the performances with some previous methods. The simplest questionnaire and improved modifying method help materials designers and engineers to apply the analytic hierarchy process method in materials design and optimization problems, much more actively.