Hot Water Heating Research Articles

Exergy-economic analysis and multi-objective optimization of a multi-generation system based on efficient waste heat recovery of combined wind turbine and compressed CO2 energy storage system

Due to the intermittent feature of renewable energies, their combination with energy storage systems seems efficient and profitable. In this regard, a wind turbine system is coupled with a compressed CO2 energy storage (CCES) system for multi-generation propose. This combination has not been done yet and seems very attractive and efficient with the present popularity of wind energy and energy storage systems. A fraction of the output power of the wind turbine is sent to the compressor and electric heater of the CCES layout in the charging and discharging period. In the CCES system, a thermoelectric generator (TEG 1), an absorption chiller, and a domestic hot water heat exchanger are used to waste energy elimination and the waste energy of the wind turbine is recovered by a trilateral cycle (TLC). The produced power of the TEG 1 and TLC is transmitted to a reverse osmosis desalination unit and an alkaline electrolyzer for freshwater and hydrogen production. Hence, the considered system is converted to a multi-product one. Energy, exergy, and exergy-economic (3E) studies are done on the whole layout through parametric analysis and multi-objective optimization. Exergy round trip efficiency and unit cost of products are obtained as 37.027% and 30.41 $/GJ in the optimization process. The considered system can produce 1960 kW of power, 336.1 kW of heating, 183.3 kW of cooling, 1.077 kg/s of freshwater, and 0.0138 kg/h of hydrogen in this case.

Thermodynamic performance of heat pump with R1234ze(E)/R1336mzz(E) binary refrigerant

In order to solve the temperature mismatch issue of cold and hot fluids in evaporation and condensation processes for heat pump system, binary refrigerant R1234ze(E)/R1336mzz is recommended in the present research due to its large temperature glide. Through theoretical analysis, multiple configurations under conditions of three different temperature heat sources (70/50 °C, 60/40 °C and 50/30 °C) and two different heat targets (steam above 100 °C and hot water with 70 °C) are constructed adopted Ebsilon code. The optimum mass proportion is obtained as 0.3/0.7 for R1234ze(E)/R1336mzz(E), because of its maximum temperature glide (can reach 21.52 °C) and excellent thermal performance (large COP, ECOP and exergy efficiency). COP of steam high temperature heat pump with R1234ze(E)(0.3)/R1336mzz(E)(0.7) binary refrigerant and the ratio of transferred heat of 110 °C condenser to all output heat (containing 110 °C and 100 °C steam intercooler and condensers) respectively increase up to 67.25% and 335.16% under some certain conditions, compared with that with pure R1336mzz(E). COP of hot water heat pump with R1234ze(E)(0.3)/R1336mzz(E)(0.7) binary refrigerant are respectively 10.31 and 6.89 under 60/40 °C and 50/30 °C heat source conditions, which greatly increases compared with that of heat pump with pure R1234ze(E) (6.67 and 5.03) and R1336mzz(E) (6.74 and 4.54). The present research may lay a foundation for binary refrigerant adoption to replace the scheme of multi-stage evaporator or multi-stage condenser, which could reduce the irreversible loss of phase change equipment and improve thermodynamic performance of heat pumps.

Exergy analysis and finite-time assessment of a multi-generation system based on solar and wind energies

This paper studies a multi-generation system by exergy and finite-time assessment based on solar and wind energies. The proposed system provides electricity, cooling, heating, hydrogen, desalinated water, and domestic hot water. The subsystem includes a solar cycle, Kalina cycle, wind turbine, electrolyzer, single-effect absorption chiller, photovoltaic panel, and desalination unit. The multi-generation system studied in Bandar Abbas climate of Iran. The results reveal that the total exergy destruction of the system is 440.4707 kW, 42.86% of this is related to the solar collector, and 25.18% is associated with the wind turbine. Also, the maximum energy efficiency of the multi-generation system is 79.55% in the spring equinox and 17.77% in the summer solstice. In addition, the optimisation of the system based on thermodynamic and economic criteria show that the maximum power, energy & exergy efficiencies, maximum ecological and ecologicost are 398 kW, 63.36%, 16.68%, –49.2273 kW, and –0.000091433 kW/$, respectively. Finally, by using the ecologicost criterion, the proposed system can produce 0.015 kg/s hydrogen.

ЭКОНОМИЧЕСКИЙ АСПЕКТ ДИАГНОСТИКИ НАКИПЕОБРАЗУЮЩИХ СЛОЕВ В ПЛАСТИНЧАТЫХ ТЕПЛООБМЕННИКАХ

The reliability and efficiency component of the 3rd generation heat and power network is characterized by the use of heat exchange devices, namely the plate type. Its main function is to heat the coolant for the needs of hot water supply and heating systems. However, the peculiarities of the chemical composition of the heat carrier cause contamination of heat exchangers in the form of scale layers on the heating surfaces. The process of scale formation on the plates of heat exchangers is one of the key factors affecting the failure of equipment and an increase in the energy intensity of heat distribution points, which leads to a decrease in the quality of services provided and an increase in financial costs in the field of heat supply. In the course of the study, by summarizing the known data, a sequence is formed for calculating the transport costs for the operation of plate heat exchangers under various conditions of scale formation. At the same time, the influence of scale thickness on the total cost of pumping one square meter of coolant is taken into account. This allows comparing transportation costs and the cost of removing scale from heating surfaces (according to the accepted cleaning method) depending on the thickness of the salt-forming layer and cleaning periods. The results of the study confirm the feasibility of regular monitoring of the thickness of salt-forming layers in plate heat exchangers to reduce operating costs for pumping the coolant.

4E analysis and optimization of a biomass-fired waste-to-energy plant integrated with a compressed air energy storage system for the multi-generation purpose

A novel multi-generation system is introduced based on the combination of biomass gasifier-fired steam Rankine cycle (SRC) and compressed air energy storage (CAES) system. The output power of SRC feeds the compressor and electric heater of the CAES system. A domestic hot water heat exchanger and an absorption chiller are used to waste heat utilization of gasifier-SRC and a trilateral cycle (TLC) is utilized to waste energy recovery of the CAES system. Then, the output power of TLC is sent to a proton exchange membrane electrolyzer for the production of hydrogen. Hence, the considered system is converted to a power, heating, cooling, and hydrogen multi-generation system. Energy, exergy, exergy-economic and environmental studies are done on the layout in a base case, parametric analysis, and design optimization. The three-objective optimization results in the exergy round trip efficiency (ERTE), total cost rate, and unit cost of multi-generation of 41.205%, 708.136 $/h, and 17.206 $/GJ. The improvement of ERTE (30.23%) is the most visible one in comparison to the base case outputs.

TRNSYS Simulation of the Use of Solar Collector-based Domestic Hot Water System in Central and Eastern European Countries (CEEC)

With the prevailing energy crisis and the public’s growing environmental awareness, renewable energy sources (sun, wind, water) are playing an increasingly important role in Europe and around the world. Due to its easy availability and relatively high efficiency, it is the solar energy that is attributed with great potential in decarbonizing the energy sector. Among the most popular devices that enable the use of solar radiation are solar collectors. They are used in heating and domestic hot water preparation systems, as well as for heating swimming pool water. However, their efficiency depends on many factors, of which the main one being the climatic conditions. This paper presents the results of energy simulations of a solar collector-based domestic hot water system for the capitals of five selected Central and Eastern European Countries (CEEC) – Riga (Latvia), Warsaw (Poland), Prague (the Czech Republic), Bratislava (Slovakia), and Zagreb (Croatia). The system model was developed using the TRNSYS software, in which dynamic simulations were also performed for an entire year (8760 h). For each location, the efficiency of the flat-plate solar collectors, the amount of useful energy generated by them, as well as the amount of energy needed to meet the load and auxiliary energy requirements were analyzed and compared. The extent to which increasing or decreasing the area of solar collectors affects the operation and efficiency of the system for different locations was also estimated. The results showed that in terms of efficiency, the use of solar collectors is most favorable in Slovakia and placed southernmost-located Croatia, where it also achieved the lowest annual auxiliary energy demand. The least favorable location, on the other hand, turned out to be the capital of Latvia. It is also worth noting that regardless of location, the area of solar collectors has a significant impact on the efficiency of the entire system.

Forecasting of residential unit’s heat demands: a comparison of machine learning techniques in a real-world case study

AbstractA large proportion of the energy consumed by private households is used for space heating and domestic hot water. In the context of the energy transition, the predominant aim is to reduce this consumption. In addition to implementing better energy standards in new buildings and refurbishing old buildings, intelligent energy management concepts can also contribute by operating heat generators according to demand based on an expected heat requirement. This requires forecasting models for heat demand to be as accurate and reliable as possible. In this paper, we present a case study of a newly built medium-sized living quarter in central Europe made up of 66 residential units from which we gathered consumption data for almost two years. Based on this data, we investigate the possibility of forecasting heat demand using a variety of time series models and offline and online machine learning (ML) techniques in a standard data science approach. We chose to analyze different modeling techniques as they can be used in different settings, where time series models require no additional data, offline ML needs a lot of data gathered up front, and online ML could be deployed from day one. A special focus lies on peak demand and outlier forecasting, as well as investigations into seasonal expert models. We also highlight the computational expense and explainability characteristics of the used models. We compare the used methods with naive models as well as each other, finding that time series models, as well as online ML, do not yield promising results. Accordingly, we will deploy one of the offline ML models in our real-world energy management system in the near future.

Optimization framework for evaluating urban thermal systems potential

The increase in space cooling demand worldwide calls more than ever for efficient ways to meet buildings combined hot and cold demands. Building scale technologies present interesting advantages such as modularity but also numerous drawbacks such as architectural issues, urban heat island effect, low efficiency and stress on the electrical network. Yet, a literature gap exists regarding the optimal equilibrium between local and centralized thermal equipment. This paper presents a framework to evaluate the performances of urban thermal architectures. It relies on an existing building typology database to derive hourly profiles of space heating, space cooling and domestic hot water demands. An object-oriented energy hub implementation eases the gathering of production, storage and distribution components. Optimal components are finally selected through a MILP-based optimization. The framework application shows its abilities to sort pre identified thermal architectures by performance level. For the addressed case studies, 4th generation district heating (4GDH) performs the best regarding CO2 emissions and exergy destruction, while 2GDH is often cost-effective. In the selected configurations, 5thgeneration district heating and cooling (5 GHDC) performs hardly better than individual solutions. The use of different components depending on the techno-economic context indicates the need to challenge many solutions, which is possible using the framework.

Comparative study regarding retrofitting with a low GWP refrigerant in an ice rink with energy recovery implementation

The authors make a comparative study between an existing R407C indirect refrigeration system which serves an ice rink refrigeration plant with a modern R744 indirect refrigeration system incorporating heat recovery, by using “Pack Calculation Pro” software. The proposed solution involves no alterations in the water-ethylene glycol circuit that ensures the rink’s cooling load. By considering the need for retrofitting to comply with current legislation, the study aims to identify the best solution in terms of environmental impact and the CO2-equivalent release into the atmosphere. The recovered energy can be further used for space heating, ventilation, and domestic hot water preparation. This study is targeted on an existing ice rink placed in Iasi, Romania, and the analysis demonstrates that the implementation of this solution reduces the environmental impact of CO2-equivalent reduction, and the global COP (Coefficient of Performance) value increases.

Modeling and Simulation of Indirect Collector Solar Hot Water Heating System Based on TRNSYS

The use of solar energy is one of the important ways of clean energy heating in rural areas in the north, and the collector solar water heating system is an effective way to use solar energy. This paper takes a typical single residential house in a rural area of Shenyang as a research case to design an indirect collector solar hot water heating system. Based on the meteorological data of the winter heating period (November 1 - March 31 of the following year) in Shenyang, TRNSYS software was used to research the heat collection efficiency and scheme design of the heating system. The research results showed that: 1) The best material of the heat exchange coil of the hot water storage tank in the solar water heating system of the indirect collector is stainless steel with a thickness of 0.8mm; 2) The optimal installation angle of solar collectors in Shenyang is 55°; 3) The optimal area of the heat exchanger coil in the hot water storage tank is 4.40m2.

Heat transfer and performance enhancement investigation of biomimetic honeycomb gas coolers in transcritical CO2 heat pumps

CO2 air source heat pump heating technology has characteristics of strong adaptability to outdoor temperature in cold areas and high outlet temperature, which is widely used in heating and domestic hot water supply. A gas cooler is one of the crucial components in CO2 heat pump systems, while its performance and different structural forms will directly affect the performance of the whole CO2 heat pump system. In order to improve its heat transfer efficiency, a biomimetic honeycomb gas cooler is proposed in this paper, the steady-state simulation model of the biomimetic honeycomb gas cooler is established, and the reliability of the model is verified by experimental data. In addition, the effect of structural parameters and operating parameters on the heat transfer performance is studied, also the heat transfer performance of the biomimetic honeycomb gas cooler is compared with that of the internal spiral tube gas cooler and triple tube-in-tube gas cooler. The results show that the performance of the biomimetic honeycomb gas cooler can be effectively improved by reducing the water flow rate. Under the same working condition, the performance evaluation criteria1 of the 1st, 2nd and 3rd layer biomimetic honeycomb gas cooler s are about 193.4%, 239.9% and 357.0% higher than that of the internal spiral tube gas cooler, and about 197.2%, 205.9% and 237.7% higher than that of triple tube-in-tube gas cooler. This research is helpful to provide the reference for the design and optimization of this type of gas cooler and is conducive to the popularization and application of CO2 air source heat pumps.

On-site solar PV generation and use: Self-consumption and self-sufficiency

As energy storage systems are typically not installed with residential solar photovoltaic (PV) systems, any “excess” solar energy exceeding the house load remains unharvested or is exported to the grid. This paper introduces an approach towards a system design for improved PV self-consumption and self-sufficiency. As a result, a polyvalent heat pump, offering heating, cooling and domestic hot water, is considered alongside water storage tanks and batteries. Our method of system analysis begins with annual hourly thermal loads for heating and cooling a typical Australian house in Geelong, Victoria. These hourly heating and cooling loads are determined using Transient System Simulation (TRNSYS) software. The house’s annual hourly electricity consumption is analysed using smart meter data downloaded from the power supplier and PV generation data measured with a PV system controller. The results reveal that the proposed system could increase PV self-consumption and self-sufficiency to 41.96% and 86.34%, respectively, resulting in the annual imported energy being reduced by about 74%. The paper also provides sensitivity analyses for the hot and cold storage tank sizes, the coefficient of performance of the heat pump, solar PV and battery sizes. After establishing the limits of thermal storage size, a significant impact on self-efficiency can be realised through battery storage. This study demonstrates the feasibility of using a polyvalent heat pump together with water storage tanks and, ultimately, batteries to increase PV self-consumption and self-sufficiency. Future work will concentrate on determining a best-fit approach to system sizing embedded within the TRNSYS simulation tool.

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.

Optimization of Heat Pump Systems in Buildings by Minimizing Costs and CO2 Emissions

District heating systems are gaining global recognition as an essential tool for reducing greenhouse gas emissions and transitioning to a low-carbon-energy future. In this context, heat pumps are becoming an important technology, providing an effective solution for improving energy efficiency and reducing the reliance on fossil fuels in heating systems. Therefore, this study is focused on the optimal selection of heat pump systems for different types of buildings considering technical, economic, environmental, and social factors. This paper proposes a novel methodology based on mixed-integer nonlinear programming and multi-objective optimization that minimizes total costs and reduces CO2 emissions for heat production and supply systems over a desired period. The methodology is applied to various building types, including renovated and unrenovated apartment buildings, schools, kindergartens, and a supermarket. The study analyzes various types of heat pumps and electric heaters for space heating and domestic hot water production. Optimization results showed that the optimal heating system includes air-to-water heat pumps and electric heaters. Furthermore, for schools and a supermarket, these systems are combined with hybrid heat pumps. The goal of making the heating system neutral in terms of CO2 emissions was achieved for eight out of eleven buildings analyzed. The most profitable investments were in the heating systems of renovated five-story and unrenovated nine-story apartment buildings due to their low energy costs (0.0831 EUR/kWh), short payback periods, and high returns on investment.

Study on performance of a gas engine-driven heat pump system with R410A for heating and domestic hot water applications

Traditional gas engine-driven heat pump (GHP) systems were switched off in the transitional season, and the engine waste heat could no longer be used for producing domestic hot water. Most studies on GHP systems used piston compressors with low efficiency, and the refrigerants used were R134a or R407C. This paper presents an innovative GHP system using open scroll compressors with R410A which can be used throughout the year. The novel GHP system can be switched freely between heating mode-H, which produced heating water combined with domestic hot water, and heating mode-D which only produced domestic hot water. In these two heating modes, the effects of different condenser water outlet temperatures (tw,out1), domestic hot water outlet temperatures (tw,out2), engine speeds (Neng), and total domestic hot water outlet temperatures (tw,out3) on performance of the GHP system for heating and domestic hot water applications were experimentally investigated. The results show that tw,out1 and tw,out3 have greater effect on primary energy ratio (PER), Neng has significantly larger effect on heating capacity and the recovered waste heat, whereas tw,out2 has little effect on the comprehensive performance. The change between heating mode-H and heating mode-D hardly affects the system heating performance. For the experiments, the waste heat recovery rates are between 42.05 % and 61.08 %. The total PER of the GHP system ranges from 1.179 to 1.453 without waste heat recovery, while it ranges from 1.521 to 1.834 when the engine waste heat is recovered. It indicates that the total PER can be significantly improved by recovering the engine waste heat.

Carbon reduction technology pathways for existing buildings in eight cities

We work with policymakers in eight cities worldwide to identify technology pathways toward their near- and long-term carbon emissions reduction targets for existing buildings. Based on policymakers’ interests, we define city-specific shallow and deep retrofitting packages along with onsite photovoltaic generation potential. Without further grid decarbonization measures, stock-wide implementation of these retrofits in the investigated neighborhoods reduces energy use and carbon emissions by up to 66% and 84%, respectively, helping Braga, Dublin, Florianopolis, Middlebury, and Singapore to meet their 2030 goals. With projected grid decarbonization, Florianopolis and Singapore will reach their 2050 goals. The remaining emissions stem from municipalities not planning to electrify heating and/or domestic hot water use. Different climates and construction practices lead to varying retrofit packages, suggesting that comparable technology pathway analyses should be conducted for municipalities worldwide. Twenty months after the project ended, seven cities have implemented policy measures or expanded the analysis across their building stock.

ANALYSIS OF HOT WATER HEATERS FOR INDIVIDUAL HEATING STATION WHEN THE TEMPERATURE CHART OF THE DISTRIBUTION HEAT NETWORK IS CHANGED

The aspects of the functioning of centralized heating systems of residential urban districts after additional insulation of this district existing buildings were considered. The influence of the heat carrier temperature in the district distribution heating network on the heat transfer surface of the heat exchangers that are installed in the individual heat station schemes for hot water supplying was analyzed. Estimates were made for single-stage connection of the heat exchangers to the heating systems. When determining the heat transfer surface, known criterion equations for plate heat exchangers of heat supply systems were used. The range of changes in the heat transfer surface of hot water heaters and the consumption of network water is determined depending on the selected temperature chart of the distribution heat network. The proposed recommendations can be useful in developing a heat supply quality control schedule for a district buildings heating systems in a district when the building thermal insulation process is completed. Possible approaches to the thermal design of heat exchangers of the hot water supply system for insulated buildings individual heating stations are considered when changing the temperature chart of the district heating supply system of the residential urban districts. Estimates were made to understand the influence of the reduced temperature chart for heat supply of the districts on the network water consumption for hot water heating and the surface of heat exchangers of insulated buildings heaters. It was shown that the increase in network water consumption for building hot water supply can be 1.5 to 3 times higher. The analysis presented for the surface of the heat exchangers of heating installations for insulated buildings hot water supply shows that it can be even double increase of heaters heat transfer surface depending on the temperature chart. The results obtained should be taken into account when planning the temperature chart of the heat carrier for a distribution heating network. Keywords: district heating, heat supply systems reforming, individual heating station, hot water heaters, plate heat exchanger, heat exchanger thermal design.

Relative Water Age in Premise Plumbing Systems Using an Agent-Based Modeling Framework.

Tools used to predict hydraulics and water quality within premise plumbing systems have gained recent interest. An open-source Python-based tool-PPMtools-for modeling and analyzing premise plumbing systems with WNTR or EPANET is presented. A relative water age-the time water has spent in a home-study using three real-world single-family homes was used to demonstrate PPMtools. Results showed that increased use-more people or higher flow fixtures-led to a general decrease in relative water ages. However, even with more use, one user could still experience water for a drinking activity with a relative water age equal to, or longer than, the duration of the longest stagnant period (sleeping or absence from home). Simulations also showed that the general relative water ages increased if the homes were plumbed with larger diameter piping [19.1 mm (3/4 in.) versus 12.7 mm (1/2 in.)]. Hot water heaters were found to have the largest impact on relative water age. Smaller volume uses generally had more variability in relative water ages, while larger volume uses (e.g., showering) resulted in generally low relative water ages with less variability because larger uses fully replaced water in the home with water from the main. This study highlights the potential for using PPMtools to explore more complex water quality modeling within premise plumbing systems.

Design of a multigenerational energy system with hydrogen production for clean cement plants

The article aims to provide the design and analysis of a new and unique multigeneration system. This multigeneration system primarily produces methane/natural gas by extracting carbon dioxide from the cement production processes through calcium looping. The hydrogen gas generated in the system was synthesized through polymer electrolyte membrane electrolysis, supported by hydroelectric power. After this, a portion of the hydrogen produced from the system is reacted with carbon dioxide to produce methane. The other useful outputs of the system include electricity, space heating, and domestic hot water. The implemented system design also harnesses other renewable resources, such as solar energy, to enhance other aspects of the design. The system achieved hydrogen and methane production rates of 0.01028 kgs-1 and 0.02045 kgs-1, respectively. Additionally, the system's exergy and energy efficiencies are obtained to be 44.5% and 77.5%, respectively. Furthermore, the energy and exergy heating coefficient of performance values are found to be 1 and 0.5624, respectively.

A novel and versatile solar Borehole Thermal Energy Storage assisted by a Heat Pump. Part 1: System description

The paper reports a system combining Solar Thermal Collectors (STC), Borehole Thermal Energy Storage (BTES), a Heap Pump (HP) and a backup boiler for space heating and Domestic Hot Water (DHW) production. The integration of the components and the overall control strategy are described. The system is flexible, being able to select the best thermal source and to use it directly or through a HP, while only the excess solar heat is stored into the BTES. The contribution of every subsystem to the energy mix is discussed. For a “reference configuration” combining the three subsystems (“Design D”) and characterized by heating and DHW needs of 510.5 MWh.y−1 and 226.7 MWh.y−1 respectively, a BTES volume of 15000 m3, a distance between boreholes of 3 m, a STC area of 2500 m2, and a solar tank volume of 100 m3, the system uses 274 units of gas and electricity to provide 1000 units of heating and DHW. This reference configuration outperforms any alternative design: Design A (STC only), Design B (STC and HP) and design C (STC and BTES) would respectively require 612, 480 and 591 units of gas and electricity to do so. A one-at-a-time analysis reveals that the STC area, azimuth and inclination, the solar tank volume, the BTES volume, the borehole density and the HP power are key parameters to the overall system performance.