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Thermoacoustic air-to-water air source heat pumps (TAWASHP) are the eco-friendly, simple, compressor less, low cost and likely looking future substitute for the existing compressor-based heat pumps. In this work, the design optimization of the 1-kW TAWASHP with helium for the temperature difference of 15 to 70 K for pumping heat from the atmospheric air to water using the linear thermoacoustic concepts was discussed. The optimized design can fit for both cooling and water heating applications without wasting the heat rejection to the surrounding atmosphere, rather supplied to the insulated hot water tank. The optimized one-fourth wavelength resonator TAWASHP shows the coefficient of performance of 1.1 to 2.34. The theoretical results are validated with the DeltaEC software results, and the results are in concurrence with each other. The DeltaEC predicts the TAWASHP can supply 1.55 to 3.35 kW of heat to water, which is equivalent to 37.3 to 80.3 kWh of heat energy per day. [ABSTRACT FROM AUTHOR]

The use of solar water heating systems (SWHSs) has grown as an alternative source of energy to heat water. In Kenya, commercial premises are required to install these systems to conserve energy and the environment; however, after the SWHS has been designed and installed according to the relevant standard, post‐installation factors significantly influence its performance. In this study, the impact of user behavior and waiting time for hot water on the performance of SWHS is investigated using experimental tests and analysis. In the operations of SWHS, water that cools off in the piping system during idle time must be flushed before hot water is supplied, and generally, the cold water goes to waste. This wastage increases the water demand, the amount of liquid waste for disposal, the cost of recycling, and the energy demand for pumping the water. The proposed system involves installing instantaneous water heaters controlled by a fuzzy logic controller in an SWHS to heat water during waiting time and reduce energy and water wastage associated with waiting time and user behavior. The study was carried out in 15 hotels in Kenya. It was observed that installing instantaneous water heaters in an SWHS reduces the waiting time for hot water by 96.90%, saving 14.4 liters of cold water while the user behavior losses were reduced resulting in a saving of 54.6 liters of hot water. The energy savings associated with pumping water was 0.025 kWh per hotel room on average. From these savings, the running cost was reduced by 80.6%. With this hybrid system, an additional 0.117 kWh of energy was consumed by the 4.8 kW instantaneous heater to heat water during waiting time. From these findings, it's feasible to effectively reduce waiting time, reduce water wastage, and mitigate user behavior losses in hotels by incorporating instantaneous water heaters in SWHS. [ABSTRACT FROM AUTHOR]

The influence of flow step ratio (FSR) on the startup characteristics of instant heat pump water heaters (IHPWHs) with natural mixture M (R744/R290 (12/88)) under nominal conditions was studied experimentally to verify the feasibility of a new quick startup method. The results show that the FSR had a marked effect on the startup time of system performance parameters. Under the optimal FSR of 0.6, the shortest system startup time and available hot water supply time were 700 s and 250 s, respectively, which were markedly shorter than those in the conventional startup. Therefore, rapid startup of the system and rapid production of usable domestic hot water can be realized by controlling the flow step. The influence of flow step on the variation trend of system performance parameters was obviously different, and there was no slow warming section for the heat sink outlet temperature (HSOT) under three FSRs. The HSOT, heating capacity, and high pressure side pressures had the maximum values in the quick startup, and the maximum values were obviously affected by the FSR. The FSR had no marked effect on the minimum suction pressure. The refrigerant pressures and refrigerant temperatures fluctuated markedly in both rapid and conventional starts. [ABSTRACT FROM AUTHOR]

In this paper, a direct-expansion heat pump water heater system integrated uninsulated micro-channel PV/T solar collector (UMC-PVT-SC) is proposed. This system can realize storage for both thermal energy and electricity, ensuring the supply of domestic hot water. The theoretical models of micro-channel PV/T solar collector, hot water storage tank, compressor and electronic expansion valve are established to investigate the performance of the micro-channel PV/T heat pump water heater system. R134a is used as refrigerant. The system performance is numerically simulated using MATLAB for different solar radiation intensity, ambient temperature and wind speed. The results show that solar radiation intensity has the largest influence on the system performance, followed by ambient temperature and wind speed. The coefficient of performance of the heat pump (COP HP) and the overall coefficient of performance (COP pvt) of the integrated system increase while the required operating time reduces, as solar radiation intensity and ambient temperature increase. The uninsulated micro-channel PV/T solar collector (evaporator) can absorb thermal energy from both ambient air and solar radiation and therefore achieve high COP HP , electric efficiency and COP pvt. Even under cold weather conditions, the proposed solar collector and heat pump heater demonstrate high efficiencies, heating and power generation capacities. When ambient temperature is −18.6 °C and solar irradiance is 322 W/m2, the collector efficiency and electric efficiency of UMC-PVT-SC are still at 0.718 and 0.244, respectively, and the COP HP and COP pvt of the heat pump heater are 3.5, 5.63, respectively. The present work is of potential value for delivering net zero. • A novel uninsulated micro-channel photovoltaic/thermal solar collector is designed. • The photovoltaic/thermal solar collector can absorb heat from air without sun. • The overall energy efficiency of photovoltaic/thermal solar collector can reach 1.86 in winter. • It is a simple and low-cost solution of the combination of solar energy and heat pump. • The solar assisted heat pump can operate independently without external electric power. [ABSTRACT FROM AUTHOR]

The photovoltaic thermal system has a limitation in supplying hot water at the required temperature since it requires a supplementary heating system. One such system can be an air source heat pump operated by electricity from a PV/T system, which can be used to raise the temperature of the water preheated by PV/T to the required level. Such type system can also be called a hybrid PV/T-heat pump system, and it delivers thermal (hot water) and electrical energy. The performance of the hybrid PV/T-heat pump system was analyzed using the computational model for two Ethiopian cities, namely, Addis Ababa and Dire Dawa, which represent the highland and lowland regions, respectively. The simulation was conducted by inputting climatic data, daily hot water demand, and hourly hot water consumption patterns. Also, system design parameters such as PV/T area and peak Watt, PV/T warm water tank volume, air source heat pump water heater COP as a function of ambient temperature and circulating water temperature, and heat pump hot water tank volume. Besides, the effect of hot water consumption patterns (variability effect in three dissimilar cases constant, restaurant, and motel) on the system performance was examined. In addition, the effect of electric energy supply to the compressor of the heat pump using battery storage on the system performance was also investigated. In those diverse situations, the system in most of the cases generated hot water above 55°C and scored a COP of 3. The maximum value of hot water end-use efficiency of 66% was also obtained by making the hot water tank capacity about 50% of the daily hot water consumption size. [ABSTRACT FROM AUTHOR]

Heat pump water heaters are highly efficient hot water supply systems that effectively utilize the heat of outdoor air via heat pump technology. Many studies have been conducted to optimize the design and operation of heat pump water heaters from the perspective of climate change mitigation. Air-source heat pump water heaters, which absorb heat from the outdoor air and emit cold exhaust, can also be expected to alleviate the urban heat island effect; however, this has not been studied extensively. To estimate the impact of cold exhaust on building-scale climate, we conducted a multipoint measurement of the outdoor thermal environment around a low-rise apartment building equipped with air-source heat pump water heaters, in both summer and winter. Observations showed a substantial cooling effect that decreased air temperatures by 1 °C within the site boundary on summer nights when multiple heat pump water heaters operated concurrently. The analysis revealed that the sensitivity of the ambient temperatures to cold exhaust depends strongly on local atmospheric conditions. The most influential factor was the wind direction: the sensitivity increased significantly when the exhaust outlet location was at the lee side of the building. Naturally, the wind speed also affected the sensitivity, which tended to be higher when the wind speed was lower. The convective stability near the ground surface, however, showed no significant influence over the sensitivity. [ABSTRACT FROM AUTHOR]

This study selects titanium dioxide (TiO2) and multi-walled carbon nanotubes (MWCNTs) as far-infrared materials (FIRMs), and further adds water-based acrylic coatings to prepare far-infrared coatings (FIRCs). FIRCs are uniformly coated on #304 stainless steel sheets to make the test samples, which are then installed between the shell and insulation material of the hot water heater to measure the influences of various FIRCs on the performance of the hot water heater. The research results show no significant difference in the heating rate or heat insulation performance of the hot water heater with or without FIRCs coating. However, the uniformity of the water temperatures of the test samples is significantly improved with FIRCs. Considering that the uniformity of water temperature will inhibit the heating rate and heat insulation performance of the hot water heater, TiO2-FIRC should provide better performance improvement when applied to the hot water heater in this study. The application of TiO2-FIRC to large-scale hot water heaters with a high aspect ratio will effectively improve the quality of hot water supply in the future. [ABSTRACT FROM AUTHOR]

Water heating is a major component of domestic electrical energy usage, in some countries contributing to 25% of the residential sector energy consumption. Demand response strategies can reduce the time-of-use costs and overall electrical energy consumption. We present a method to reduce the electrical energy usage itself. Our novel heating schedule control minimises the electric water heater's energy usage without compromising user convenience. We achieve optimal control, while taking into account the natural temperature stratification of the water in the tank, using the A* search algorithm. Since previous research assumes a one-node thermal model, we also assess the effect of excluding stratification. We match three optimal control strategies to a baseline: the standard "always on" thermostat control. The first two strategies respectively match the temperature and the energy of the hot water supplied by the water heater. The third, a variation on the second, includes a method of preventing the growth of Legionella bacteria. We tested 77 water heaters over four weeks, a week for each season, and all three strategies saved energy. The median savings were 6.3% for temperature-matching, 21.9% for energy-matching and 16.2% for energy-matching with Legionella prevention. Taking stratification into account increased these savings by 1.2%, 5.4% and 5.5% respectively. • Developed technique to solve optimal control problem for electric water heaters. • Stratification accounted for through using two-node model. • A*-based algorithm used for optimisation of two-node optimization. • Energy savings from 6% for temperature matching to 22% for energy matching. • Inclusion of stratification in planning increased savings up to 5% vs. without. [ABSTRACT FROM AUTHOR]

A cogeneration solar system for a building located in Sabzevar (Iran) is investigated in this study. In this system, a combination of a solar evacuated tube collector field and an auxiliary natural gas burner drive a single effect absorption chiller. Solar energy is also used to produce consuming hot water. Hourly cooling demands of the building were calculated during April to September. In order to perform a more obvious assessment, important parameters such as COP and efficiencies were obtained based on the total cooling load, the total amount of absorbed solar energy and consumed natural gas, and the total produced hot water during April to September. Energetic, exergetic, and economic analyses were performed in order to find the most efficient generator temperature. Considering the results, the minimum consumption of natural gas happened at a generator temperature of 104 ° C while the highest chiller exergy efficiency is observed at the generator temperature of 97 ° C. Also by assuming the required gas fuel to supply the consuming hot water -which is produced by solar energy-as a saving parameter, the economic optimum generator temperature to drive the absorption chiller and to supply the consuming hot water is obtained at the generator temperature of 96 ° C. • Presenting a transient model of a solar-gas driven absorption chiller integrated with a consuming water heater. • Considering the hourly variations of cooling load and solar radiations. • Obtaining the most efficient generator temperature based on energetic, exergetic and economic concerns. [ABSTRACT FROM AUTHOR]

The article herein presents a new technique of controlling the system of collecting, storing and processing the information from the solar collectors, which might be applied to heating the industrial and domestic compartments for hot water supply. The most profitable usage of the solar collectors in the industry is replacement of a human interference with wireless sensor nets. The solar collector standard system consumes in average 30% of the heat due to poor control and configuration. Our monitoring and control system allows upgrade the performance of heating the industrial and domestic premises by means of solar collector for hot water supply. [ABSTRACT FROM AUTHOR]

Abstract Energy consumption for domestic hot water (DHW) preparation is one of the main components of the energy balance of the existing and newly designed buildings. However, based on the number of existing buildings and the related opportunities to improve energy efficiency, an important issue is to propose effective and low cost methods that allow to reduce the heat consumption in existing domestic hot water systems and are fast in the implementation. This article presents the results of an experimental research conducted in 12 objects (9 multifamily buildings and 3 thermal substations) assigned to three groups (A, B and C), depending on the analyzed feature of the domestic hot water system. The objects in the group A were analyzed in detail (each 1 h during one full heating season) in order to clearly show the amount of the heat used for circulation of hot water. The group B of objects characterized by the installation of temperature control valves (TCVs) under the risers of circulation installation. The third group consisted of the objects in which the temperature of hot water was decreased during the night hours. The objects from group B and C were analyzed over 8 years. The share of heat losses associated with the circulation of hot water in the total heat consumption supplied for its preparation was in the range from 56.7% to 70.5% for the Group A objects. On the other hand, the energy savings were calculated using different methodologies and for the recommended one they ranged from 8.5% to 49.5% for group B objects and from 6.0% to 14.4% for group C objects. [ABSTRACT FROM AUTHOR]

A direct-expansion solar-assisted heat pump (DX-SAHP) system by using R410A as refrigerant is described, which can supply domestic hot water during the whole year. Based on the distributed parameter and homogeneous flow models of collector/evaporator and condenser, the lumped parameter models of compressor and electronic expansion valve, and the refrigerant charge model, a numerical model is developed to estimate the thermal performance of the system. Given the structure parameters, meteorological parameters, initial and final water temperatures, for a fixed superheat degree, the effects of the refrigerant charge quantity on the performance parameters of the system are analyzed, such as compressor power, heat gain of collector, heating time, collector efficiency and system COP. Furthermore, for a fixed refrigerant charge quantity, the effects of various parameters, including solar radiation, ambient temperature, compressor speed and initial water temperature, have been simulated and analyzed on the thermal performance of the system. [ABSTRACT FROM AUTHOR]

Hydrocarbons can be interesting refrigerants in domestic facilities such as heat pumps for domestic hot water production called heat pump water heaters (HPWH). However, due to flammability and submission to severe regulations, the use of hydrocarbons requires improvements in design and optimisation of components to reduce the refrigerant charge. This paper first reviews the regulations applied to hydrocarbon technologies then discusses possibilities of charge reduction for a R290 HPWH. Mainly by selecting condensers with high thermal efficiency and low internal volume, the charge may be reduced to extremely low levels. Using the same base of refrigerating system, three types of condensers were tested: tank-wrapped D-tube, roll-bond and microchannel heat exchangers. The D-tube has a low compactness. Microchannels are penalised by the diameter of their distributors. The best performance is obtained by the roll-bond HPWH with a charge of 224 g: COP of 3.17 and heating time under 7 h. [ABSTRACT FROM AUTHOR]

The numerical simulation, design, and construction of a double glazed integrated collector storage (ICS) with compound parabolic concentrators (CPC) reflectors are presented. The design of the double glazing is optimized by means of numerical simulations under Tunisian climatic conditions. The numerical program used for the simulation consists on the transient resolution of the balance energy equations of each component of the solar water heater. Different proposed models of a double glazing are studied and compared with a reference case of a single glass ICS model. The simulation results have shown that the use of double glazing with argon layer and low-e coated lower glass instead of one glass cover significantly improves the thermal behavior of the ICS heater and visibly reduces its thermal losses during night. Taking into account these numerical results, a double-glazing ICS prototype-collector is constructed. The details of the construction, geometry, optical properties, and dimensions of the prototype are presented. [ABSTRACT FROM AUTHOR]

This paper presents a study which was conducted to evaluate the performance of a commercially available heat pump water heater (HPWH) with modified controls. The HPWH is first characterized experimentally under a series of different thermal conditions and draw parameters. The test tank contains a 1500 W electric auxiliary heater that provides on demand heat to the top 0.30 m (1 ft) of the tank, and a wrap-around heating coil. An air source heat pump (ASHP), using R-134A as the refrigerant, draws air from, and returns air to the surrounding space and provides heating to the whole tank through the coil. The tank has been tested using Canadian Standards Association draw profiles to characterize performance under different hot water demands. Electricity consumption and thermal flux is measured for each vertical tank section, and various performance metrics are calculated using energy balances. A trnsys model is then calibrated to the experimental data to allow for the flexibility of varying multiple parameters over various climates. Using this calibrated trnsys model, an optimal control strategy and tank setpoints can be determined for use in cold climates. As expected from previous work, there is a decrease in performance of the HP when heating the tank to higher temperatures to facilitate thermal storage, but the benefits from taking advantage of shifting electrical demand (of water heating) to space heating demand can outweigh the loss of performance. [ABSTRACT FROM AUTHOR]

This study focuses on the environmental impact assessment through Life Cycle Analysis (LCA) of two innovative 10 kW pellet boilers. In particular, the second boiler represents a technological evolution of the first one developed to improve its performance in terms of efficiency and environmental impact. For both boilers, emission factors measured during laboratory tests (full load tests and specific load cycle tests representative of real life boiler operation) have been used as input data in the life cycle analysis. The SimaPro software (v.8.0.4.30) was used for the LCA and the ReCiPe Midpoint method (European version H) was chosen to assess the environmental impact of all boilers (according to LCA ISO standards). In addition, the ReCiPe Endpoint method was used to compare the final results of all 5 boilers with literature data. The pelletisation process represented the most relevant share of the overall environmental impact followed by the operational phase, the manufacturing phase and the disposal phase. A sensitivity analysis performed on the most efficient pellet boiler evidenced the variation of the boiler’s environmental impact as a function of PM10 and NO X emission factors with respect to emission factors monitored during boiler full load operation. Moreover, the reduction of the boiler’s weight and the adoption of new electronic components led to a consistent reduction (−18%) of its environmental impact with respect to the previous technology. A second LCA has been carried on for a 15 kW oil boiler, a 15 kW natural gas boiler and a 15 kW pellet boiler, representative of the state of the art of EU technology, to finally compare all LCA results. Results showed the environmental impact reduction of BW10 and BW10 2 pellet boilers with respect to fossil fuelled boilers mainly due to their reduced impact on CC (reductions by 86–90% and 88–91% with respect to the NG and oil boilers respectively), NLT (reductions by 77–79% and 86–87% with respect to the NG and oil boilers respectively) and FD (reductions by 89–92% and 90–93% with respect to the NG and oil boilers respectively) ReCiPe Midpoint subcategories. [ABSTRACT FROM AUTHOR]

Legionella pneumophila is frequently detected in hot water distribution systems and thermal control is a common measure implemented by health care facilities. A risk assessment based on water temperature profiling and temperature distribution within the network is proposed, to guide effective monitoring strategies and allow the identification of high risk areas. Temperature and heat loss at control points (water heater, recirculation, representative points-of-use) were monitored in various sections of five health care facilities hot water distribution systems and results used to develop a temperature-based risk assessment tool. Detailed investigations show that defective return valves in faucets can cause widespread temperature losses because of hot and cold water mixing. Systems in which water temperature coming out of the water heaters was kept consistently above 60 °C and maintained above 55 °C across the network were negative for Legionella by culture or qPCR. For systems not meeting these temperature criteria, risk areas for L. pneumophila were identified using temperature profiling and system's characterization; higher risk was confirmed by more frequent microbiological detection by culture and qPCR. Results confirmed that maintaining sufficiently high temperatures within hot water distribution systems suppressed L. pneumophila culturability. However, the risk remains as shown by the persistence of L. pneumophila by qPCR. [ABSTRACT FROM AUTHOR]

Highlights: [•] A tube-in-tube heat exchanger model applicable for CO2 gas cooler is developed. [•] The calculations are in line with the experimental results. [•] Local maximum and minimum of heat transfer rate may occur in the trans-critical process. [•] The CO2 temperature drop is very small when it is close to the pseudo-critical region. [•] The phenomenon becomes more pronounced as the pressure is close to the critical pressure. [Copyright &y& Elsevier]

Domestic evacuated tube collector (ETC) solar water heaters have shown outstanding performance under standard testing conditions and promising output under everyday use conditions. Considered is the daily performance of the solar collector during the cold and hot seasons and under conditions approaching actual domestic water use. The solar water heater seasonal and annual contribution to domestic hot water (DHW) in an apartment is found. The solar system in actual use installed as back-up to the various DHW systems is investigated. The results showed a significant annual solar contribution of no less than 85% to domestic hot water supply and also show valuable savings in the cost of energy to pay back in five years. [ABSTRACT FROM AUTHOR]

Residential water heating is linked to growth of pathogens in premise plumbing, which is the primary source of waterborne disease in the United States. Temperature and disinfectant residual are critical factors controlling increased concentration of pathogens, but understanding of how each factor varies in different water heater configurations is lacking. A direct comparative study of electric water heater systems was conducted to evaluate temporal variations in temperature and water quality parameters including dissolved oxygen levels, hydrogen evolution, total and soluble metal concentrations, and disinfectant decay. Recirculation tanks had much greater volumes of water at temperature ranges with potential for increased pathogen growth when set at 49°C compared with standard tank systems without recirculation. In contrast, when set at the higher end of acceptable ranges (i.e., 60°C), this relationship was reversed and recirculation systems had less volume of water at risk for pathogen growth compared with conventional systems. Recirculation tanks also tended to have much lower levels of disinfectant residual (standard systems had 40–600% higher residual), 4–6 times as much hydrogen, and 3–20 times more sediment compared with standard tanks without recirculation. On demand tankless systems had very small volumes of water at risk and relatively high levels of disinfectant residual. Recirculation systems may have distinct advantages in controlling pathogens via thermal disinfection if set at 60°C, but these systems have lower levels of disinfectant residual and greater volumes at risk if set at lower temperatures. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with exergoeconomic analysis of a dormitory heated by a conventional boiler in a central heating system. The energy and exergy flows are examined from the generation stage to the envelope of the building. The energy and exergy flows between the stages are obtained using a predesign tool for an optimized building design. Exergetic and exergoeconomic analyses of some heating equipment are comprehensively evaluated. A conventional boiler and a water heater in the central heating system are considered in the analysis. Based on the analysis results obtained, the total exergy input rate is calculated to be 1455kW while the largest exergy loss rate is found to be 987.6kW. Exergetic efficiencies of the conventional boiler and the water heater are also obtained to be 15.6% and 20.4%, respectively. [Copyright &y& Elsevier]

Abstract: Because they store hot water, water heaters are easily-shifted loads that can be controlled to reduce peak demands. However, load shifting may have some detrimental consequences on the domestic hot water supply temperature if the heating element is deactivated for a long period of time. Furthermore, a new peak may be caused if a significant number of heaters are reactivated at the same time. This study presents a control strategy for water heaters that minimizes the pick-up demand when the heating elements are reactivated at the end of a load shifting period and that ensures, in all cases, the client''s hot water supply. The study is based on a simulation model of a water heater that was experimentally validated and takes into account the diversity of the population''s hot water withdrawal profile. More specifically, the data of 8,167 real water withdrawal profiles of several clients were input into the simulation model in order to evaluate the performance of water heaters under different operating conditions. [Copyright &y& Elsevier]

Abstract: Following typical phases of any technology development, initially there have been research works focusing mainly on the solar hot water systems’ (SHWS) technology development then followed by economic aspects. This has resulted in techno-economically feasible standardized solar hot water systems. Owing to these favourable features, SHWS in general and Domestic SHWS (DSHWS) in particular attracted several promotional measures with a view to make them as the alternative for conventional water heating options in India. However, even after the implementation of these measures for more than two decades in India, the potentials-achievements difference remains to be extremely large, the reasons for which are attributed to the so-called “barriers for dissemination”. This paper presents a consolidated review of solar water heating related issues covering these technological developments, techno-economics, promotional measures, present dissemination status and barriers for dissemination, all with a special reference to the Indian context. Also presented in this paper is the identified need for “viability” studies of DSHWS and “essentials for viability evaluations of DSHWS” in multi-dimensional environment that aid in developing decision making tools to improve dissemination of DSHWS. [Copyright &y& Elsevier]

Tankless water heaters (TWH) have several advantages and disadvantages when compared with storage water heaters. One disadvantage is that the outlet temperature of the water is difficult to control. To address this problem, the authors apply seven different control approaches and conduct experiments to test the effectiveness of each approach. The experiments are carried out on a commercially available electric TWH, using a test method and apparatus developed by the authors. The seven approaches include various configurations of feedback or feed-forward control, or both. One fairly simple approach devised in this project combines feedback and feed-forward control. This combined approach gives excellent performance, even when compared to a very sophisticated and complex approach (model predictive control). Furthermore, the approach does not impose a manufacturing cost premium for the subject TWH. The improvements in control that are possible with the approaches described in this paper are considerable when compared with approaches being used in electric TWH that are currently available to consumers. [ABSTRACT FROM AUTHOR]

Abstract: In a typical solar water heating system, cold water is replenished into the storage tank as soon as the load is served. However, it is possible to determine the water replenishment profile (i.e., the quantity of the cold makeup water to be supplied to the storage tank over a day) that optimizes the overall system. In this paper, the effect of water replenishment on the system sizing is studied and a novel strategy for water replenishment is proposed to improve the design and performance of solar water heating systems. Based on an analytical technique, an approximate water replenishment profile is proposed to size a solar water heating system near-optimally. The problem is analyzed using a methodology called design space approach. Design space of a solar water heating system identifies all possible and feasible designs on a collector area vs. storage volume diagram. For illustration of the proposed methodology, an example problem is solved. It is observed that the annualized system cost can be reduced by 13.7%. For the cost-optimal system configuration, a reduction of 12.7% in the collector area and 10.2% reduction in the storage volume are observed. The proposed methodology is particularly important and advantageous for large commercial and industrial solar water heating systems. [Copyright &y& Elsevier]

Abstract: Nowadays there are several ways of supplying hot water for showers in residential buildings. One of them is the use of electric storage water heaters (boilers). This equipment raises the water temperature in a reservoir (tank) using the heat generated by an electric resistance. The behavior of this equipment in Brazil is still a research object and there is not a standard in the country to regulate its efficiency. In this context, an experimental program was conducted aiming to collect power consumption data to evaluate its performance. The boilers underwent an operation cycle to simulate a usage condition aiming to collect parameters for calculating the efficiency. This 1-day cycle was composed of the following phases: hot water withdrawal, reheating and standby heat loss. The methods allowed the identification of different parameters concerning the boilers work, such as: standby heat loss in 24h, hot water withdrawal rate, reheating time and energy efficiency. The average energy efficiency obtained was of 75%. The lowest efficiency was of 62% for boiler 2 and the highest was of 85% for boiler 9. [Copyright &y& Elsevier]

Abstract: This study presents a theoretical and experimental analysis of the thermal performance of a solar water heater prototype with an internal exchanger using a thermosiphon system. The heat exchanger made of a rolled copper tube is placed diagonally in the storage tank so that the hot fluid crosses a significant mass of stored water. The results focus mainly on the levels of the heat fluxes, temperatures recorded, mass flow rate and efficiency of the collector. During the main insulation period, one obtains satisfactory qualitative and quantitative agreement between the experimental and theoretical results of mass flow rate and temperatures. Those indicate heat fluxes whose peak reaches 989W/m2, collector outlet water temperature levels of more than 85.5°C and a collector thermal effectiveness around 58%. [Copyright &y& Elsevier]

Abstract: Parameters that affect the efficiency of a flat plate integrated collector storage solar water heater (ICSSWH) are examined experimentally and numerically. This specific ICSSWH contains water that is not refreshed. The service water is heated indirectly through an immersed heat exchanger (HE) in contact with the front and back major surfaces. A forced convection mechanism consisting of a pump that brings the storage water into motion by recirculation is used for heat transfer intensification. The two major (front and back) flat plate surfaces need to be well interconnected so that they are not deformed by the weight of the contained water and the exerted high-pressure. Two main factors that influence the performance are optimized: the position and size of the recirculation ports and the arrangement and size of the interconnecting fins. Both factors are explored to maximize the velocity flow field of the recirculated storage water. Consequently, the heat transfer rate between the two water circuits is maintained at high levels. Various 3D computational fluid dynamics (CFD) models are developed using the FLUENT package. An experimental model, made by Plexiglas, is used for the visualization of the flow field. Flow velocities are measured using a laser doppler velocimetry (LDV) system. The optimal arrangement increases the mean storage water velocity by 65% and raises the outlet temperatures up to 8°C. [Copyright &y& Elsevier]

Abstract: The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2m were tested. The pump could operate at the collector temperature of about 70–90°C and vapor gage pressure of 7–14kPa. It was found that water circulation within the SWHS ranged between 12 and 59l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one. [Copyright &y& Elsevier]

The aim of this paper is to simulate the performance of an air source heat pump water heater using carbon dioxide (CO2) as a working fluid. The heat pump water heating system consists of a compressor, a gas cooler, an expansion device and an evaporator. The computer simulation model has been developed by using the heat transfer data and the thermodynamic properties of CO2. The effects on the heat pump performance by the operating parameters such as the compressor rotational speed, the inlet water temperature at the gas cooler, the inlet air temperature at the evaporator and the mass flow rate ratio of water to refrigerant were presented. For rated capacities of a 4 kW compressor with a 10 kW gas cooler and a 6 kW evaporator, the coefficient of performance is found to be between 2.0 and 3.0. The mass flow rate ratio of water and CO2 between 1.2 and 2.2 is the most suitable value for generating hot water temperature above 60°C at 15–25°C ambient air temperature. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work is to present the development of an automatic solar water heater (SWH) fault diagnosis system (FDS). The FDS system consists of a prediction module, a residual calculator and the diagnosis module. A data acquisition system measures the temperatures at four locations of the SWH system and the mean storage tank temperature. In the prediction module a number of artificial neural networks (ANN) are used, trained with values obtained from a TRNSYS model of a fault-free system operated with the typical meteorological year (TMY) for Nicosia, Cyprus and Paris, France. Thus, the neural networks are able to predict the fault-free temperatures under different environmental conditions. The input data to the ANNs are various weather parameters, the incidence angle, flow condition and one input temperature. The residual calculator receives both the current measurement data from the data acquisition system and the fault-free predictions from the prediction module. The system can predict three types of faults; collector faults and faults in insulation of the pipes connecting the collector with the storage tank and these are indicated with suitable labels. The system was validated by using input values representing various faults of the system. [Copyright &y& Elsevier]

Abstract: Prediction accuracy is a fundamental modeling requirement. This work explores different models for a solar domestic water heating system located near Viña del Mar, Chile, in order to improve model prediction accuracy over some existing alternatives. The main approach is semi-physical modeling, which combines phenomenological modeling and system identification. The former helps to organize in a conceptual form the available system knowledge, and the latter allows to adjust that knowledge into a particular model structure for a working system. Thus, with semi-physical modeling we take advantage of a basic property of classical identification models: they are linear-in-the-parameters, but may contain nonlinear regressors. Hence, while physical knowledge suggests nonlinear data regressors, system identification adjusts linear weighting parameters. The models proposed here incorporate nonlinearities based on physical system knowledge and they include, among other inputs and disturbances, air wind speed (v) and air relative humidity (RH), signals not usually considered in these model structures. Specifically, this work shows model predictive accuracy of storage tanks temperature for three model types: semi-physical, state-space and, a combination of semi-physical and a feedforward neural network with one hidden layer and eight neurons. The best models found here, according to prediction accuracy, are of semi-physical nature, and are obtained using stepwise regressor elimination algorithms which retain disturbances such as v and RH. Additionally, final models are validated with classical statistical tests such as AIC and correlation analysis. [Copyright &y& Elsevier]

Abstract: The Integrated Collector Storage Solar Water Heater (ICSSWH) developed from early systems comprised simply of a simple black tank placed in the sun. The ICSSWH, by its combined collection and storage function suffers substantial heat losses to ambient, especially at night-time and non-collection periods. To be viable economically, the system has evolved to incorporate new and novel methods of maximising solar radiation collection whilst minimising thermal loss. Advances in ICS vessel design have included glazing system, methods of insulation, reflector configurations, use of evacuation, internal and external baffles and phase change materials. [Copyright &y& Elsevier]