Optimization of Serial Combined System of Ground-Coupled Heat Pump and Solar Collector

A mathematical optimization model was set up for a ground-solar combined system based on in-situ experimental results, in which the solar collector was combined serially with a ground-coupled heat pump (GCHP). The universal optimal equations were solved by the constrained variable metric method considering both the per-formance and economics. Then the model was applied to a specific case concerning an actual solar assisted GCHP system for space heating. The results indicated a system coefficient of performance (COP) of 3.9 for the optimal method under the serial heating mode, and 3.2 for the conventional one. In addition, the optimum solution also showed advantages in energy and cost saving, leading to a 16.7% improvement in the heat pump performance at 17.2% less energy consumption and 11.8% lower annual cost, respectively.

An Analytical Model for the Thermal Assessment of a Vertical Double U-Tube Ground-Coupled Heat Pump System in Steady-State Conditions

An analytical model was built to predict the thermal resistance of a vertical double U-tube ground-coupled heat pump that operates under steady-state conditions.It included a geometry obstruction factor for heat transfer throughout the backfill medium due to the presence of the second loop.The verification of the model was achieved by the implementation of five different borehole configurations and a comparison with other correlations in the available literature.The model considered a U-tube spacing range between(2)and(4)times the U-tube outside diameter producing a geometry configuration factor range of(0.29-0.6).The results of the model were utilized for the assessment of the DX ground heat exchanger coupled heat pump system.For similar geometrical configurations,the borehole thermal resistance experienced a decrease as the geometry factor increased.The single U-tube borehole thermal resistance was higher than that of the double U-tube heat exchanger by(10-27)%for the examined geometry configurations.The borehole thermal resistance at tube spacing of twice the tube diameter was higher than the predicted value at the triple diameter and fell in the range of(18-34)%.

Energy saving analysis of a hybrid ground-coupled heat pump project

A hybrid ground-coupled heat pump（HGCHP）project in Nanjing,China is chosen to analyze the building energy-consumption properties in terms of different control strategies,building envelope and the terminal air-conditioning system.The HGCHP uses a supplemental heat rejecter to dissipate extra thermal energy to guarantee underground soil heat balance.The software EnergyPlus is employed to simulate the project and design the heat flow of the cooling tower and the borehole heat exchanger（BHE）.Then two feasible control strategies for the cooling tower and the borehole heat exchanger are proposed.The energy-saving potential of the building envelope is analyzed in terms of the surface color of the wall/roof.With the same terminal system,it is found that in the cooling season the heat flow of the insulated building with black wall/roof is 1.2 times more than that with white wall/roof.With the same insulated building and gray wall/roof,it is concluded that the heat pump units for a primary air fan-coil system show an annual energy consumption increase of 44.7 GJ compared with a radiant floor system.

Performance analysis of deep borehole heat exchangers for decarbonization of heating systems

Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.

Scanning PIV Method and Its Application to the Calorimetry of Ground Source Heat Pump Systems

Ground source heat pump (GSHP) systems that use a direct expansion method?are expected to have higher energy-saving performance than conventional air conditioning systems. The heat transfer rate is evaluated by measuring the temperature, humidity, and flow rate at the indoor unit of the GSHP system. However, it is difficult to evaluate the flow rate by measuring the flow velocity distribution at the outlet of the indoor unit. In this study, the Scanning PIV method is proposed to improve the accuracy of the flow rate measured by hot wire anemometers. The flow rates obtained by the hot wire anemometers were 60.6% and 15.2% higher than those from the PIV method during cooling and heating operation, respectively. Compensation formulas are generated using the results of the Scanning PIV method to correct the measurements from the hot wire anemometers. This compensation formula reduced the error generated by the nonuniformity of velocity distribution. It was 60.6% to 2.5% in cooling operation and 15.2% to 0.9% in heating operation, respectively. The compensation formulas were applied to evaluate the performance of a GSHP system, and the result shows that the GSHP system provides improved performance stability compared to traditional air conditioning systems.

Case Studies of Energy Saving and CO₂Reduction by Cogeneration and Heat Pump Systems

This paper describes two case studies: 1) a cogeneration system of a hospital and 2) a heat pump system installed in an aquarium that uses seawater for latent heat storage. The cogeneration system is an autonomous system that combines the generation of electrical, heating, and cooling energies in a hospital. Cogeneration systems can provide simultaneous heating and cooling. No technical obstacles were identified for implementing the cogeneration system. The average ratio between electric and thermal loads in the hospital was suitable for the cogeneration system operation. An analysis performed for a non-optimized cogeneration system predicted large potential for energy savings and CO2 reduction. The heat pump system using a low-temperature unutilized heat source is introduced on a heat source load responsive heat pump system, which combines a load variation responsive heat pump utilizing seawater with a latent heat-storage system (ice and water slurry), using nighttime electric power to level the electric power load. The experimental coefficient of performance (COP) of the proposed heat exchanger from the heat pump system, assisted by using seawater as latent heat storage for cooling, is discussed in detail.

Heat balance of solar-soil source heat pump compound system

Based on the state-of-the-art studies of solar-soil source heat pump compound system, operation patterns of solar-soil compound system were analyzed, particularly the advantages of parallel operation pattern. It is found that parallel operation pattern is better for solar-soil compound system. Furthermore, the heat balance issue of solar-soil compound system was emphatically analyzed from four aspects, which were annual analysis of heating and cooling load, the heat exchange of ground heat exchanger, capacity determination of solar-assisted heat sottrce and heat balance calculation of solar-soil compound system. Moreover, annual rate of heat balance in a solar-soil source heat pump compound system was calculated with a case study. It is shown that the annual heat unbalance ratio is 19%, which is less than 20%. As a result, the practical solar-soil compound system can basically maintain the heat balance of soil.

Applicability of sewage heat pump air-conditioning system

A sewage heat pump system and its application based on a project in Chongqing,China,were discussed. Based on the sewage conditions,a feasibility analysis of the sewage heat pump air conditioning system was conducted. The theoretical and quantitative calculations indicate that sewage flux in the city sewage main pipe in the project can satisfy heat exchange requirements,and taking water from the pipes has relatively small influence on the pipe net in summer and winter. The sewage heat pump air-conditioning system can save 21.5% operating cost in one year,which is energy efficient and environmentally friendly.

Economic Model Predictive Control for Hot Water Based Heating Systems in Smart Buildings

This paper presents a study to optimize the heating energy costs in a residential building with varying electricity price signals based on an Economic Model Predictive Controller (EMPC). The investigated heating system consists of an air source heat pump (ASHP) incorporated with a hot water tank as active Thermal Energy Storage (TES), where two optimization problems are integrated together to optimize both the ASHP electricity consumption and the building heating consumption utilizing a heat dynamic model of the building. The results show that the proposed EMPC can save the energy cost by load shifting compared with some reference cases.

结合空气源热泵能耗分析及光伏辅助的建筑供热设计方法

随着国家对北方地区冬季集中供热方式的普及,煤燃烧供暖方式造成的环境污染和能源消耗问题更加严重。为了优化北方建筑供热系统的能耗问题,研究设计了光伏辅助的空气源热泵供热系统。研究方法通过数值模拟构建了建筑能耗模型,结合供热需求优化了空气源热泵供热系统,增设了保温层和除霜模式。同时,研究评估了建筑供热系统的热负荷,以最小二乘法修正热泵的实际效能。并借助光伏供电方式协调了空气源热泵的能耗,结合供热系统的整体效益优化了供热控制系统。研究结果显示,光伏辅助的空气源热泵平均供热量可以达到23.74 kW,在模拟环境下的整体节能效益为77.19%~83.26%,相较于传统锅炉供热节能效益提升了59.24%。可见改进供热系统在同等制热效果下表现出更高的节能效益。因此,改进供热设计在节能效果上具有更高效的节能效果,为建筑供暖提供了一种环保节能的供热方式。

Evaluation of non-azeotropic mixtures containing HFOs as potential refrigerants in refrigeration and high-temperature heat pump systems

With the increasing environmental concern on global warming, hydrofluoro-olefin (HFOs), possessing low GWP, has attracted great attention of many researchers recently. In this study, non-azeotropic mixtures composed of HFOs (HFO-1234yf, HFO-1234ze(z), HFO-1234ze(e) and HFO-1234zf) are developed to substitute for HFC-134a and CFC-114 in air-conditioning and high-temperature heat pump systems, respectively. The cycle performances were evaluated by an improved theoretical cy-cle evaluation methodology. The results showed that all the mixtures proposed herein were favorable refrigerants with excel-lent thermodynamic cycle performances. M1A presented lower discharge temperature and pressure ratio and higher COPc than that of HFC-134a. The volumetric cooling capacity was similar to HFC-134a. It can be served as a good environmentally friendly alternative to replace HFC-134a. M3H delivered similar discharge temperature as CFC-114 did. And the COPh was 3% higher. It exhibits excellent cycle performance in high-temperature heat pump and is a promising refrigerant to substitute for CFC-114. And the gliding temperature differences enable them to exhibit better coefficient of performance by matching the sink/source temperature in practice. Because the toxicity, flammability and other properties are not investigated in detail, ex-tensive toxicity and flammability testing needs to be conducted before they are used in a particular application.

Experimental study on heat exchange of several types of exchangers

Aiming at the ground-coupled source heat pump that possesses the shortcomings of occupying larger land,this article studies the heat exchanged of heat exchanger in piling,and compares it with common heat exchangers buried directly. The result indicates that the heat exchanger makes the best use of structure of building,saves land,reduces the construction cost,and the heat exchanged is obviously more than exchangers buried directly. In winter condition,when W-shape pipe heat exchanger in pile foundation is 50 m deep and diameter is 800 mm,it transfers 1.2-1.3 times as large as the one of single U-shape buried directly at the flow rate of 0.6 m/s,whose borehole diameter is 300 mm. And in summer condition it does about 2.0-2.3 times as that of U-shape one.

太阳能-空气源热泵牧草干燥系统制热性能研究

以太阳能-空气源热泵牧草干燥系统为研究对象,通过系统不同工作模式的温升、恒温制热试验及带载试验,分析了温升速率、单位温升能耗、COP及除湿效率。研究结果表明:联合制热模式与太阳能单独制热相比,单位温升耗电量降低了86.2%,温升速率提高了99~112倍。联合制热模式与热泵单独制热试验相比,在温升过程中温升速率降低了7.7%~17.6%,单位温升耗电量降低8.0%;在恒温制热过程中,前者COP比后者提高了6.5%~11.1%,耗电量降低了5.8%~10.7%;在升温制热过程中前者COP比后者提高了6.0%~10.4%,耗电量降低了6.6%~11.1%。联合干燥模式比热泵单独干燥模式的SMER值高19.8%~36.2%。

光伏光热联合双源热泵系统运行模式研究(1):最佳切换模式验证

讨论了光伏光热联合双源热泵系统制热运行的最佳切换模式。利用TRNSYS软件建立了仿真模型,对双源(水源、空气源)热泵系统性能系数(COP_(s))进行了计算,提出以某时刻空气源热泵模式或水源热泵模式运行COP_(s)较大者优先运行作为COP_(s)切换模式。通过前期实验结果验证了模拟结果的正确性,并与常规的集热水箱温度切换模式进行了对比实验,验证了COP_(s)切换模式的有效性。结果表明,该实验系统以COP_(s)最佳切换模式运行时发电量和发电效率较集热水箱温度切换模式分别提高了5.35%和1.73%,耗电量降低了17.03%,COP_(s)提高了4.91%。

严寒地区空气源热泵耦合电磁能系统模拟运行研究

目的 为了促进空气源热泵耦合电磁能供热系统在严寒地区住宅建筑中的应用,研究该系统的运行性能和稳定性。方法 以沈阳地区某住宅建筑为例,应用Trnsys软件建立了空气源热泵耦合电磁能供热系统仿真模型,并用实测值对模型进行了验证;深入探讨空气源热泵耦合电磁能供热系统在供热期的运行特点,并与空气源热泵和电磁能供热系统分别进行比较。结果 空气源热泵耦合电磁能供热系统模型可靠,相对误差可以控制在15%以内;在供热期,室内平均温度可保持在17.97~21.84℃;空气源热泵耦合电磁能供热系统比电磁能供热系统的COP提高了59.17%,空气源热泵耦合电磁能供热系统CO_(2)减排量比空气源热泵和电磁能供热系统分别提高1.47%和59.50%。结论 空气源热泵耦合电磁能供热系统运行和COP变化更为稳定,系统环境效益更佳,室内热舒适性更高。

光伏幕墙辅助双源热泵系统在不同地区的多目标优化配置

为克服单一可再生能源应用的局限性,提出一种光伏幕墙辅助双源热泵系统。利用TRNSYS建立仿真模型,以系统能耗和生命周期成本为目标函数,采用非支配排序遗传算法(NSGA-Ⅱ),对不同地区系统配置规模进行多目标优化设计,并利用加权和法确定均衡解。结果表明:哈尔滨、长春、沈阳3个地区优化后的系统运行能耗比优化前分别增加5.9%、5.0%和3.9%,生命周期成本降低13.6%、17.1%和12.9%;与单目标优化相比,多目标优化在兼顾性能的前提下能明显降低生命周期成本,具有明显的优势。

R32热泵系统稳定性与变工况特性实验研究

实验研究了变热源进口温度工况和变热水进口温度工况下膨胀阀开度对R32热泵系统稳定性和系统性能的影响规律。结果表明:不同工况下系统存在不同的过热度振荡区间,且热源进口温度对起始振荡过热度的影响较显著,而热水进口温度对其影响则不明显;变热源进口温度(15~25℃)工况下,制热量随着过热度的变化呈现不同的变化规律,而其COP则呈现相同的变化规律,且系统均在过热度振荡区间内获得最大COP;变热水进口温度(30~40℃)工况下,制热量和COP均随着过热度的变化呈现相同的变化趋势,且两者均在过热度振荡区间内取得最大值;热源进口温度的升高和热水进口温度的降低均可使系统获得的最大制热量和最大COP增大,且两者在热源进口温度为25℃时分别为9.287 kW和4.646,而在热水进口温度为30℃时则分别为9.148 kW和5.665。

中深层地埋管热泵供热系统运行特性实测研究

通过大量工程实测研究,总结了中深层地埋管热泵供热技术的运行特性。中深层地埋管具有出水温度高、取热功率大、长期运行稳定的特点,为热泵系统提供了高品位的低温热源,以提升其运行性能;同时中深层地埋管自身存在间歇蓄热特性,能很好地满足建筑供热需求变化与柔性用能;无级变频热泵机组更适合与中深层地埋管匹配运行,节能减排效果显著;热源侧水系统具有小流量、大扬程,且阻力随着流量变化而大幅度变化的特性。研究结果可为提升该技术的供热性能提供关键指导。

风机转速对CO_(2)空气源热泵热水器性能影响的试验研究

为了定量探究CO_(2)空气源热泵热水器系统性能随风机转速的变化规律,通过试验研究了不同工况下,改变风机转速对排气压力、过热度、CO_(2)质量流量、系统制热量、系统总功耗以及制热性能系数COP的影响;利用响应曲面法对试验进行了优化分析,同时利用试验数据拟合了COP回归模型,并进行可信度分析;通过回归模型预测了系统的最优运行工况并进行试验验证。结果表明:在压缩机频率和电子膨胀阀(EEV)开度一定的情况下,存在着最佳风机转速;在45~85 Hz范围内,随着压缩机频率的提高,COP先增大后减小,增幅最高可达8.97%,各频率下COP最大时对应的最佳风机转速不断减小;随着EEV开度在35%~55%范围内不断增大,COP先增大后减小,增幅可达到6.6%,各EEV开度下COP最大时对应的最佳风机转速不断增大;当压缩机频率为65 Hz、EEV开度为50%时,对应的最佳风机转速为1000 r/min,系统COP达到峰值(4.09)。本文所拟合的COP回归模型最大误差为4.5%;预测系统最优运行工况为:压缩机频率68 Hz、EEV开度52%、风机转速956 r/min,此时系统COP最大,可达到4.29,预测误差为3.7%。本研究可为CO_(2)空气源热泵热水器系统保持高效运行提供理论指导。

基于恒热流法和恒温法的岩土热物性试验分析研究

目前岩土热物性测试仪采用的方法包括两种:恒热流法和恒温法,通过介绍两种测试方法的区别及模型算法,以北京市某公建项目岩土热物性测试结果为基准,利用TRNSYS软件分别模拟了恒热流法和恒温法的测试工况,针对模拟结果展开分析研究。经对比,试验时间至48 h时,两种测试方法利用软件模拟出的延米换热量与现场测试结果的误差在10%以内,表明若已知项目周边的地层热物性参数如地层的导热系数、热扩散率等,可将软件模拟结果作为前期地埋管系统设计的依据,并作为后续热物性勘察结果验证的参考数据。此外,根据模拟结果,由于夏季地埋管流体在设计工况下与土壤的温差值较大,为了使流体尽快达到设计工况点,恒温法测试时应选用较大的功率,否则48 h内的测试值结果与实际值偏差较大。