Heat Source System Research Articles

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%.

Temperature field inversion of heat-source systems via physics-informed neural networks

Temperature field inversion of heat-source systems (TFI-HSS) with limited observations is essential to monitor the system health. Although some methods such as interpolation have been proposed to solve TFI-HSS, those existing methods ignore correlations between data constraints and physics constraints, causing the low precision. In this work, we develop a physics-informed neural network-based temperature field inversion (PINN-TFI) method to solve the TFI-HSS task and a coefficient matrix condition number based position selection of observations (CMCN-PSO) method to select optimal positions of noisy observations. For the TFI-HSS task, the PINN-TFI method encodes constrain terms into the loss function and thus the task is transformed into an optimization problem of minimizing the loss function. In addition, we have found that noise significantly affect reconstruction performances of the PINN-TFI method. To alleviate the effect of noises in observations, we propose the CMCN-PSO method to find optimal positions, where the condition number of observations is used to evaluate positions. The results demonstrate that the PINN-TFI method can significantly improve prediction precisions and the CMCN-PSO method can find good positions to improve the robustness of the PINN-TFI method.

Operating performance analysis of cold and heat sources composite based on ground source heat exchanger and hot water exchange tanks

Aiming at the air-conditioning system of underground space engineering, it is proposed to use ground source heat exchanger and hot water exchange tanks in parallel as a composite cold and heat source, which can simultaneously achieve energy-saving requirements. In order to explore the operating heat transfer characteristics of the composite cold and heat source system, a mathematical model of buried pipes and hot water exchange tanks was established. The simulation analysis of the influencing factors such as inlet temperature and fluid flow rate shows that under the condition of small flow rate, increasing the fluid flow rate can significantly improve the buried pipe and the hot water tank and the heat exchange effect; the greater the temperature difference between the inside and outside of the pipe, the better the heat exchange effect of the heat exchanger, under the same flow rate, the heat transfer coefficient of the spiral coil is KDN15>KDN20>KDN25. According to three different load conditions, the flow ratio of the composite cold and heat source is optimized and analyzed. The results show that as long as the flow ratio is properly controlled, the composite cold and heat source can meet the cooling requirements of the air-conditioning system under different working conditions. There is an optimal flow ratio between the heat sources. The greater the ratio R of the extreme working condition load change value to the standard working condition load value, the smaller the value of the optimal flow ratio, and it is not affected by the loop flow rate and the inlet water temperature change.

Mechanical Booster Pump-Assisted Thermochemical Mode for Low-Grade Heat Storage and Upgrading: A Thermodynamic Study

To assure stable and dependable functioning of the thermochemical energy storage (TCES) system under unstable low-grade heat temperatures, three mechanical booster pump-assisted TCES (MBP-assisted TCES) modes operating with SrBr2·H2O/H2O, LiOH/H2O, and CaCl2·H2O/H2O are proposed for the application of heat storage and upgrading. The operating modes are the MBP-assisted charging mode (A mode), MBP-assisted discharging mode (B mode), and MBP-assisted charging and discharging mode (C mode). A thermodynamic model is established to evaluate the influences of condensing temperature, compression ratio, MBP isentropic efficiency, and reaction advancement on the heat source temperature and system performance from both energy and exergy perspectives. The results indicate that compared with the other two modes, the B mode is more effective in reducing the heat source temperature and achieving better system performance. Compared to the conventional TCES mode, the proposed modes can operate at lower heat source temperatures that can be minimized by up to 21∼25°C by employing the B mode with a compression ratio of 3.0 at the condensing temperature of 24°C. The B mode with SrBr2·H2O/H2O exhibits the highest energy and exergy efficiencies that the coefficients of performance based on total energy input and electric power consumed (COPtotal and COPelec), and exergy efficiency varies in the range of 0.53∼0.59, 7.4∼19.6, and 0.78∼0.95, respectively. In contrast, CaCl2·H2O/H2O shows the lowest system performance, but a higher heat output temperature can be required. In addition, to maintain the MBP discharge temperature below 180°C, there is a maximum permitted compression ratio that varies depending on the operating modes, operating conditions, and working pairs. The findings of this research can be used as theoretical references and suggestions for selecting MBP-assisted TCES modes, operating conditions, and working pairs for low-grade heat storage and upgrading.

Dynamic Characteristic Study of Supercritical CO2 Recompression Brayton Cycle System

The supercritical carbon dioxide (SCO2) Brayton cycle has been regarded as the main development direction of future nuclear power generation by more and more scholars, due to its high environmental efficiency and high thermoelectric conversion rate. However, due to fluctuations in the operation of the primary loop of the system with nuclear energy, parameters such as the power of the heat source and the mass flow of the working medium in the system will change, which will affect the dynamic performance and operation of the SCO2 Brayton cycle system. Therefore, it is necessary to study the dynamic response of the system performance under disturbance conditions, analyze the operating characteristics of the SCO2 Brayton cycle system. In this paper, a comprehensive dynamic model of SCO2 recompression Brayton cycle, which analyzes the response curves of critical parameters under the disturbance of heat source heating power and system mass flow rate, is accurately developed based on Simulink software. In order to verify the validity of the proposed model, the simulation results are compared with the experimental results conducted by Sandia Laboratory under the same conditions. The results show that the model has high accuracy, and can reflect the dynamic response of system performance under parameter perturbation. In this paper, the closed-loop simulation is innovatively performed to show the dynamic response to step-change in the heat source power and mass flow rate. And the thermal efficiency is about 31.85%, when the system operates stably at the design point of working condition. If a disturbance is applied to the system, the temperature change will be mainly concentrated near the heat source of the cycle, and the change near the precooler will be relatively small. The change of the heat source power will lead to a large monotonic variation of cycle efficiency. By contrast, an inflection point in cycle efficiency will be resulted in by changing the system mass flow rate. The results of this paper would provide good approaches for the design, control, and improvement of the SCO2 Brayton cycle.

Modelling the Heat Loss of a Building

The aim of this paper is to calculate the heat loss and annual energy demand for heating of an administrative building for three variants of thermal-technical design and their evaluation. The heat losses were determined according to the legislation in force and in accordance with the normative requirements. The calculations made can be used in the next phase for the design of the heat source and heating system for heating and for the design of forced ventilation with heat recovery. Based on the optimum choice of technical equipment, it is also possible to evaluate the investment and operating costs for the installation of the different heating and ventilation concepts. Given the current significant increase in energy prices, the present topic is very topical.

Matching-design for inverter air-source heat pump system based on heating load characteristics of civil buildings

Although the inverter air-source heat pump (IASHP) and composite systems have a characteristic of energy conversion, the design of IASHP and the application of IASHP assisted with additional heat sources are absent based on the relationship between the demand side and supply side. Therefore, this paper proposes a heating load decomposition method to design IASHP with an auxiliary heat source system to offer users heating in severe cold regions. Specifically, the heating load decomposition method divides the heating load of the civil building into three regions by seeking heating energy balance points. It can get an optimal heating energy balance point with the best HSPF and an optimal design heating energy balance point with the best evaluating parameter. On these grounds, we produce an IASHP prototype. The experimental results confirm the superiority of the heating load decomposition method. Compared to the traditional design method, it improves by 6.5%-12.6% of heating capacity and 2.3%-17.4% of COP of IASHP porotype. Besides, the heating performance of IASHP assisted with an electric heating system selected by an optimal heating energy balance point is better than that of an independent IASHP heating system. In contrast, electric heating only pays 6.7% of the heating capacity of the IASHP unit operated at −27.0 °C of ambient temperature.

Rapid Identification of Economic Indicators of Integrated Energy Systems Based on Data Analysis

The construction of integrated energy systems has received widespread attention. In addition to system design and operating optimization, clarifying the internal relationship between the project’s own characteristics and its economic indicators is also important for high-value project selection and implementation. Based on various energy prices and the climatic characteristics of typical cities, 60 integrated energy supply projects in 4 typical cities were used as a case study, and the cold and heat source system solutions with the shortest investment payback period for each project were calculated through a system optimization model. We calculated the correlation coefficient between the initial investment of system equipment, annual energy supply, annual energy sales revenue, annual equivalent full-load energy supply hours, initial equipment investment indicators for annual unit energy supply, and the project’s static investment payback period. The key factors affecting the static investment payback period of the project were identified. The results show that, under the optimal system scheme, even for buildings of the same type in the same area, the economic indicators of different integrated energy projects are still quite different. Under the current design, operation, and operation conditions, load distribution is the decisive factor for the economic feasibility of the project. The static investment payback period of the project can be quickly calculated based on the equivalent full-load energy supply hours of the project throughout the year. Compared with the current numerical and system dynamics model for point-to-point single system optimizing modeling, the proposed statistical regression model can help reveal the main factors of integrated energy system’s economically feasible.

Physics-Informed Deep Reversible Regression Model for Temperature Field Reconstruction of Heat-Source Systems

Temperature monitoring during the life time of heat source components in engineering systems becomes essential to guarantee the normal work and the working life of these components. However, prior methods, which mainly use the interpolate estimation to reconstruct the temperature field from limited monitoring points, require large amounts of temperature tensors for an accurate estimation. This may decrease the availability and reliability of the system and sharply increase the monitoring cost. To solve this problem, this work develops a novel physics-informed deep reversible regression models for temperature field reconstruction of heat-source systems (TFR-HSS), which can better reconstruct the temperature field with limited monitoring points unsupervisedly. First, we define the TFR-HSS task mathematically, and numerically model the task, and hence transform the task as an image-to-image regression problem. Then this work develops the deep reversible regression model which can better learn the physical information, especially over the boundary. Finally, considering the physical characteristics of heat conduction as well as the boundary conditions, this work proposes the physics-informed reconstruction loss including four training losses and jointly learns the deep surrogate model with these losses unsupervisedly. Experimental studies have conducted over typical two-dimensional heat-source systems to demonstrate the effectiveness of the proposed method.

A Novel Poi Temperature Prediction Method for Heat Source System Based on Graph Convolutional Networks

A Novel Poi Temperature Prediction Method for Heat Source System Based on Graph Convolutional Networks

Fault Detection and Diagnosis in Building Heat Source Systems Using Machine Learning

Fault Detection and Diagnosis in Building Heat Source Systems Using Machine Learning

A Novel Poi Temperature Prediction Method for Heat Source System Based on Graph Convolutional Networks

A Novel Poi Temperature Prediction Method for Heat Source System Based on Graph Convolutional Networks

Heating Systems for Small, Scattered and Remote Residential Areas in the Tibetan Plateau

This paper targets the heating needs of small, scattered and remote residential areas in the Tibetan Plateau. Considering the severe cold, high altitude, high radiation intensity, long sunshine duration and large temperature difference between day and night, etc. in this region, through the comparative analysis of the performance of heating terminals and heat source systems, it is proposed in this paper that the multi-energy complementary intelligent energy and clean heating approach can effectively reduce operating and maintenance costs, mitigate pollutant emissions and improve the indoor heating environment. Then, with Pagri Town, Shigatse City, Tibet as the pilot area, the multi-energy complementary smart energy and clean heating approach (with solar energy storage heat pump as the heat source + radiators as the heating terminal) was actually applied in the project. Through analysis of the indoor and outdoor temperature changes, electricity consumption and operating costs during the heating period of the pilot project, it is finally concluded that the heating model with solar energy storage heat pump as the heat source + radiators as the heating terminal is a rational choice for the heating systems for small, scattered and remote residential areas in the Tibetan Plateau.

Study on energy efficiency and economic performance of district heating system of energy saving reconstruction with photovoltaic thermal heat pump

Actively promoting the reconstruction of clean heating is the key direction of the “Planning for clean heating in winter in northern China (2017–2021)”. The photovoltaic thermal heat pump system was introduced in this paper to improve the comprehensive energy efficiency and reduce the operation energy consumption of the heat source system, which provided a new idea for the energy saving reconstruction of clean district heating. In order to verify the feasibility of the energy saving reconstruction by photovoltaic thermal heat pump, following studies were carried out in this paper: First, the integrated energy system engineering based on photovoltaic thermal heat pump was constructed to study the heating performance of the system in winter. Subsequently, the prediction model of heating performance based on back propagation neural network was established and optimized to simulate the heating performance throughout the year. Then, the calculation model of district heating system was established and the evaluation method of system operation energy efficiency and economic performance based on “equivalent electricity consumption of heating” was introduced. Finally, a residential area of Dalian was taking as an example to study the economic performance of energy saving reconstruction of district heating system based on three conventional heat sources by photovoltaic thermal heat pump. The results showed that after the capacity expansion and energy saving reconstruction based on photovoltaic thermal heat pump were conducted, the payback period of energy saving reconstruction investment was 5 years. Besides, with the increase of the configuration ratio of photovoltaic in the system from 1 to 2, the payback period was further shortened to 3 years.

Analysis and Optimization of Saline-alkaline Water Comprehensive Utilization System

On the basis of the previous field experiment and the actual situation in Xinjiang, four saline-alkaline water comprehensive utilization systems are proposed to optimize concentration and desalination process. Based on chemistry, thermodynamics and heat transfer, combined with economic costs and benefits, steam production and entransy are analyzed in this paper, the results show that the comprehensive efficiency of the dual heat source system is better than that of the single heat source system. Two-stage dual heat source system with series and parallel multi pass heat collecting has the best efficiency, but the comprehensive efficiency is similar to that of single-stage dual heat source system. These systems have their own strengths, which provide reference for brine treatment in salinization areas.

Energy Saving and Economic Evaluations of Exhaust Waste Heat Recovery Hot Water Supply System for Resort

The objective of this study is to investigate the energy savings and economics of the hot water supply system for the luxury resort. The hot water was generated using the waste heat from the exhaust gas heat (EGH) of internal combustion engine (ICE) installed at the luxury resort. The capacity and characteristics of waste heat source, flow demand and supply system of hot water were surveyed, and data is collected from the real system. The new heat exchanger system which utilizes the EGH to produce the hot water is designed considering the dew point temperature and the back pressure of exhaust gas system. The results show that the proposed system could supply hot water at a temperature of 55 °C corresponding to the present resort demand of 6 m3/h using EGH of ICE at 20% load. The proposed system could achieve the saving of 400 L/day in diesel oil (DO) fuel consumption and the payback time of new system could be evaluated as 9 months. The proposed system could produce hot water of 14 m3/h at 25% of engine load and 29 m3/h at full engine load which are sufficient to satisfy the regular and maximum hot water demand of resort. The presented results show the capability of the proposed system to satisfy the current hot water demand of resort and suggest the larger potential to save energy by recovering EGH of ICE. The novelty of the present work involves detailed methodology to design heat exchangers and evaluate system economics for hot water supply system based on EGH of ICE.

Optimal operation of heat source and air conditioning system with thermal storage tank using nonlinear programming

In this paper, we consider the optimal operations of a thermal system for heat source and air conditioning system with a thermal storage tank using nonlinear programming. Firstly, we develop the mathematical model of the system components by applying the energy and mass balance principles. Secondly, the static balance of the system model is validated by the operational data. Thirdly, by applying the nonlinear programming method, IPOPT (Interior Point OPTimizer), to the mathematical model, we show the optimal operations of a thermal system under variable conditions of chilled water temperature, such as the number of person, heat generating equipment, outdoor and indoor air conditions. Finally, dynamic simulation results showed that, the variable set points of the chilled water temperature for thermal storage tank have an effect on reducing the running cost of a day.

Scheme design and economic analysis of an office building’s cold and heat source system in hot-summer and cold-winter zone

In the context of green development and sustainable development, in response to the national policy of “carbon neutrality and peak carbon dioxide emissions”, we will fully implement clean energy heating and reduce air pollution. Air energy is the representative, bringing the comfortable, efficient, safe and energy-saving environment to people. For an office building in Nanjing, which is located in hot-summer and cold-winter zone, an air source heat pump unit is designed as a cold and heat source system to meet the demand for heating in winter and cooling in summer. At the same time, compared with the traditional cold and heat source system which is designed central heating in winter and multi-line refrigeration in summer, the result of economic analysis shows that the use of air source heat pump as the cold and heat source system of office buildings is more economical and energy-saving. It is suitable to popularize and apply in China’s hot-summer and cold-winter zone.

Analysis on Air Conditioning Heat Source and Conveyance System Design Specifications Using Input Data from a Calculation Program to Confirm Compliance with Building Energy Code

Analysis on Air Conditioning Heat Source and Conveyance System Design Specifications Using Input Data from a Calculation Program to Confirm Compliance with Building Energy Code

New global thermal numerical model of vertical U-tube ground heat exchanger

This paper presents a new numerical model of the vertical U-tube ground heat exchanger (GHE). Objective of creating the new model was to obtain more accurate, detailed and reasonably fast simulation of the GHE system, which guarantees proper sizing of such a system during design process. Different approaches for modelling GHE are described with emphasis on the new thermal resistance model (TRM) of an U-tube GHE. The 1D model of the heat transfer between working fluid of a GHE and the borehole is applied. This model was coupled with a 3D model of heat transfer in the ground surrounding the GHE. The global model of a ground heat source system is obtained by connecting segments representing volume of ground influenced by each of the GHE. The paper describes a discretization scheme, coupling method, boundary conditions and limitation of the proposed model. The simulation results and the measured in-situ data from literature are compared, it differ by 3% taking into account the heat extracted from the ground. Simulation results of heat extracted from the ground, working fluid temperature and ground temperature distributions around GHE are presented. Conclusions concerning obtained results shows possible use for simulation of the operation of GHE.