Thermal performance analysis and economic evaluation of roof-integrated solar concrete collector

This paper examines the thermal performance of a roof-integrated solar concrete collector for reducing heat gain to a house and providing domestic hot water. The solar concrete collector is made of PVC pipes embedded in deck slab or concrete roof. No glazing on the top of the solar concrete collector or insulation at the back has been used as in conventional solar water heaters. To compare the energy saving, two test rooms of 2.3 m width, 2.5 m length and 2.5 m height were built. In the first room, the reinforced cement concrete (R.C.C.) slab was used as deck slab whereas the second room was equipped with a cement concrete solar collector. The experimental results showed that the cement concrete solar collector is extremely interesting as it can produce up to 40 l of hot water per day at water temperatures ranging from 40 to 50 °C. A mathematical model based on the conservation equations of energy is developed to predict the performance of the cement concrete solar collector. There is reasonable agreement from the comparison between measured data and predicted results. The economic analysis indicates that the payback period is rather fast.     

Modeling of an integrated solar system

The feasibility of using low-cost solar collection and storage technology to provide energy for residential units is investigated. Different construction strategies were compared including traditional housing practice against newly innovative ideas such as low radiant heating system, desiccant dehumidification, integrated low-cost solar collection, and phase-change material (PCM) storage. The selected building, located in Blacksburg, VA, integrated a solar thermal roof collection system consisting of a low-temperature flat-plate collector integrated within a concrete building envelope linked to a PCM storage tank. For the considered location and weather conditions (Blacksburg, VA), the proposed collection and storage solar system can supply 88% of the building's space heating and hot water needs averaged throughout the year saving the homeowner approximately 61.5% of the annual heating bills. However, the use of a storage system is not economical for the considered conditions. The paper also shows a month-by-month demand and supply distributions for the modeled building's heating and hot water needs.     

Build-up and performance test of a novel solar thermal roof for heat pump operation

Global increase in energy demand and fossil fuel prices loaded ever-increasing pressure on identifying and implementing new means to utilise clean and efficient energy resources. Due to the environmental benefits, technical and economic possibilities of Solar-Assisted Heat Pump Systems, there has been a growing interest for such hybrid systems with a variety of system configurations for various climates. International Energy Agency Task 44 of the Solar Heating and Cooling Programme has recently started working on finding methods to most effectively use solar heat pump systems for residential use. In the present study, a novel solar thermal roof collector was developed by primarily exploiting components and techniques widely available on the market and coupled with a commercial heat pump unit. The proposed indirect series Solar-assisted Heat Pump system was experimentally tested and system performance was investigated. Yet, the analysis based on indoor and outdoor testing predominantly focuses on the solar thermal roof collector. A detailed thermal model was developed to describe the system operation. Also, a computer model was set up by using Engineering Equation Solver to carry out the numerical computations of the governing equations. Analyses show that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Data processing of the series covering the test period represents that Coefficient Performance of the heat pump (COP_HP) and overall system (COP_SYS) averages were attained as COP_HP?=?3.01 and COP_SYS?=?2.29, respectively. An economic analysis points a minimum payback period of about three years for the system.     

Numerical simulation of an integrated solar louvre collector system

External louvres are increasingly used to provide solar protection for building glazed surfaces. This work concerns the modification of existing louvre designs to integrate a solar collector in the shading device. A numerical model for the integrated solar collector was developed, and collector efficiency was quantified. Thermal performance for a water heating system was obtained, on a month-to-month basis, under the climatic conditions of Portugal.     

陶瓷太阳板及其应用的研究

陶瓷太阳板以普通瓷土、工业废弃物为原料,具有制造工艺简单、生产耗能少、成本低、寿命长、效率高的优点。建造的陶瓷太阳能房顶与原房顸共用结构层、保温层、防水层,结构简单,可与建筑一体化,与建筑同寿命,且隔热、保温效果优于普通房顶,可为建筑物提供热水和取暖。陶瓷太阳板还可用于沙漠太阳能发电、海水淡化、苦成水淡化等。太阳能使用成本低于常规能源。     

陶瓷太阳板及其应用的研究

陶瓷太阳板以普通瓷土、工业废弃物为原料,制造工艺简单、生产耗能少、成本低、寿命长、效率高建造的陶瓷太阳能房顶与原房顶共用结构层、保温层、防水层,结构简单、与建筑一体化、与建筑同寿命隔热、保温效果优于普通房顶,为建筑物提供热水、取暖、空调;用于沙漠太阳能发电、海水淡化、苦咸水淡化、改造沙漠成为耕地;可能实现太阳能使用成本低于常规能源。     

Controlling power output of solar chimney power plant according to demand

ABSTRACT

The solar chimney power plant (SCPP) is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The numerical simulations were performed for the geometry of the prototype in Manzanares, Spain. Using computational ?uid dynamics (CFD) techniques; we have simulated a two-dimensional axisymmetric model of a SCPP with the RNG k-ε turbulence. In this model, the discrete ordinates (DO) radiation model was implemented to solve the radiative transfer equation, using a two-band radiation model. The main objective of this work is to explore dynamic control over plant power output. We have presented a technique to control the power output of the solar chimney power plant, in order to deliver power according to specified demand patterns. In order to present this, the reference plant model was modified to include a secondary and tertiary collector roof under the existing main collector. In terms of base load electricity generation, the inclusion of a secondary and tertiary collector roof produces good control over plant output.     

Performance evaluation of green roof and shading for thermal protection of buildings

The present paper describes a mathematical model for evaluating cooling potential of green roof and solar thermal shading in buildings. A control volume approach based on finite difference methods is used to analyze the components of green roof, viz. green canopy, soil and support layer. Further, these individual decoupled models are integrated using Newton's iterative algorithm until the convergence for continuity of interface state variables is achieved. The green roof model is incorporated in the building simulation code using fast Fourier transform (FFT) techniques in Matlab. The model is validated against the experimental data from a similar green roof-top garden in Yamuna Nagar (India), and is then used to predict variations in canopy air temperature, entering heat flux through roof and indoor air temperature. The model is found to be very accurate in predicting green canopy-air temperature and indoor-air temperature variations (error range ±3.3%, ±6.1%, respectively). These results are further used to study thermal performance of green roof combined with solar shading. Cooling potential of green roof is found adequate (3.02 kWh per day for LAI of 4.5) to maintain an average room air temperature of 25.7 °C. The present model can be easily coupled to different greenhouse and building simulation codes.     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

Analysis on the optimum matching of collector and storage size of solar water heating systems in building space heating applications

The overall thermal performance of a solar water heating (SWH) system is significantly affected by the mismatch between the temporal distribution of solar radiation and the heating load. Therefore, a favorable correlation between the collector and storage size should be generated based on the dynamic characteristics of the system. This study focuses on the optimal matching of solar collector area with storage volume for an SWH system (with short-term heat storage capability) for a space heating application. A simplified model of an SWH system based on hourly energy flow is established. System control strategy is integrated into the model in a simple manner without sacrificing computing speed. Based on this model, the combined effect of collector area and storage volume on system thermal performance and economy is analyzed, and a simple procedure for determining the optimal system size is illustrated. A case study showed that for an SWH system utilized for space heating application, the optimized ratio between storage volume and collector area is dependent on the total collector area of the system, and is dominated by the requirement of overheating prevention. The minimum storage volume for a specific collector area that can prevent the storage tank from being overheated can be adopted as the optimum storage volume for that collector area. The optimum ratio between storage volume and collector area increases as the collector area increases. Therefore, a trade-off between heat collection and heat loss has to be made while attempting to increase solar fraction by improving collector area.     

平板分体式太阳能在工程中的应用

平板分体式太阳能与曼宁家斜屋面一体化施工,使太阳能与斜屋面融为一体,实现了太阳能与建筑载体的结合。在提高了太阳能的抗风压、抗风揭和避雷性能的同时,降低了成本,改变了太阳能的工作环境,提高了太阳能的得热率。     

高层住宅太阳能热水系统集热面积调查与研究

针对杭州市居民生活热水使用习惯做了调查,区分不同季节（冬季、春秋季和夏季）,分析得出了太阳能热水系统设计的关键参数,即日均热水用量的取值建议,并进一步探讨了杭州地区住宅建筑最佳屋面集热面积的配置;同时基于调查结果分析了阻碍太阳能热水系统推广应用的因素。     

Occupants’ impact on indoor thermal comfort: a co-simulation study on stochastic control of solar shades

This paper investigates the impact of manually operated solar shades on indoor thermal comfort. A developed stochastic model for manual solar shades was modelled in Building Controls Virtual Test Bed, which was coupled with EnergyPlus for co-simulation. Movable solar shades were compared with two unshaded windows (clear double-pane and low-e double-pane). Two objective indices (room base temperature and transmitted solar radiation) and one subjective index (modified predicted mean vote (PMV) index (PMVrad) that considers solar radiation on the human body) were used to evaluate the indoor thermal performance. Results show that external solar shades achieve the best performance in terms of all three indices, especially for PMVrad, hours of comfortable conditions are higher than unshaded windows by 20.6–37.3%. Despite achieving relatively high performance, solar shades are operated infrequently and for about 30% of work time they are not adjusted appropriately, leading to a decrease in indoor thermal comfort.     

直通式真空管太阳能空气集热器的实验研究

研究了一种新型的直通式多根真空管空气集热器装置,包括直通式(两端开口)真空集热管和上下分集管。直通式真空管太阳能空气集热器安装在南墙的外面,室内空气进入集热器,加热后送回房间,实现了太阳能供暖,不需要风机或者水泵,简单可靠。搭建了试验台并测试了冬季供暖时的热性能。通过实验得出,该装置集热效率最高的点出现在14:00,集热效率为51%,其集热效率最低的点出现在16:00,集热效率为46%,全天的总效率为36.3%,具有较高的热效率。     

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

An experimental investigation of an evacuated tube solar air collector coupled to a latent thermal energy store for generating hot air when no solar radiation is incident was undertaken. Acetamide was used as a phase change material (PCM). The latent thermal energy store was integrated with the manifold of the solar collector and water was used as the working fluid transferring solar gain to the air being heated. The maximum measured temperature differential between the heated air and the ambient air was 37°C and 20.2°C during conditions of incident and non-incident solar radiation, respectively. This occurred using a circular fin configuration at a flow rate of 0.018?kg?s^?1. The efficiency at low (0.018?kg?s^?1) air flow rates was 0.05–0.50 times less as compared to high (0.035?kg?s^?1) air flow rates. This system has advantages over systems using sensible storage as it can be used after sunset due to better heat storing capacity of the PCM.     

Solar powered absorption air conditioning

The design of buildings to provide a suitable thermal environment is discussed and the reasons for artificial heating or cooling introduced. The problem of sizing a solar-powered cooling plant is investigated. An iterative method of estimating heat flow and resultant temperatures in buildings subject to fluctuating heat loads is described. A model is developed to allow investigation of the performance of a solar collector and thermal storage system and some of the basic relationships between performance and physical parameters are determined.

An iterative method of predicting the cooling output from a lithium bromide-water absorption refrigeration plant having variable heat input is described.

The design of a solar collector/thermal storage) absorption cooler system, its performance on a particular building and its fine tuning are examined.     

基于太阳辐射利用的寒地建筑组团形态优化设计研究

寒地气候严酷,采暖能耗高,太阳辐射时长短。寒地建筑太阳辐射利用对降低能耗、改善室内热舒适均具有重要意义。建筑形态作为室内外环境交互界面,决定着建筑太阳辐射利用水平。研究旨在基于多目标进化算法,应用建筑信息建模、参数编程和建筑太阳辐射性能模拟工具,探索太阳辐射利用导向下的寒地建筑组团形态优化设计方法,并结合工程项目展开实践。结果表明：形态优化设计可将屋面太阳辐射可利用面积百分比于64.71%显著提高至94.15%,制冷季太阳辐射得热量于423.87kWh/m2降低至343.28kWh/m2,并将采暖季太阳辐射得热量于212.19kWh/m2提高至259.29kWh/m2;同时,形态优化设计获得了150项建筑组团形态非支配解,可助力设计者权衡采暖、制冷季太阳辐射得热量与屋面太阳辐射可利用面积百分比性能目标。     

The use of a heavy internal wall with a ventilated air gap to store solar energy and improve summer comfort in timber frame houses

This paper considers supplementary heating and cooling within timber frame houses. The transmission of solar energy to an internal concrete cavity wall by air is analyzed. The objective of this work was initially to study the dynamic insulation in timber frame houses. The initial studies showed that it is more efficient to recover solar energy rather than heat losses, which is the principle of dynamic insulation. Clearly, the thermal regulations lead to lower heat losses through walls by conduction. Due to these factors we have decided to study a wall with an integrated solar air collector and a heavy ventilated internal wall. This internal wall, which is used to store solar energy will allow the reduction of heat demand in winter and will improve thermal comfort in summer because thermal mass increases and ventilation during the night will cool the internal wall. We have selected a closed loop air circulation system because, with an air to air heat exchanger, it can be proved to be more effective and the risk of unhealthy air pollution is reduced because the flow of fresh air will not pass through the ventilated air gap. We are constructing an integrated air collector prototype.     

Year-round numerical simulation of a parabolic solar collector under Lebanese conditions: Beirut case study

A detailed thermal and optical numerical model is developed to simulate the performance of a small-scale parabolic collector having an evacuated receiver line with selective coating, taking into account different energy balances and interactions with the surrounding. An analytical model is developed to estimate the direct, diffuse and global solar radiation intensities on inclined surfaces. The collector performance model was validated using published experimental data. A year-round dynamic simulation for the collector performance under Beirut climatic conditions was carried out with an economic and environmental analysis. The outlet water temperature could reach a maximum of 114°C in July and 52°C in December by employing a collector of about 6 m² aperture area with 0.01 kg/s water flow rate. The maximum daily thermal energy production is attained in July with 22.267 kWh while January exhibits the lowest thermal energy production with 6.704 kWh per day with a maximum thermal efficiency of 72%.     

高层住宅太阳能集热屋顶一体化设计形式探讨

在高层住宅集中太阳能热水系统一体化设计的初始阶段,建筑师就需考虑集热器与建筑的有效结合,既能充分利用太阳能,又满足建筑美学要求。鉴于上述要求,提出一种折线双坡不对称集热屋顶设计思路,供建筑设计者参考。