Solar Domestic Hot Water Systems Research Articles

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.

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.

Assessment of the thermal accumulating solar stations efficiency

The impact of heat-generating facilities on the environmental condition of adjacent territories is assessed. The possibility of using solar energy to reduce the anthropogenic impact on the environment is substantiated. It is proposed to create cascade solar installations to provide hot water supply to residential buildings and industrial facilities. A scheme of a solar power station with a seasonal solar energy accumulator based on depleted quarries to ensure year-round supply of hot water is proposed. A mathematical model is proposed for calculating the efficiency of solar collectors with transparent and rear insulation, which make up the third stage of a three-stage solar DHW system. The relative error of mathematical models in comparison with test data is presented. The average monthly efficiency of the third cascade of calculated mathematical models for climatic conditions of the Crimean peninsula is given. A refined algorithm for calculating the efficiency of solar collectors of the third stage has been developed.

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.

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.

A stochastic thermo-economic analysis of solar domestic hot-water systems in compliance with building energy code requirements: The case of Spain

Spanish residential buildings typically cover the required domestic hot-water renewable fraction regulated by building codes using solar thermal systems, typically through solutions based on flat-plate collectors and water storage tanks. For medium or large buildings (with high domestic hot-water demands), the energy savings produced by the solar system operation easily exceed the owning, operating, and maintenance costs, with its installation being highly advantageous under current energy prices. However, this situation is much less clear when small residential buildings are taken into consideration, as energy savings produced by solar domestic hot-water systems may not be sufficiently large to compensate for those costs, often operating below economically feasible levels. The energy savings associated with the operation of the solar systems were estimated using the simulation tool TRNSYS, using its output results as input data to conduct two different economic feasibility assessments (based on deterministic, and stochastic approaches). The deterministic analysis revealed that solar DHW-systems installed in small buildings with fewer than 5 apartments are not economically feasible. The stochastic economic analysis identified a wide probability range (between 70 and 90% of all the simulated cases) for economically feasible solar domestic hot-water systems, when they serve buildings with more than 48 apartments.

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.

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.

Improvement of the thermal performance of a solar triple concentric-tube thermal energy storage unit using cascaded phase change materials

In this study, the thermal performance of the storage unit of a solar domestic hot water (SDHW) system incorporating triple concentric-tube latent heat storage modules filled with cascaded phase change materials (cascaded PCMs) was numerically investigated. The triple concentric-tube storage modules were filled with three marks of phase change material (RT62HC, RT54HC and RT44HC) with melting points of 63 °C, 54 °C and 43 °C, respectively. The heat transfer fluid (HTF: water) was received solar thermal energy from the solar collector absorber and transferred it by forced convection to the cascaded PCMs which stored it as latent heat. A model based on the enthalpy method was elaborated to predict the combined heat transfer and phase change processes. The natural convection effect during phase change was taken into consideration through an effective thermal conductivity of liquid PCMs. The elaborated numerical model was verified and validated by comparing the predictions with the previously published experimental and numerical results. The thermal performance of the cascaded thermal energy storage tank was evaluated under the weather conditions of the month of July in Marrakesh city (Morocco), and compared with that for single-PCM storage tank during the charging process.

New Deterministic Mathematical Model for Estimating the Useful Energy Output of a Medium-Sized Solar Domestic Hot Water System

According to the authors of this paper, the mathematical point of view allows us to see what sometimes cannot be seen from the designer’s point of view. The aim of this study was to estimate the influence of the most important parameters (volume of heat storage tanks, daily consumption of domestic hot water, optical efficiency, heat loss coefficient, and total area of a solar collector) on the thermal power output of solar domestic hot water (SDHW) system in European climatic conditions. Three deterministic mathematical models of these relationships for Madrid, Budapest, and Helsinki were created. The database for the development of these models was carried out using computer simulations made in the TRNSYS software environment. The SDHW system located at the Bialystok University of Technology (Poland) was the source of the measurement results used to validate the simulation model. The mathematical optimization procedure showed that the maximum annual useful energy output that can be obtained from 1 m2 of gross collector area is 1303 kWh in the case of Madrid, 918.5 kWh for Budapest, and 768 kWh for Helsinki weather conditions.

Field Study on the Thermal Performance of Vacuum Tube Solar Collectors in the Climate Conditions of Western Norway

A significant part of energy consumption in Northern countries goes to heating. There is no consensus about the most efficient source of renewable heat there. This paper presents a field study for a 7.8 m2 vacuum tube solar collector facility that is conservatively located in the cloudy and cold climate conditions of western Norway. We analyse a year-long operation by examining the rig’s statistics. We show that in Nordic latitudes with rainy climate conditions, a domestic solar hot water system can produce 2200 kWhth/y at a thermal efficiency of up to 72%. The average amount of heat produced by the collectors was up to 14.7 kWhth/d. This was enough to sustain the domestic hot water demand in an average Norwegian household for 6 months with a short period of auxiliary heating. In conclusion, we calculated that a 3× upscaled area facility would deliver over 25 kWhth covering six months of total heat consumption. The payback period for the facility is 12 years.

Improving solar domestic hot water effectiveness using Al2O3 and ZnO nanoparticles: Focusing on annual energy-saving

Backgroundsolar collectors can meet the sanitary hot water requirements. In this way, the use of nanofluids in solar domestic hot water (SDHW) can improve the effectiveness. The main purpose of this paper was to examine the thermal behavior of SDHW in the presence of nanoparticles for three climate zone. MethodsThe efficacy of using Al2O3 and ZnO nanoparticles into the water on energy-saving parameter was examined utilizing transient techniques. Findingsthe results revealed that owing to using SDHW filled with water, the annual energy usage was reduced by 1002.5, 939.25 and 758.5 kWhm2 for zones A, B and C. It was found that the addition of nanoparticles could improve the usefulness of SDHW system. If Al2O3 nano-scale particles were added to water, the SDHW effectiveness was improved by 12.1% (for zone A), 13.3% (zone B) and 18.7% (zone C). For ZnO nanoparticles, this figure was 6%, 6.6 and 10.8% for zones A, B and C, respectively. Therefore, the profitability of solar energy was intensified further by the addition of Al2O3 nanoparticles.

Phase change materials in solar domestic hot water systems: A review

• Storage of solar energy by utilizing the latent heat content of phase change materials. • Generation of domestic hot water by phase change materials. • Harvesting and storing solar radiation. • Methods of improving the performance of thermal energy storage systems. In this work, technologies related to the storage of solar energy, utilizing the latent heat content of phase change materials for the production of domestic hot water are reviewed. Many researchers have been involved in this field in order to accomplish the targets of environmentally friendly solutions and higher efficiency. For domestic use, materials with melting temperature between 40 and 80 °C are commonly studied, with paraffins, fatty acids, salt hydrates and alcohols being the most popular. For harvesting the solar radiation, usually flat plate or evacuated tubes solar collectors are used, either commercial ones or modified. The storage unit may include only phase change material or it can have a hybrid form combined with water. The outcome of the most studies, is that the addition of phase change materials in comparison to systems without latent storage, increases the duration of heat release towards the domestic water at the end of the day and also increases the solar collector's efficiency because it does not experience large temperature fluctuations. However, difficulties emerge during the selection of the appropriate storage material as this must have a high melting temperature in order to provide hot enough domestic water, but not higher than the temperature that the solar collector can produce, in order to fully melt the material. Moreover, investigation is necessary for the selection of the optimum water flow rate that minimizes the charging duration and maximizes the system efficiency and hot water amount. Another challenge that researchers face is the low thermal conductivity of many phase change materials. For this purpose, methods for improving the performance of the systems have been examined and they are also reported.