Solar multi-mode heating system based on latent heat thermal energy storage and its application

为克服太阳能间断性和不稳定性的缺点进而实现太阳能集热与采暖的能量供需调节和全天候连续供热,提出了基于相变储热的太阳能多模式采暖方法（太阳能集热直接采暖、太阳能集热采暖+相变储热、太阳能相变储热采暖）,并在西藏林芝市某建筑搭建了太阳能与相变储热相结合的采暖系统,该系统可根据太阳能集热温度和外界供热需求实现太阳能多模式采暖的自动控制和自动运行。实验研究表明：在西藏地区采用真空管太阳能集热器可以和中低温相变储热器很好地结合,白天储热器在储热过程中平均储热功率为10.63 kW,储热量达到92.67 kW·h,相变平台明显;晚上储热器在放热过程中供热量达85.23 kW·h,放热功率和放热温度平稳,储放热效率达92%,其储热密度是传统水箱的3.6倍,可连续供热时间长达10 h,从而实现了基于相变储热的太阳能全天候连续供热,相关研究结果对我国西藏地区实施太阳能采暖具有一定的指导作用。     

低温空气源热泵与太阳能联合供暖系统分析

通过介绍一种低温空气源热泵和太阳能联合供热系统,将太阳能集热器置于室外空旷地带或建筑屋面上,通过管道与储热水箱相连,储热水箱通过水泵与板式换热器相连,室内供暖回水管与板换相连,且设置相应的电动阀门,与储热水箱热水循环泵联动运行。增加单独利用太阳能的时间,充分利用空气能,减少空气能能耗,减少化石能源的使用,降低系统运行费用。     

大规模太阳能跨季节土壤储热系统设计优化

以太阳能跨季节储热系统为研究对象,在已有低品位集中供热项目案例基础上,设计太阳能跨季节储热系统,通过数值模拟对储热体积、短周期蓄热水箱体积和循环流量进行分析,并利用Hooke-Jeeves算法,以储热效率最高为优化目标,获得太阳能集热面积与上述设计参数的匹配关系。分析结果表明:太阳能跨季节储热具有规模效应,储热体积越大,单位储热体积对应表面积越小,热损失越小。对于高径比为1,储热期和取热期入水温度分别为80和20℃的圆柱形跨季节储热体,当其体积由1万m³增加至10万m³时,体表比由0.3下降至0.13,储热效率由40%增加至75%。此外,短期蓄热水箱体积对系统性能也有较大影响,当水箱体积偏小时,集热系统运行温度偏高,集热效率偏低;水箱体积偏大时,水箱热损失率偏高。系统取热量随取热期循环流量的增加而增加,循环介质进出口温差随取热期循环流量的增加而减小。从提高系统经济性的角度考虑,集热面积、储热体积、短期蓄热水箱体积及循环流量应根据取热装置和太阳能系统动态特性进行匹配设计,系统规模不宜过大或过小。针对10万m³地埋管储热系统...     

SUNFLOWER,永远向着太阳(下)——记天津大学参加“太阳能十项全能竞赛”

五太阳能热利用系统采用PV-T、低温集热板及玻璃真空管集热器相结合的方式收集太阳热能,系统循环介质分为低温热媒和高温热媒两种,以收集更多的热量和进行热能的梯级利用。所收集热能分高、中、低温分别储存在三个储热罐中,用于满足烹调、生活热水、HVAC等不同的温度需求。生活热水系统设计中根据日常使用需要计算热水供应量,水箱则根据不同用水量和温度要求分别设置储、供热水箱,以确保不同用水点的水温要求和最大限度地节约热能。     

太阳能供热采暖技术讲座(6) 太阳能供热采暖系统的设计(下)

<正>五控制系统设计太阳能供热采暖系统控制应包括太阳能集热系统运行控制、辅助热源运行控制、供热系统运行控制、防冻保护控制、防过热保护控制及运行工况的切换。控制系统依据温度、压力和水位传感器获得的信号控制水泵、阀门的启闭或改变阀门的开度,此外系统一般设置温控阀、压力控制阀、自动排气阀、止回阀、安全阀等控制元件以保证系统安全、稳定运行。     

太阳能采暖系统储热水箱体积匹配研究

以太阳能光热采暖系统的集热面积与储热水箱体积的匹配为研究对象,搭建基于小时级热量流动的太阳能采暖系统模型。基于此模型,对集热面积和储热体积匹配关系对系统运行效率、经济性及安全性的综合影响进行讨论。并以一个典型算例为例,结合经济性分析方法,给出太阳能采暖系统最优集热面积和水箱体积的设计流程。研究表明:单位集热面积匹配储热体积的最优值并非是一个定值,而是与系统的总集热面积有很强的相关性。系统集热面积越大,单位集热面积对应的最优储热体积越大。相应地,系统的热损失也越大,单位集热面积的有效供热量越小。因此,需要从集热量与热损失2个方面综合权衡系统规模,并合理匹配储热体积,以保证系统运行的经济性和安全性。     

太阳能应用于土壤源热泵低温热源侧的实验研究

为了提升热泵机组的性能系数COP,合理利用不同温度层次的太阳能集热量,文章基于太阳能—土壤源复合热泵系统的大量实验结果,分析了蒸发器进口温度对热泵系统各项性能的影响,并在此基础上,分析了复合源热泵工况和太阳能热泵工况的运行特点。分析结果表明:随着蒸发器进口温度的升高,热泵机组吸热量逐渐增大,热泵机组输入功率略有增加,导致热泵机组的供热量和COP均逐渐增大;复合源热泵工况下,存在土壤源和太阳能共同供热,以及土壤短期储热与太阳能单独供热同时进行的两种运行情况;为了提升热泵机组的工作性能,在太阳能集热量较低时,优先运行复合源热泵工况;土壤源温度的自然恢复能力较差,需要利用太阳能集热系统对土壤源进行跨季强制蓄热,以提高土壤源温度,缓解土壤源冷堆积现象。     

蓄热水箱水温和水箱体积对太阳能集热系统的性能影响分析

采用实验和模拟计算方法对太阳能集热系统蓄热水箱的水温和水箱体积影响因素开展探究，分析日有用得热量、集热器功率和水箱内平均温度等参数随水箱初始温度和水箱体积的变化规律。研究结果表明：水箱初始温度从10.34℃增加到29.88℃时，日有用得热量减少了19.52%；换算成日太阳辐照量为17MJ/m2时的储热水箱中水的温升值下降了17.66%，储热水箱结束水温下降了10.73%；单位面积日有用得热量减少了17.64%。通过TRNSYS模拟软件，分析出太阳能集热系统全年运行工况时的水箱变量参数对系统性能的影响，获得了日有用得热量、集热器功率和水箱内平均温度的变化规律。通过选取不同月份的若干个时段进行对比分析，得出水箱体积对太阳能供热系统的影响较水箱初始温度大；当下调水箱初始温度和缩小水箱体积时，日有用得热量提升，但集热器功率降低；当上调水箱初始温度和缩小水箱体积时，水箱内平均温度升高；且随着太阳能集热系统运行时间的累加，水箱初始温度和水箱体积对上述各性能参数的影响减弱。日有用得热量、集热器功率和水箱内平均水温随着季节变化明显，秋季和冬季气候下的日有效得热量，集热器功率和水箱内平均水温均低于春季和夏季。     

光伏直驱的太阳能跨季节储热系统试验研究北大核心CSCD

针对太阳能跨季节储热系统中存在控制复杂、电耗较高等问题,文章设计一种光伏直驱的太阳能跨季节储热系统,并搭建试验平台,探究不同工况下系统电、热性能。结果表明,光伏直驱的太阳能跨季节储热系统运行无需控制系统及市电消耗,光伏电池通过影响水泵输入功率来控制系统流量,系统在2.45 m^(2)光伏电池驱动下,于辐照度420 W/m^(2)时启动。辐照度小于750 W/m^(2)时,流量变化趋势与辐照度变化趋势相同;大于750 W/m^(2)时,流量趋近稳定。该系统晴天与多云天太阳能储热率分别为35.68%和29.12%,较温差控制式系统分别高6.56%和7.29%,光伏利用效率分别为78.60%和86.01%。集热/储热流量比的变化对系统性能影响较小,应关注水泵启停辐照度的合理优化设计及蓄电池等储能装置的加入。     

双水箱太阳能集中热水系统关键参数优化及建筑类型的适用性研究

为对供热水箱容积、供热水箱控制最低水位、补水泵流量、集热水箱放水温度等关键参数进行系统优化,建立典型的双水箱太阳能集中热水系统仿真模型,以太阳能保证率和集热效率为主优化指标。结果表明:部分工况下供热水箱容积的增大会引起太阳能保证率的增大,但集热器的集热效率会有所减小;对于供热水箱通过水位控制的双水箱太阳能集中热水系统,建筑类型对系统补水泵流量的影响较大;对于集热水箱到供热水箱的热水通过温差控制的热水系统,放水温度应大于用户用水温度;双水箱太阳能集中热水系统,更适于24 h连续供水的建筑类型。     

ICS solar systems with two water tanks

Integrated collector storage (ICS) systems are compact solar water heaters, simple in construction, installation and operation. They are cheaper than flat plate thermosiphonic units, but their higher thermal losses make them suitable mainly for application in locations with favourable weather conditions. Aiming to the achievement of low system height and satisfactory water temperature stratification, new types of ICS systems with two horizontal cylindrical storage tanks, properly mounted in stationary CPC reflector troughs are suggested. The non-uniform distribution of solar radiation on the two absorbing surfaces is combined with the seasonal sun elevation, resulting to effective water heating. In addition, the inverted absorber concept design can be applied to ICS systems with two storage tanks. In this paper, we present the design and performance of double tank ICS solar systems, which are based on the combination of symmetric and asymmetric CPC reflectors with water storage tanks. The analytical equations of the collector geometry of all models are calculated with respect to the radius of the cylindrical water storage tank and the reflector rim angles. Experimental results for the variation of the water temperature inside storage tanks, the mean daily efficiency and the coefficient of thermal losses during night are given for all experimental models. The tests were performed without water draining and the results show that the double tank ICS systems are efficient in water temperature rise during day and satisfactory preservation of the hot water temperature during night, with the upper storage tank being more effective in performance in most of the studied models.     

Analysis and performance of a low-cost solar heater

One of the alternatives to reduce the consumption of electricity for heating water is by popularizing the use of solar energy. This work contributes with studies on a Low-Cost Solar Heater (LCSH), a new concept of solar water heater made entirely of polymeric materials, which requires a relatively low investment and is user-assembled. The solar collector, which absorbs solar energy and transfers it to water in the form of heat, is composed of uncovered flat panels of rigid PVC. The storage tank that holds the water heated during the day is made of polyethylene coated with polystyrene. The results of the LCSH were compared with those of a conventional solar heater composed of a glass-covered copper collector and a stainless steel storage tank. The efficiency of the systems was evaluated by measuring the incident solar radiation and water temperature with the systems operating naturally (thermosiphon). The heat loss in the hot water storage tanks was measured to estimate the thermal performance of the solar heaters. Considering that the target temperature for the heated water is slightly above the ambient temperature, the results indicated that the LCSH showed a satisfactory global heat transfer coefficient for storage tanks and that it attained an excellent thermal performance, although it is not as efficient as the conventional heater.     

太阳能地面采暖系统蓄热水箱容积分析

通过分析太阳能采暖系统所需蓄热鼍与建筑热负荷、太阳能集热量日变化规律之间的关系,得出太阳能采暖系统所需蓄热水箱容积的理论算式.根据拉萨、银川、西宁、西安等地的太阳辐射强度及建筑热负荷的日变化规律,模拟得出系统所需蓄热量变化规律;并对各种蓄热温差下对应的蓄热水箱容积进行了模拟分析,结果表明:太阳能采暖系统所需蓄热量随太阳集热器的集热量与建筑热负荷之间的差值增大而增加;蓄热水箱容积随蓄热温差增大而减小,当蓄热水温达到80℃时,在各种地面采暖系统取水温度下,单位集热器面积所需蓄热水箱容积趋于相等.     

Discharge of a thermal storage tank using an immersed heat exchanger with an annular baffle

A number of solar domestic hot water systems and many combined space and water heating systems have heat exchangers placed directly in the storage fluid to charge and/or discharge the tank. Operation of the heat exchanger produces a buoyancy-driven flow within the storage fluid. With a view toward controlling the flow field to increase heat transfer, a cylindrical baffle is inserted in a 350 l cylindrical storage tank. The baffle creates a 40 mm annular gap adjacent to the tank wall. A 10 m-long, 0.3 m² copper coil heat exchanger is placed in the gap. The effects of the baffle on the transient heat transfer, delivered water temperature, heat exchanger effectiveness, and temperature distribution within the storage fluid are presented during discharge of initially thermally stratified and fully mixed storage tanks. The baffle increases the storage side convective heat transfer to the heat exchanger by 20%. This increase is attributed to higher storage fluid velocities across the heat exchanger.     

EVALUATION OF THE DYNAMIC PERFORMANCE OF A HOT WATER TANK WITH BUILT-IN HEATING COIL

Hot water tanks with a built-in water-heating coil are commonly used in district heating house stations in Denmark for domestic hot water (DHW) production and storage. In this study, an evaluation of the dynamic performance of a hot water tank with built-in heating coil is carried out by applying a dynamic simulation programme which has been made previously, based on a simple dynamic model developed by the authors. System evaluation of the way in which system parameters, such as control valve size, heat loss coefficient of the DHW circulation pipe, position of the temperature sensor (for DHW temperature control) and fouling of the heating coil, affect the domestic hot water capacity and the average district heating water cooling for a given hot water tank is presented and discussed in this paper. The evaluation results show the importance of the correct design of the control valve size, the reduction of heat loss from DHW circulation pipes, the careful adjustment of temperature sensor position and temperature sensor set-point, and the reduction of the heat coil fouling growth rate in order to operate the hot water tank in an efficient way and to achieve significant cooling of the district heating water. © 1997 by John Wiley & Sons, Ltd.     

Experimental results of a sensible heat storage system for residential and light commercial application

This paper presents the performance results for a sensible heat storage system. The system under study operates as an air source heat pump which stores the compressor heat of rejection as domestic hot water or hot water in a storage tank that can be used as a heat source for providing building heating. Although measurements were made to quantify space cooling, space heating, and domestic water heating, this paper emphasizes the space heating performance of the unit. The heat storage system was tested for different indoor and outdoor conditions to determine parameters such as heating charge rate, compressor power, and coefficient of performance (COP). The thermal storage tank was able to store a full charge of heat. The rate of increase of storage tank temperature increased with outdoor temperature. The heating rate during a charge test, best shown by the normalized rate plots, increased with evaporating temperature due to the increasing mass flow rate and refrigerant density. At higher indoor temperature during the discharge tests, the rate of decrease of storage tank temperature was slower. Also, the discharge heating rate decreased with time since the thermal storage tank temperature decreased as less thermal energy became available for use. Copyright © 1999 John Wiley & Sons, Ltd.     

Modelling and analysis of the dynamic behavior of a forced circulation solar water heating system with storage tanks in series

A generalized model for a forced circulation solar water heating system with storage tanks in series is presented in which the loss of heat through an insulation lagging is considered, and the periodic time variation of the intensity of solar radiation, as well as both the ambient air temperature and the temperature of cold water entering the first main tank, is taken into account. Using the Laplace transformation, an exact solution is presented which, under certain conditions, reduces to an approximate solution. The conditions for convergence to the approximate solution are discussed, and figures are presented comparing it with the exact solution for several different sets of conditions. In this communication, the effect of the number of storage tanks on the outlet temperature of the hot water and the effect of various water heating system parameters on its performance have been analytically investigated. Numerical calculations have been made for a typical cold day.     

基于太阳能利用的相变蓄热水箱结构优化

为解决因太阳能的不稳定性等因素导致的太阳能蓄热水箱储热/放热能力的不保证性问题,提出采用中低温有机相变材料58号石蜡作为相变蓄热材料的圆台式太阳能相变蓄热水箱。采用计算流体力学(computational fluid dynamics,CFD)数值模拟的计算方法,在保证总蓄水体积(以100 L为例)不变的情况下,对水箱中不同内胆倾斜角度分别为75°、80°、85°、90°、95°、100°、105°的放热过程进行数值模拟,综合对比和分析水箱放热性能模拟结果,得到当倾斜角度为105°时的相变蓄热构件放热性能最佳,可为太阳能相变蓄热水箱的结构优化设计提供理论依据。     

Optimal flow control of a forced circulation solar water heating system with energy storage units and connecting pipes

This paper focuses on pump flow rate optimization for forced circulation solar water heating systems with pipes. The system consists of: an array of flat plate solar collectors, two storage tanks for the circulation fluid and water, a heat exchanger, two pumps, and connecting pipes. The storage tanks operate in the fully mixed regime to avoid thermal stratification. The pipes are considered as separated components in the system so as to account for their thermal effects. The objective is to determine optimal flow rates in the primary and secondary loops in order to maximize energy transfer to the circulation fluid storage tank, while reaching user defined temperatures in the water storage tank to increase thermal comfort. A model is developed using mainly the first and second laws of thermodynamics. The model is used to maximize the difference between the energy extracted from the solar collector and the combined sum of the energy extracted by the heat exchanger and corresponding energies used by the pumps in the primary and secondary loops. The objective function maximizes the overall system energy gain whilst minimizing the sum of the energy extracted by the heat exchanger and corresponding pump energy in the secondary loop to conserve stored energy and meet the user requirement of water tank temperatures. A case study is shown to illustrate the effects of the model. When compared to other flow control techniques, in particular the most suitable energy efficient control strategy, the results of this study show a 7.82% increase in the amount of energy extracted. The results also show system thermal losses ranging between 5.54% and 7.34% for the different control strategies due to connecting pipe losses.     

分层-掺混切换式蓄热水箱热特性实验及评价研究

稳定分层、充分掺混是蓄热水箱实现高效供暖和恒温出水2种功能的重要手段。该研究设计一种分层-掺混一体式蓄热水箱,可实现2种功能的有效切换,满足分层高效供暖和恒温生活热水在不同时段、不同季节的灵活需求。搭建一套蓄热水箱热力学特性测试实验系统,利用分层效率、效率等蓄热水箱热性能评价指标,研究不同尺寸、流量、温度下分层-掺混式蓄热水箱的热力学性能及动态响应特征。以125 L的实验蓄热水箱为例,结果表明：在分层模式下,热分层速率、稳定性显著优于常规水箱,效率和分层效率明显提高,效率可达90%以上;在掺混模式下,掺混速度明显提高,分层效率迅速降低到0.10,实现了蓄热水箱的完全混合,结果对分层-掺混双效水箱的开发与应用具有一定指导。