Domestic Hot Water Heating System Research Articles

Artificial neural network model for predicting CO2 heat pump behaviour in domestic hot water and space heating systems

The natural refrigerant, CO2, possesses thermophysical properties that make it highly suitable for domestic hot water (DHW) production using heat pump technology. In this study, the development and validation of an artificial neural network (ANN) model that enables efficient design and control of a CO2 heat pump is presented. The study employs experimental data from a CO2 heat pump with a nominal heat capacity of 8 kW. The fully instrumented rig includes the heat pump and a pump rig designed to generate system temperatures representative of various space heat and DHW demands. A comprehensive dataset was generated through systematic variation of inlet temperatures and setpoints. The ANN provides predictions for outlet temperatures, heat production, and electricity consumption utilizing inlet flow rates, temperatures, and setpoints as inputs. These predictions are important for condition monitoring or in a smart operation management framework that determines optimal schedules for the machine.

Data-driven predictive control for demand side management: Theoretical and experimental results

Demand side management is perceived as a tool to support a secure and reliable energy system operation amid growing integration of renewable energy resources. However, the lack of scalable modeling and control procedures hinders the practical implementation. To address this challenge, this paper proposes a novel signal matrix model predictive control algorithm. Compared to existing data-driven methods, this approach explicitly provides stochastic predictions considering both disturbance and measurement errors with few tuning parameters, ensuring reliability by high-probability constraint satisfaction. The performance is extensively compared with three state-of-the-art algorithms in a space heating case study using a high-fidelity simulator. The results are further validated with physical experiments using the same system that the simulator is based on. To assess transferability, the algorithm is further implemented on diverse controlled systems, including a domestic hot water heating system and a stationary electric battery. The simulation results show that, compared to existing data-driven methods, the proposed approach improves constraint satisfaction and energy savings by up to 90 % and 8 %, respectively. The experimental results further confirm that the algorithm is applicable to multiple tasks of demand side management, with reasonable control performance observed in all case studies.

Techno-economic assessment of solar assisted precinct level heating systems with seasonal heat storage for Australian cities

District or precinct level heating systems are a promising way to incorporate solar for decarbonising the building heating sector. Despite growing interest in these technologies in Europe and China, there are no large-scale district heating systems in Australia. This study shows that a combined solar heat driven Domestic Hot Water (DHW) and Space Heating (SH) system with seasonal storage is technically and economically feasible for major Australian cities. A precinct scale solar-assisted domestic hot water and space heating system with seasonal heat storage has been designed and evaluated for Australian conditions. Technical performance was evaluated using solar fraction, storage efficiency and heat collection efficiency parameters. Economic performance was evaluated using the Levelized Cost of Heat for solar thermal (LCOHst) and whole system Levelized Cost of Heat (LCOH) with a combination of component cost data from China and Europe and energy cost data from Australia. A parametric study to identify optimal collector area and storage volume sizes shows that the proposed system could achieve technical and economic targets in all five Australian cities considered. The lowest LCOHst is 0.0597 USD/kWh in Hobart. Sydney and Perth could use nearly 100% solar energy to cover the heating demand with the proposed design.

Measures for Assessing the Effectiveness of Investments for Electricity and Heat Generation from the Hybrid Cooperation of a Photovoltaic Installation with a Heat Pump on the Example of a Household

In recent years, one of the key postulates in the European Union’s policy has become the development of renewable energy sources. In order to achieve the desired synergy effect, the idea of combining two selected sources of energy appeared. This article presents a technical and economic analysis of a hybrid connection of a ground source heat pump with a photovoltaic installation. Taking into account the heat demand of the building, a ground heat pump with a catalog nominal heating power of 25 kW was selected. This article presents the problem of the economic profitability of using a hybrid combination of a heat pump and photovoltaic panels in domestic hot water and central heating systems. The justification for the use of such heat sources in these installations is due to global trends and the gradual departure from conventional energy sources such as oil or gas boilers. This paper presents the economic and ecological results of using the pump heat connected together with photovoltaic panels. In the economic analysis, with the assumed installation costs related to the use of the considered heat pump and PV, two parameters commonly used in the investment analysis (static and dynamic) were used, namely, the simple payback period and the net present value of the investment. For the adopted assumptions, the usable area of the facility and the number of years of use were indicated, at which the investment in question is competitive with other alternative investment interest methods and will start to bring tangible benefits. The performed analysis also has measurable environmental benefits in the form of a reduction in carbon dioxide emissions at the level of 2893 kg/year into the atmosphere. The presented solution will help future investors understand the investment profitability mechanism for their households.

Performance analysis of a prototype solar photovoltaic/wickless heat pipe embedded aluminum curtain wall-heat pump water heating system

In this study, a novel glazed photovoltaic heat pipe based curtain wall (PV-HPCW) heat pump system composes of the wickless heat pipe embedded aluminum veneer curtain wall as solar thermal collecting system and heat pump water heating system is proposed. This system assists in heat redistribution on the outer wall of the room to increase solar collection rather than transmission, and in which the collected heat is then transferred to the cold feed of the domestic hot water heating system. A dynamic model is developed to analyze the energy conversion and heat transfer process in the entire system by utilizing the energy balance approach to understand inter-connection and definition of the sorted equations. An experiment is executed and tested under the real outdoor weather conditions in Hong Kong, which is done by measuring the operational parameters, such as solar radiation, PV power generation, temperature at various points and compressor consumption. The simulation results reflect good consistency with the observation data, and indicating that the established model has reasonable accuracy to predict system performance. In outdoor condition, the results indicate that the average electrical and thermal efficiency of PV-HPCW module are around 9.44% and 20.22%, respectively; Similarly, the overall thermal efficiency and overall electrical efficiency (exergy) of the system are 44.6% and 12.8%, respectively; whilst the mean coefficient of performance, COP and the comprehensive coefficient of performance, COPpvt of the system are 3.64 and 5.12 respectively. The PV-HPCW heat pump system has a significant potential and benefits relating to solar heat and electricity. Thus, this innovative PVT technology based building envelop could be a promising building energy supply system with the advantage of proper resource utilization and compact structure, and all these positive implication would encourage the development of such high performance technology, which will contribute to the reduction of carbon emissions in the building sector and ultimately to reduce the urban heat island effect.

Thermal Characterization of Medium-Temperature Phase Change Materials (PCMs) for Thermal Energy Storage Using the T-History Method.

To reduce energy consumption and increase energy efficiency in the building sector, thermal energy storage with phase change materials (PCMs) is used. The knowledge of the thermophysical properties and the characteristics of PCMs (like their enthalpy changes and the distribution of stored energy over a specified temperature range) is essential for proper selection of the PCM and optimal design of the latent thermal energy store (LHTES). This paper presents experimental tests of the thermophysical properties of three medium-temperature PCMs: OM65, OM55, RT55, which can be used in domestic hot water installations and heating systems. Self-made test chambers with temperature control using Peltier cells were used to perform measurements according to the T-history method. In this way the temperature range of the phase transition, latent heat, specific heat capacity, enthalpy and the distributions of stored energy of the three PCMs were determined. The paper also presents measurements of the thermal conductivity of these PCMs in liquid and solid state using a self-made pipe Poensgen apparatus. The presented experimental tests results are in good agreement with the manufacturers’ data and the results of other researchers obtained with the use of specialized instruments. The presented research results are intended to help designers in the selection of the right PCM for the future LHTES co-working with renewable energy systems, waste heat recovery systems and building heating systems.

Determination of Heat Losses from the Pipeline in SDHW System during the Continuous Change of the Supply Temperature

In this article, the research object is the solar domestic hot water (SDHW) heating system that has been in operation since 2015 and is located on the campus of the Bialystok University of Technology (Poland). The thermal performance of solar collectors are thoroughly investigated so far. Therefore, special attention was paid to the issue of the heat loss from pipes. The measurements showed that the heat transfer in circulation pipes is quite complex due to continuous fluctuations in water temperature at the supply of this loop. As it turned out, the application of the classical method of energy balancing and the readings from heat meters gave inaccurate results in this case. The main aim of this study was to develop a different approach to solving the problem of determination of heat losses. The method presented in this article is based on computational fluid dynamics (CFD) and measurement results as the input data. The practical result of this study was the development of two relationships for calculating the heat loss from pipes. A separate issue, that is discussed in this paper, concerns the impact of the time intervals used in numerical simulations on the accuracy of calculation results.

Operating the hot water supply system problems during transfering the hostel to the apartment house status

The energy infrastructure modernization is a complex social and technical problem requiring an integrated approach. After analyzing the hot water system operation in a residential apartment building, being previously a hostel, the reason for the temperature regime violation was determined. In connection with the building status change, the residents number has significantly decreased, the service block, which led to a change in water consumption conditions has been eliminated. In addition, the requirements for minimum water temperature in centralized hot water systems have changed. The question of using a dead-end hot water supply system possibility, provided by the project or its reconstruction into the circulation network, was considered. The studies were conducted in accordance with the methodology described in MIC 4.3.2900-11 “The centralized hot water supply systems hot water temperature measurement”. There was a discrepancy in the temperature coolant standard indicators at the dismantling points on different floors of the building. The difference in temperature at the input (the heat meter and thermometer readings) and at the end user is associated with additional water cooling in the supply pipes of the domestic hot water heating system. When transferring the public buildings to housing stock, it is necessary to revise not only water consumption rates, but also the hot water supply scheme in general. The lack of circulation leads to waste of hot water and increases the cost to the consumer. To ensure the required temperature standards for a full day in a dead-end hot water supply system, which is provided for by the project, continuous dismantling of the water is required, which is difficult to achieve with a changed building status. The resolution of the problem is possible only when the domestic hot water heating system is switched to the circulation mode with the circulation piping and the circulation pump installation.

Gas vs Electric: Space and Domestic Hot Water Heating System Fuel Source Implications on Low-Energy Single-Family Dwelling Sustainability Performance

Gas vs Electric: Space and Domestic Hot Water Heating System Fuel Source Implications on Low-Energy Single-Family Dwelling Sustainability Performance

Numerical and experimental study on the thermal performance of the concrete accumulator for solar heating systems

The article presents the concept of the solar facility operating in the domestic hot water and space heating system, equipped with thermal energy storage based on a water tank and an auxiliary storage module made of concrete elements. A mathematical model of transient heat transfer in the concrete structure using the Control Volume Finite Element Method (CVFEM) has been proposed. The method allows modelling the transient heat conduction based on a rare mesh of nodes in a relatively short time, with accuracy comparable to traditional Finite Element Method (FEM) results including CFD modelling. A laboratory stand has been made for the verification of the model, and a set of comparative measurements has been carried out.

End user engagement with domestic hot water heating systems: Design implications for future thermal storage technologies

The strategies used by householders for heating and using hot water heating have a significant impact on energy consumption in domestic buildings. A better understanding of the interaction between occupants and hot water heating systems can improve the energy efficiency of a building. This paper maps the interaction between occupants and their current domestic hot water heating systems to provide insights for the design of future thermal energy storage systems. A total of 35 householders from the Midlands region of the UK took part in semi-structured contextual interviews about their current strategies for the provision of hot water and the way they engage with their heating systems. Using the DNAs framework as an analysis lens, drivers, needs and actions relating to the provision of hot water were evaluated and four distinct hot water heating types are presented: On Demand, For All Eventualities, Just Enough and Sunny Days. Findings provide insights into occupants’ behaviour in relation to hot water heating usage and design implications for thermal energy storage technologies.

Design of a New Solar Thermal Collector with Ceramic Materials Integrated into the Building Facades

The work presented here aims to demonstrate the technical, architectural, and energy viability of solar thermal collectors made with ceramic materials and their suitability for domestic hot water (DHW) and building heating systems in the Mediterranean climate. The proposal is for the design of a ceramic shell, formed by collector and non-collecting panels, which forms part of the building system itself, and is capable of responding to the basic requirements of a building envelope and harnessing solar energy. Ceramics considerably reduce the final cost of the collector system and offer the new system a variety of compositional and chromatic finishes, occupying the entire building surface and achieving a high degree of architectural integration, although less energy-efficient compared to a conventional metallic collector.

Compact latent heat storage decarbonisation potential for domestic hot water and space heating applications in the UK

A performance comparison is presented for a domestic space and hot water heating system with a conventional gas boiler and an air source heat pump (ASHP) with latent heat storage, both with solar thermal collectors for a typical UK climate, to demonstrate the potential of phase change material based energy storage in active heating applications. The latent heat thermal storage system consisted of 10 modules with RT54HC comprising a total storage capacity of 14.75 kWh that provided 53% extra thermal storage capacity over the temperature range of 40–65 °C compared to a water only store. The simulations predicted a potential yearly CO2 reduction of 56%, and a yearly energy reduction of 76% when operating the heat pumps using the economy 10 electricity tariff i.e. a low tariff between 00.00 and 05.00 and 13.00–16.00 with current grid emission values compared to the conventional gas boiler system; successfully offsetting the electrical load to meet the required heat demand. Due to the high capital costs of the heat pump system with latent heat storage, its levelized cost of energy was 117.84£/MWh, compared to 69.66£/MWh for the gas boiler, on a 20-year life cycle.

A method for supporting the design of efficient heating systems using EU product policy data

The design of heating, ventilation and air conditioning systems is still a challenging engineering task which requires experienced and informed decision-making. These systems have a great energy-saving potential at the system level rather than at the level of the individual products of which they are composed. European environmental product policies have been very useful in facilitating a homogeneous rating scheme which can be used to compare the energy performance of different products that provide the same service. This paper proposes a simplified design method which uses the performance of components that are regulated by European product policies to obtain the overall performance of heating systems in residential buildings. It is a flexible method and allows different product configurations to be assessed so as to optimise the system performance during the design phase. The method is tested on a real case study with domestic hot water and space heating systems. The case study shows the potential for improving the heating systems according to the performance levels of its products currently available in the market. Results of the domestic hot water system show that upgrading its storage tank to the maximum energy class (A+) could bring the highest energy savings ( 4162 kWh/y).

Increasing the efficiency by retrofitting gas boilers into a condensing heat exchanger

ABSTRACTWhen trying to reduce energy consumption in a central heating system or in a domestic water heating system, it is necessary to consider the annual operating efficiency of the heating and the domestic hot water heating system. A boiler operates under dynamic conditions, so it essential to know the methodology and the model of annual operating efficiency calculation for thermo technical systems. The outlet temperature of the flue gases with conventional gas boilers is considerably higher than the ambient temperature and consequently the heat loss occurs; it is then vented off into the environment as a result of heat transfer. The heat loss may be reduced if a condensing heat exchanger is installed, which will, on the other hand, increase the boiler efficiency by more than 10%. This paper studies the relations between combustion and heat transfer, which will enable the appraisal of a gas boiler efficiency increase and possible ways of energy savings. The method for cost-effectiveness of the investment is used to perform a feasibility study of retrofitting a conventional boiler into a condensing boiler with necessary details. The results of the investigation show that the most cost-effective temperature range of the flue gases is 40–60°C. The use of a working fluid in the heating system or the domestic cold water results in cooling the condensing heat exchanger. The temperature of the return water or the domestic cold water is lower than the water vapor dew point in the flue gases during most of the heating period in almost all parts of the Republic of Serbia where natural gas is used.

Dynamic modeling approach for determining buildings technical system energy performance

This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope+technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%.

A Study of the Influence of Solar Panels Coupled with Thermal Systems for a Residential Building, by Applying Methods of Evaluation as EN 15316-4-3:2014 and TRANSOL

The present study performs calculations for a series of parameters involved in the definition of energy performance of a real residential building, by applying EN15316-4-3:2014 methodology; results are compared with simulations made with TRANSOL, analysing the influence of coupling solar panels with domestic hot water production (DHW) and heating systems. In a first stage, the influence of using solar panels for DHW production is evaluated, and calculations for thermal and electric needed energy are performed. Variation of solar fraction is analised. Secondly, a combi-system (DHW+heating) was considered, and the calculations were performed accordingly, as EN 15316-4-3:2014 describes. The data provided with TRANSOL were compared with the results obtained by applying EN 15316-4-3:2014, and conclusions are extracted. At the end, a parametric study of solar fraction is followed, taking into account different numbers of solar panels, in both situation, for DHW and DHW & heating coupling systems cases. The critical approximation introduced by EN 15316-4-3 is identified. Values of determined fraction are compared.

Sizing of a Domestic Hot Water Heating and Storage System for Short Operating Cycles - A Theoretical Approach

A methodology for the sizing of domestic hot water heating and storage systems is defined, by assuming an extreme operating condition cycle composed of only two parts, a water consumption period and a system repositioning period. In both parts to respond to the extreme hot water demanding conditions, the heating is always on. The subsequent exergy analysis of this domestic hot water production system compares the irreversibility and the exergy efficiency of the water storage and the tankless situation. To carry out such analysis, some basic assumptions were made: a constant temperature heat source, a short duration operating cycle and a constant thermal energy supply. Under these circumstances it is shown that the hot water storage system leads to lower exergy losses while the tankless system is more exergy efficient, but requiring a higher instantaneous thermal power input. The use of the joule effect electricity, as the system heat source, be it a water storage one or a tankless one, maximizes the system irreversibility losses and minimizes the system exergy efficiency. The tankless system, with the joule effect electricity heat source is the worst situation.

Net energy analysis of a solar combi system with Seasonal Thermal Energy Store

EU targets require nearly zero energy buildings (NZEB) by 2020. However few monitored examples exist of how NZEB has been achieved in practise in individual residential buildings. This paper provides an example of how a low-energy building (built in 2006), has achieved nearly zero energy heating through the addition of a solar domestic hot water and space heating system (“combi system”) with a Seasonal Thermal Energy Store (STES). The paper also presents a cumulative life cycle energy and cumulative life cycle carbon analysis for the installation based on the recorded DHW and space heating demand in addition to energy payback periods and net energy ratios. In addition, the carbon and energy analysis is carried out for four other heating system scenarios including hybrid solar thermal/PV systems in order to obtain the optimal system from a carbon efficiency perspective.

An investigation of the technoeconomic feasibility of solar domestic hot water heating for the Canadian housing stock

This study evaluates the impact on energy consumption and GHG emissions as well as the technoeconomic feasibility of retrofitting solar domestic hot water (DHW) heating systems to all houses in the Canadian housing stock (CHS). The study was conducted using the Canadian Hybrid Residential End-Use Energy and GHG Emissions Model (CHREM). It was assumed that all houses that have a DHW system with a tank, and a roof facing south, south–west or south–east could be retrofitted with a solar DHW system. As to be expected, the energy and GHG emissions impact of retrofitting SDHW systems into the CHS is substantial. If all eligible existing DHW systems (30% of those existing in the CHS) were to be retrofitted with SDHW systems, the energy consumption and GHG emissions of the Canadian residential sector would be reduced by about 2%. This is equivalent to 22.7 PJ of end-use energy savings and 1 Mt of GHG emissions reduction, or 11.8% and 11.9%, respectively, of the current amounts associated with domestic hot water heating. The energy savings potential with SDHW systems in all provinces are similar, while the GHG emission reductions vary significantly due to the substantially different fuel mix used in different provinces. The economic feasibility results demonstrate the impact of installation and fuel costs, as well as interest and energy price escalation rates on payback period.