Hot Water Tank Research Articles

4th generation district heating (4GDH) in developing countries: Low-temperature networks, prosumers and demand-side measures

The aim is locating low-cost renovation measures to support the efficiency of district heating (DH). The topology analysis and GIS Zulu© are applied for hydraulic simulation and to verify the scenario viability. The scenarios are compared by life cycle cost, levelized cost of heat (LCoH), capital and operational costs, energy production and consumption, network length, heat losses, linear heat density, heat pump usage, peak load reduction, nominal power duration or the equivalent full load time. As demand-side measures (DSM), improved control, thermostats with an indoor temperature sensor and variable frequency drive (VFD) pumps reduce heat demand. Prosumer scenario imply installing a base-load heat pump. It means a consumer no longer receives heat from the DH system, because the households are now adapted to lower space heating (SH) supply temperature. Prosumer concept also allows placing a heat pump on the DH return line. The simplest configuration includes only the booster heat pump and domestic hot water (DHW) tank storages enough to cover morning or evening consumption peak. To limit piping cost, only supply and return pipes are considered for low-temperature DH, no additional (service) pipes or mixing valves are assumed. Converting single-family houses to prosumers decreases energy consumption, primary network flows and temperatures. LCoH ranges 19.7-35.4 EUR/MWh, depends on the decommissioned pipe length and its proportional pipe investment cost. LCoH decreases as the share of consumers converted to prosumers increases. Discounted payback time is 10 years for DSM and 41 years for prosumer case. For a base-load heat pump, the payback time is much higher than the reference scenario. It implies the same share of heat losses (16% of heat supplied from the CHP plant) with generally worse environmental and energy saving effect due to higher greenhouse gas (GHG) emissions and higher consumption of primary energy. Energy production is expected to follow the pattern of the useful energy consumption to compensate heat losses. The effects are decreasing residential heat demand (-4%), additional capacity to connect new consumers (+6%) and decreasing the network length.

The predictive management in campus heating system based on deep reinforcement learning and probabilistic heat demands forecasting

As a promising technology for replacing the rule-based decision-making in region heating systems (RHS), deep reinforcement learning (DRL) is a practical solution to identify the optimal control for heating equipment. However, as residential customers perform more casual energy-consumption behaviors, the intermittency and volatility of heat demands make managing heat supply and storage much harder for DRL agents. This study proposes a novel predictive management method for campus heating systems (CHS) with air-source heat pumps (AHP) and thermostatic water tanks. The novelty of the proposed method lies in the combination of the heat demands forecasting model and DRL-based adaptively controlling for heat supply equipment, which is firstly proposed to improve the heating supply reliability and reduce the storage dependence for CHS. Specifically, an enhanced rule, namely minimum length hamming encoding, and an input array constructing method is introduced to deal with discrete feature data and then improve the accuracy of deterministic heat demands forecasting based on long-short term memory (LSTM), and the Kernel density estimation (KDE) are employed to obtain the prediction intervals (PIs) from H-step ahead heat demands forecasting series. Followed by these, the twin delayed deep deterministic policy gradient, a model-free DRL control algorithm, is adopted for adaptively adjusting the output flow rate of AHP and then the storage of the hot water tank. To demonstrate the validity of the proposed method, a case study is presented where a campus heat demands forecasting achieves a maximum accuracy gain of 4.52%, and an optimal AHP operating controlling determined from PIs achieves a better cost reduction and supply reliability, which is superior over the conventional method using real-time heat demands or deterministic forecasting results as input.

Reliability and availability modelling of a retrofitted Diesel-based cogeneration system for heat and hot water demand of an isolated Antarctic base

The reduction of greenhouse gas emissions is a relevant challenge for a sustainable development. Waste heat could be used to produce hot water by using a recovery system. This article studies the availability of a combined heat and power systems (CHP) in extreme area (Antarctic) through the integration of a waste heat recovery system with a diesel generator to produce hot water. The reliability and availability principles are incorporated to explore how the profile of hot water consumption and the hot water storage tank size affect system availability. Different combined heat and power systems are thus classified, and their availability indexes modelled by adopting the continuous Markov approach and the state space model. The results indicate that the CHP systems availability is strongly influenced by the daily hot water demand profile. As a useful recommendation, one of the considerations for increasing availability, reducing costs and greenhouse gas emissions with the CHP system is to include a hot water tank in the analysis.

Study and Characterization of a Spherical Solar Collector. I. Efficiency and Thermal Losses Coefficient

This paper studies and characterizes a solar collector with spherical geometry to produce hot water for sanitary and domestic applications and other facilities. The new geometry enlarges the solar collector surface and allows full sun tracking during the day without needing a solar tracking system. Although this geometry has been in use for some time, its market penetration is low due to the lack of perfect knowledge of solar collector behavior and the benefits compared with conventional solar collectors. The studies carried out in the lab for small domestic application has shown that this new geometry has better efficiency than flat plate collectors because its particular structure maintains water temperature inside the hot water tank for longer, which allows better production and longer use. The carried-out tests have shown an increase of up to 38% in the collector’s efficiency at high-range operation and 13% at the low range. This increase is enlarged to 40% and 15% when dealing with the compact system (collector-storage tank). Global losses coefficient is also lower, around 50%, than for a flat plate solar collector of an equivalent cross-section.

Performance evaluation of an enhanced self-storing evacuated tube solar collector in residential water heating application

Phase change materials (PCMs) offer higher levels energy storage density than conventional hot water tanks commonly used with solar hot water systems. The present study aims at investigating the integration of a selected PCM within the structure of an evacuated tube solar hot water system to create some compact thermal storage capacity. Then conventional solar water heater is compared with this novel PCM-based self-storing design. The results show that the proposed self-storing design can maintain the collector output temperature at around 63 °C after 15 h of not receiving any sunlight. That is whilst the output temperature of the normal collector drops down to ambient temperature in the same period. The obtained energy storage efficiency is 57 % and 75 %, and overall thermal efficiency is 49 % and 72 %, for the normal and the self-storing collectors, respectively. For the small-scale system used in this study, the proposed design helps reduce the size of the hot water storage tank required to supply the hot water demand by 55 %. The study also shows that the same design can even yield better performance at larger scales used in practical applications.

A Study on The Presence of Legionella pneumophila in Hospital Water Samples from Eastern Turkey

Objective: Legionnaires' disease is a fatal form of pneumonia brought on by an infection mostly caused by the 60 different species of Legionella pneumophila. Legionnaires' illness is caused by Legionella spp.-contaminated water systems. In this work, we sought to analyze Legionella species, serogroups (SG), and contamination in the water sources of hospitals in five regions in eastern Turkey.
 Methods: Between January 2017 and December 2018, a total of 1008 samples were examined, including 2 cooling towers, 62 hot water tanks, 104 cold water tanks, and 840 faucet shower heads. Samples were collected by the standard culture method L. pneumophila SG 1, it was analyzed for L. pneumophila SG 2-16 and Legionella spp. The samples were inoculated into BCYE and GVPC medium, and the colonies were assessed using a latex agglutination test, followed by species- and serotype-level identifications.
 Results: In our study, a total of 1008 water samples were examined, of which 35.31% (356) belonged to 2017, while 64.68% (652) belonged to 2018. 83.33% of the water samples were taken from faucets and shower heads, 10.32% from the cold water tank, 6.15% from the hot water tank, and 0.2% from the cooling tower, and the highest positivity rate was observed in the hot water tank with 12.60%. 7.04% (71) of the samples were positive, and 16.9% (12) of the positive samples were L. pneumophila SG 1, 77.46% (55) L. pneumophila SG 2-14 was detected, while 5.63% (4) were nonpneumophila (Legionella spp) it has been determined as.
 Conclusions: Legionella disease remains a significant public health threat. The water tanks of hospitals and hotels should be investigated more thoroughly, the necessary disinfection procedures should be carried out frequently. All hospitals should have water management policies, and towns and large buildings should establish comprehensive water system management programs that decrease Legionella growth and transmission. To enhance prevention measures and clinical diagnosis, we also need quicker ways of detecting Legionella in water systems and clinical samples.

Techno-economic analysis and optimization of near-zero energy and emission neighborhoods using biomass waste

The present study aims to simulate and design a near-Zero Energy neighborhood in one of the most significant industrial cities for reducing greenhouse gas emissions. For this building, biomass wastes are used for energy production, and also energy storage is provided using a battery pack system. Additionally, the Fanger model is used to assess the passengers' thermal comfort, and information on hot water usage is given. The transient performance of the aforementioned building is tested for one year using TRNSYS software, which was employed for this simulation. Wind turbines are considered electricity generators for this building, and any extra energy generated is stored in a battery pack for usage when the wind speed is insufficient and electricity is needed. Hot water is created using a biomass waste system and is kept in a hot water tank after being burned using a burner. A humidifier is utilized to ventilate the building, and a heat pump provides both the building's heating and cooling needs. The produced hot water is used to supply the residents' hot water. In addition, The Fanger model is considered and used for the assessment of occupants' thermal comfort. Matlab software is a powerful software used for this task. According to the findings, a wind turbine with a 6 kW generation capacity may supply the building's power needs while also charging the batteries beyond their initial capacity, and the building will have zero energy. Additionally, biomass fuel is used to give the building the required water which should be hot. On average, 200 g of biomass and biofuel are used per hour to maintain this temperature.

Comprehensive analysis of hot water tank sizing for a hybrid solar-biomass district heating and cooling

Different sizing criteria for thermal energy storage (TES) has been developed through the years, regarding specific situations for thermal solar panels, which tend not to be representative for new, more complex systems, in which heating and cooling are provided through using also solar thermal collectors. This article aims to provide a simplified and elegant solution for future tank selection in a more variable combination of technologies, through the use of parametric simulation and an inhouse developed methodolgy.

Energy use and energy efficiency in cruise ship hotel systems in a Nordic climate

In light of climate change, the shipping industry is committed to reducing its greenhouse gas emissions. When transitioning from fossil fuels to low-carbon fuels, it is crucial to also reduce the ships' energy need. For cruise ships, the hotel system is a major energy consumer and the focus of this paper. This study aims to investigate the energy use of an existing fossil-fuelled cruise ship operating in a Nordic climate, and evaluate the effectiveness of various passive and active energy-saving measures. For this purpose, a dynamic energy model of the hotel system was developed in the building simulation tool IDA Indoor Climate and Energy (IDA ICE), including a customised weather file. Validation of the model was achieved through comparison with literature and some operational data from the actual cruise ship. Simulation results showed a total annual energy use of 55 MWh/passenger, with the hotel system accounting for 20%. The passive measures, such as increased insulation and improved windows, each resulted in less than a 1% reduction in the hotel's annual energy use. Larger energy savings were achieved by using heat pumps (38%), improved ventilation system (8–24%), and heating setback in port and during the night (5%). A hot water storage tank, charged with the engines' waste heat during sea operation, could reduce the use of auxiliary boilers, especially in port. A hot water tank of 600 m3 could cover 97% of the heating demand in port, thereby minimising the use of fuel-fired boilers.

Techno-economic design of a solar combisystem in a residential building

A solar combisystem is utilized to supply domestic hot water (DHW) and heat a residential building. This system decreases the fossil fuel consumption and, hence, reduces air pollution and global warming. This paper proposes an innovative method to design and optimize a suitable solar combisystem for a residential building with respect to technical and economic parameters. First, different configurations of solar combisystems, including various components, are considered. Then, the optimum design variables are determined for each configuration using Grouped Method of Data Handling (GMDH) type of Artificial Neural Network (ANN) and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). Total Solar Fraction (TSF) and Life Cycle Cost (LCC) are considered as objective functions. Finally, the optimum design is chosen for the solar combisystem. Typically, researchers have focused on evaluating the performance of a single solar combisystem configuration in each study. However, this research takes a different approach by optimizing multiple configurations, resulting in a significant improvement in the total solar fraction by 7.3%. This is the main novelty of this paper. Based on the results, the optimum configuration of the solar combisystem includes 17.91 m2 of evacuated-tube collectors with a tilt angle of 50°. Also, the volume of the hot water tank and heating buffer tank are, respectively, equal to 204 and 500 L (L). In this system, solar energy provides 94% of the required energy for supplying DHW and 23% of the energy for heating the building. Moreover, reduction of annual CO2 emissions is 1806 kg. This paper presents a guideline to design solar systems for the residential buildings considering technical and economic aspects.

Determination of Thermocline Heat Transfer Coefficient by Using CFD Simulation

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems.

Calculation of Volume of Hot Water Storage Tank in Air Source Heat Pump System

Air source heat pump integrated with hot water storage tank may enhance the efficiency of heating, and the volume of hot water storage tank is closely related to the thermal efficiency of the hot water system. Referring to the relevant formulas of building water supply and drainage design standards, this paper simulates the operation conditions of heat pump, and combined with the measured annual data of hot water using in a hospital, systematically discusses the adaptability of heat pump water production and seasonal hot water usage, as well as the actual regulating volume of hot water storage tank. Assumed the heat pump is altered by the working condition of the vernal equinox, the daily storage and discharge of the hot water tank can be accurately calculated, the hot water tank should charge 2.94 times of average hourly water yield of air pump during the peak water usage period. considering the safety and economy of the air source heat pump system, it is strongly recommended that the volume of hot water storage tank can be designed as the 5 ~ 6 times of hourly average water yield of air source heat pump, which can meet the usage of hot water for most of the time and it is inspected under various accidental conditions.

InterConnect: A European project that is changing the way energy is consumed.

Project InterConnect is a major European project focusing on energy consumption. With 25 sites in Europe and more than 3,500 users, the InterConnect project has a dual economic and educational benefit for users, which should lead to responsible and sustainable behaviour. Fully meeting the needs of the moment and the choices of the future in terms of energy consumption and management is in line with the ambitious objectives of the European Union set out in the Paris Agreement of December 2015. The originality of this project lies mainly in the choice not to create innovation for its own sake but rather to create innovations that make the existing equipment (heaters, hot water tanks, etc.) more modern and more economical. In a context of economic and social crisis, this approach is bound to be met with a favorable response from low-income households or consumers who are also the most frequent users of energy-consuming equipment. This article is an opportunity, at the beginning of the analysis phase of the data collected during the InterConnect project, to highlight the pedagogical virtues and the capacity of such a project to influence behaviour.

Predictive investigation of the combined heat storage system using at NPPs with VVER

The increase in the share of nuclear power plants in the energy systems leads to the need for their participation in covering the irregularities in the electrical load schedules. NPPs unloading is economically unsustainable. Combining NPPs with storage systems can be a solution to this problem, as it will allow the reactors to operate at a constant capacity utilization factor, while excess energy will be stored during load dip hours and converted into electrical energy during peak load hours. The authors have developed a thermal storage system based on the combination of a phase change accumulator with hot and cold water tanks. The system also contains a steam turbine to generate electricity during peak hours using stored energy. Earlier the authors proved that a low-power turbine can be used to supply power to the NPP auxiliary needs with a blackout using only residual heat energy. In this paper, a methodology for determining the necessary operating parameters of the storage system for using under the required conditions is presented. The investigation of economic efficiency was carried out on the example of a range of electricity tariffs for the world’s energy systems. Accumulated net present value ranged from $0 to $85 million.

Mechanical Strength and Microstructure of Ultrahigh-Performance Concrete under Long-Term Autoclaving

Solar thermal energy is a technology that collects radiant energy from the sun to generate heat or electricity. Thermal energy storage is required to compensate for the solar thermal energy variations across time scales, and a popular strategy is storing thermal energy in hot water tanks. Due to superior strength and durability, ultrahigh-performance concrete (UHPC) is exploited to construct such water tanks for applications at 200°C. Therefore, the mechanical strength and microstructure of UHPC after long-term temperature-pressure load (autoclaving) is studied. The compressive strength of UHPC can stay robust due to the accelerated formation of hydrates, while the flexural strength is vulnerable to long-term autoclaving due to the transformation of amorphous calcium silicate hydrate (C-S-H) to more ordered phases. The main hydrates in autoclaved samples are poorly crystallized C-S-H, hydroxylellestadite, and hydrogarnet. The porosity of autoclaved samples is not strictly related to the mechanical strength, and the influence of hydrate assemblage outweighs that of porosity on mechanical strength after long-term autoclaving. The partial replacement of cement by limestone powder can decrease crystalline hydrates and increase poorly crystallized C-S-H, which densifies the microstructure and enhances the mechanical strength. However, excessive poorly crystallized C-S-H aggravates the thermal mismatch between the matrix and quartz aggregates after autoclaved samples cool to room temperature, leading to interstice in matrix-quartz interfaces and, thus, reduced mechanical strength. Therefore, an appropriate addition of limestone powder is required to induce the hydrate assemblage with appropriate poorly crystallized C-S-H, ensuring durable UHPC structures under autoclaving.

Domestic thermal energy storage applications: What parameters should they focus on?

Thermal energy storage (TES) is required to allow low-carbon heating to meet the mismatch in supply and demand from renewable generation, yet domestic TES has received low levels of adoption, mainly limited to hot water tanks. Current reviews and studies primarily focus on the comparison of storage materials neglecting the performances at a system level and analysis studies tend to solely look at hot water tanks, missing the key technology developments in thermal storage systems which are under development. Therefore, this paper investigates performance and cost variations of TES from material-level to system-level analysis and assesses impacts of emerging heat storage technologies. By simulating different types of TES materials and varied system integration options, a significant reduction in energy densities and increase in specific costs of TES systems were found compared to the material-level analysis. Direct electrical heating has much greater potential to integrate with TES from its high operating temperature with TES compared to heat pumps or solar thermal which are constrained to lower temperatures. TES properties are simulated in various scenarios in a domestic heating techno-economic framework. It was found that for heat pumps there is economically-limited potential for TES, even if very high energy densities are possible. In addition, the priority for TES coupling with heat pumps is low capital cost, although current high tariff rates due to the energy-crisis do improve economic viability of TES. On the other hand, with direct electrical heating, high energy density is the most valuable parameter for TES, as it allows significant quantity of demand to be shifted to very low-tariff times, in particular for low demand dwellings where negligible amounts of peak electricity could be required for heating.

An optimization study on the performance of hot water tank integrated phase change material

In this paper, a new structure of a phase change thermal storage tank is proposed with the aim of enhancing the thermal storage capacity of the domestic hot water tank without occupying the water storage volume. The structure of the proposed tank is that the phase change material is filled in the outer side wall of the tank and the cavity formed by an insulation layer, which does not occupy the water storage space inside the tank. The cavity is equipped with metal spacers in parallel with each other as a method to strengthen heat transfer. The effects of three structural design parameters, namely the thickness of phase change material, the number and thickness of spacers on the charging and discharging process were investigated by the means of numerical calculations. A numerical model was developed by using COMSOL Multiphysics, and the accuracy of the model was verified with experimental data from the literature. The average temperature of phase change material, average water temperature, and liquid/solid phase fraction were used to evaluate the thermal performance of the phase change thermal storage tank.It was found that the low thermal conductivity of the phase change material affected the thermal performance. When the thickness of the phase change material was 30 mm, the discharging time was prolonged by 10 %, which was 5 h longer than the common water tank. The installation of metal spacers was an effective method to enhance heat transfer. During the charging process, the phase change material had a stronger liquefaction trend, and the lowest value of the solid fraction was 0.25. During the discharging process, when the number of spacers was 17 and the thickness was 5 mm, the discharging time was extended to 80 h, which was 1.5 times of the common water tank. The results help to understand the optimized design parameters of the phase change thermal storage tank from the perspective of the structural design.

Performance Analysis of a Solar Continuous Adsorption Refrigeration System

A study is conducted on the performances of a solar powered continuous-adsorption refrigerator considering two particular days as references cases, namely, the summer solstice (June 21st) and the autumn equinox (September 21st). The cooling capacity, system performance coefficient and the daily rate of available cooling energy are assessed. The main goal is to compare the performances of a solar adsorption chiller equipped with a hot water tank (HWT) with an equivalent system relying on solar collectors with no heat storage module. The daily cooling rates for the solar refrigerator are found to be 102.4 kWh and 74.3 kWh, respectively, on June 21st and on September 21st, using a total collector’s area of 43.47 m2. The corresponding values for the adsorption chiller equipped with a hot water tank of 2 m3 (and using a total collector’s area of 72.45 m2), are 127.1 kWh and 106.13 kWh, respectively.

Variable research of the efficiency of a combined thermal storage system when used at NPPs with VVER

The energy sector has the problem of covering the unevenness of daily energy consumption. Electric stations are unloaded during hours of reduced electrical load in the power system, which leads to a decrease in their economic efficiency and resource indicators. This problem is especially relevant for nuclear power plants. This is justified by their high cost with relatively cheap fuel, which makes it logical to fully load them. However, an increase in the number of nuclear installations in the energy system leads to the need to unload them. The authors developed a system for combining thermal accumulators (phase change accumulator and hot water tanks) with a nuclear power plant and an additional low-power steam turbine. An additional turbine makes it possible not to overload the main turbine of a nuclear power plant. In addition, when a nuclear power plant is de-energized, an additional turbine can provide power to the station’s own needs using only the decay heat energy of one reactor. The conditions for economic efficiency and payback of the accumulation system were studied in the work. Boundary values of the maximum net present value for three steam turbine power options for a range of operating conditions were obtained.

Performance Assessment of Three Latent Heat Storage Designs for a Solar Hot Water Tank

Solar hot water tanks (SHWT) based on a latent heat storage system are gaining momentum for their integration into solar heater water collectors. They can efficiently store daytime solar thermal energy and shift on-peak period loads to off-peak periods. However, their performance is generally limited by the tank configuration, the design of the thermal storage system, and the selection of the appropriate phase change material (PCM). This work presents a numerical investigation of three SHWT-PCM storage designs. A mathematical model was developed to predict the effectiveness of the geometric design and operating conditions in the SHWT-PCM system. Moreover, a sensitivity analysis was performed on the PCM type and PCM thermo-physical properties. The obtained numerical results demonstrated that the energy efficiency of the SHWT-PCM system was significantly impacted by the PCM thermo-physical properties (melting temperature, thermal conductivity, and enthalpy). In addition, it was found that using encapsulated PCM tubes with an external PCM jacket in the SHWT can result in a thermal efficiency of 70%.