Flat-plate solar-collector performance evaluation with a solar simulator as a basis for collector selection and performance prediction

The use of a solar simulator for performance determination permits collector testing under standard conditions of wind, ambient temperature, flow rate and “Sun”. The performance results determined with the simulator have been found to be in good agreement with outdoor performance results.This paper reports the measured thermal efficiency and evaluation of 23 collectors which differ according to absorber material (copper, aluminum, steel), absorber coating (nonselective black paint, selective copper oxide, selective black nickel, selective black chrome), type of glazing material (glass, Tedlar, Lexan, anti-reflection glass), the use of honeycomb material and the use of vacuum to reduce thermal convection losses. The collectors are given performance rankings based on noon-hour solar conditions and all-day solar conditions. The determination with the simulator of an all-day collector performance is made possible by tests at different incident angles. The solar performance rankings are made based on whether the collector is to be used for pool heating, hot water, absorption air conditioning, heating, or for a solar Rankine machine.Another test which aids in selecting collectors is a collector heat capacity test. This test permits a ranking of collectors according to their heat capacity (and time constant), which is a measure of the rapidity of a collector's response to transient solar conditions. Results are presented for such tests.Final considerations for collector selection would of course be made on the basis of cost and the reliability of performance over the required life of a collector. Results of a cost-effectiveness study is given for conditions corresponding to those required for absorption or heating. These results indicate that the additional cost involved in the upgrading of collector performance (selective surfaces, anti-reflection glass, etc.) appears to be cost effective and therefore justified. Some data are also presented to illustrate a method for the determination of outdoor performance degradation by use of simulator tests carried out before and after a period of outdoor operation.     

Validation of a computer aided design tool for assessing building thermal performance characteristics

Computer aided design (CAD) tools of various complexities are being used extensively to predict the energy performance of buildings. A simple user-friendly CAD software was employed to estimate the cooling load profile of an energy efficient institutional building as a case study. At the same time, its air conditioning load pattern was measured and was found to be in good agreement with the predicted values. Parametric studies were carried out to assess the contribution of the various features incorporated in this energy efficient building. The results show that, by using such a simple tool, it is possible to identify the modifications which contribute to appreciable energy and demand reductions, and to gauge their economic viability. Such CAD tools are suitable not only for analysing new constructions at the design stage, but also for retrofitting of existing buildings.     

Market performance and bidders' bidding behavior in the New York Transmission Congestion Contract market

Using publicly available bidder level bids data for Transmission Congestion Contracts (TCCs) and the realized awards of TCCs in the NYISO monthly reconfiguration auctions from June 2000 to December 2004, we examine both market performance and bidders' bidding behavior in the auctions. The data show significant under-pricing in the realized awards of TCCs. Theories suggest that under-pricing may arise from risk-aversion, monopsonistic market power or winner's curse. Our empirical analysis illustrates that all of the three effects play a role in the NYISO TCCs market. Both market performance and bidders' bidding strategies can be best explained by the theoretical model with asymmetric information and risk-averse bidders.     

Thermal performance evaluation of an energy and environmental research center building during winter

The building is constructed on a ground area of 3300 m² and consists of five floors of total area of 6361 m² with an air conditioned area of 3351 m². The heating system comprises 1577 evacuated-tube collectors, two accumulation tanks of 15 m³ each, two thermal storage tanks of 150 m³ each, two auxiliary boilers of 443,000 kcal/h each, pumps, heat exchangers and control equipment. The thermal performance evaluation shows that the inside temperature was kept at the desired value (22°C) which demonstrates the system's ability to meet the building load. The performance also shows that the collection efficiency for the whole season was 50% and the collected and stored energy was higher than the required load which indicates that the solar fraction to the load was 100%.     

Development of autonomous monitoring and performance evaluation system of grid-tied photovoltaic station

This work aims to improve the existing monitoring systems MS for two grid-connected PV stations GCPVS of URERMS ADRAR, to eliminate its limitations. This improvement consists of developing an MS which is used for two PV stations with different configurations. This MS contains new LabVIEW-based monitoring software for visualizing real-time measured data and evaluating GCPVS performance. In addition, it illustrates the 2D and 3D real-time relationships of PV system parameters, which allow us to understand the dynamic behavior of PV system components. This developed monitoring software synchronizes also the various data acquisition units DAU of GCPVS, allowing simultaneous data access.To perform a reliable performance analysis and a comparative study of different GCPVS based on accurate measurements, the sensor's calibration is performed with its DAU. The MS autonomy is ensured by integrating developed PV-UPS. A graphical user interface is provided for the evaluation of PV-UPS performance.     

A tool for creating energy market scenarios for evaluation of investments in energy intensive industry

The energy intensive industry can be a major contributor to CO₂ emissions reduction, provided that appropriate investments are made. To assess profitability and net CO₂ emissions reduction potential of such investments, predictions about future energy market conditions are needed. Energy market scenarios can be used to reflect different possible future energy market conditions. This paper presents a tool for creating consistent energy market scenarios adapted for evaluation of energy related investments in energy intensive industrial processes. Required user inputs include fossil fuel prices and costs associated with policy instruments, and the outputs are energy market prices and CO₂ consequences of import/export of different energy streams (e.g. electric power and biomass fuel) from an industrial process site. The paper also presents four energy market scenarios for the medium-term future (i.e. around 2020) created using the tool.     

A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

既有建筑外保温系统性能检测与评定标准探究

在既有建筑围护结构中,较为常见的系统为外墙外保温系统,但此类系统通过使用却暴露出一些不容忽视的问题。因此,为了使建筑物展现出良好的保温效果,有必要对外墙外保温系统的性能进行准确检测,并选择有效的评价方法。基于此,论述了既有建筑外保温系统性能检测所包含的主要内容,指出了外保温系统的评价方法、评价标准与评价定级,其中评价定级涉及5个方面,即外墙外保温系统连接安全性评价、防火安全性评价、保温功能评价、美观耐久性评价及综合性能评价,最后以阐明如何评价外保温系统的连接安全性为目的,对具体的案例进行了深入剖析。     

Design and performance of a solar-powered air-conditioning system in a green building

A solar-powered adsorption air-conditioning system was designed and installed in the green building of Shanghai Research Institute of Building Science. The system contained 150 m² solar collectors and two adsorption chillers with nominal refrigeration capacity of 8.5 kW. Based on performance characteristics of the adsorption chiller, the operation mode of the solar-powered air-conditioning system was optimized by maintaining a phase shift of 540 s between the two adsorption chillers. Thereafter, the whole system realized stable operation by the balance of heat consumption and refrigeration output. From June to August of 2005, the solar-powered air-conditioning system continuously ran between 9:00 and 17:00. The operation performance of the system under representative working condition showed that the average refrigeration output of the solar-powered air-conditioning system was 15.3 kW during an 8 h operation and the maximum value exceeded 20 kW. Solar fraction for the system in summer was 71.7%, which corresponded to the designed cooling load (15 kW). Compared with the ambient temperature, it was deduced that solar radiant intensity had a more distinct influence on the performance of solar-powered air-conditioning system.     

A new test cell for the evaluation of thermo-physical performance of facades building components

How do the new building façade components work under real climatic conditions? The question is especially related to the dynamic behaviour of new and complex components such as the ventilated walls, the Phase Change Material, or others that use nano-technologies and aerogels. One of the objectives of the undergoing research activity, named Abitare Mediterraneo, is the evaluation of their thermal behaviour through the use of an outdoor test cell, in order to reproduce under the real external conditions the performance of these components, and consequently define the main thermal parameters such as the attenuation factor and the thermal inertia, characterising the component; moreover, the results will be used to write new algorithms for dynamic simulation tools allowing an appropriate evaluation of the complex behaviour of the whole building at a real scale condition. The new test cell is realised in Florence, Italy. The design starts from the study of the experience of the existing PASSYS test cells, overtaking the main weakness of the building structure and of the heat-flux sensors.     

Effect of storage on thermal performance of a building

The effect of thermal storage on the thermal performance of a non-airconditioned room of size 6 × 4 × 2.7 m has been analysed. It is found that the presence of thermal storage decreases the swing in room temperature and that the increased surface area is more effective in reducing the temperature swing than large thermal capacity of the storage material.     

Effect of orientation on thermal performance of a building

The effect of aspect ratio and orientation of a non-airconditioned building on its thermal performance has been analysed in terms of discomfort index for hot-dry and composite climates. It is shown that the discomfort index for east-west orientation is smaller than that for north-south orientation but the difference even for the largest aspect ratio considered is not more than 10%.     

On the evaluation of market power and market dominance—The Nordic electricity market

This paper studies different concentration and dominance measures using structural indexes used to initially screen the competitive situation in a market. The Nordic and Swedish electricity markets are used as the empirical cases. Market concentration issues in the Nordic electricity market in general and in Sweden in particular have been, at least in initial screenings, approached by the Herfindahl–Hirschman Index (HHI). This article uses an alternative measure to HHI, which is based on market shares of the two largest firms in the market. The results shows that only the Swedish wholesale market has a firm that can be regarded as dominant, but only during very short periods. The results from a hypothetical merger between the second and third largest company in the Swedish wholesale market shows that when the dominant position of the largest firm is reduced, by increasing the size of the second largest firm, the threshold value indicates that competition actually will increase (contradicting to the HHI).     

BIPV: a real-time building performance study for a roof-integrated facility

Building integrated photovoltaic system (BIPV) is a photovoltaic (PV) integration that generates energy and serves as a building envelope. A building element (e.g. roof and wall) is based on its functional performance, which could include structure, durability, maintenance, weathering, thermal insulation, acoustics, and so on. The present paper discusses the suitability of PV as a building element in terms of thermal performance based on a case study of a 5.25?kW_p roof-integrated BIPV system in tropical regions. Performance of PV has been compared with conventional construction materials and various scenarios have been simulated to understand the impact on occupant comfort levels. In the current case study, PV as a roofing material has been shown to cause significant thermal discomfort to the occupants. The study has been based on real-time data monitoring supported by computer-based building simulation model.     

An advanced framework for real-time market operations and monitoring

This paper reviews the relationship between specific power system operations and market functions, introduces a definition of market conditions that correspond to grid operating states, and proposes an integrated approach for real-time power market operations and monitoring, which will help ensure reliable operations at the lowest cost in decentralized markets and provide effective incentives for market participants.     

PEEM—a spectromicroscopic tool for mc-Si surface evaluation

The photo emission electron microscope (PEEM) with its direct imaging of the sample surface is a convenient tool for fast evaluation of large sample areas. It is possible to handle samples with a size of 30 mm × 30 mm.With PEEM it is possible to visualise grain boundaries and crystal displacements without removing the native oxide. No special sample treatment is needed except chemical polishing of the sample surface and a HF-dip to obtain a thin (1…2 nm) oxide layer.The quality of that oxide was proofed by high resolution photo electron spectroscopy (PES) at a synchrotron. The results were compared to native oxide on single-crystalline Si and no suboxides (e.g. SiO) were found. Our spectromicroscopic PEEM measurements show no difference in the oxide qualities of different grains and on grain boundaries or crystal displacements. Furthermore no difference in the binding energy of Si2p core levels were found.In addition to grain boundaries other spot-like features were found on the sample surface. These could be identified in some cases as precipitation of Ca underneath the native oxide.     

Performance evaluation of a passive solar building in Western Himalayas

Under the Passive Solar Building Programme, more than 100 buildings have been constructed in the high altitude region of the Indian State of Himachal Pradesh. A policy decision has been taken by the State that all government/semi-government buildings are to be designed and constructed as per passive solar housing technology. The evaluation studies of some of these buildings have been carried out by our group. In the present study, the thermal performance of a passive solar bank building at Shimla, has been evaluated. This solar building incorporates a heat-collecting wall and a roof-top solar air heater with an electric heating backup, sunspaces and double-glazed windows. The monitoring of the building shows that the solar passive features in the building results in comfortable living conditions. The study shows that the high cost central electric/gas/wood-fired heating systems can be replaced by a low cost solar heating system with backup heaters. This will result not only in reducing higher installation costs of these systems but also the annual running and maintenance costs. It is shown that the solar passive features save electricity required for space heating and reduce the heat losses in the building by about 35%. The strategy to be followed for the propagation of passive solar technology on large scale in this Himalayan State or in any other cold hilly region is also presented.     

Measuring temperatures in a high concentration solar simulator - Demonstration of the principle

A new single color pyrometric method for samples heated radiatively via an artificial light source is presented. The method allows separation of the external radiation reflected by a sample from its thermal emission as the intensity of arc lamps, commonly used in high concentration solar simulators, can be electrically modulated at frequencies well above the thermal response (ω ? 1/τ_th) of the sample. Thus, the external radiation reflected off the sample can be measured separately using a phase sensitive detection scheme at the modulation frequency of the light source. In addition, a composite signal consisting of the thermal emission with the reflected external radiation superimposed is detected. This signal is obtained by observing the sample with a mechanical chopper operating at a different frequency placed in the observation path. The composite signal is measured simultaneously with identical optics and detector. The thermal emission of the sample can then be extracted as the difference of the two measured signals after suitable calibration. The working principle of the method and its calibration is explained and the performance of the method is demonstrated using its implementation on a lab scale.     

某供电大楼冰蓄冷空调测试的分析与评估

通过实测、调研某供电大楼冰蓄冷空调系统,从技术和优化运行角度对该冰蓄冷空调系统所测数据进行分析,指出该系统中蓄冰槽蓄冷率低、释冷不足的问题,并进行分析。接着论述了冰蓄冷空调系统的蓄冰槽不仅要在蓄冰量上与系统主机容量相匹配,同时还要考虑到蓄冰槽的蓄冰、融冰特性,最后说明系统运行管理人员对冰蓄冷空调系统在节能运行上产生的影响。