Domestic Hot Water Systems Research Articles

A study on automatic optimal operation of a pump for solar domestic hot water system

The objective of this research is to determine optimal control variables of a collector pump placed on a collector loop to improve the performance of a solar domestic hot water system. A mathematical model of the system is developed to predict its operating performance under real weather conditions at Jeju Island, South Korea. The optimum control variables of the collector loop are investigated based on the relationship between the useful heat gain of the solar collector and the electricity consumption of the collector pump. In addition, the effects of various parameters such as solar collector area, initial water temperature, and volume of storage tank are analyzed. The results of the simulation showed that the optimum variable flow rate was determined at m=0.05ΔTAc/60(kg/s) (Kv=0.05). At this value, the useful heat gain of the solar collector Qu increased by about 1.54% while the electricity consumption of the collector pump Ep sharply decreased to 65.6% when the constant flow was replaced by the variable flow for the collector loop. Furthermore, the system performance is significantly affected by the change of initial water temperature and volume of the storage tank, as well as the collector area.

자연형 및 설비형 태양열 온수기의 이용특성에 대한 실험적 연구

There are the stirring test and drain test in the daily performance test to determine the thermal performance of a domestic solar hot water system. The drain test is a test that measures the discharge heating rate while drain the hot water from the top of the storage tank and supply the city water to the bottom of the tank. From the perspective of the user, this drain test is more effective than the stirring test. In this study, the thermal performance were compared through the drain test for a passive type and an active type domestic solar hot water systems consisting of the same storage tank and collectors. At this point, a passive type was used the horizontal storage tanks, and an active type was used vertical storage tank. In the drain test, when the hot water drained up to the reference hot water temperature, an active type which have vertical storage tank represents excellent daily performance than a passive type which have horizontal storage tank regardless of weather conditions. The reason for this is because the vertical storage tank is advantageous to thermal stratification in the tank. After the drain test, the residual heat for the horizontal storage tank was much more than the vertical storage tank, but in the next day the amount of discharged heat were less than the those of vertical storage tank neither. Thus, the solar water heating system which have horizontal storage tank should be adopted preheating control method rather than separate using control method when connected with auxiliary heat source device.

Efficiencies and improvement potential of building integrated photovoltaic thermal (BIPVT) system

Building integrated photovoltaic thermal (BIPVT) system has been designed to produce both electricity and hot water and later integrated to building. The hot water is produced at the useful temperatures for the applications in Malaysia such as building integrated heating system and domestic hot water system as well as many industrial including agricultural and commercial applications. The photovoltaic thermal (PVT) system comprises of a high efficiency multicrystal photovoltaic (PV) module and spiral flow absorber for BIPVT application, have been performed and investigated. In this study, it was assumed that the absorber was attached underneath the flat plate single glazing sheet of polycrystalline silicon PV module and water has been used as a heat transfer medium in absorber. Performances analysis of BIPVT system based on energy and exergy analyses. It was based on efficiencies including energy and exergy, and exergetic improvement potential (IP) based on the metrological condition of Malaysia has been carried out. Results show that the hourly variation for BIPVT system, the PVT energy efficiency of 55–62% is higher than the PVT exergy efficiency of 12–14%. The improvement potential increases with increasing solar radiation, it is between 98 and 404W. On the other hand, BIPVT system was produced primary-energy saving efficiency from about 73% to 81%.

Thermal behaviour of a modular storage system when subjected to variable charge and discharge sequences

This paper presents the results of an experimental study conducted on a multi-tank thermal storage. The purpose of the study was to investigate the thermal behaviour of the stratified tank system when subjected to standard draw profiles. The experimental setup consisted of a charge loop to simulate a solar collector input, three commercially available 270L domestic hot water tanks and three side-arm, natural convection heat exchangers. The system was charged using two 3kW electric heaters which produced a variable input power to simulate the variation in output of a typical fixed orientation solar collector. Realistic hot water draws were conducted according to the specifications of the Canadian Standard Association, CSA-F379.1, for Solar Domestic Hot Water Systems. Experimental tests were conducted over 2days for three different plumbing configurations, and compared with simulation results produced in the TRNSYS simulation environment. The plumbing configurations which were considered include: series charge and series discharge, parallel charge and parallel discharge, and series charge and parallel discharge. Comparisons between system configurations were based on stratification levels, hot water delivery temperatures, and solar fractions. Results of the study showed that charging and discharging the system in parallel produced the highest solar fraction when compared to the other multi-tank configurations, with solar fractions of 0.62 and 0.67 from experimental testing and TRNSYS simulation, respectively. When compared to a single tank configuration, the parallel charge and parallel discharge configuration achieved 97.7% of the delivered solar energy of a stratified single tank system with the same storage volume and heat exchanger performance.

Impact of remineralized desalinated water on domestic services and hot water systems: experience at Adelaide Desalination Pilot Plant

AbstractMembrane desalination technology is undergoing rapid expansion in Australia in response to drought and climate change. In preparation for the operation and maintenance of the 300 ML/day, Adelaide Desalination Plant (ADP), a pilot plant (ADPP), was constructed to evaluate several anticipated operational challenges. A main area of investigation was the control of downstream corrosion after remineralization. Desalinated water requires remineralization before distribution as its very low mineral content renders it highly corrosive. The impact of remineralized desalinated water on small scale, downstream infrastructure was investigated at the ADPP. Two domestic hot water systems (HWS) and a series of network pipe segments were fed with mains water and desalinated product water, and the effects on these assets was assessed. Differences in mains and desalinated water chemistry contributed to increased calcium carbonate scale formation in remineralized desalinated water fed HWS; however, calculations base...

Experimental study of the phase change and energy characteristics inside a cylindrical latent heat energy storage system: Part 1 consecutive charging and discharging

Solar domestic hot water (SDHW) systems are a cost effective and efficient way to pre-heat domestic water for hot water use in buildings. Currently used sensible energy storage systems (commonly using water as the storage medium) are simple and inexpensive, but require large amounts of storage material, and therefore are heavy and take up considerable space. Latent heat energy storage systems (LHESS) store the energy absorbed/released when a material goes through a phase transition: these materials are called phase change materials (PCMs). Because of the large quantities of energy that are stored during a phase change, latent heat energy storage is more dense than sensible energy storage, and can therefore reduce the weight and space requirements of the energy storage system. The main objective of this research is to study the heat transfer processes and phase change behavior of a PCM during consecutive charging and discharging of a LHESS. This leads to better understanding of the melting and solidification processes in order to optimize future LHESS design.In part 1 of this paper the design of a LHESS that can operate under both consecutive and simultaneous charging and discharging modes is introduced. Dodecanoic acid is used as the PCM, as it has been shown to be safe, relatively inexpensive, and has a melting temperature in a range suitable for use with SDHW. Experimental results of consecutively charging and discharging the system are presented and the effect of the heat transfer fluid flow rate is explored. It was found that during charging a faster flow rate leads to shorter melting times; however, during discharging, the flow rate does not affect the rate of solidification.

The Energy and Exergy Efficiencies of Renewable Energy Utilization in a Building Stock

An surface water heat pump (SWHP) system and some solar domestic hot water (SDHW) systems were constructed in a building stock located in Xiangtan for the purpose of energy saving and environmental improvement. This study aims to evaluate the energy and exergy efficiencies of renewable energy utilization based on energy and exergy analysis. We found the energy and exergy efficiencies of the SWHP system in heating mode to be 395% and 17.78%, respectively. The energy and exergy efficiencies for the SDHW systems were found to be 34.96% and 17.5%, respectively. Some measures for the exergy efficiency improvement are discussed in this paper.

Maximizing performances of variable tilt flat-plate solar collectors for Belgrade (Serbia)

In Serbia, for heating of domestic hot water (DHW) it is customary to use electricity. As around 70% of electricity is produced by using low quality coal with high greenhouse emission, it is beneficial to environment to use solar energy by flat-plate solar collectors for heating of DHW in a solar DHW system (SDHWS). The SDHWS with variable tilt flat-plate solar collectors placed in north-south direction at roofs of houses are investigated for their optimal operation in Belgrade, Serbia. The investigated variable-tilt collectors annually take 2 tilts, 4 tilts, and 12 tilts. The used weather data are from the meteorological station. These investigations use three computer codes: EnergyPlus, GenOpt, and Hooke-Jeeves search algorithm. For different solar collectors, the investigations revile their optimum tilts that maximize the solar fraction by the SDHWS. Then, the solar fraction and avoided fossil energy by the SDHWS are maximized. In addition, the deficit in the solar fraction is estimated when the solar collectors are not at their optimum tilt.

A Transient Immersed Coil Heat Exchanger Model

The aim of this paper is to present a transient one-dimensional (1D) radial immersed coil heat exchanger model that accounts for the effect that geometry and operating conditions have on heat transfer performance. Insights gained through its use in both an analysis of experimental data and an implementation in the simulation environment TRNSYS are shown and discussed. While variation in the external convection coefficient of immersed coil heat exchangers has little effect on the annual solar fraction of a generic solar domestic hot water system, variation in collector side flow can influence the solar fraction as great as ±5%, in particular low collector side flow improves stratification inside the store.

Rule-based demand-side management of domestic hot water production with heat pumps in zero energy neighbourhoods

Grid saturation has been reported in electricity distribution systems with a high penetration of photovoltaic (PV) systems. This saturation is often caused by overvoltage and results in curtailing or shutting down of the PV inverters, leading to a loss of renewable electricity generation. The presented work assesses the potential of rule-based demand-side management (DSM) applied to domestic hot water (DHW) production with heat pumps in dwellings for reducing the non-renewable energy use of the neighbourhood. The studied case consists of 33 single-family dwellings connected to a single phase distribution grid in a moderate European climate. Each dwelling is designed as a net-zero energy building by adequate design of a heat pump and PV system. A detailed dynamic simulation model is implemented by use of a cross-domain Modelica library for integrated district energy assessment. The user behaviour is obtained from a stochastic model based on Markov chains and survival analysis. Different rule-based DSM control strategies are applied to the individual dwelling's DHW systems. The results show that for balancing the PV production, active thermal energy storage in the DHW storage tanks is very promising. Even with very basic control algorithms and small storage tanks of 0.3 m3, curtailing losses can be reduced by 74%. This represents a net energy saving on a neighbourhood level of 3.4%.

Numerical Optimization of Domestic Hot Water Systems Based on Global Cost

The scope of this work is motivated by the large number of solar heaters recently installed by the government in joint housing developments for the low-income population in Brazil, the technical challenges inherent in deploying domestic hot water systems, and innovative new models of sustainability technology being developed in Brazil. Computational algorithms were developed to establish the criteria for optimization, such as minimizing the required recycling, the energy consumption in pumping, and the diameter of the pipes in the secondary circuit of the distribution network. The numerical method adopted, the conjugate gradient method combined with a genetic algorithm, has exhibited a very satisfactory degree of convergence, even though high-oscillation amplitudes were observed, which are attributed to slight variations in the pipe diameters (commercial).

Investigation of the performance of a combined solar thermal heat pump hot water system

The use of a heat pump as an auxiliary energy source for solar domestic hot water systems can achieve significant energy savings, due to the remarkable potential of heat pumps on the efficient provision of thermal energy. In this work, the performance of a combined solar thermal heat pump hot water system is investigated. A component based simulation model for the whole system was experimentally validated. Emphasis was paid on the formulation of a simple and efficient approach for the modeling of the heat-pump. The performance of the system on an annual basis is investigated, with regard to the methodology used in solar domestic hot water systems testing. According to the results of the analysis, the system achieves significant auxiliary energy savings, which can present a value in the order of 70% for the climatic data of Athens. The temperature set-point for the activation of the heat pump proves to be an important parameter for the performance of the system, noting that the higher the value of the set-point, the lower the efficiency of the heat pump.

Three eco-tool comparison with the example of the environmental performance of domestic solar flat plate hot water systems

Life Cycle Analysis (LCA) is a procedure used as an analytical tool for the evaluation of the environmental impact caused by a material, a manufacturing process or product. For an end product, LCA requires both the identification and quantification of materials and energy used in all stages of the product’s life, together with their environmental impact. It requires therefore a huge amount of data about materials, components, manufacturing processes, energy consumption and the relevant environmental impacts. For this reason, a number of software and databases have been developed, in order to facilitate LCA users. These are the so-called Eco-Tools, used in an effort to minimize the environmental impact of a product from the materials and the energy used for production. In this paper, LCA is conducted for solar thermosyphonic systems, with the aid of three commercially available Eco-Tools, usually used by LCA practitioners, namely: Eco-It, GEMIS and SimaPro, and the results are compared. Although all three tools claim accordance with the international standards and guidelines, differences do exist. A typical solar thermosyphonic system (DSHWS) with a 4 m2 collector area and a capacity of 150 dm3 that covers the hot water needs of a three person family in Thessaloniki is used as case study. The results of the three tools are compared for each component of the solar system as well as for each material used and for the conventional energy substituted by the system.

The monitored performance of the first new London dwelling certified to the Passive House standard

The monitored performance of the first new London dwelling certified to the Passive House standard is presented. The first detailed analysis of the energy consumption of the heating, ventilation and domestic hot water systems are given. The annual space heating demand of the 2 bedroom, 101m2 dwelling was 12.1kWh/m2, achieving the 15kWh/m2 Passive House target. The annual primary energy demand was 125kWh/m2, marginally above the 120kWh/m2 target. The measured internal heat gains of 3.65W/m2 are much greater than the 2.1W/m2 suggested as standard for dwellings. The Passive House Planning Package, PHPP, is found to be a good predictor of space heating demand and the risk of summer time over heating. Winter space heating demand is sensitive to occupant blind use. With a total metered energy consumption of 65kWh/m2, the Camden Passive House is one of the lowest energy, small family dwellings, monitored in the UK.

Viability Evaluation of Domestic Solar Hot Water Systems using two Multi Criteria Evaluation Techniques: Case Study of an Urban Area in India

Despite the proven favourable techno-economic feasibilities along with the organised promotional measures, solar hot water systems are not diffused to the extent they should be, even in the domestic front of urban India where the potential for such dissemination is high. The reasons for such a low dissemination of domestic solar hot water systems (DSHWS) could be due to multi-criteria covering various dimensions of viability of domestic water heating options. This paper presents the work taken up to study the viability of DSHWS vis-à-vis other competing water heating options, on multi-criteria covering technical, economic, commercial, social and behavioural dimension in the urban India context, with a special reference to Bangalore. The strengths and weaknesses, significant dimensions and criteria for better dissemination of DSHWS vis-à-vis other competing water heating options, as obtained from the analysis using two multi criteria evaluation techniques viz. PROMETHEE and AHP are presented.

Heat Consumption Assessment of the Domestic Hot Water Systems in the Apartment Buildings

This study presents the analysis of energy consumption for domestic hot water in apartment buildings in Riga, Latvia. The aggregate data contains information about 39 apartment buildings, including heat energy consumption and domestic hot water (DHW) consumption. The analysis is focused on the heat energy consumption and seasonal characteristics in the DHW system. The analysis characterizes the DHW consumption, energy consumption for DHW and energy losses in the DHW systems in apartment buildings. The energy consumption of DHW needs of households and some other building sectors constitutes a significant part of the building's energy balance. The building energy efficiency improvement measures reduce the heating energy required proportion and logically increase the share of energy consumption for DHW needs. It is likely that the production and distribution of DHW in buildings will constitute a dominant share of both the present, and in particular, the future energy design requirements of buildings. (1) Previously studies carried out in various European countries (2), (3), (4), China (5), (6), Japan (7), (8), (9), USA (10), (11), Canada (12) points the many differences in DHW consumption as well as the tendency to change over time due to a global increase of energy prices, changes in technologies, introducing of individual metering, as well as wide variety of other factors that may appear on local or regional level. Measurements in Denmark documented not only a relatively high energy consumption for DHW in apartment buildings, but also recorded surprisingly large heat losses from the DHW circulation lines (13), (14). Recent investigation of 24 buildings in Danmark shows that most of the energy demand for DHW is lost in the circulation system. The efficiency was 0.30-0.77 (heat loss 23-70%) in apartment buildings and efficiency 0.11- 0.46 (heat loss 54-89%) in office buildings. (1) The Energy Performance of Buildings Directive (EPBD) (15) in the version of 2010, the so-called recast EPBD, demands in annex I 'Common general framework for the calculation of energy performance of buildings (referred to in Article 3)' that '(1) the energy performance of a building shall be determined on the basis of the calculated or actual annual energy that is consumed in order to meet the different needs associated with its typical use and shall reflect the heating energy needs and cooling energy needs (energy needed to avoid overheating) to

Solar Hot System and Design of Buildings

Domestic solar hot water system, the use of the status quo and existing problems, by analyzing the solar water heating equipment and building integrated and building integrated design.

THE USE OF SOLAR ENERGY FOR PREPARING DOMESTIC HOT WATER IN A MULTI-STOREY BUILDING / SAULĖS ENERGIJOS PANAUDOJIMAS KARŠTAM VANDENIUI RUOŠTI DAUGIABUČIAME NAME

The article analyses the possibilities of solar collectors used for a domestic hot water system and installed on the roofs of modernized multi-storey buildings under the existing climate conditions. A number of combinations of flat plate and vacuum solar collectors with accumulation tank systems of various sizes have been examined. Heat from the district heating system is used as an additional heat source for preparing domestic hot water. The paper compares calculation results of energy and economy regarding the combinations of flat plate and vacuum solar collectors and the size of the accumulation tank. The influence of variations in the main indicators on the final economic results has also been evaluated. Research has been supported applying EC FP7 CONCERTO program (‘‘Sustainable Zero Carbon ECO-Town Developments Improving Quality of Life across EU - ECO-Life’’ (ECO-Life Project) Contract No. TREN/FP7EN/239497/”ECOLIFE”). Santrauka Straipsnyje analizuojamos saulės kolektorių, skirtų karšto vandentiekio sistemai ant modernizuojamų daugiabučių namų stogų įrengti esamomis klimatinėmis sąlygomis galimybės. Nagrinėjamos įvairaus dydžio plokščiųjų ir vakuuminių saulės kolektorių su akumuliacinėmis talpyklomis sistemų kombinacijos. Kaip papildomas šilumos šaltinis karštam vandeniui pašildyti naudojama iš centralizuotų šilumos tinklų tiekiama šiluma. Lyginami plokščiųjų, vakuuminių saulės kolektorių ir akumuliacinio bako dydžio kombinacijų energinių ir ekonominių skaičiavimų rezultatai. Įvertinama kai kurių esminių rodiklių pokyčių įtaka galutiniams ekonominiams rodikliams.

Production and distribution of domestic hot water in selected Danish apartment buildings and institutions. Analysis of consumption, energy efficiency and the significance for energy design requirements of buildings

The goal of this work has been to document the efficiency of domestic hot water (DHW) distribution systems and to propose more energy efficient and environmentally friendly solutions for DHW systems based on analyses of existing conditions.In the article, measurements from 13 apartment buildings and two institutions are presented, i.e. consumption of DHW, heat loss from circulation lines and efficiency of the DHW system. The heat load and the cooling of the district heating water for DHW are documented as well.Possibilities for improving the DHW system include new types of circulation pipes, which have the potential of a 40% reduction of heat losses. In addition to the reduction of heat losses inside the building, a low return temperature from the hot water system will have a large impact on the heat losses from the district heating network when the building is being heated by district heating.It is likely that the production and distribution of DHW in buildings will constitute a dominant share of both the present, and in particular, the future energy design requirements of buildings. The results of this project could influence not only future buildings, but also existing buildings when renovation of installations take place.

Negative buoyant plume model for solar domestic hot water tank systems incorporating a vertical inlet

Thermal stratification in solar energy storage tanks plays an important role in enhancing the performance of solar domestic hot water systems. The mixing that occurs when hot fluid from the solar collector enters the top of the tank is detrimental to the stratification. Mathematical models that are used for system analysis must therefore be able to capture the effects of this inlet jet mixing in order to accurately predict system performance. This paper presents a computational study of the heat transfer and fluid flow in a thermal storage tank of a solar domestic hot water system with a vertical inlet under negative buoyant plume conditions. The effects of parameters such as the fluid inlet velocity and temperature as well as inlet pipe diameter on the thermal mixing were considered. The work culminated in the development of a one-dimensional empirical model capable of predicting the transient axial temperature distribution inside the thermal storage tank. Predictions from the new model were in good agreement with both experimental data and detailed computational fluid dynamics predictions.