Hot Water Circulation Research Articles

Design and development of solar parabolic concentrator, closed-loop pressurized hot water for a household baking system – For the case of injera baking in Ethiopia

A laboratory setup with two axis of manual sun-tracking was designed and built. To get the predicted values for a solar injera stove, a 20-min heating time to prepare it for baking, 3.1 kWh power in the first hour, and 5.8 kWh (with only an 87 percent increase) in the second hour were acquired to bake 9 and 28 injera using electric injera stove, respectively. The temperature distribution on the clay surface was the range of 180 °C–220 °C. Solar injera baking stove was designed and built using the average energy required to bake one injera from an electrical injera stove. The laboratory setup was put to the test, temperatures at the receiver's surface ranging from 315 to 318 °C and an average solar radiation of 1000 W/m2 was obtained on the first test. The injera stove inlet reached a maximum temperature of 180.92 °C with a pressure of 14.5 bars during a pressurized hot water production and circulation test (load test). The surface temperature of the solar injera stove clay plate reached a maximum of 62.69 °C. Temperature of more than 60 °C was maintained on the surface of the solar injera stove plate for nearly 2 h.

Camellia meal-based adhesive with synergistic crosslinking of physical and chemical interaction for preparing aldehyde-free, anti-mildew, water-resistant wood-based composites

Wood adhesives containing toxic aldehyde-based adhesives play a vital role in the performance of wood-based panels, while the mechanical properties and water and mildew resistance of aldehyde-free adhesives are lacking. In this study, a high-strength aldehyde-free adhesive was constructed via a combination of physical and chemical crosslinks. Inexpensive alum was used to ensure a high degree of crosslinking and to increase the crystallinity. Metal ions in alum opened the protein helix, exposed the active groups, increased the number of hydrogen bonds, and ultimately improved the internal physical crosslinking ability of the adhesive. The compound formed by the Schiff base reaction formed coordination bonds with metal ions, thus forming a covalently-crosslinked network. The high-strength polymer produced in this study contained multiple physical and covalent crosslinks, resulting in significantly improved mechanical properties of the adhesive. Its water-resistant adhesive strength reached 1.96 MPa, which was 180.2% higher than that of ordinary phytogenic protein adhesive (0.69 MPa), and it can still reach 1.28 MPa after hot water circulation soaking experiment. The adhesive also possessed antifungal properties and flame-retardant capabilities, achieving a V-1 rating in the UL-94 test. This strategy expanded the application of phytogenic protein adhesives in environmentally friendly wood composite materials by replacing synthetic resins that released formaldehyde and provided an economical and feasible industrial scale production method for the preparation of high strength, water, and mildew resistant, flame retardant indoor and outdoor wood-based panels.

Heat Hazards in High-Temperature Tunnels: Influencing Factors, Disaster Forms, the Geogenetic Model and a Case Study of a Tunnel in Southwest China

The construction of extensive tunnels in regions characterized by high geothermal activity presents significant challenges and inherent risks that affect both the safety and operational efficiency of construction personnel. This study investigated the factors influencing geothermal fields in shallow crustal rock formations through a comprehensive examination of existing literature and a detailed analysis of case studies. In addition, this study categorizes the geogenetic models of high-temperature heat hazards into three major classifications. Research findings indicate that several key factors significantly influence the geothermal fields. These factors, which include the deep geothermal background, heat transfer conditions, and localized additional heat sources, are paramount in shaping the geothermal field. Notably, it is observed that among these factors, the presence of additional heat sources, particularly the circulation of underground hot water, poses the most considerable threat to safety and operational efficiency. Moreover, this study utilizes a representative high geothermal tunnel in Southwest China to conduct a field investigation. This investigation assesses the potential for high-temperature thermal hazards within the tunnels, evaluates the geological conditions, verifies the factors governing the geothermal field, and outlines specific measures for the prevention and control of high geothermal tunnels. In conclusion, this study provides a structured analysis of lessons learned from these experiences, along with practical countermeasures for addressing high-temperature thermal hazards during the various stages of tunnel construction. The findings of this research serve as a valuable reference for those investigating the mechanisms behind geothermal disasters in tunnel construction. Furthermore, they offer practical guidance to ensure the secure and efficient excavation and sustainable operation of tunnels in the challenging geological environments characterized by high geothermal temperatures.

Feasibility analysis of storing solar energy in heterogeneous deep aquifer by hot water circulation: Insights from coupled hydro-thermo modeling

Feasibility analysis of storing solar energy in heterogeneous deep aquifer by hot water circulation: Insights from coupled hydro-thermo modeling

A Mini Review on Working Mechanism, Standard Operating Procedure (SOP) and Preventative Maintenance of Low Temperature Long Term (LTLT) Milk Pasteurizer

A small-scaled batch Low Temperature- Long Term (LTLT) pasteurizer is one of many types of pasteurizers that is being utilized in food-based industries particularly in dairies. It has a capacity of heating up the milk and holding the temperature for a certain amount of time to kill pathogenic microorganisms. The instantaneous heat up is caused by heat exchangers either in the form of plates or metal coils depending on the machine. The coil is circulated within the jacket of the tank where it heats up and holds the temperature. Hot water circulation will be in continuous movement around the milk to heat it up and maintain the desired temperature. After certain period, the efficiency of LTLT pasteurizer starts declining due to cumulated issues. Decline in efficiency will affect the output of the machine too. Instantaneous heat exchanges, leaking, unstable pressure and electrical problem degrades the machine over period if it is not complying with Standard Operating Procedure (SOP) and a proper Preventative Maintenance (PM) plan. The SOP and PM will increase the machine’s lifespan and maintain a good efficiency rate for longer period. This mini review paper will compile the possible PM plan and establish a sustainable SOP for the LTLT Pasteurizer.

Screening of thermal characteristics and assessment of comparative energy efficiency potential in a residential district

ABSTRACT By identifying buildings with poor thermal performance and prioritizing these in terms of energy efficiency potential, a sustainable transformation of the building stock may be accelerated. However, there is currently a lack of thermal characteristics (TCs) differentiating total energy use from hot water circulation (HWC), hot tap water (HTW) and space heating in large building portfolios. This research demonstrates a methodology based on a change-point model for identifying and prioritizing TCs, which also enables prediction of the Comparative Energy Efficiency Potential (CEEP). The change-point model allows for the differentiation of various processes, i.e. space heating, HWC and HTW, using only heating supply data and outdoor temperature. The studied district consists of 70 multi-family buildings in the Vasastaden district in Linköping, Sweden. The findings demonstrate that the proposed methodology allows for identifying and prioritizing TCs connected to HWC, HTW and space heating. The highest CEEP is in space heating, corresponding to a maximum of 2,016 MWh (16% of the district’s energy use), followed by HWC, 699 MWh (6% of the district’s energy use) and HTW, 520 MWh (4% of the district’s energy use). Consequently, a total decrease of 3,235 MWh (26%) is made possible according to the studied energy efficiency targets. HIGHLIGHTS A methodology for the prediction of the Comparative Energy Efficiency Potential (CEEP) in a building portfolio based on the identification and prioritization of TCs is proposed The study is enabled by the use of a unique change-point model (DTPC) for differentiating TCs solely from digital heating supply data and outdoor temperature 70 multi-family buildings (total heated area of 121,692 m2) in the Vasastaden district in Linköping, Sweden, are investigated The methodology is successful in identifying and prioritizing TCs related to HWC, HTW and space heating The highest CEEP is in space heating calculated at a maximum of 2016 MWh, which corresponds to 16% of the district’s total energy use

Flow boiling heat transfer characteristics over horizontal smooth and microfin tubes: An empirical investigation utilizing R407c

The flow boiling heat transfer performance of horizontal smooth and microfin tubes was investigated using the refrigerant R407c. The evaporator test tube contains an outside, inner diameter and length of 9.52, 8.52, and 1000 mm, respectively. The investigations were performed out at 283.15 and 303.15 K saturation temperatures with hot water circulation heat flux of 75 kW.m-2, refrigerant heat flux varying from 5 to 85 kW.m-2, and mass flux varied from 15 to 250 kg.m-2.s-1, keeping the area ratio of microfin tube 1.68%. The experimental results are compared to several previously recognised correlations. Experimental outcomes demonstrated that the heat transfer rate of the microfin tube is superior to the smooth tube. The percentage of heat transfer enhancement was considered to exceed in microfin tube by 28–280%. The pressure drop in regard to R407c was found to be augmented than smooth tube according to the experimental results and enhancement was achieved in microfin tube by 68–110%. Finally, a sensitivity analysis is carried out in flow boiling heat transfer phenomenon via the smooth tube.

Installation of an ultrafiltration plant in a multi-family house to reduce the hot-water temperature and energy demand: A case study in Germany

Hot-water generation complicates energy efficiency and emission reduction efforts in buildings. High water temperatures are designated for thermal disinfection to prevent human harm from pathogenic microorganisms. Therefore, almost 200 Mt CO2 are annually emitted in the US, Germany and Canada. Heat pumps can replace fossil energies. However, lower temperatures are required to enhance efficiencies.In this case study, the hot-water temperature of the drinking-water installation of a retrofitted multi-family house was decreased by 5 °C to 50 °C. For physical separation of microorganisms, an ultrafiltration plant was installed in the hot-water circulation. To control hygienic safety, microbiological conditions were assessed by laboratory methods such as the cultivation of Legionella spp. and counting of total cells using flow cytometry. The filtrated hot-water was constantly Legionella-free. The cleaning effect of ultrafiltration was 91.15%. Cold-water was not filtrated so that contaminations occurred. As cold- and hot-water pipes (including circulation) are embedded in the same riser strands, temperature transfer occurred promoting bacterial growth. An energy demand calculation revealed that heat losses of the distribution network accounted for 55.25% of the total heat quantity required for hot-water generation. The actual heat up process of water and storage losses constituted 42.74% or 2.01%. Lowering the water temperature by 5 °C saved 7355 kWh yr−1 (equiv. to 1.77 t CO2e yr−1) in this multi-family house. Extrapolation of this case building results in a saving potential of 7.78–14.50 TWh yr−1 (equiv. to 1.87–3.48 Mt CO2e yr−1) in Germany alone, if the energy source is natural gas.

Direct evidence of hydrogen absorption from the skin – a pig study

IntroductionIt has not been experimentally proven whether hydrogen gas (H2) is absorbed into the body through the skin by hydrogen-rich hot-water bathing.Material and methodsIn this study, Hairless mini pigs, whose skin closely resembles that of humans, were bathed in hydrogen (H2)-rich hot water to assess the absorption of H2 through the skin. An H2-rich water generation line was developed to maintain a high concentration of H2 via the circulation of hot water in an 80-litre bathtub. Two hairless mini pigs (14.2 ±1.4 kg, 60 days old, 1 male and 1 female) were first placed in the H2-dissolved bath. After a washout period, one pig was bathed in an H2-dissolved bath and the other in a bath containing no H2 for 20 min. During the experiment, blood was collected from the pigs’ jugular vein, carotid artery, inferior vena cava (IVCs), and portal vein to measure the blood H2 concentration.ResultsThe H2 concentration at the IVC of the pig in the H2-dissolved bath increased from 0.733 ±0.636 ppb (w/w) to 16.9 ±4.46 ppb (w/w) after 2 min, 37.2 ±13.8 ppb (w/w) after 10 min, and 45.7 ±7.73 ppb (w/w) (H2 saturation level: 3%) after 20 min. The blood H2 concentration levels of the pig in the non-H2 bath remained below the detection limit of 0.3 ppb.ConclusionsBathing in water with a high concentration of dissolved hydrogen was considered an effective means of supplying H2 to skin tissues and beyond.

Systematic active environmental surveillance successfully identified and controlled the Legionella contamination in the hospital

IntroductionLegionella disease can manifest as severe respiratory tract infection with a high mortality rate and is sometimes associated with a hospital outbreak by a contaminated water supply. A patient with breast cancer admitted about a month before. High fever was observed 18 days after admission and the Legionella antigen test showed the positive result. MethodsDue to the incidence of Legionella infection, we demonstrated the active surveillance of Legionella contamination in the entire hospital. ResultsCultures of her environmental samples revealed that hot water in two bathrooms were contaminated with Legionella. In our hospital, the hot water is heated and pumped up on the roof and distributed to each room. The contaminated bathrooms were related to the same plumbing. Therefore, we further collected samples throughout the hot water system. Legionella was not detected in the central part of the system. However, we detected Legionella in the hot water sampled from other five rooms, which were also associated with the same plumbing of the two bathrooms. The temperature and chlorine concentration of the hot water were not high enough to inactivate Legionella at the end of the plumbing. After the adjustment of the water temperature and chlorine concentration, Legionella became undetectable. Our prompt and active surveillance successfully identified the plumbing of the hot water system as the source of Legionella contamination and took precautions against future outbreaks. ConclusionsMonitoring of water temperature and chloride concentration at the end of the hot water circulation is important to prevent nosocomial Legionella disease.

Research on Foundation Deformation and Structural Stress Variation of Shaft Tower under the Influence of Frost Heave and Thaw Settlement

As the laws of structure deformation and structural stress variation under freezing construction around high-rise buildings are not clear and no engineering experience can be referred to, freezing method construction in this situation is paired with huge safety risks. In this paper, freezing construction was successfully carried out around the main shaft tower in Chensilou Coal Mine by taking the following protective measures: symmetrical drilling, local freezing and hot water circulation. The elevation of the shaft tower foundation is continuously measured during the process of drilling, frost heaving and thaw settlement (hereinafter referred to as the DHS process). Benefiting from these protective measures, the maximum inclination value (−0.406 mm/m) of the shaft tower is controlled at well below the allowable value. The observation data informed the settlement and inclination of the tower foundation during the DHS process. A numerical model of the shaft tower is further established based on the observation data to reveal the tower structure’s law of stress variation during the DHS process. In addition, the fitting equation between the tower inclination value and the structural stress is obtained, which can provide a reference for freezing construction of similar high-rise buildings.

Research on security technology of tower foundation based on precise control of freezing temperature field

Freezing method is used in the main shaft slotting repair project in Chensilou Coal Mine in China. According to the actual conditions of Chensilou Coal Mine, this paper established a numerical calculation model which included the following influence factors: thermodynamic parameters, borehole layout, original formation temperature, groundwater seepage, hot water circulation protection. The calculation results show that the reasonable brine temperature for the freezing project in Chensilou Coal Mine should be controlled between -30 °C and -25 °C and the reasonable freezing time should be 160 days. When the freezing time extends to 80–120 days, the freezing front has developed to the temperature-control hole. In this case, the hot water circulation of the temperature-control hole needs to be started and the hot water temperature is not lower than 20 °C. The freezing construction was implemented in accordance with the optimized brine temperature and freezing time, and the freezing of tower foundation has been successfully avoided. The measured results show that the tower tilts to the northeast as a whole during formation freezing and the tilt values are all less than the allowable value.

Energy Consumption by DHW System with a Circulation Loop as an Energy Efficiency Component, Based on an Example of a Residential Building

In the EU countries, almost 50% of the produced energy is used in residential buildings. More than 25% of this energy is used to produce domestic hot water, of which almost 80% is used to heat water in domestic hot water circulation systems. This is due to high expectations on the part of residents based on their comfort, in particular regarding the supply of heat for heating and domestic hot water. In the course of their long-term research conducted on real systems, the authors confirmed that the operation of domestic hot water distribution systems causes significant costs, mainly due to heat losses. Therefore, typical variants of energy optimization of such systems were analyzed. Tests have shown that selected solutions, such as the use of control automation, are not sufficient, and recommended additional thermal insulation may not be applicable due to technical reasons. With an aim of finding a solution to the problem, the publication analyzes operational data from an existing heat source and domestic hot water circulation system in a residential building. On the basis of these analyses, a solution was proposed to reduce energy consumption within the installation by means of its hydraulic optimization. The reduction of heat losses in domestic hot water installation by means of a method presented by the authors is estimated at approximately 20%.

Hydrogeochemical Characteristic of Geothermal Water and Precursory Anomalies along the Xianshuihe Fault Zone, Southwestern China

Hydrogeochemical changes in association with earthquakes are considered as a potential means of identifying earthquake precursors. The Xianshuihe fault zone (XSHF) is considered one of the most active seismic fault zones in China; 43 hot springs were sampled and analysed in the laboratory for major elements, silica, stable isotopes (δD and δ18O) and strontium isotopes were investigated from 2008 to 2021. The meteoric water acted as the primary water source of the hot spring in the XSHF, and recharged elevations ranged from 1.9 to 4.8 km. The geothermometers method was used to estimate the region of thermal storage temperature and its temperature between 8 and 142 °C. And the circulation depth ranged from 0.1 to 6.9 km. Most of the hot spring water was immature water with a weak degree of water-rock reaction. However, the degree of water-rock reaction and the depth of hot spring water circulation were high in part of the Kangding and Daufu segments, which also had the highest reservoir temperature and the most frequent strong earthquakes. Temporal variations of hydrogeochemical showed that Na+, Cl− and SO42− decreased obviously following the 12 May 2008 Wenchuan Ms8.0 and existed abnormal value fluctuations from the 20 April 2013 Lushan Ms7.0 to 22 November 2014 Kangding Ms6.3 occurred and after 20 July 2017 returned to the normal levels. And the ion concentrations in hot springs increased by 5% to 35% three months before 22 November 2014 Kangding Ms6.3 with the obvious precursor anomaly. Hydrogeochemical anomalies could be useful for predicting an earthquake in the study area.

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m2 PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m2 evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between −0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.

Modeling of a solar water heating system for a private hospital in Sana’a, Yemen using TRNSYS

The objective of the present work is to simulate and analysis the performance of a proposed solar water heating system for a 160-bed capacity private hospital in Sana’a City-Yemen. The systems consist of solar collectors, hot water circulation pump, a storage tank with an electrical heater, and identical auxiliary components. The simulation and the thermal performance analysis have been done using TRNSYS software. In addition, a comparison between the performance of evacuated tubes collectors and flat plate collectors was done to justify the selection of ETC for the designed. The thermal performance analysis shows that the evacuated tubes collectors have an annual contribution of 87.73 MWh with an annual average solar fraction of 63 percent and annual average installation efficiency of 68 percent.

Maximum production point tracking method for a solar-boosted biogas energy generation system

Low biogas yield in cold climates has brought great challenges in terms of the flexibility and resilience of biogas energy systems. This paper proposes a maximum production point tracking method for a solar-boosted biogas generation system to enhance the biogas production rate in extreme climates. In the proposed method, a multi-dimensional R–C thermal circuit model is formulated to analyze the digesting thermodynamic effect of the anaerobic digester with solar energy injection, while a hydrodynamic model is formulated to express the fluid dynamic interaction between the hot-water circulation flow and solar energy injection. This comprehensive dynamic model can provide an essential basis for controlling the solar energy for digester heating to optimize anaerobic fermentation and biogas production efficiency in extreme climates. A model predictive control method is developed to accurately track the maximum biogas production rate in varying ambient climate conditions. Comparative results demonstrate that the proposed methodology can effectively control the fermentation temperature and biogas yield in extreme climates, and confirm its capability to enhance the flexibility and resilience of the solar-boosted biogas generation system.

Feasibility of a booster for DHW circulation in apartment buildings

With increasing focus on the performance of district heating systems, a concept is developed to obtain low district heating return temperatures from domestic hot water systems with a high share of circulation loss. For these systems, it is challenging to realize a low district heating return temperature by direct heat exchange only, due to the high flow of circulation return water at 50 °C. The concept is termed Circulation Booster. The purpose of the Circulation Booster is to boost the domestic hot water circulation temperature and at the same time secure a low district heating return temperature from this part of the service. The domestic hot water circulation temperature is heated in two steps: direct heat exchange and a heat pump. The heat source for the Circulation Booster is district heating, and the heat pump itself is driven by electricity. The paper includes the field experiences from a 1-year test period, concluding that the concept is operating as intended. Further, the performance results regarding electric consumption and district heating return temperatures and an economic feasibility study are presented. The current tariff structure in Denmark related to the district heating return temperature and electric costs gives a feasible economic case for the Circulation Booster concept with a direct payback time of 5,1 years. An increasingly progressive tariff scheme for low district heating return temperature or lower electric costs could further improve the economic feasibility of the Circulation Booster concept.

Ice drilling system with near-bottom hot water circulation

Ice drilling systems with near-bottom hot water circulation can be used for many challenging scientific tasks in the study of ice sheets, glaciers, and subglacial environments. These systems melt ice using water jets heated directly at the bottom of the hole, thus eliminating the use of long heavy hoses and surface pumps. To investigate the influence of the drill tip shape and nozzle diameter on the drilling process, a simplified laboratory prototype of the drill was designed and tested. The rated power of the downhole electric heater was 5.5 kW. A total of six melting tips in two groups were tested: three tips having a conical shape with different heights/angles and three parabolic tips with different focal parameters. In general, the conical tips provided a more stable drilling process. The experimental results showed that the rate of penetration (ROP) was highest when the specific load on the thermal tip was ~0.5 N cm−2 or 30% of the total drill prototype weight. The highest ROP of 2.5–3.1 m h−1was achieved with a nozzle diameter of 3.0 mm (at a flow rate of 3.0 L min−1). At the same time, the higher the flow rate, the faster the drilling speed was.

On the efficiency of the control of the circulation of hot water

PURPOSE. Perform analysis of the actual heat energy consumption for cold water heating for the hot water utility to the approved standard. Compare different methods of flow control in circulation pipelines of hot water supply systems. Identify ways to improve the efficiency of hot water systems. METHODS. The passive engineering experiment was used to study the operating modes of hot water supply systems of several groups of houses, in which various methods of regulating water consumption in hot water supply systems are implemented. Data collection was carried out using the online system of control and commercial accounting of energy resources. RESULTS. Existing hot water supply systems in residential buildings of Ulyanovsk were inspected under various methods of flow control in circulation pipelines. Features of static and dynamic load control of hot water supply systems were investigated. Analysis of influence of methods of control of thermal load of hot water supply systems on their actual heat consumption was performed. The possibility of bringing the actual operation mode of hot water supply systems to the standard value, on the basis of which consumption is calculated, is estimated. CONCLUSION. Known methods of load control in hot water supply systems and their actual operating conditions do not allow to reach the level of heat consumption that meets the established standards. Conclusions were drawn on the need to revise the regulated indicators of hot water quality and to adjust the method of calculating consumption in hot water supply systems.