For a very long time activities related to efficient domestic hot water (DHW) production and distribution have been neglected and left behind due to an insignificant share in total energy use for ...buildings. It is in recent years that DHW has emerged as one of the key energy factors in the total energy use in buildings and its share is continuously increasing as energy use in other segments is continuously decreasing, for example space heating, ventilation, and energy for lighting. It becomes suddenly undeniable that efforts in the field of energy-efficient DHW must be strengthened, and as such, there is increased activity in the field. However, the work reported is very dispersed and fragmented. The objective of this review article is to collect and present recent works related to improve performance of a DHW system in terms of energy. The scope and content of the paper aims to address the topics of high relevance to the field, these are shift towards the new situation in which DHW becomes a significant energy use responsible factor in buildings, distribution and weighting of losses related to DHW systems and purpose of DHW use. The article focuses on novel actions to obtain energy-efficient DHW in the following domains: DHW production, DHW distribution and circulation, wastewater heat recovery, and control strategies. The article finishes with conclusions.
•Share of the energy for domestic hot water (DHW) in the total energy balance of buildings has significantly increased.•Measured data on energy use for domestic hot water (DHW) and spatial distribution of DHW is scarce.•Comprehensive literature review on domestic hot water (DHW) production possibilities.•Circulation losses are dominant loss in DHW distribution system.•Literature review on drain water heat recovery systems – system solutions and recovery efficiencies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The EU Directive 2018/2001 recognized wastewater as a renewable heat source. Wastewater from domestic, industrial and commercial developments maintains considerable amounts of thermal energy after ...discharging into the sewer system. It is possible to recover this heat by using technologies like heat exchangers and heat pumps; and to reuse it to satisfy heating demands. This paper presents a review of the literature on wastewater heat recovery (WWHR) and its potential at different scales within the sewer system, including the component level, building level, sewer pipe network level, and wastewater treatment plant (WWTP) level. A systematic review is provided of the benefits and challenges of WWHR across each of these levels taking into consideration technical, economic and environmental aspects. This study analyzes important attributes of WWHR such as temperature and flow dynamics of the sewer system, impacts of WWHR on the environment, and legal regulations involved. Existing gaps in the WWHR field are also identified. It is concluded that WWHR has a significant potential to supply clean energy at a scale ranging from buildings to large communities and districts. Further attention to WWHR is needed from the research community, policymakers and other stakeholders to realize the full potential of this valuable renewable heat source.
The European Union declared wastewater as a renewable energy source in its Green Deal. To meet these targets, the scientific community has been proposing new technologies to improve energy conversion ...efficiency of renewable energy powered thermal systems. The present research examines heat recovery from commercial kitchen grease traps (GT) as a means of reducing the net energy requirement of commercial hot water use in food related activities. A GT was integrated with heat recovery unit and is referred to as a hybrid GT system. Two designs of thermal recovery units comprising a planar and rectangular coil type heat exchanger (HX) were assessed individually to compare their thermal recovery capabilities. The planar HX equipped GT was first experimentally investigated and subsequently examined in more detail using 3D numerical analysis. Thermal stratification was observed along the GT depth for which the rectangular HX showed greater potential for thermal recapture from the high temperature kitchen wastewater. The novel rectangular HX design was found to save 2.6 kW of thermal energy in the kitchen GT and was 48% more efficient compared to the planar HX. The proposed GT hybrid design enables more sustainable production of food via a clean auxiliary thermal back-up, reducing greenhouse gases emission released in water heating. Heat recovery from commercial kitchen GTs has been shown in this study to be technically viable with strong potential for economic viability and positive environmental impact through reducing the carbon footprint of water heating.
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•Investigated thermo-hydraulic performance of hybrid Grease-Trap device.•Planar and upgraded rectangular thermal recovery unit designs were compared.•Performance discussed in terms of thermal recovery potential and effectiveness.•Proposed design could save up to 40% of the heat embedded in kitchen wastewater.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Energy crisis caused by the population growth, increasing demand, and the limited availability of fossil fuels has led to wastewater-based heat recovery emerging as an alternative energy source. As ...wastewater-based resource recovery systems are location-specific, a holistic view of their sustainability requires a comprehensive analysis of the effect of local conditions on these systems. This study evaluated the role of climate and population density on the economic and environmental sustainability of drain water heat recovery systems (DWHRS) and compared it to that of a medium-scale district heating system. The DWHRS installed in a cold location showed about 2–2.6 times higher energy recovery and 4 times higher greenhouse gas emissions than that in a hot place. The economic impact was predominantly influenced by the cost of electricity, while the environmental sustainability was found to decrease with a decrease in the ambient temperature and solar radiation. Lower population density increases economic sustainability and lowers environmental sustainability of the system. The DWHRS is more sustainable than the medium-scale district heating system in low population density regions irrespective of the climatic conditions. However, in cold places with a high population density, the trade-off between the economic and environmental sustainability must be evaluated to decide whether to install a small- or medium-scale system. Therefore, it is essential to perform a detailed location-specific analysis before deciding the optimal type of heat recovery system for the location under consideration. The model can be utilized as an evaluation tool to quantify the sustainability of the DWHRS and help consumers decide the most suitable method of waste heat recovery.
•The influence of climate and population density on heat recovery is evaluated.•Ambient temperature and solar radiation significantly affect system sustainability.•Using a Drain Water Heat Recovery System (DWHRS) reduces consumers’ electricity bill.•Implementing the DWHRS decreases global warming due to shower water heating by 65–75%.•The small-scale DWHRS is economically more beneficial than a district heating system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
In December 2018, wastewater was officially recognized by the European Union as a renewable source of energy, thus wastewater heat recovery can be included in efforts to reduce greenhouse gas ...emissions. Given the fact that wastewater treatment plants can generate enormous heat surpluses, this decision gives leeway to couple the wastewater infrastructure with the energy system in order to increase energy efficiency at the system level, allow for power to heat solutions in order to integrate volatile renewable electricity generation and, thus, foster a sustainable energy transition and cleaner production. Yet, the success of these system integrations depends on the availability of energy consumers in proximity of the wastewater treatment plants, and the temporal patterns of energy supply and energy demand. So far, the importance of both temporal and spatial variations in performance of wastewater heat recovery systems have been discussed in literature, but only as separate considerations to date. In order to exhaust the potential of wastewater energy, the combination of both aspects still has to be studied sufficiently, and this paper aims at filling that gap. A three-step methodology is proposed, including an energetic analysis at the wastewater treatment plant, a spatio-temporal analysis of supply and demand in potential supply areas, and an integrated analysis, overlaying the supply and demand profiles. This allows to account for both the proximity of consumers and potential temporal mismatches between supply and demand. The methodology was applied on a case study in Ireland, being able to clearly identify potentials and pitfalls for laying out grids and dimensioning the energy generation systems. It can be concluded, that wastewater energy is a well-suited source of energy to supply baseloads, but the spatio-temporal patterns reveal that both periods of excess wastewater heat potentials as well as additional heating in bivalent systems is required. Therefore, the spatial – urban and regional – fabric, the mix of land uses and their density, largely determine the layout and the useable amount of this renewable energy source. Finally, it can be concluded, that the use of wastewater energy provides feasible and valuable contributions for sustainable urban energy supply systems and cleaner production if the electricity sources for the respective heat pump systems are renewable guaranteeing low-to zero-emission operation.
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•An integrated spatio-temporal analysis of wastewater heat recovery is proposed.•5 zones, within 2 km of the plant, were considered as a heat consumer.•On 21–136 days, the heat supply was insufficient to meet demand.•58 % to 93 % of all demand can be supplied by the heat recovery system.•The recovered heat did not reach its full potential, due to temporal mismatches.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The drain water heat recovery device (DWHR) is a vertical, counter-flow heat exchanger, which is designed to recover heat from warm grey water in buildings. In this study, the transient ...characteristics of a DWHR device is experimentally and analytically investigated. A transient model is developed to predict the response time of the DWHR device under different flow conditions. The thermal performance of the system is evaluated with the transient and steady state effectiveness. The effect of system operating conditions and geometry on the response time was investigated experimentally and well predicted analytically. It was found that the response time increases with the volume of water in the system and decreases with the water flow rate. In addition, a large decrease in the effectiveness is observed when short and frequent use of hot water occurs. An economic analysis concluded that there is a 37% overall reduction in annual savings when the device transient performance is taken into consideration, where individually the sink and shower usage annual saving decreases by 56% and 13% respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•Prototype of a plate exchanger with 3 baffles for flow directing have been created.•The efficiency of the new prototype in real operating conditions reaches up to 62 %.•Efficiency rises up to 4% for ...vertical position of 6 mm above the casing bottom.•Height of the exchanger casing for installation has been minimised to just 74 mm.•Heat energy savings for a family house are up to 300 kWh/a for proposed prototype.
The article describes an experimental development of a new prototype of the horizontal plate shower exchanger for wastewater heat recovery. The prototype is designed so that while achieving the highest possible value of efficiency, it also respects the requirements of the spatial arrangement of the heat exchanger casing and, thus, allows an appropriate flow of wastewater on both sides of the heat transfer surface. At the same time, emphasis is placed on the smallest possible height of the heat exchanger casing with regard to the minimisation of the built-up space and the expected wastewater flow during the shower cycle. Experimental testing was performed according to the conditions meeting the certification criteria of the Passive House Institute, while for a given heat exchanger, the investigated flows and water temperatures, as well as the heat transfer efficiency of the new prototype was determined, reaching peak values of up to 62%. An energy analysis and derivation of the equation was also performed, according to which it is possible to determine the achieved heat savings in the preparation of domestic hot water from the heat transfer efficiency of the exchanger, including all heat losses of the system. With new prototype, heat savings more than 21% are achieved.
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This paper focuses on the experimental characterization of horizontal, spiral heat exchangers used for heat recovery from sewage pipes. Such non-intrusive heat exchanger configurations are appealing ...for this application, but they often exhibit reduced heat exchange performances compared to more compact designs. To compare the performance of this configuration with that of an ideal counter-flow heat exchanger, a representative test setup was constructed. As the sewer pipes are generally not completely filled, tests were conducted using three different fillings (100%, 50%, 33%) and a filling parameter z was introduced in the heat transfer equations. Correction factors to be applied in the Logarithmic Mean Temperature Difference (LMTD) design method for this specific spiral configuration were derived from the test results. It was found that the filling of the sewer pipe has minimal impact on the correction factor, which ranges between 0.78 and 0.83. The average value of 0.81 is recommended for design purposes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•A characterisation method for residential grey water streams is presented.•Urban energy saving and cost calculation methods are proposed.•In-building shower and grey water heat recovery systems are ...assessed.•Integrated energy savings of 28–41% can be achieved in high efficiency buildings.•Urban energy assessments considering grey water heat recovery are improved.
Residential domestic hot water energy consumption represented 16% of the EU household heating demand in 2013. With the improvement of the building insulation envelope, domestic hot water contribution to energy consumption is expected to increase significantly, with values between 20% and 32% in single family buildings, and between 35% to almost 50% in multifamily buildings. This energy, currently lost to the environment, can be recovered by waste water heat recovery systems inside buildings (in-building solutions). While most publications in this field focus on shower heat recovery and on waste water as heat source for heat pumps, the detailed impact of waste water heat recovery at a city scale by aggregating building data has not been addressed yet. Furthermore, waste water heat recovery potential and relevance was not yet quantified as a function of the specific inhabitant and household numbers, end-use occurrence, and building type and age.
A method to quantify the building-specific energy cost and energy saving potentials, based on pinch analysis, at the urban scale of in-building waste water heat recovery systems is therefore proposed. A complementary method to spatially allocate and characterise grey water streams as to thermal load and temperature levels in function of the building specificities is also developed.
These methods are applied in two case studies, first as retrofitting solution in a city in Luxembourg and, second, as optimisation measure for high efficiency residential buildings. Grey water heat recovery would reduce the residential fuel consumption of the city by 6.3%. An integrated approach combining grey water heat recovery for hot water preheating and a heat pump yields up to 28% and 41% electricity savings for passive single family houses and multifamily buildings, respectively.
With the detailed characterisation of various grey water streams as a function of inhabitant number and end-use occurrence, the quantification of the energy savings and costs through heat recovery is improved. The outcomes of urban energy and cost assessments concerning grey water heat recovery are more specific, as the results at building level are aggregated to the considered geographical scope. The proposed method therefore complements current urban energy and cost assessments with the detailed integration of in-building grey water heat recovery systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The use of greywater reduces the consumption of many resources and is an effective tool for achieving Sustainable Development Goals. In order to assess the rationality of its use as an alternative ...source of energy and water in buildings, a holistic literature review was carried out based on a bibliometric analysis of publications in these fields. The main bibliographic source was the Web of Science database. This review contributed to a better understanding of the analyzed research field. It also revealed trends in greywater energy recovery and recycling research, indicating that these are developing fields. In recent years, there has been a marked increase in the number of publications on the most popular ways of using greywater in buildings, with the territorial scope of research carried out in the greywater recycling domain being considerably larger than research on greywater energy recovery. The analysis revealed poor cooperation between different universities, especially in the field of greywater energy recovery. In light of previous literature reviews, some important research gaps and further proposals for future research were also identified. They concern, in particular, the simultaneous use of greywater as an alternative source of energy and water. Together with the findings of other researchers and people related to the subject matter, this review can contribute to the further development of greywater energy recovery systems and greywater recycling systems.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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