Wastewater Heat Recovery System Research Articles

Design and Long-Term Performance of a Pilot Wastewater Heat Recovery System in a Commercial Kitchen in the Tourism Sector

This paper assesses the performance of waste heat recovery from commercial kitchen wastewater in practice. A pilot study of heat recovery from the kitchen at Penrhyn Castle, a tourist attraction in North Wales (UK), is outlined. The pilot heat recovery site was designed and installed, comprising a heat exchanger, recirculation pumps, buffer tank and an extensive temperature/flow monitoring system for performance monitoring of the waste heat recovery system. Continuous monitoring was conducted for a period of 8 months, covering the 2022 tourist season. The recovered heat from the kitchen wastewater preheats the incoming cold freshwater supply and consequently reduces the amount of energy consumed for subsequent water heating. Retrofitting the pilot heat recovery system to the kitchen drains resulted in a heat saving of 240 kWh per month on average, a reduction of 928.8 kg CO2e per year, and a payback period for the investment costs of approximately two years, depending on the cost of energy supply. The presented results illustrate the potential of this form of renewable heat in reducing the carbon footprint of water heating activities in buildings and the hospitality sector.

Waste Water Heat Recovery Systems types and applications: Comprehensive review, critical analysis, and potential recommendations

One of the most effective ways to deal with the effects of the current global energy crisis is to reduce energy consumption and rely energy management strategies. As a result, waste heat/energy recovery might be a helpful option for decreasing energy costs and environmental effect. It entails finding a practical way to apply any engineering system’s wasted heat where the percentage of wasted heat is too high in global. In this context, waste hot water is a rich source of wasted energy that, if recovered, can significantly cut down on the amount of electricity used worldwide. Within this framework, the present research paper provides a thorough analysis of Waste Water Heat Recovery Systems (WWHRS) in terms of performance, design, tools and applications. In addition, it is highlighting the key elements associated with WWHRS, including the wastewater sources and approaches used in the literature for waste water heat recovery. Moreover, the present paper demonstrates the effect of the heat recovery from the drain waste water on economically and discuss the technical barriers to using WWHRS. It will be demonstrated that the feasibility of recovering heat from waste water could decrease significantly the cost of energy consumption for residential or industrial application. In addition, the main tools that are used for heat recovery systems is the heat exchanger where various types are used and the thermal performance are strongly affected by the choice of heat exchangers. Moreover, based on the literature review, it is shown that the methods of studying the thermal performance of the heat recovery system are experimental and/or numerical and in some cases the study is performed analytically. Finally, all discussed and presented studies demonstrate that the WWHRS has a significant benefits and could be considered for new residential construction.

Energy, environmental and economic assessment of wastewater heat recovery systems in hotel buildings

Wastewater heat pump system has been extensively researched due to its benefits in terms of energy conservation and environmental preservation. Most of these studies, however, use R134a or R22 as refrigerants, which are being phased out. This research selects the transcritical CO2 heat pump for wastewater heat recovery, the model is built in TRNSYS software, and the energy, environment, and economy analyses of the three systems are examined. The results reveal that the regenerative heat pump system (RHPS) can save 76.67% more energy than the regenerative boiler system (RBS). The RHPS has a larger initial investment than the RBS, but the yearly carbon dioxide emission is reduced by 33.99 tons, and the life cycle cost is lowered by 1452.55 thousand CNY. Furthermore, RHPS can reach the peak of the annual average cost difference earlier with the support of government policy, and the annual average cost difference has increased by around 21–29% more than that without the subsidies. This research will help to promote the combination and implementation of the transcritical CO2 heat pump in wastewater heat recovery technology.

Optimizing wastewater heat recovery systems in textile dyeing processes using pinch analysis

• An optimal WWHR system for textile dyeing was developed using a two-step approach. • The two-step approach comprises the scenario definition and pinch analysis. • The cost-optimal WWHR system lowered the energy usage by 28.64% and TAC by 73.65%. • The PBP of the optimal WWHR system was 4.32 y. Textile manufacturing discharges large amounts of wastewater containing significant amounts of thermal energy. The textile dyeing process consists of several complex processes with different operating times, temperatures, and water usage. The absence of a suitable wastewater heat recovery (WWHR) system requires a large amount of energy for heating fresh water and cooling wastewater. Therefore, recovering wastewater while satisfying the operating conditions of each process is crucial. Herein, we suggest an optimal design for WWHR systems to maximize the energy efficiency in the textile dyeing process using pinch analysis by a novel two-step approach. First, the scenarios for all feasible WWHR methods were defined, and the WWHR systems were designed accordingly by integrating a heat pump and heat exchanger. Second, the heat exchanger network of the developed WWHR systems was modified based on pinch analysis to maximize the waste-heat recovery efficiency. Finally, to derive the cost-optimal WWHR system, a techno-economic analysis was conducted. The total annualized cost (TAC), based on the capital and operating cost, was determined based on current and potential future economies. The proposed energy-saving measures reduced the TAC by 28.6% and obtained a payback period of up to 4.3 y.

A short review of recent studies on wastewater heat recovery systems: Types and applications

Reducing energy consumption has its direct impact on the worldwide environmental status. Smart energy processes must be adopted in order to enhance the reduction capacity of energy usage. In this view, both renewable energy as well as heat recovery strategy has been used in a wide range of engineering applications. With this in mind, hot wastewater is considered as a valuable source of energy that could be recovered. The present paper illustrates an overall review on the waste water heat recovery systems (WWHR). All systems can be classified based on their structural configuration and application. It has been shown that under some conditions a 50% energy could be stored or recovered using a heat recovery system. In addition, all systems are considered as an economic as well as environmental effective methods.

Optimization of Heat Exchanger Network via Pinch Analysis in Heat Pump-Assisted Textile Industry Wastewater Heat Recovery System

Reactive dyeing is primarily used in the textile industry to achieve a high level of productivity for high-quality products. This method requires heating a large amount of freshwater for dyeing and cooling for the biological treatment of discharged wastewater. If the heat of the wastewater discharged from the textile industry is recovered, energy used for heating freshwater and cooling wastewater can be significantly reduced. However, the energy efficiency of this industry remains low, owing to the limited use of waste heat. Hence, this study suggested a cost-optimal heat exchanger network (HEN) in a heat pump-assisted textile industry wastewater heat recovery system with maximizing energy efficiency simultaneously. A novel two-step approach was suggested to develop the optimal HEN in heat pump-assisted textile industry wastewater heat recovery system. In the first step, the system was designed to integrate the heat exchanger and heat pump to recover waste heat effectively. In the second step, the HEN in the newly developed system was retrofitted using super-targeted pinch analysis to minimize cost and maximize energy efficiency simultaneously. As a result, the proposed wastewater heat recovery system reduced the total annualized cost by up to 43.07% as compared to the conventional textile industry lacking a wastewater heat recovery system. These findings may facilitate economic and environmental improvements in the textile industry.

Optimizing Wastewater Heat Recovery Systems in Textile Dyeing Processes Using Pinch Analysis

Optimizing Wastewater Heat Recovery Systems in Textile Dyeing Processes Using Pinch Analysis

Case studies of four installed wastewater heat recovery systems in Sweden

The energy demand for tap water heating is significant in the developed world and significant to buildings energy performance. However, little attention is given to this untapped potential of heat recovery from wastewater. The purpose of this investigation is to investigate performance of different wastewater heat recovery systems to obtain more knowledge on how these systems perform in reality. Four systems were investigated showing that the annual heat recovery ratios between 17 and 43% and annual heat recovery per heat transfer areas between 1586 and 13 108 kWh/m2.The paper also proposes a design equation with a validated accuracy of ±15% for sizing horizontal wastewater heat exchangers in wastewater heat recovery systems.

Spatial and temporal considerations in the performance of wastewater heat recovery systems

Abstract 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.

Energy and exergy analysis of waste-water heat recovery in a multi-family residential complex

This article provides an approach to analysing the energy and exergy efficiency of a waste-water heat recovery system. The system studied is installed in a multi-family residential complex in Stockholm, Sweden. The heat recovery unit in question consists of eight coaxial, counter-flow heat-exchangers connected in parallel, with waste-water flowing through the internal pipe and cold brine (propylene glycol 25%) ducted through the external pipe. The analysis was carried out based on data collected by a building monitoring system (BMS) during five winter months (heating season). The energy analysis (using average hourly values) showed that on average 10.7 kW (Span: 1.1 - 38.7 kW) of waste-water heat was delivered to the cold brine. On the other hand, the exergy analysis (using the same data) showed that on average 12% (Span: 3 - 24%) of the exergy contained in the waste-water was delivered to the cold brine, while on average 76% (Span: 60 - 88%) was consumed during the process. Access to accurate and detailed performance measurement data was found to be essential for analysing the exergy and energy performance of the heat recovery system. In conclusion, this article demonstrates that it is vitally important to consider both the first and second laws of thermodynamics to achieve a wholesome understanding of heat recovery from waste-water systems.

Reducing the defrosting needs of air-handling units by using heat from wastewater in apartment buildings in cold climates

This paper is the second part of a two-part series that investigates the energy-saving potentials of a novel wastewater heat recovery system connected to mechanical ventilation with heat recovery (MVHR). The main idea is to use the heat from stored wastewater to preheat the incoming cold outdoor airflow to the MVHR and thereby reduce the defrosting needs of the MVHR. The study evaluated the potential of two air preheaters, AP0.4 m x 0.4 m x 0.4 m and AP0.8 m x 0.8 m x 0.4 m, placed in front of the existing MVHR. Dynamic simulations in this study have shown that the smaller air preheater could lower the frost threshold temperature by 5 °C and the larger one could reduce it by 11 °C. Without an air preheater, the defrosting was needed during nearly two-thirds of January in the studied climate. By contrast, with the evaluated air preheaters in front of the MVHR, the defrosting was needed during 45% and 20% of the evaluation period, respectively. The results also showed that frost growth inside the heat exchanger could be reduced by 38% with AP0.4 m x 0.4 m x 0.4 m and by 62% with AP0.8 m x 0.8 m x 0.4 m during the peak load. The main conclusion is that the suggested heat recovery system has good potential for improving the overall performance of MVHR systems in cold climates.

Possibilities of heat energy recovery from greywater systems

Waste water contains a large amount of heat energy which is irretrievably lost, so it is worth thinking about the possibilities of its recovery. It is estimated that in a residential building with full sanitary fittings, about 70% of the total tap water supplied is discharged as greywater and could be reused. The subject of the work is the opportunity to reuse waste water as an alternative source of heat for buildings. For this purpose, the design of heat exchangers used in the process of greywater heat recovery in indoor sewage systems, public buildings as well as in industrial plants has been reviewed. The possibility of recovering heat from waste water transported in outdoor sewage systems was also taken into consideration. An exemplary waste water heat recovery system was proposed, and the amount of heat that could be obtained using a greywater heat recovery system in a residential building was presented. The work shows that greywater heat recovery systems allow for significant savings in preheating hot tap water, and the rate of cost reimbursement depends on the purpose of the building and the type of installation. At the same time, the work shows that one should adjust the construction solutions of heat exchangers and indoor installations in buildings to the quality of the medium flowing, which is greywater.

Urban water networks as an alternative source for district heating and emergency heat-wave cooling

Urban water networks can contribute to the energy transition of cities by serving as an alternative source for heating and cooling. Indeed, the thermal energy potential of the urban water cycle is considerable. Paris is taken as an example to present an assessment of the field performance of a district-scale waste water heat recovery system and to explore potential techniques for emergency cold recovery from drinking or non-potable water networks in response to heat-waves. The heat recovery case study was found to provide significant greenhouse gas emission reductions (up to 75%) and limited primary energy savings (around 30%). These limited savings are found to be mainly due to the performance of the heat pump system. Three emergency cold recovery techniques are presented as a response to heat-waves: subway station cooling, ice production for individual cooling, and “heat-wave shelter” cooling in association with pavement-watering. The cold generation potential of each approach is assessed with a special consideration for mains water temperature sanitary limitations. Finally, technical obstacles and perspectives are discussed.

In-building waste water heat recovery: An urban-scale method for the characterisation of water streams and the assessment of energy savings and costs

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.

SWOT analysis of wastewater heat recovery systems application

Limited availability of fossil fuels and various issues connected with environment conservation lead to a growing interest in unconventional sources of energy. The latter include wastewater carried via sewage systems. Yet, the possibility to extract thermal energy from this source depends on a number of factors, location of heat recovery system being one of them. Viability of utilizing raw wastewater and effluent discharged to a receiving body after treatment process, as potential sources of energy, was assessed using SWOT/TOWS analysis. Strategies for developing systems of heat recovery from both types of wastewater have been defined, and recommendations related to their use in Poland have been formulated.

Investigating the interactions of decentralized and centralized wastewater heat recovery systems.

In the urban water cycle there are different sources for extracting energy. In addition to potential and chemical energy in the wastewater, thermal energy can also be recovered. Heat can be recovered from the wastewater with heat exchangers that are located decentralized and/or centralized at several locations throughout the system. It can be recovered directly at the source (e.g. in the showers and bathrooms), at building block level (e.g. warm water tanks collecting all grey water), in sewers or at the wastewater treatment plant. However, an uncoordinated installation of systems on such different levels can lead to competing technologies. To investigate these interactions, a modelling environment is set up, tested and calibrated based on continuous sewer temperature and flow measurements. With that approach different heat recovery scenarios on a household level (decentralized) and of in-sewer heat recovery (centralized) are investigated. A maximum performance drop of 40% for a centralized energy recovery system was estimated when all bathrooms are equipped with decentralized recovery systems. Therefore, the proposed modelling approach is suitable for testing different future conditions and to identify robust strategies for heat recovery systems from wastewater.

Hybrid Ventilation with Innovative Heat Recovery—A System Analysis

One of the most important factors when low energy houses are built is to have good heat recovery on the ventilation system. However, standard ventilation units use a considerable amount of electricity. This article discusses the consequences on a system level of using hybrid ventilation with heat recovery. The simulation program TRNSYS was used in order to investigate a ventilation system with heat recovery. The system also includes a ground source storage and waste water heat recovery system. The result of the analysis shows that the annual energy gain from ground source storage is limited. However, this is partly a consequence of the fact that the well functioning hybrid ventilation system leaves little room for improvements. The analysis shows that the hybrid ventilation system has potential to be an attractive solution for low energy buildings with a very low need for electrical energy.

Experimental Study on a Shower Waste Water Heat Recovery Device in Buildings

Large amounts of heat were waste during showering process, especially in public buildings. In this paper, a waste water heat recovery system containing a clever concept device was designed and set up to investigate the potential for shower water heat recovery. The device can be installed directly on the floor of the shower room and can be used to preheat the cold water going to the water heater. The principle of the device was introduced, and the energy saving effects of the device was studied experimentally with different conditions. The results indicated that more than 50% of the shower waste water heat can be recycled by the high-performance heat recovery device, which indicated that this device has good economic property and could lead to obvious social and economic benefits.