太阳能辅助二氧化碳热泵热水系统实验研究

利用实验的方法,研究了太阳辐照度、外界气温和风速、初始水温、蒸发器出口温度和压力等对太阳能辅助二氧化碳热泵热水系统运行状况和COP的影响。实验结果表明,系统COP随初始水温的升高而增大;太阳辐照度、外界温度和风速对热泵系统性能的影响主要体现在对系统循环水温的影响;在一定范围内,蒸发压力和蒸发温度越高,热泵系统的COP越大。     

小型太阳能吸收式空调系统的仿真研究

以20 kW太阳能溴化锂单效吸收式制冷系统为仿真对象,从制冷量及系统能效比(COP)两方面分析了热媒水、冷却水、冷冻水对系统的影响,同时,考虑到太阳辐射与其他外界环境的不断变化,在仿真过程中将模糊控制与PID(比例-积分-微分)控制相结合,使得电加热量不断做出调整,以更节能的方式避免了热媒水水温的波动,仿真结果表明:集热器瞬时效率随入口水温的升高而降低;随着热媒水由92℃增长到98℃,COP由0. 62提升到0. 74;冷却水入口温度的上升会使COP及制冷量逐渐降低;制冷量与COP随冷冻水入口温度升高均有所增加,但增长速率逐渐放缓。     

一种太阳能隔热墙体的实验研究

将太阳能光伏发电方阵、热电热泵与建筑有机结合,构建一种具有环境自适应功能的建筑-光伏-热电一体化(BIPVTE)墙体系统。测试不同倾斜角度、不同太阳辐照度下新型墙体的隔热性。结果表明:新型墙体的隔热性能随太阳辐照度增强而更好;试验期间隔热墙体内表面温度平均低于室内砖墙温度6~8℃,说明该文所建立新型隔热墙体的隔热性能较好。     

CO2跨临界冷热联供循环性能分析

以CO2跨临界循环冷热联供系统为研究对象,通过理论计算分析了传热窄点温差约束下系统供热温度、供冷温度、制热系数（COPh）和制冷系数（COPc）随压缩机排气压强、气体冷却器出口工质温度和蒸发温度的变化规律。结果表明：供热温度随压缩机排气压强和气体冷却器出口工质温度的提高而升高,随蒸发温度的提高而降低;供冷温度只随蒸发温度变化;COPh和COPc随气体冷却器出口工质温度的提高而减小,随蒸发温度的提高而增大;当气体冷却器出口工质温度为30~40 ℃时,随压缩机排气压强的增大,COP减小,当气体冷却器出口工质温度为45 ℃时,COP先增大后减小;在考察工况下,当蒸发温度为-25 ℃、气体冷却器出口温度为45 ℃时,循环系统在压缩机排气压强为14 MPa可以达到最大供热温度120.65 ℃、最低供冷温度-15 ℃,此时系统COP为2.94。     

直接式原生污水源热泵的自控调节特性

主要研究了直接式原生污水源热泵冬季供暖工况下的自控调节特性。通过对系统的自动控制可知,当室内温度从20℃降到18℃时,频率控制器启动,系统各参数维持稳定,房间热负荷约为15kW,控制器未做出大的调节;随着室内温度从18℃上升,压缩机的频率降低,通过PID的调节控制,室内温度保持在18℃附近,此时热负荷为9.5kW,压缩机耗功降低了48%,COP从3.4上升到4.1。当室内温度在16～20℃之间变化时,控制器随室内温度高于或低于设定温度,自动做出调节。为了维持温度在18℃附近,房间的热负荷量约为11.5kW,功耗3kW,COP为4,蒸发器和冷凝器的传热系数分别为1192和292W/(m~2·K)。     

R290直膨式太阳能热泵供暖系统实验研究

为分析直膨式太阳能热泵耦合地板辐射供暖系统在北方寒冷地区的实际运行特性,设计并搭建以丙烷(R290)为工质的直膨式太阳能热泵供暖实验平台,分析冬季不同运行工况下环境参数对系统热力性能的影响。实验结果表明：系统可实现室内供暖的稳定性,实验测试期间平均室温保持在16.1～20.8℃之间,热泵系统性能系数(COP)保持在2.57～4.30之间,供暖系统COP保持在2.24～3.98之间。太阳辐照度每增加50 W/m²,热泵系统COP提升4.9%;环境温度每升高1℃,热泵系统COP提升2.4%。太阳辐照度对热泵系统的电子膨胀阀开度和工质质量流量影响较为显著。当终止水温从45℃提升至55℃时,热泵系统COP降低12.2%;而在终止水温为50℃时,供暖系统COP达到最大值3.37。     

液体除湿空调实验台的性能分析及实验研究

针对上海气候环境条件设计制造了利用80℃以下低品位热源驱动的全新风送风LiCl液体除湿空调实验台,用于为100m2空调区域提供19℃以下的送风,独立承担室内热湿负荷.分析测试了系统送风温度的影响因素,表明再生热源温度是主要影响因素.该系统结构适合采用除湿再生同时运行模式,该模式下系统运行性能为:夏季工况新风制冷量为35～49kW,热力COP为0.72～0.98;秋季工况为17～29kW,热力COP为0.30～0.51.最后验证了除湿再生独立运行模式的可行性与实际效果:新风制冷量45kW,热力COP为1.1,为今后实验台的改进指明了方向.     

真空管直膨式太阳能热泵系统性能分析

该文将真空管集热器与直膨式太阳能热泵结合,提出一种真空管直膨式太阳能热泵系统。实验研究典型工况下太阳辐照度、循环水温度对系统性能的影响,并探讨压缩机变频条件下系统的动态性能。结果表明,提高太阳辐照度、降低循环水温度有利于提高系统性能,在太阳辐照度为850 W/m2,循环水温度为55℃时系统取得最大COP,为5.36。压缩机频率为42 Hz的系统COP为4.08,较45、47、50 Hz分别提高1.23%、8.5%、13.6%。     

夏季工况条件下空调/冷柜一体机性能实验研究

空调冷柜一体机系统是通过中间冷却器将空调与冷柜耦合,可以将空调系统中的部分制冷剂节流至中间冷却器对冷柜系统中的制冷剂进行过冷以提升其系统性能。实验研究了夏季工况条件下冷柜温度、室外环境温度及质量流量比对一体机系统制冷量及COP的影响。实验结果表明:在夏季工况条件下,冷柜系统的制冷量和COP随质量流量比的增大而增大,但质量流量比大于12%后其增速放缓;空调系统制冷量随质量流量比的增大而减小,而其COP随质量流量比的增大而略有增大。综合分析认为夏季工况条件下,质量流量比控制在8%～12%时可以提高空调及冷柜系统COP,同时空调器制冷量衰减也较小。     

被动式太阳房供暖实验研究

通过对新建被动式太阳房及相同结构的对比房室内温度及室外温度、太阳辐照度等参数的监测,研究了寒冷季节室内温度随室外气象条件以及太阳辐照度的变化情况。通过分析发现,在室内无热源及辅助热源条件下,太阳房室内平均空气温度比对比房室内平均空气温度高7.2℃,最高温差达18.3℃,最低温差0.3℃。通过对太阳房供暖节能率ESF分析计算得出太阳房供暖保证率较高,证明了在此建立被动式太阳房建筑的可行性和经济性。     

An experimental investigation to augment the efficiency of photovoltaic panels by using longitudinal fins

The temperature of a photovoltaic (PV) panel has a negative effect on the generated power. As the solar irradiance that falls on the PV increases, the operating PV temperature rises, which leads to a decrease in electrical efficiency. Therefore, there arises a need to introduce a cooling system to minimize PV temperature. In this study, the simple passive cooling method of extending its surfaces with fins was used to reduce the PV temperature. Different numbers of longitudinal aluminum fins were attached to the bottom surface of a PV panel and their effects were examined under realistic weather conditions for Baghdad, Iraq. Results show that the use of the passive cooling method under natural convection will be more effective in reducing PV temperature before solar noon than after solar noon. The maximum power enhancement was about 2.5 W and occurred at solar noon when using 10 aluminum fins. The peak efficiency value of the PV panel with fin cooling was about 15.3% against 14% for the unfinned PV panel.     

基于太阳辐射值的喷射制冷系统动态性能分析

为了了解气象参数对喷射制冷系统性能的影响,选取HCFC-134a作为制冷剂,基于EES软件建立了太阳能喷射制冷系统动态性能仿真程序,模拟研究了太阳辐射值对系统性能的影响。研究表明:一定运行工况下,随着太阳辐射量的增加,系统COP呈现先升高后下降的趋势;发生热量和发生温度均呈现递增趋势;制冷量则呈现先增加,当太阳辐射到达一定值时,系统的制冷量则基本不变的趋势。系统在相同蒸发温度和冷凝温度下运行时,存在一个最佳发生热量工作区,在该最佳发生热量区,系统COP最大,出冷量也最多。     

Thermal management of solar photovoltaics modules for enhanced power generation

Industry and government interest in solar energy has increased in recent years in the Middle East. However, despite high levels of solar irradiance in the Arabian Gulf, harsh climatic conditions adversely affect the electrical performance of solar photovoltaics (PV). The objective of this study is to compare the annual performance characteristics of solar PV modules that utilize either sun-tracking or water cooling to increase electrical power generation relative to that of stationary, passively cooled modules in the Middle East climatic conditions. This is achieved using an electro-thermal model developed and validated against experimental data acquired in this study. The model is used to predict the annual electrical power output of a 140 W PV module in Abu Dhabi (24.43°N, 54.45°E) under four operating conditions: (i) stationary geographical south facing orientation with passive air cooling, (ii) sun-tracked orientation with passive air cooling, (iii) stationary geographical south facing orientation with water cooling at ambient air temperature, and (iv) stationary geographical south facing orientation with water refrigerated at either 10 °C or 20 °C below ambient air temperature. For water cooled modules, annual electrical power output increases by 22% for water at ambient air temperature, and by 28% and 31% for water refrigerated at 10 °C and 20 °C below ambient air temperature, respectively. 80% of the annual output enhancement obtained using water cooling occurs between the months of May and October. Finally, whereas the annual yield enhancement obtained with water cooling at ambient air temperature from May to October is of 18% relative to stationary passive cooling conditions, sun-tracking over the complete year produces an enhancement of only 15% relative to stationary passive cooling conditions.     

Numerical simulation and experimental validation of indirect expansion solar-assisted multi-functional heat pump

A novel indirect expansion solar-assisted multi-functional heat pump (IX-SAMHP) system which composes of the multi-functional heat pump system and solar thermal collecting system is proposed and studied in this paper. This system can fulfill space heating, space cooling and water heating with high energy efficiency by utilizing solar energy. For solar water heating mode and solar space heating mode, a dynamic model is presented and validated with the experimental results. The simulation results show good consistency with the experimental data, and the established model is able to predict the system performance at a reasonable accuracy (with the root mean square deviations less than 5%). On this basis, the performances of the IX-SAMHP system are investigated under different parametric conditions. For solar water heating mode, simultaneously operating the solar thermal collecting system and multi-functional heat pump system can be an energy efficiency method. With the solar irradiation rising from 0W/m² to 800W/m², the COP increases from 2.35 to 2.57. In solar space heating mode, the effect of the mass flow rate of water in evaporator is investigated. To balance the heating capacity and COP, the mass flow rate of water should be adjusted according to different temperature demands and heat load.     

太阳能压气机系统优化及实验研究

针对太阳能空气压气机结构优化问题进行实验研究,测试并分析压缩空气罐内加装扰流风机之后的加热、冷却特性及太阳能利用率的变化情况。实验结果表明,在风机风速2.0~6.7 m/s的变化范围内,存在一个最佳风速使得太阳能热机效率最高,其冷却系数从0.34~0.44提升至0.78~0.84,压气机在冷却之后的吸气能力也显著提升。以名义太阳能利用率来衡量,风机+肋化吸热管结构相比于不设置风机的肋化吸热管或光滑吸热管结构有大幅提高,提高幅度在10.8%~145.8%之间,风机强化传热效果明显。     

Evaluation of adding flash tank to solar combined ejector–absorption refrigeration system

Performance of the absorption cooling system is still a challenge due to the coefficient of performance (COP) that is generally poor when compared with the conventional vapor compression cycle. High solar radiation in hot climates is usually associated with high ambient temperature and consequently peak cooling demand. Absorption cooling cycles can be powered by solar but the performance is limited by heat source temperature (solar collector) and high ambient temperature that can affect the condensation process. Efficiency enhancement of the system components is essential to increase the COP of the system. A modification in the combined absorption–ejector cooling system is adopted. Adding a removable flash tank between the condenser and evaporator could improve entrainment ratio of the ejector, along with improving the cooling effect inside the evaporator. A computer simulation program is developed to evaluate the performance of the modified combined cycle using aqua-ammonia (NH₃–H₂O) refrigerant. The performance of the proposed combined cooling cycle is compared with basic absorption, and combined absorption–ejector cooling cycles. Results showed a significant improvement in the COP of the modified cycle at different operating conditions. Cooling effect and capacity of the evaporator is enhanced due to the reduction of flash gas delivered to the evaporator. Furthermore, the flash tank optimized the ejector entertainment ratio and consequently increasing the condenser pressure. This optimization will enable the system to perform well in hot climates where the condenser efficiency is limited by ambient temperature.     

Experimental investigation and theoretical analysis of the solar adsorption cooling system in a green building

A solar adsorption cooling system was constructed in the green building of Shanghai Institute of Building Science. The system consisted of evacuated tube solar collector arrays of area 150 m², two adsorption chillers with nominal cooling capacity of 8.5 kW for each and a hot water storage tank of 2.5 m³ in volume. A mathematical model of the system was established. According to experimental results under typical weather condition of Shanghai, the average cooling capacity of the system was 15.3 kW during continuous operation for 8 h. The theoretical analysis of the system was verified and found to agree well with the experimental results. The performance analysis showed that solar radiant intensity had a more distinct influence on the performance of solar adsorption cooling system as compared with ambient temperature. It was observed that the cooling capacity increased with the increase of solar collector area, whereas, solar collecting efficiency varied quite contrary. With the increase of water tank volume, cooling capacity decreased, while, the solar collecting efficiency increased. The system performances can be enhanced by increasing the height-to-diameter ratio of water tank. Additionally, it was observed that solar collecting efficiency decreased with the increase of the initial temperature of water in the tank; however, cooling capacity varied on the contrary. Also can be seen is that optimum nondimensional mass flow rate is 0.7 when the specific mass flow rate exceeds 0.012 kg/m² s.     

风冷式太阳能吸收式制冷机性能模拟研究

在环境温度和太阳辐射动态变化的情况下,对制冷量为5 kW的风冷式太阳能吸收式制冷机的性能进行了模拟,得出了集热器出口水温和热水储槽温度随时间变化的规律曲线以及在此规律的影响下吸收式制冷机的性能曲线.模拟结果表明风冷式太阳能吸收式制冷机在理论上是切实可行的,但是环境温度的变化以及风冷系统的散热能力对系统性能有较大的影响,环境温度的升高会使需要风冷降温的冷凝器、吸收器温度升高,从而提高了发生温度的要求,这不利于太阳能的利用和系统的制冷.为此需要强化冷凝器和吸收器的散热效果,来降低境温度对系统的不利影响.     

Collector selection for solar ejector cooling system

The performance of a solar ejector cooling system is simulated using three different collectors: a conventional flat plate collector, a high efficiency flat plate collector and a vacuum-tube collector. It is shown that with the proper selection of the generating temperature an optimum COP can be achieved. The solar ejector cooling system using the single-glazed solar collector with selective surface and an enhanced air insulating layer can be most economical when operated at the optimum generating temperature of the ejector cooling machine. In this case, the solar system cost is around 1 USD per watt of cooling capacity for air conditioning applications.     

Evaluation of a solar intermittent refrigeration system for ice production operating with ammonia/lithium nitrate

A novel solar intermittent refrigeration system for ice production developed in the Centro de Investigación en Energía of the Universidad Nacional Autónoma de México is presented. The system operates with the ammonia/lithium nitrate mixture. The system developed has a nominal capacity of 8 kg of ice/day. It consists of a cylindrical parabolic collector acting as generator-absorber. Evaporator temperatures as low as −11 °C were obtained for several hours with solar coefficients of performance up to 0.08. It was found that the coefficient of performance increases with the increment of solar radiation and the solution concentration. A dependency of the coefficient of performance was not founded against the cooling water temperature. Also it was found that the maximum operating pressure increases meanwhile the generation temperature decreases with an increase of the solution concentration.