Domestic Hot Water Systems Research Articles

OS-33 新時代の省エネ型給湯設備の計画・評価手法に関する調査・研究 : (第6報)ヒートポンプ給湯機のモデル化

OS-33 新時代の省エネ型給湯設備の計画・評価手法に関する調査・研究 : (第6報)ヒートポンプ給湯機のモデル化

OS-29 新時代の省エネ型給湯設備の計画・評価手法に関する調査・研究 : (第2報)ヒートポンプ給湯機の効率実測

OS-29 新時代の省エネ型給湯設備の計画・評価手法に関する調査・研究 : (第2報)ヒートポンプ給湯機の効率実測

Feasibility Study of a Heating, Cooling and Domestic Hot Water System Combining a Photovoltaic-Thermal System and a Ground Source Heat Pump

Renewable energy systems have received a lot of attention as sustainable technology in building sector. However, the efficiency of the renewable energy systems depends on the surrounding conditions, and it could gradually decrease by excessive and long-term operation. As a solution, a hybrid system can increase the reliability of energy production and decrease investment costs through by reducing the system capacity. The hybrid system operates at the ideal performance, but the design and operation method for hybrid system have not been established. In this paper, the performance of the hybrid system combined with photovoltaic/thermal (PVT) system and ground source heat pump (GSHP) system was analyzed using TRNSYS 17 and feasibility was assessed. The energy consumption and performance efficiency of hybrid system were calculated according to operating modes. Furthermore, seasonal performance factor (SPF) of hybrid system was compared with that of conventional GSHP system. System performance was analyzed in various conditions such as the usage of storage tank heating and set temperature for solar heating. As a result, the average SPF of the developed system increased about 55.3% compared with the GSHP system.

A novel solar-geothermal district heating, cooling and domestic hot water system: Dynamic simulation and energy-economic analysis

In this paper a novel low temperature district heating and cooling system based on renewable energy sources is investigated by means of a dynamic simulation model and an energy-economic analysis. A novel solution consisting of geothermal, solar and biomass energy sources integration is considered. Low enthalpy geothermal well, evacuated solar collectors and auxiliary wood-chip boiler are used to supply the district heating system during the winter season. During summer, an adsorption chiller is activated in order to provide district cooling, while during all year, the system produces domestic hot water for the district users.The case study is developed for the district area of Monterusciello, near the city of Pozzuoli, in Southern Italy. For the case study under investigation, a geothermal source is available at about 55 °C with typical irradiance conditions of Mediterranean climate. A rehabilitation of the buildings located in the considered district area is considered.The proposed system is modelled in TRNSYS environment, where a novel and detailed control strategy is implemented in order to manage the system operation and to match the thermal energy demand of the district users. A comprehensive model of the district network and a detailed heating and cooling demand of network users are considered in the dynamic simulation model of the system.A 1-year simulation is performed and the system performance is analyzed with daily, weekly and yearly time bases. The system analysis is completed with a sensitivity analysis, performed in order to evaluate the system energy and economic profitability as a function of the solar collector field area. The results outline that geothermal and solar energy are only used to match the thermal demand of the district users during winter, while only during summer the activation of the auxiliary biomass boiler is mandatory to match the space cooling demand. The novel system achieves a satisfactory yearly performance in terms of solar collector field efficiency (above 40%) and adsorption chiller Coefficient of Performance (0.5). The system is not economically feasible without any public funding (Simple Pay Back of 20.9 years), while a significant primary energy ratio is achieved (above 75%). In case of public funding policies, the Simple Pay Back period can be halved.

A method for supporting the design of efficient heating systems using EU product policy data

The design of heating, ventilation and air conditioning systems is still a challenging engineering task which requires experienced and informed decision-making. These systems have a great energy-saving potential at the system level rather than at the level of the individual products of which they are composed. European environmental product policies have been very useful in facilitating a homogeneous rating scheme which can be used to compare the energy performance of different products that provide the same service. This paper proposes a simplified design method which uses the performance of components that are regulated by European product policies to obtain the overall performance of heating systems in residential buildings. It is a flexible method and allows different product configurations to be assessed so as to optimise the system performance during the design phase. The method is tested on a real case study with domestic hot water and space heating systems. The case study shows the potential for improving the heating systems according to the performance levels of its products currently available in the market. Results of the domestic hot water system show that upgrading its storage tank to the maximum energy class (A+) could bring the highest energy savings ( 4162 kWh/y).

Energy-efficient Legionella control that mimics nature and an open-source computational model to aid system design

Although there is no direct connection, the incidence of Legionnaire’s disease has increased concurrently with increased usage of energy efficient domestic hot water (DHW) systems, which serve as ideal growth environments for Legionella pneumophila, the bacteria responsible for Legionnaire’s disease. The Duck Foot Heat Exchange Model (DFHXM) was developed to aid design of energy efficient thermal pasteurization systems with Legionella control specifically in mind. The model simulates a system design imitating the countercurrent heat exchange in the feet of ducks, an evolutionary adaption reducing environmental heat losses in cold climates. Such systems use a heat exchanger to preheat fluids prior to pasteurization and cool the same fluid after pasteurization. Thus, the design requires minimal addition of heat to achieve pasteurization temperatures and to cover environmental heat losses. This article describes the underlying principles and use of the freely available Microsoft Excel model, as well as compares results from the DFHXM to measurements of an experimental pilot system. Simulation outputs agreed well with experimental results for transient and steady-state temperatures, the largest discrepancy in steady-state temperatures being 4.6%. Lastly, we discuss the flexibility of the DFHXM to simulate a wide variety of designs with special emphasis on Legionella control and solar-thermal water disinfection.

Effect of PCM application inside an evacuated tube collector on the thermal performance of a domestic hot water system

The article presents an analysis of the effect of PCM application inside an evacuated tube collector on the characteristic operating parameters of a solar water heating system. The temperature of hot water inside the tank and the solar fraction in a domestic hot water system were determined for a typical meteorological year in the Polish city of Czestochowa. A methodology for determining the thermal performance of the evacuated tube collector/storage unit was proposed. The charging efficiency of the evacuated tube collector/storage in a range from 33 to 66% was obtained depending on the solar radiation intensity and the temperature of PCM. An application of latent heat storage (technical grade paraffin) inside the evacuated tube collector allowed the delayed release of heat in the evening, when the intensity of solar radiation was insufficient. As a result, an increase in the temperature of hot water inside the tank was observed during the hot water peak loads in every characteristic period of a typical meteorological year. Furthermore, an evacuated tube collector/storage improved the annual solar fraction in a domestic hot water system by 20.5% compared with the reference evacuated tube collector without storage.

PVT collector technologies in solar thermal systems: A systematic assessment of electrical and thermal yields with the novel characteristic temperature approach

Abstract Photovoltaic-thermal PVT collectors generate solar electricity and heat in a single component. The annual electrical and thermal yields depend in particular on the efficiency of the PVT collector technology, climate, and the type of solar thermal system. This paper provides a systematic comparison of the performance of unglazed, glazed, and PVT collectors with low-emissivity coatings. The yields of these PVT technologies are assessed in four types of solar thermal systems including domestic hot water systems and combi systems in single and multi-family homes at four European locations. For this purpose, an empirical PVT performance model is presented, validated and implemented into TRNSYS. Analyzing the simulation results, the assessed PVT collector technologies reach either high electrical or high thermal yields. This compromise originates from the technological trade-off between a good optical efficiency versus a high level of insulation. Thermally optimized glazed PVT collectors with low-emissivity coatings achieve the highest overall yields and the best energetic utilization of the collector area. These collectors achieve up to three times the electrical output compared to a side-by-side installation of flat plate collectors and PV modules with equal thermal output. The variations between the investigated systems can be attributed to the governing operating temperatures of the PVT collector which are found to be of central relevance. A novel approach puts these temperatures into the focus and introduces the characteristic temperature Tchar as new indicator with a strong correlation to both electrical and thermal yields. This approach can be used to assess electrical and thermal yields of PVT systems and select a suitable collector technology for a given application.

Evaluation of biofilm development on various pipelines in the domestic hot water system

Abstract Biological safety of hot water is important, and it is affected by pipeline material to a certain degree. Polypropylene random (PPR), polyvinyl chloride (PVC) and stainless steel (SS) are the common materials for pipelines in domestic hot water systems (DHWS), and biofilm growth characteristics, and biofilm microbial communities and biological diversity on the walls of pipelines are affected by the pipeline materials to a certain extent. In this paper, the effects of different materials on the growth characteristics and diversity of microbial communities were studied. The results showed that after about 60 days, the bacteria of the biofilm on the wall of pipelines completed a microbial growth cycle. Compared with PPR and SS, a greater amount of the total number of bacteria, Escherichia coli and heterotrophic plate count (HPC) attached to the PVC pipeline. Although the types of bacteria on the pipelines were similar, the proportions of species were different. Proteobacteria were the dominant bacteria at the phylum level on all the walls of the PPR, PVC and SS pipelines, and the dominant bacteria at the genus level changed before and after the exfoliation of biofilm. Some potential pathogens, such as Pseudomonas and Legionella, were detected in biofilm, so effective biofilm disinfection should be considered to ensure biological safety in DHWS.

An experimental investigation of a realistic-scale seasonal solar adsorption storage system for buildings

The mismatch between the abundant available solar energy in summer and the heat demand in winter can be overcome by compact seasonal thermal energy storages, which are characterized by low thermal losses and avanvanvan high energy density. A promising technology to meet these special requirements is through closed sorption storage. Within this paper a demonstration system for domestic hot water and space heating for a single family house was designed and demonstrated. The working pair binderfree zeolite 13X and water vapor was chosen for this purpose. Since the novel charge boost mode was applied, an energy density of 178 kWh/m3 has been achieved, which is almost 3 times higher compared to the conventional sensible water storage energy density. The demonstration system was tested successfully during the heating period 2015/16 in full automatic operation. A solar fraction of 83.5% for covering the space heating and domestic hot water demand was reached during this period.

Performance analysis and economic assessment of solar thermal and heat pump combisystems for subtropical and tropical region

In the present research, combinations of solar collectors and air-source heat pumps for domestic hot water (DHW) are addressed in terms of hydraulic layout and climate conditions. TRaNsient SYstems Simulation (TRNSYS) software was implemented to simulate and examine the heating capacities of various DHW systems. For validating the numerical results, a demonstration site featuring a solar collector and heat pump combisystem with real-time monitoring sensors was established in Tainan, Taiwan. The corresponding parameters of TRNSYS modules were also tested and validated using experimental data. For comparison with the electrical heating water system, three common DHW systems—a conventional solar DHW system, a single-tank solar combisystem, and a dual-tank solar combisystem—were selected, and their technical and economical aspects were assessed. To determine the effect of climate conditions, two metropolitan cities in Taiwan were simulated: Taipei represented subtropical cities and Kaohsiung represented tropical cities. Results for both Taipei and Kaohsiung showed that the dual-tank solar combisystems had the lowest electrical consumption levels and operating costs. The incremental capital costs of the solar combisystems were considered, and realistic payback periods were calculated to determine economic feasibility.

Thermal inactivation analysis of water-related pathogens in domestic hot water systems

This study aims to investigate whether hot water systems supplied with harvested rainwater present an increased risk to health over hot water systems supplied with potable mains water. It reviews previous studies investigating the health effects of utilising rainwater within domestic systems. The main risk to public health of mains-supplied hot water systems is the operation, maintenance, age, location and temperature of the system. Rainwater-harvesting systems contain an inherent water treatment train consisting of flocculation, settlement, sorption and bioreaction, and stored rainwater quality improves as metal and chemical contaminants settle to form sludge. Laboratory experiments were conducted using a variety of water-related bacteria to determine the time required to reduce a bacterial population by 90% at a given temperature. The results of this study show that after 5 min of exposure at 60 and 55°C, respectively, Salmonella, Pseudomonas aeruginosa and total viable count at 22 and 37°C concentrations were reduced to zero. Irish standards require hot water systems to be maintained at temperatures at or above 60°C. The conclusion from this pilot study is that hot water systems supplied with harvested rainwater do not present an increased risk to health over hot water systems fed with mains water.

Measured load profiles and heat use for “low energy buildings” with heat supply from district heating

In the development towards nearly zero energy buildings (nZEB) the load profiles for the heat demand and the heat use of the buildings are expected to be changed considerably compared to the situation today. This change will influence the design and the overall profitability of district heating (DH). Earlier heat use measurements have shown that the real heat use of LEB, for several reasons, quite often seems to be somewhat higher than the values from theoretical calculations. This means that knowledge on measured values of the total heat load profiles and the heat use from all types of LEB will be important for evaluating the economy and the competitiveness of DH in the future.The primary goal of the paper is to present measured load profiles and yearly heat use for three different blocks of flats connected to the DH-system in Trondheim, Norway. Official dimensioning outdoor temperature in Trondheim is −19°C.The presented load profiles show statistical hourly mean specific maximum values for the three buildings. Specific values for the yearly heat use and the outdoor temperature value when the heat demand goes down to zero, change point temperature (CPT) are also presented. System efficiency of the domestic hot water (DHW) system in the buildings is also given. The presented information is assumed to be useful in the planning of DH-systems for the future.

Evaluation of thermal characteristics of a flat plate solar collector with a back mounted air channel

Flat plate solar collectors for domestic hot water systems are known to experience problems under stagnation conditions, when the heat transfer fluid is at rest in the absorber flow passages. The solar collector absorber plate may reach temperatures approximately 170°C or more especially when power supply fails or periods when there is minimal energy demand. This paper evaluates the thermal characteristics of an commercial Enerworks Residential Collector integrated with a back mounted air channel under stagnation conditions which is the continuation of previous investigations of current authors both experimentally and numerically to optimize the performance of the collector during both operation and stagnation. Air flow and thermal conditions in the inclined air channel of the solar collector were simulated using the validated numerical model adopting the Reynolds Averaged Navier-Stokes (RANS) modeling approach with SST-k-ω turbulence model. The radiation exchange between the surfaces of the air channel was modeled using the Discrete Ordinate radiation Model. The numerical results for velocity contours, turbulence intensity, temperature distribution, heat transfer coefficient and averaged Nusselt numbers were obtained. A correlation of averaged Nusselt numbers with modified Rayleigh numbers was developed. From the results obtained it was concluded that the incorporation of a passive air cooling channel at the back of flat plate solar collectors with a suitable control valve at the outlet opening could be helpful in reducing the maximum temperature arrived under stagnation conditions approximately from approximately 170°C to 120°C and will prolong the life of solar collectors.

A comparative survey of the energy performances of dwellings across Cyprus

Cyprus, due to a long-lasting political conflict, has been divided for nearly 50 years, Greek Cypriot community living in the southern and Turkish Cypriot community living in the northern part of the island. Research has been carried out on both sides of the island separately, to meet the requirements of the Directive 2002/91/EC on energy performance of buildings. In the present study, an attempt was made to characterize the energy performances of dwellings across Cyprus since the negotiations to settle the problem between the two communities are still in progress. The methodology and the results of a recent survey conducted in the northern part are presented together with an earlier data reported for the residential building stock in the southern part of the island. It is noted that the dwellings in the northern part had relatively smaller mean floor area and lower electricity consumptions. The utilization of central heating systems and double glazed windows were more common in the southern part. Nevertheless, similar house types with often poor external wall insulations, extensive use of solar domestic hot water systems, significant cooling energy consumptions and almost the same primary energy demand per total area appear to be the common features of most dwellings in both parts of the island.

Inclusive analysis and performance evaluation of solar domestic hot water system (a case study)

In recent years Solar Domestic Hot Water systems have increased significantly their market share. In order to better understand the real-life performance of SDHW systems, a single detached house was selected for extensive monitoring. Two solar panels were installed on the house roof to provide thermal energy to the Domestic Hot Water (DHW) system. The house was equipped with data logging system and remotely monitored with performance data collected and analyzed over one year. The paper presents the inclusive analysis and performance evaluation of SDHW system, including DHW recirculation loop, under Canadian weather conditions for average family occupancy (two adults and two kids) with daily average DHW, draws of 246L. Moreover, the study is carried out a significant recommendation to improve the SDHW performance, decrease the gas energy consumption and reduce greenhouse gas (GHG) emissions. The SDHW performance depends mainly on DHW flow rate, draw time and duration, city water temperature, DHW recirculation loop control strategy and system layout. The performance analysis results show that 91.5% of the collected solar energy is transferred to the DHW heating load through the solar tank. The contribution to DHW heating load is about 69.4% from natural gas and 30.6% from solar. The recirculation loop is responsible for close to 34.9%, of DHW total energy.

Control strategy and thermal inertia influence on evacuated tube solar water heating systems

The main objective of this article is to investigate the effect of a control scheme on the behavior of a solar domestic hot water system, consisting of two evacuated tubes with compound-parabolic concentrator (CPC) collectors and a storage tank. In this regard, a transient thermal analysis of the system was performed using an original mathematical model. The developed model was validated by comparing the results with the data provided by the manufacturer. Simulations were conducted during a 48-h period in the meteorological conditions of Bucharest, Romania (latitude 44°24′N, longitude 26°05′E). The second objective of the present work relates to the working fluid thermal inertia. An analysis was made to determine whether the solar collectors’ fluid thermal inertia has an impact on the storage tank water temperature. Three different working fluids have been considered. The results showed that for the entire 2-day period in which simulations have been conducted, differences between the useful energy delivered to the storage tank water in the case with mass flow rate adjusted depending on the incident solar radiation and the cases with constant mass flow rate were approximately 1 kWh in summer and 0.72 kWh in winter. In addition, it has been concluded that the time required to heat the storage tank water from 30 to 60 degrees centigrade is approximately an hour less when the system is working with water compared to the propylene glycol case.

Energy efficiency of a solar domestic hot water system

The solar domestic hot water (SDHW) system located on the campus of Bialystok University of Technology is the object of the research described in the current paper. The solar thermal system is composed of 35 flat plate collectors, 21 evacuated tube collectors and eight hot water tanks with the capacity of 1 m 3 of each. Solar facility is equipped with hardware for automatic data collection. Additionally, the weather station located on the roof of the building provides measurements of basic parameters of ambient air and solar radiation. The main objective of Regional Operational Program was the assessment of the effectiveness of this solar energy technology in the climatic conditions of the north-eastern Poland. Energy efficiency of SDHW system was defined in this research as the ratio between the useful heat energy supplied to the domestic hot water system and solar energy incident on the surface of solar panels. Heat loss from water storage tanks, and from the pipe network to the surrounding air, as well as the electrical energy consumed by the pumps have been included in the calculations. The paper presents the detailed results and conclusions obtained from this energy analysis.

The efficiency of the heat pump water heater, during DHW tapping cycle

This paper discusses one of the most effective systems for domestic hot water (DHW) production based on air-source heat pump with an integrated tank. The operating principle of the heat pump is described in detail. Moreover, there is an account of experimental set-up and results of the measurements. In the experimental part, measurements were conducted with the aim of determining the energy parameters and measures of the economic efficiency related to the presented solution. The measurements that were conducted are based on the tapping cycle that is similar to the recommended one in EN-16147 standard. The efficiency of the air source heat pump during the duration of the experiment was 2.43. In the end of paper, authors conducted a simplified ecological analysis in order to determine the influence of operation of air-source heat pump with integrated tank on the environment. Moreover the compression with the different source of energy (gas boiler with closed combustion chamber and boiler fired by the coal) was conducted. The heat pump is the ecological friendly source of the energy.

Life cycle assessment of domestic heat pump hot water systems in Australia

Water heating accounts for 23% of residential energy consumption in Australia, and, as over half is provided by electric water heaters, is a significant source of greenhouse gas emissions. Due to inclusion in rebate schemes heat pump water heating systems are becoming increasingly popular, but do they result in lower greenhouse gas emissions? This study follows on from a previous life cycle assessment study of domestic hot water systems to include heat pump systems. The streamlined life cycle assessment approach used focused on the use phase of the life cycle, which was found in the previous study to be where the majority of global warming potential (GWP) impacts occurred. Data was collected from an Australian heat pump manufacturer and was modelled assuming installation within Australian climate zone 3 (AS/NZS 4234:2011). Several scenarios were investigated for the heat pumps including different sources of electricity (grid, photovoltaic solar modules, and batteries) and the use of solar thermal panels. It was found that due to their higher efficiency heat pump hot water systems can result in significantly lower GWP than electric storage hot water systems. Further, solar thermal heat pump systems can have lower GWP than solar electric hot water systems that use conventional electric boosting. Additionally, the contributions of HFC refrigerants to GWP can be significant so the use of alternative refrigerants is recommended. Heat pumps combined with PV and battery technology can achieve the lowest GWP of all domestic hot water systems.