Domestic Water Heating Systems Research Articles

Theoretical analysis to determine the efficiency of a CuO-water nanofluid based-flat plate solar collector for domestic solar water heating system in Myanmar

Abstract The efficiency of a flat plate solar collector using water based CuO nanofluid as a working fluid is analyzed theoretically. A mathematical model and a program, written in MATLAB code were used for calculating the efficiency of a flat plate solar collector for a domestic solar water heating system considering weather conditions of a city in Myanmar. This calculation includes three aspects. Firstly, the maximum solar energy availability for the flat plate solar collector tilted at the optimum angle was estimated. Secondly, the convective heat transfer coefficient of nanofluid was calculated as a function of volume concentration and size of the nanoparticle. Thirdly, the overall heat loss coefficient of the flat plate solar collector was calculated using a method of iteration. Through these calculations, the collector efficiency was obtained as a function of volume concentration and size of the nanoparticle. The results showed increasing in collector efficiency by increasing the volume concentration up to 2% while the effect of nanoparticle size on the efficiency was marginal. The use of the CuO-water nanofluid as a working fluid could improve the efficiency of flat plate solar collector up to 5% compared with water as a working fluid under the same ambient, radiant and operating conditions.

The brinesiphon: A homolog of the thermosiphon driven by induced salinity and downward heat transfer

The basis of a novel method for passive solar water heating homologous to the thermosiphon but driven by induced salinity, which causes a fluid to circulate without the need for a mechanical pump and with inverse natural convection (downward heat transfer), is outlined. The brinesiphon, like the thermosiphon, operates by harnessing the tendency of a less dense fluid to rise above a denser fluid, resulting in fluid motion through a collector, but with two exceptions: first, the buoyancy is controlled by induced salinity gradients rather than thermal gradients, and second, as a result, natural convection is in the opposite direction than that in the homologous thermosiphon concept; i.e., hot fluid flows down, and cold fluid rises. A brinesyphon may be more suitable for solar domestic water heating systems than the thermosiphon because the direction of flow allows downward transfer from a solar collector to a lower storage tank without any type of mechanical pumping system.

Energetic performance assessment of solar water heating systems in the context of their energy labeling

The present work investigates the suitability of a new method for the calculation of the performance indicators of domestic solar water heating systems, within the framework of the European Directive implementation for energy labeling of water heating devices. The various methodology approaches suggested by the directives for the calculation of the expected energy yield from the solar thermal products are being analyzed. The presence of significant issues of reliability and objectivity is being brought out, particularly with regard to the SOLCAL method, which is used for the estimation of the expected energy yield of a thermal energy system, by means of the characteristics of each individual component which the system consists of. A detailed documentation and experimental validation of a new method for the estimation of the expected energy yield of a solar only water heater is outlined. The performance of the proposed method is assessed based on an extensive experimental investigation, whereby discrepancies of the order of 7% or less were obtained for the daily energy yield. From the comparison of performance of the new method against that of the SOLCAL method it is inferred that the former constitutes a reliable alternative choice in the context of energy labeling.

Review of the phase change material (PCM) usage for solar domestic water heating systems (SDWHS)

The shortage in energy resources combined with the climb in greenhouse emissions is the main incentive beyond the deployment of solar energy resource in various applications. One of the most successful applications is the utilization of solar energy in the domestic water heating systems (DWHS) because 70% of the consumed energy in the residential segment is utilized for space heating and appliances in cold climates 1. However, the full deployment of solar energy in domestic water heating is only possible when an energy storage system with acceptable price is available. Recently a new tendency for deploying phase change materials (PCMs) as an energy storage system is introduced in several solar DWHS. These systems are known as integrated PCM in solar DWHS and offer several advantages including high storage capacity, low storage volume, and isothermal operation during the charging and discharging phases. The present study reviews various techniques utilized for integrating the PCM in solar water heating systems and the utilized methods for enhancing the heat transfer characteristics of the PCM through the usage of extended surfaces and high conductive additives. Copyright © 2017 John Wiley & Sons, Ltd.

Impacts of Domestic Solar Water Heating (DSWH) systems on the cost of a hot shower in low-income dwellings in Brazil

This work presents a method to evaluate, from the distribution utility's perspective, the impacts of adopting Domestic Solar Water Heating (DSWH) systems in Brazil, based on demand measurements carried out on two groups of residential households. For the 12 months period evaluated, the case-study shows that using DSWH results in savings of 198 kWh (38%), and active power demand savings at peak times of 860 W (42%) per individual unit. For the distribution utility and per individual unit, using DSWH leads to avoided costs of $ 27.59 (38%), avoided costs due to peak time demand reduction of $ 170.2 (42%), and annual avoided costs of $ 197.79 (41%). This work clearly shows that in the residential section the tariff model and structure is strongly distorted, since it only accounts for the energy consumption per residential unit, and completely disregards the costs associated with power demand availability. Our results show that in Brazil the distribution utility charges only some 15% of the real cost of a hot shower based on electric showerheads.

Increasing the efficiency by retrofitting gas boilers into a condensing heat exchanger

ABSTRACTWhen trying to reduce energy consumption in a central heating system or in a domestic water heating system, it is necessary to consider the annual operating efficiency of the heating and the domestic hot water heating system. A boiler operates under dynamic conditions, so it essential to know the methodology and the model of annual operating efficiency calculation for thermo technical systems. The outlet temperature of the flue gases with conventional gas boilers is considerably higher than the ambient temperature and consequently the heat loss occurs; it is then vented off into the environment as a result of heat transfer. The heat loss may be reduced if a condensing heat exchanger is installed, which will, on the other hand, increase the boiler efficiency by more than 10%. This paper studies the relations between combustion and heat transfer, which will enable the appraisal of a gas boiler efficiency increase and possible ways of energy savings. The method for cost-effectiveness of the investment is used to perform a feasibility study of retrofitting a conventional boiler into a condensing boiler with necessary details. The results of the investigation show that the most cost-effective temperature range of the flue gases is 40–60°C. The use of a working fluid in the heating system or the domestic cold water results in cooling the condensing heat exchanger. The temperature of the return water or the domestic cold water is lower than the water vapor dew point in the flue gases during most of the heating period in almost all parts of the Republic of Serbia where natural gas is used.

Effect of Dimples on Solar Concrete Plate Collectors and its Comparison with Other Domestic Water Heating Systems

Though solar water heater is an environment-friendly and a well-established effective method of heating water, yet it is not used on large scale in a country like India where abundant solar energy is available for most of the year. A large proportion of population prefers the use of electric geysers or stoves over solar water heaters as they have cheaper initial costs. Thus with an objective of low-cost solar collector water heater, an investigation is conducted on concrete as collector plate. In order to improve the efficiency of concrete plate collector, a serpentine tube is used instead of parallel tubes, with the addition of metal fibers in concrete mixture to improve its thermal conductivity and dimples are created on the serpentine tube to enhance heat flow from tube to water flowing through it. In order to calculate the exact effect of dimples on concrete plate collector, dimpled tube collector is compared with smooth tube collector. It is observed that dimples lead to an increase in outlet water temperature and improved efficiency for all water flow rates. Also in this paper, comparison of concrete plate collector with existing systems of domestic water heating for the bathing purpose is presented.

Experimental Investigation and Comparison Between an Integrated Compound Parabolic Domestic Solar Water Heater with and Without an Air Gap Introduced at the Arms of the CPC

The introduction of a concentrator in a domestic solar water heating system is not yet commercialized but research studies have been carried out and model validation done with symmetrical and asymmetrical type of reflectors. With concentrating collectors it becomes imperative to track the sun. Now the method of tracking to be adopted and the number of adjustments required depends upon the collection efficiency and its application. However for households, systems operating at the lower temperature range the optical system best suited are the compound parabolic concentrator. The advantage is that it has large acceptance angle and therefore requires only occasional tracking. The model studied is batch type heater, as the receiver serves the dual purpose of absorber and storage tank, unlike conventional design which consist of a large number of smaller diameter tubes and separate storage tank. The concentrator i.e. the reflector in this case, is supported on a wooden cradle which comprises the two parabolas of the compound parabolic concentrator. In the present work experimental studies have been carried out and mean collector efficiency computed on model with an air gap introduced in the side walls (arms of the CPC) and performance compared with the model without an air gap. This work is built on a model but without the air gap. Results have shown that there is 37.7% percentage increase in collector collection efficiency with air gap.

Detailed modeling of a novel photovoltaic thermal cascade heat pump domestic water heating system

A domestic water heating system that combines photovoltaic thermal (PVT) solar collectors with two heat pumps, in a novel cascade arrangement, is presented and analyzed in this paper. The goal of this analysis is to determine and compare the annual thermal energy output of the PVT cascade heat pump system with an evacuated tube and simultaneous consumption PVT single heat pump water heating system. The computational technique that was developed to analyze the PVT cascade heat pump system, which determines solar panel energy outputs, and heat pump operating characteristics, is described in detail. Case study simulation results are also presented, which include transient power output profiles, temperature profiles, and yearly energy output results. Hourly weather data, including air dry-bulb temperatures and solar flux values, from locations with a range of climates was used in these simulations. The results of this study show that the PVT cascade heat pump system has an annual thermal energy output improvement over the evacuated tube heating system ranging from 37% to 68%, depending on the selected simulation location.

Thermal Performance Test for Centralized Domestic Solar Water Heating System

Thermal Performance Test for Centralized Domestic Solar Water Heating System

Multi-objective optimization of a residential solar thermal combisystem

Solar thermal systems for domestic hot water and space heating, referred to as solar combisystems, can significantly reduce primary energy consumption for residential buildings. In most studies, single-objective optimization algorithms are used for the design and operation strategies of such complex systems. This paper presents the use of two conflicting objective functions, the life cycle cost and life cycle energy, for the optimization of a residential solar combisystem in Montreal, Quebec, Canada. Since the design the solar combisystem is treated as a multi-objective optimization problem, two different approaches for solving such problems are presented and compared: the weighted sum method (WSM) using a hybrid particle swarm optimization/Hooke-Jeeves (PSO/HJ) algorithm, and a multi-objective particle swarm optimization (MOPSO). Finally, a hybrid (MOPSO/HJ) is proposed to enhance the local search of MOPSO. The results show that the WSM was time-consuming for such an optimization problem. MOPSO/HJ was more than six times faster than the WSM. Compared with the base case combisystem, MOPSO/HJ found different design options, where the life cycle cost and life cycle energy were reduced by up to 88.6% and 63.9%, respectively.

Dynamic modeling approach for determining buildings technical system energy performance

This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope+technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%.

A Study of the Influence of Solar Panels Coupled with Thermal Systems for a Residential Building, by Applying Methods of Evaluation as EN 15316-4-3:2014 and TRANSOL

The present study performs calculations for a series of parameters involved in the definition of energy performance of a real residential building, by applying EN15316-4-3:2014 methodology; results are compared with simulations made with TRANSOL, analysing the influence of coupling solar panels with domestic hot water production (DHW) and heating systems. In a first stage, the influence of using solar panels for DHW production is evaluated, and calculations for thermal and electric needed energy are performed. Variation of solar fraction is analised. Secondly, a combi-system (DHW+heating) was considered, and the calculations were performed accordingly, as EN 15316-4-3:2014 describes. The data provided with TRANSOL were compared with the results obtained by applying EN 15316-4-3:2014, and conclusions are extracted. At the end, a parametric study of solar fraction is followed, taking into account different numbers of solar panels, in both situation, for DHW and DHW & heating coupling systems cases. The critical approximation introduced by EN 15316-4-3 is identified. Values of determined fraction are compared.

Experimental and Computational Study for Household Equipment System in a Smart House with Solar Collectors

In**troduction of renewable energy, in particular the use of solar energy is one of the most efficient strategies to improve building energy efficiency. The objective of this study is to clarify the whole system efficiency of the solar collector combined with gasdriven auxiliary boiler to supply both domestic water and floor heating system. The verification of simulation results based on TRNSYS17 was performed first by comparing to the measurement results, which has been confirmed well. Another objective of this study is to optimize the use of solar energy. In the combined system, three using options of the solar energy gathered by solar collectors are considered reasonable, to supply to floor heating system only, to supply to domestic water system only, and to supply to the both. On the other hand, the efficiency of the gas-driven auxiliary boiler, varies with the inlet water temperature, also affects the system performance, and in consequence links to the primary energy consumption. System control strategy depends on several elements, including weather condition, schedule of domestic water supply, return water temperature of floor heating and the water temperature in tank for heat storage. The total primary energy consumption is consumed as the index to evaluate the whole system performance.

WPŁYW ZASTOSOWANIA KOLEKTORÓW SŁONECZNYCH NA EKONOMIKĘ PRZYGOTOWANIA CIEPŁEJ WODY UŻYTKOWEJ

One of the principal actions arising from the need for rational energy management, is the increase of renewable energy sources use. Application of solar energy photothermal conversion for domestic hot water preparation is a solution that, by reducing demand for conventional energy, allows to minimize the cost of system operation effectively. In this paper, a performance of solar hot water installation working in a typical apartment building is analyzed. The building is located in Lublin, in the third climate zone. Energy demand for heating domestic water was monitored in 2010–2013. The operational effects of the system were comparedin terms of energy and cost with the most commonly used systems for domestic hot water heating.

Sizing of a Domestic Hot Water Heating and Storage System for Short Operating Cycles - A Theoretical Approach

A methodology for the sizing of domestic hot water heating and storage systems is defined, by assuming an extreme operating condition cycle composed of only two parts, a water consumption period and a system repositioning period. In both parts to respond to the extreme hot water demanding conditions, the heating is always on. The subsequent exergy analysis of this domestic hot water production system compares the irreversibility and the exergy efficiency of the water storage and the tankless situation. To carry out such analysis, some basic assumptions were made: a constant temperature heat source, a short duration operating cycle and a constant thermal energy supply. Under these circumstances it is shown that the hot water storage system leads to lower exergy losses while the tankless system is more exergy efficient, but requiring a higher instantaneous thermal power input. The use of the joule effect electricity, as the system heat source, be it a water storage one or a tankless one, maximizes the system irreversibility losses and minimizes the system exergy efficiency. The tankless system, with the joule effect electricity heat source is the worst situation.

The Effect of Measurement Uncertainty and Environment on Domestic Solar Water Heating Systems’ Energy Efficiency Grades

Abstract In China, two important national standards were implemented on Aug 1st, 2012, one is ‘Specification of domestic solar water heating systems’ (GB/T 19141-2011), the other is ‘Minimum allowable values of energy efficiency and energy efficiency grades for domestic solar water heating systems’ (GB 26969-2011). According to these two standards, the energy efficiency grades indicator CTP (coefficient of thermal performance) should be tested and calculated by daily useful energy and average heat loss factor of domestic solar heating system. Through experiment and calculation, the effect of measurement uncertainty and daily average ambient temperature on the migration of domestic solar water heating systems’ (DSWHS) energy efficiency grades was discussed. The calculation and analysis methods may be helpful for data consistency co-verfication between different inspection organizations.

Experimental Study of a Novel Testing Platform for the Thermal Performance of Solar Domestic Water Heating Systems

Solar domestic water heating systems (SDWHS) are widely used in China, with an installed collector area of more than 330 million square meters by the end of 2014.Many relevant products keep on launching and upgrading in the market. To regulate the market, the performance of products, especially new products should be evaluated by thequality supervisionagency. However, all the existing national standards of thermal performance tests forSDWHSrequire that the daily solar irradiationgain should be more than 16 MJ/m2.Thus, only a small part of days in a year meet this criteria, which constrained quality supervisionagencies to regulate the solar heater market. A new approach of testing platform for the thermal performance of SDWHS is also presented in this manuscript. The testing platform consists of a sun-tracking flat-mirror reflector which not only directs the sunlight to the collector to increase the daily solar irradiation gain but also produces a light spot of 2×2 m2. A large number of experiments have been conducted to measure the performance of the testing platform. Results show that on one hand the platform can increase the daily gain of solar irradiation to 16 MJ/m2 from 12 MJ/m2, and on the other hand the light spot has a non-uniformity of less than 3%. Experiments onSDWHShavebeen performed on the platform as well as on the ground, respectively. It has been found that the relative difference of the daily thermal efficiency measured by the two methods is lower than 3%.

Net energy analysis of a solar combi system with Seasonal Thermal Energy Store

EU targets require nearly zero energy buildings (NZEB) by 2020. However few monitored examples exist of how NZEB has been achieved in practise in individual residential buildings. This paper provides an example of how a low-energy building (built in 2006), has achieved nearly zero energy heating through the addition of a solar domestic hot water and space heating system (“combi system”) with a Seasonal Thermal Energy Store (STES). The paper also presents a cumulative life cycle energy and cumulative life cycle carbon analysis for the installation based on the recorded DHW and space heating demand in addition to energy payback periods and net energy ratios. In addition, the carbon and energy analysis is carried out for four other heating system scenarios including hybrid solar thermal/PV systems in order to obtain the optimal system from a carbon efficiency perspective.

Demand response visualization tool for electric power systems

Abstract Background Demand response (DR) is referred to programs designed to manage and control electric loads. DR represents one of the vital tools utilized in power distribution networks to improve network efficiency. Effective implementation of DR programs delivers operational benefits such as reduced peak demands and relieved overloads, which are essential in a power system with growing penetration of fundamentally intermittent renewable energy sources. Methods This paper presents a visualization tool for optimising DR programs for domestic hot water systems in distribution power networks. The tool accurately models and predicts potential peak demand reductions through direct load control of domestic hot water systems. It employs a multi-layer thermally stratified hot water cylinder model and Monte Carlo simulations to generate hot water load profiles of domestic customers. To meet peak reduction targets set by the tool user, switching programs found via iterative optimizations are applied to hot water systems. Results The structure and individual components of the tool are described, and case studies are presented. Impacts of different switching programs on customer’s comfort are evaluated and discussed. Conclusion The visualization tool is designed to recommend optimum DR switching programs for domestic water heating systems. The tool can assess the performance of a DR switching program by estimating potential peak load reductions and customer comfort characterized by the probability of cold showers. A power system operator can use this tool to determine the available domestic water heating load in a controlled area, and predict the potential reduction in peak load.