Thermal performance and energy saving investigation in a modified baseboard radiator and compare it with conventional heating systems—Experimental and CFD approach

In the present work, thermal performance of a new modified baseboard radiator is investigated experimentally based on the European Standard EN-442. Temperature distribution and thermal comfort conditions of the floor heating system and panel radiator is compared with the present system numerically. To validation of the simulation results, a comparison has been made between the simulation and the experimental obtained results. Comparison shows that there is a good agreement between them. The heat output rate of the new system increased about 46.06% compared with conventional baseboard radiant model and also the baseboard heating system is capable of providing better thermal comfort conditions than two other systems. Energy consumption in three systems is investigated experimentally by smart temperature control mechanism. Results show that energy consumption in the baseboard radiant is 83.03% and 55.96% lower than floor heating system and panel radiator, respectively.     

CFD simulation of a Gifford–McMahon type pulse tube refrigerator

Pulse tube refrigerator has the advantages of long life and low vibration over the conventional cryocoolers, such as Gifford–McMahon (GM) and Stirling coolers because of the absence of moving parts in low temperature. This paper performs a two-dimensional computational fluid dynamic (CFD) simulation of a Gifford–McMahon type double inlet pulse tube refrigerator (DIPTR), operating under a variety of thermal boundary conditions. A commercial Computational Fluid Dynamics (CFD) software package Fluent 6.1 is used to model the oscillating flow inside a pulse tube refrigerator. Helium is used as working fluid for the entire simulation. The simulated DIPTR consists of a transfer line, an after cooler, a regenerator, a pulse tube, a pair of heat exchangers for cold and hot end, an orifice valve with connecting pipe, a double inlet valve with connecting pipe and a reservoir. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary condition is sinusoidal pressure inlet by user defined function at one end of the tube and constant temperature or heat flux boundaries at the external walls of the hot end and cold-end heat exchangers. The general results, such as the cool down behaviors of the system, phase relation between mass flow rate and pressure at pulse tube section and the temperature profile along the wall of the cooler are presented.The simulation shows the minimum decrease in temperature at cold-end heat exchanger for a particular combination of cryocooler assembly. The CFD simulation results are compared with available experimental data. Comparisons show that there is a reasonable agreement between CFD simulation and experimental results.     

严寒地区单体建筑太阳能-相变墙系统蓄热特性研究

利用太阳能对水加热并通入相变墙进行蓄热，对减少严寒地区单体建筑供热能耗有重要意义。以大庆市某单体建筑为例，结合该地区太阳能分布特点及建筑热负荷大小，对适用于该地区的太阳能-相变墙系统进行集热与储热能力计算，并采用CFD方法研究单一工况下该系统的热工变化规律及不同热水参数、换热管规格对相变墙蓄热特性的影响。结果表明：该相变墙热稳定性良好，但受自然对流影响，底部相变材料熔化较慢；管径DN25、入口流速0.3m/s、供水温度310.15K、回水温度309.15K、管间距107mm可使相变材料在4小时内完成蓄热，平均节能率为31.8%。研究结果可望为降低严寒地区建筑供热能耗提供新思路。     

Evaluation and optimization of water source heat pump for district heating: A case study in steel plant

Using high-temperature heat pump technology to recover waste heat of circulating cooling water in a steel plant for central heating system not can only reduce the temperature of circulating cooling water to meet the needs of smelting process but also can save energy and protect environment as well as bring great economic benefits to steel plant that can sell heat to the heat users. The energy consumption equation of heat pump central heating system was established based on the energy consumption of heat pump, energy consumption of water pump, and heat loss. The optimal inlet water temperature, inlet flow rate, and the number of operating heat pump modules at different outdoor temperatures were calculated by genetic algorithm. The superiority and operating control strategy of heat pump central heating system were discussed. The results show that with the increase of outdoor temperature, the optimal inlet flow rate and the number of operating heat pump module decrease. However, the inlet water temperature almost does not change. It is more suitable for the heat pump central heating system to change the inlet flow and the number of operating heat pump modules. The operating control strategy equation was established by linear fitting, which provides guidance for the engineering application of heat pump central heating system.     

Modeling and simulating the transcritical CO2 heat pump system

In this paper, a mathematical model for steady-state simulation of transcritical CO₂ water-to-water heat pump system with an expander has been developed. It is used to simulate the performance of transcritical CO₂ system with CO₂ expander prototype. Simulated results are compared with experimental data to verify the accuracy of the simulation model. The comparison results show the average deviation of about 15% for COP_c(cooling coefficient of performance) and COP_h(heating coefficient of performance), about 17% for cooling and heating capacity at experimental high pressure ranges. With this model, which has been validated in a limited high pressure range, the influence of water mass flow rate and water inlet temperature of both evaporator and gas cooler on the performance of transcritical CO₂ expander system is analyzed. The results show that decreasing inlet temperature and increasing mass flow rate of cooling water cannot only increase the system performance but also reduce the optimal heat rejection pressure, at which the maximum COP (coefficient of performance) can be obtained. For chilling water, increasing its inlet temperature and mass flow rate is favorable for increasing the system performance, while the optimal heat rejection pressure does not vary very much.     

Comparison of energy and exergy analysis of fossil plant,ground and air source heat pump building heating system

The energy and exergy flow for a space heating systems of a typical residential building of natural ventilation system with different heat generation plants have been modeled and compared. The aim of this comparison is to demonstrate which system leads to an efficient conversion and supply of energy/exergy within a building system.The analysis of a fossil plant heating system has been done with a typical building simulation software IDA–ICE. A zone model of a building with natural ventilation is considered and heat is being supplied by condensing boiler. The same zone model is applied for other cases of building heating systems where power generation plants are considered as ground and air source heat pumps at different operating conditions. Since there is no inbuilt simulation model for heat pumps in IDA–ICE, different COP curves of the earlier studies of heat pumps are taken into account for the evaluation of the heat pump input and output energy.The outcome of the energy and exergy flow analysis revealed that the ground source heat pump heating system is better than air source heat pump or conventional heating system. The realistic and efficient system in this study “ground source heat pump with condenser inlet temperature 30 °C and varying evaporator inlet temperature” has roughly 25% less demand of absolute primary energy and exergy whereas about 50% high overall primary coefficient of performance and overall primary exergy efficiency than base case (conventional system). The consequence of low absolute energy and exergy demands and high efficiencies lead to a sustainable building heating system.     

Energy consumption of a residential building: comparison of conventional and RES-based systems

The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved.     

Parametric Analysis of Solar Heating and Cooling Systems for Residential Applications

Abstract

In this paper, a parametric analysis of two solar heating and cooling systems, one using an absorption heat pump and the other one using an adsorption heat pump, was performed. The systems under investigation were designed to satisfy the energy requirements of a residential building for space heating/cooling purposes and domestic hot water production. The system with the absorption heat pump was analyzed upon varying (i) the solar collectors’ area, (ii) the volume of the hot water storage, (iii) the volume of the cold water tank, and (iv) the climatic conditions. The system with the adsorption heat pump was evaluated upon varying (i) the inlet temperature of hot water supplied to the adsorption heat pump, (ii) the volume of the hot water storage, (iii) the volume of the cold water tank, and (iv) the climatic conditions. The analyses were performed using the dynamic simulation software TRNSYS in terms of primary energy consumption, global carbon dioxide equivalent emissions, and operating costs. The performance of the solar heating and cooling systems was compared with those associated with a conventional system from energy, environmental and economic points of views in order to evaluate the potential benefits.     

Optimal design of a novel nested-nozzle ejector for PEMFC's hydrogen supply and recirculation system

The ejector-based hydrogen supply and recirculation system (HSRS) for a Proton Exchange Membrane Fuel Cell (PEMFC) system has the advantages of compact size and zero power consumption, compared with the HSRS using a recirculation pump. However, the conventional ejector with a single venturi nozzle can only function within a narrow power range of the PEMFC system due to its restricted primary inlet pressure. This study proposed a novel ejector design with nested nozzles to solve this problem. The key geometric parameters, including the nozzle diameters of a large nozzle (BN), a small nozzle (SN), and the axial distance between two nozzles, were optimized using CFD simulations to obtain the maximum entrainment capability. The BN mode is responsible for the stack's higher load operations, while the SN mode supports the lower power operations. Additionally, a bypass was used parallel to the nested-nozzle ejector in the HSRS to extend the ejector operating range further. The consistent CFD simulation and testing results of the nested-nozzle ejector showed effective hydrogen entrainment capability between 9% and 100% of power output for a 150 kW PEMFC stack. Moreover, the new nested-nozzle ejector HSRS showed much-reduced anode inlet pressure fluctuation compared to the HSRS using two conventional ejectors.     

Performance of an experimental ground-coupled heat pump system for heating,cooling and domestic hot-water operation

The ground-coupled heat pump (GCHP) system is a type of renewable energy technology providing space heating and cooling as well as domestic hot water. However, experimental studies on GCHP systems are still insufficient. This paper first presents an energy-operational optimisation device for a GCHP system involving insertion of a buffer tank between the heat pump unit and fan coil units and consumer supply using quantitative adjustment with a variable speed circulating pump. Then, the experimental measurements are used to test the performance of the GCHP system in different operating modes. The main performance parameters (energy efficiency and CO₂ emissions) are obtained for one month of operation using both classical and optimised adjustment of the GCHP system, and a comparative analysis of these performances is performed. In addition, using TRNSYS (Transient Systems Simulation) software, two simulation models of thermal energy consumption in heating, cooling and domestic hot-water operation are developed. Finally, the simulations obtained using TRNSYS are analysed and compared to experimental data, resulting in good agreement and thus the simulation models are validated.     

Numerical analysis of temperature non-uniformity and cooling capacity for capillary ceiling radiant cooling panel

Capillary ceiling radiant cooling panel is a high temperature cooling system, which could pose low energy consumption to meet thermal comfort requirements. A computational fluid dynamics (CFD) simulation study on heat transfer of chilled water flow in the capillary of ceiling radiant cooling panel was performed to attain surface temperature distributions and cooling capacities. Six influencing factors included chilled water inlet parameters, conditions of gypsum plaster and capillary mats structural parameters were considered to obtain the complicated relationships between capillary radiant panel conditions and heat transfer performance. The index of temperature non-uniformity coefficient was proposed to evaluate temperature profiles of ceiling panel surface. The results of the simulation were compared with the values depicted in ASHRAE Handbook and good agreement had been achieved. The average difference between simulation results and the values reported by ASHRAE handbook was within the region of 15%. The research results showed that temperature non-uniformity coefficient was negatively correlated with temperature of chilled inlet water (linear correlation), water velocity (correlation coefficient R = −0.85), and pipe diameter (correlation coefficient R = −0.93), but positively and linearly correlated with tube spacing. Cooling capacity was found to have negative linear correlation with temperature of chilled inlet water, covering thickness and tube spacing.     

Simulation of the thermal performance of a hybrid solar-assisted ground-source heat pump system in a school building

A hybrid solar-assisted ground-source heat pump (SAGSHP) system was designed, in the frame of an energy upgrade study, to serve as a heating system in a school building in Greece. The main scope of this study was to examine techniques to reduce the capacity of the heating equipment and to keep the primary energy consumption low. Simulations of the thermal performance of both the building and of five different heating system configurations were performed by using the TRNSYS software. The results are presented in this work and show that the hybrid SAGSHP system displays the lower primary energy consumption among the systems examined. A conventional ground-source heat pump system has the same primary energy consumption, while the heat pump’s capacity is double and the ground heat exchanger 2.5 times longer. This work also highlights the contribution of simulation tools to the design of complex heating systems with renewable energy sources.     

模糊理论结合PID控制方法在集中供热系统中的应用

集中供热系统是一个具有大惯性、纯滞后特点的复杂非线性系统,为了提高系统稳定性,实现合理用热,将模糊自适应控制和常规PID控制两种控制方法结合并使用模糊工具箱进行了系统仿真实验。实际结果表明,同常规的PID控制方法相比,模糊自适应PID控制方法有效提高了集中供热系统的鲁棒性、稳定性和自适应的能力。在集中供热的复杂系统中,能更好的满足用户的热需求     

Experimental validation of a CFD and an ε-NTU model for a large tube-in-tank PCM system

An experimental validation for a computational fluid dynamics (CFD) and an effectiveness-number of transfer units (ε-NTU) model for tubes in a large phase change material (PCM) tank has been conducted. The inlet and outlet heat transfer fluid (HTF) temperatures as well as twelve temperature locations in the PCM tank were compared with the CFD results. The average effectiveness of the phase change process of each experimental point was also compared with results from the CFD as well as the ε-NTU models. From this study, it was concluded that the CFD model and the ε-NTU model developed can accurately predict the behaviour of the thermal storage system during the freezing process. There are however, discrepancies in the melting process due to the exclusion of the effect of natural convection in the models. Using the experimental results, an effective thermal conductivity has been determined to account for buoyancy for various distances of tubes. The paper gives details of the CFD model of the phase change thermal storage system, and presents results from the CFD model, experiments and ε-NTU model.     

小型燃气轮机CCHP系统变工况性能入口加热调控研究

提出了一种利用冷热电联产系统(CCHP)低温烟气与环境空气混和加热控制压气机入口温度,提升燃气轮机冷热电系统变工况性能的方法,并以1.9 MW小型燃气轮机OPRA16为例,建立了CCHP系统模型,分析了调控方法的效果、机理。结果表明,入口混和加热可以有效改善冷热电联产系统变工况下系统性能,并扩展系统节能运行范围。与传统燃料流量调控方法相比,新型调控手段下夏季制冷与冬季供热模式下系统节能率分别提升5.7%和21.6%。     

Optimization of the heat exchanger in a flat plate indirect heating integrated collector storage solar water heating system

Due to the environmental impact of energy usage, consumers need to be encouraged to use renewable energy sources such as solar energy. The indirect heating flat plate integrated collector storage solar water heating system is one of the compact systems for domestic water heating. It incorporates the collection of a solar energy component and a hot water storage component in one unit. The objectives of this study were to investigate the effect of different parameters on the thermal performance of this system with the aim of reducing both the initial and the running costs. The outlet service water temperature was used as a measure of performance, because it is an indicator of the energy acquired from the solar radiation. The continuity, momentum and energy equations of the fluids involved in the system were numerically solved in a steady state condition, using FLUENT software. Three-D CFD models were developed and validated using previous experimental results. A standard k–ω turbulent model was used in the optimization of the heat exchanger because it produced good agreement with the experimental results. The surface-to-surface radiation model was included. The effect of single and double row heat exchangers with different lengths was investigated. Circular and elliptic cross-section pipes were also examined. Mass flow rates of 500 and 650 L/h were chosen. The results showed that the single row HX of 10.8 m length for both the elliptical and type B tube gave high service water outlet temperature (acceptable for heat exchanger design) and with low pumping power. This resulted in an increase in the thermal efficiency and a significant reduction in both the initial and the operating costs of the system.     

板坯加热炉内加热特性的数值分析

以某公司热轧厂常规与双蓄热烧嘴组合供热的板坯加热炉为研究对象,建立该加热炉炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,得到炉内稳态的速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与"黑匣子"实验测量数据吻合良好。本文给出的板坯加热特性计算方法为研究加热炉新工艺、优化板坯加热温度制度提供了科学依据。     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

太阳能与空气源热泵复合式供暖系统在西安地区的应用特性分析及评价

以西安地区的某个房间为研究对象,采用TRNSYS软件针对该房间分别应用太阳能集热系统、空气源热泵系统及太阳能与空气源热泵复合式供暖系统进行供暖时的情况进行了分析。首先,建立了太阳能与空气源热泵复合式供暖系统的仿真模型,并对其正确性进行了实验验证;其次,对比分析了在3种运行模式下各个系统的运行特性;最后,以系统能耗及能效比(COP)等参数为指标,对太阳能与空气源热泵复合式供暖系统的性能进行了评价。结果表明:在整个供暖期内,太阳能与空气源热泵复合式供暖系统的总能耗为284.61kWh,其中,空气源热泵消耗的电能为264.10kWh;该复合式供暖系统的太阳能保证率为30.71%,平均COPc-sys为3.04,比单独采用空气源热泵系统进行供暖时的平均COPhp-sys提高了0.33,这表明太阳能与空气源热泵复合式供暖系统在西安地区具有较好的节能优势。这一研究结果为太阳能与空气源热泵复合式供暖系统在西安地区的应用及优化奠定了理论基础,对其推广应用具有重要意义。     

Design and testing of the Organic Rankine Cycle

We propose a new type of environmentally friendly system called the “Organic Rankine Cycle” (ORC) in which low-grade heat sources are utilized. This system combines a circulated thermosyphon with a turbine system. The working fluid used in this study is an organic substance which has a low boiling point and a low latent heat for using low-grade heat sources. A numerical simulation model of the ORC is made in order to estimate its optimum operating conditions. An experimental apparatus is also made in this study. From the numerical simulation, it is suggested that HCFC-123 gives higher turbine power than water which is a conventional working fluid, and operating conditions where saturated vapor at the turbine inlet would give the best performance. From the experimental results, HCFC-123 improves the cycle performance drastically. In addition, the turbine made for trial use in this study gives good performance.