Study of the performance of thermoelectric modules for use in active building envelopes

Active building envelope (ABE) systems are a new enclosure technology which integrate photovoltaic (PV) and thermoelectric (TE) technologies. In ABE systems, a PV system supplies electrical power to a TE heat-pump system, which can transfer heat in one direction or another depending on the direction of the current. Both the TE and PV systems are integrated into one enclosure surface. Hence, ABE systems have the ability to actively control the flow of heat across their surface when exposed to solar radiation. Applications for this technology include all types of enclosures that require cooling or heating, such as building enclosures. At this stage of our study, we are developing various ABE system prototypes by using commercially available PV and TE technologies. In this study, two types of commercial available TE modules are studied for their potential application in an ABE prototype window system. We have performed various experiments to determine the coefficient of performance for these TE modules when operating under different voltage regimes, and have tested different electrical connection diagrams. Based upon the measured data, and results based on the computational models of a TE system, the most suitable type of TE modules, the voltage and current, and the preferable connection diagrams are discussed.     

Evaluation of a prototype active building envelope window-system

Active building envelope systems represent a new enclosure technology that uses solar energy to compensate for passive heat losses or gains through building envelopes. In ABE systems, energy obtained from solar radiation is converted into electrical energy by using photovoltaic cells. This electrical energy is subsequently used to power a series of solid-state thermoelectric modules, which can control the flow of heat through the enclosure. In order to assess the practical feasibility of ABE systems, we have developed a prototype ABE window-system and an outdoor testing room. A testing system was developed to measure the ABE system's temperatures, solar radiation, current and voltage. Theoretical and experimental results are presented and compared. Finally, the performance of the ABE window-system was evaluated.     

Evaluation of a PV-integrated building application in a well-controlled outdoor test environment

This paper presents the assessment of experimental data for electrical and thermal performance evaluation of photovoltaic (PV) systems integrated as cladding components into the building envelope, giving input to modelling and analysis work. From the experience gained in several EU research projects, an improved design for a common Test Reference Environment (TRE) has been developed. This specific design of the PV module and TRE makes it possible to study, through electrical and thermal energy flow analysis, the effect on electrical performance of using different materials for PV modules and the construction design of claddings. The results for a glass–glass PV module with forced ventilation are presented.     

Effect of building integrated photovoltaics on microclimate of urban canopy layer

Building integrated photovoltaics (BIPV) has potential of becoming the mainstream of renewable energy in the urban environment. BIPV has significant influence on the thermal performance of building envelope and changes radiation energy balance by adding or replacing conventional building elements in urban areas. PTEBU model was developed to evaluate the effect of photovoltaic (PV) system on the microclimate of urban canopy layer. PTEBU model consists of four sub-models: PV thermal model, PV electrical performance model, building energy consumption model, and urban canyon energy budget model. PTEBU model is forced with temperature, wind speed, and solar radiation above the roof level and incorporates detailed data of PV system and urban canyon in Tianjin, China. The simulation results show that PV roof and PV façade with ventilated air gap significantly change the building surface temperature and sensible heat flux density, but the air temperature of urban canyon with PV module varies little compared with the urban canyon of no PV. The PV module also changes the magnitude and pattern of diurnal variation of the storage heat flux and the net radiation for the urban canyon with PV increase slightly. The increase in the PV conversion efficiency not only improves the PV power output, but also reduces the urban canyon air temperature.     

The impact of building-integrated photovoltaics on the energy demand of multi-family dwellings in Brazil

Brazil faces a continuous increase of energy demand and a decrease of available resources to expand the generation system. Residential buildings are responsible for 23% of the national electricity demand. Thus, it is necessary to search for new energy sources to both diversify and complement the energy mix. Building-integrated photovoltaic (BIPV) is building momentum worldwide and can be an interesting alternative for Brazil due its solar radiation characteristics. This work analyses the potential of seven BIPV technologies implemented in a residential prototype simulated in three different cities in Brazil (Natal, Brasília and Florianópolis). Simulations were performed using the software tool EnergyPlus to integrate PV power supply with building energy demand (domestic equipment and HVAC systems). The building model is a typical low-cost residential building for middle-class families, as massively constructed all over the country. Architectural input and heat gain schedules are defined from statistical data (Instituto Brasileiro de Geografia e Estatística—Brazilian Institute for Geography and Statistics (IBGE) and Sistema de Informações de Posses de Eletrodomésticos e Hábitos de Consumo—Consumer Habits and Appliance Ownership Information System (SIMPHA)). BIPV is considered in all opaque surfaces of the envelope. Results present an interesting potential for decentralized PV power supply even for vertical surfaces at low-latitude sites. In each façade, BIPV power supply can be directly linked to local climatic conditions. In general, for 30% of the year photovoltaic systems generate more energy than building demand, i.e., during this period it could be supplying the energy excess to the public electricity grid. Contrary to the common belief that vertical integration of PV is only suitable for high latitude countries, we show that there is a considerable amount of energy to be harvested from vertical façades at the sites investigated.     

Energy distribution analysis in full-scale open floor plan enclosure fires

Within a fast evolving built environment, understanding fire behaviour and the thermal exposure upon structural elements and systems is key for the continued provision of fire safe designs and solutions. Concepts of fire behaviour derived from research in enclosure fires has traditionally had a significant impact in general building design. At present, open floor plan enclosures are increasingly common – building design has drastically drifted away from traditional compartmentalisation. Nevertheless, the understanding of fire behaviour in open floor plan enclosures has not developed concurrently. The compartment fire framework, first conceived for under-ventilated fires in cubic compartments, has remained as standard practice. Although energy conservation within the enclosure was the basis for the current compartment fire framework that defines under-ventilated enclosure fires, little effort has been carried towards understanding the distribution of energy in design frameworks conceived for open floor plan enclosure fires. The work presented herein describes an analysis of the energy distribution established within an experimental full-scale open floor plan enclosure subjected to different fire modes and ventilation conditions. The results aim to enable the designer to estimate the fraction of the total energy released during a fire noteworthy to structural performance.     

A proposed framework for dynamic modelling of photovoltaic systems for DG applications

Dynamic modelling and simulation is essential to predict the overall electrical performance of photovoltaic (PV) systems. PV simulation models in the literature are not suitable for dynamic analysis with decentralised generation (DG) applications. This article proposes a framework for PV system dynamic modelling and simulation process. This framework presents the steps required to model the process of solar power generation, reflecting the environmental variables affecting the generation process. Based on the framework steps, a computer simulation model is developed in MATLAB-Simulink of the PV generator, and validated by comparing the developed PV electrical performance characteristic curves with those of the manufacturer's data sheet and the ones developed by commercial software. The last step of the proposed framework is dedicated for testing the developed PV model for grid-connected operation. The proposed framework resulted in a simulation photovoltaic decentralised generation model which constitutes a computer-aided design tool that is helpful for real-world solar energy engineering.     

上海地区独立住宅分布式光伏发电系统的后评估研究

基于上海一独立住宅光伏发电系统运行一年的数据,从发电量、光伏系统效率、光伏能源替代率、光伏系统效率影响因素等方面进行后评估。结果表明:过去一年度理论预测年发电量为5 738 k W·h,实际发电量为4 109 k W·h,全年度光伏系统效率为73%。为研究光伏系统效率的影响因子,在系统运行期间未对光伏组件表面实施人工清洁维护,对此条件下的运行数据进行分析发现,光伏系统效率总体呈现逐渐降低的趋势。其中在近水平安装角度的情况下,组件光电转换效率最大降低达2.08%。在该住宅按照现行理想的设计条件运行(冬季连续采暖确保室内20℃、夏季连续空调确保室内26℃)的前提下,过去一年度的总用电量为12 054 k W·h,其中空调用电量为9 332 k W·h,占到总用电量的77.4%。全年光伏能源替代率为34%,过渡季节可实现光伏能源替代率最高达180%。独立住宅上存在较大的节能空间和光伏能源替代率提升空间。     

Enabling the hybrid use of air conditioning: A prototype on sustainable housing in tropical regions

This paper demonstrates how the use of active or passive means only does not give the appropriate answers to a tropical design when considering housing. The author discusses about the idea of both modes of operation being used simultaneously or in parallel, and how this concept has been developed for one experimental building prototype in tropical areas of Brazil (Northeast region). Quantification is given through extensive parametric simulations which have been conducted using different environmental simulation programmes—TAS (EDSL, UK), ESP-r (ESRU, UK) and photovoltaic (PV)-Design PRO-G (Sandia Labs, USA). Thermal comfort levels along with energy use were assessed and compared, in terms of degree hours of overheating/under heating and cooling energy use. The prototype design has also taken into account the appropriate use of resources through sustainable design features: efficient use of energy, water and materials. The results have demonstrated that for regions such as the warm-humid tropics, the use of a mixed running strategy have optimized energy performance and provided better levels of thermal comfort in a much more effective way. For some cases, cooling energy savings up to 80% were feasible on a hybrid mode, where thermal comfort was improved up to 65%. It has also demonstrated the integration of energy efficiency and a PV grid-connected system, while enabling those daytime electrical needs to be accomplished by the photovoltaic component.     

1st Environmental conference of Thessaly region, 8–10 September 2012, Hotel Skiathos Palace,Koukounaries, Skiathos Island,Greece

This study was conducted with the aim to assess the potential performance of a photovoltaic thermal mechanical ventilation heat recovery (PV/T MVHR) system. The device is currently considered for the application to the Z-en house project undertaken by Scottish homebuilder. The house’s whole energy demand was calibrated based on the UK Government’s standard assessment procedure for energy rating of dwellings, while the PV/T performance was estimated using an ‘EESLISM’ energy and environmental design simulation tool developed by Kogakuin University. This study concluded that PV generates heat, which makes the fresh air running under the PV roof 10–15?°C warmer than the outside temperature even during the Scottish winter and this warm air extracted from roof-integrated PV modules can be used to help reduce the domestic space-heating demand. Thus, the building-integrated PV/T MVHR system was considered as one of the effective means to assist the net zero energy operation of housing in cool and cold climates, whose dominant domestic energy comsumption derives from space heating.     

Life cycle energy of single landed houses in Indonesia

Building enclosures contribute 10–50% of the total building cost and 14–17% of the total material mass. The direct as well as indirect influence of the enclosure materials plays an important role in the building life cycle energy. Single landed houses, the typical houses in Indonesia, have been chosen for this study. The life cycle energy of the house enclosures and energy consumed during their life spans shows intriguing results. The initial embodied energy of typical brick and clay roof enclosures is 45 GJ compared to the other typical walls and roof material (cement based) which is 46 GJ. However, over the 40 years life span of the houses, the clay based ones have a better energy performance than the cement based ones, 692 GJ versus 733 GJ, respectively. The material selection during the design phase is thus crucial since the buildings have at least 40–50 years’ life span.     

Experimental and numerical investigation on the performance of amorphous silicon photovoltaics window in East China

Experiments in a comparable hot-box have been carried out for the study of the thermal performance and power generation of a double-glazing window system integrated with amorphous silicon (a-Si) photovoltaic (PV) cells in Hefei, east region of China. Compared to PV single-glazing window, the indoor heat gain of PV double-glazing window is reduced to 46.5% based on experiment data. The electric efficiencies are both about 3.65% with packing factor 0.8 of PV single-glazing window and PV double-glazing window. The numerical simulation with computational fluid dynamics (CFD) method has been performed for the prediction of air flow and thermal performance of PV double-glass window. The temperature distribution and thermal performance predicted by the CFD model are in good agreement with the experimental data. Compared between the experimental and numerical results, temperature differences of PV modules are only 1.7% and 1.1% for PV double-glazing and PV single-glazing window, respectively. Because of the much lower inner surface temperature of PV double-glazing window compared with that of PV single-glazing window, the predicted mean vote (PMV) of the office work stage area with PV double-glazing window is well improved.     

Effect of thermal mass on the thermal performance of various Australian residential constructions systems

The impact of thermal mass on the thermal performance of several types of Australian residential construction, namely: cavity brick (CB), brick veneer (BV), reverse brick veneer (RBV), and light weight (LW) constructions, was examined numerically using the commercial AccuRate energy rating tool developed by the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO). The performance of each construction type was evaluated using four different hypothetical building envelopes, referred to here as building modules. It was found that the thermal mass had a dramatic impact on the thermal behaviour of the modules studied, particularly in those where the thermal mass was within a protective envelope of insulation. The RBV and CB constructions were found to be the most effective walling systems in this regard.     

Effect of fluid flow and packing factor on energy performance of a wall-mounted hybrid photovoltaic/water-heating collector system

Façade-integrated photovoltaic/thermal (BiPV/T) technology is a relatively new concept in improving the overall energy performance of PV installations in buildings. With the use of wall-mounted water-type PV/T collectors, the system not only generates electricity and hot water simultaneously, but also improves the thermal insulation of the building envelope. A numerical model of this hybrid system was developed by modifying the Hottel–Whillier model, which was originally for the thermal analysis of flat-plate solar thermal collectors. Computer simulation was performed to analyze the system performance. The combined effects of the solar cell packing factor and the water mass flow rate on the thermal and electrical efficiencies were investigated. The simulation results indicated that an optimum water mass flow rate existed in the system through which the desirable integrated energy performance can be achieved.     

Energy and exergy analysis of PV/T air collectors connected in series

In this paper an attempt has been made to derive the analytical expressions for N hybrid photovoltaic/thermal (PV/T) air collectors connected in series. The performance of collectors is evaluated by considering the two different cases, namely, Case I (air collector is fully covered by PV module (glass to glass) and air flows above the absorber plate) and Case II (air collector is fully covered by PV module (glass to glass) and air flows below the absorber plate). This paper shows the detailed analysis of energy, exergy and electrical energy by varying the number of collectors and air velocity considering four weather conditions (a, b, c and d type) and five different cities (New Delhi, Bangalore, Mumbai, Srinagar, and Jodhpur) of India. It is found that the collectors fully covered by PV module and air flows below the absorber plate gives better results in terms of thermal energy, electrical energy and exergy gain. Physical implementation of BIPV system has also been evaluated. If this type of system is installed on roof of building or integrated with building envelope will simultaneously fulfill the electricity generation for lighting purpose and hot air can be used for space heating or drying.     

Simplified method of sizing and life cycle cost assessment of building integrated photovoltaic system

This paper presents methodology to evaluate size and cost of PV power system components. The simplified mathematical expressions are given for sizing of PV system components. The PV array size is determined based on daily electrical load (kWh/day) and number of sunshine hours on optimally tilted surface specific to the country. Based on life cycle cost (LCC) analysis, capital cost (US$/kW_P) and unit cost of electricity (US$/kWh) were determined for PV systems such as stand-alone PV (SAPV) and building integrated PV (BIPV). The mitigation of CO₂ emission, carbon credit and energy payback time (EPBT) of PV system are presented in this paper. Effect of carbon credit on the economics of PV system showed reduction in unit cost of electricity by 17-19% and 21-25% for SAPV and BIPV systems, respectively. This methodology was illustrated using actual case study on 2.32 kW_P PV system located in New Delhi (India).     

Optimal size and cost analysis of stand-alone hybrid wind/photovoltaic power-generation systems

Design of sustainable energy systems for the supply of electricity need correct selection and sizing to reduce investment costs. In this article, a new sizing methodology is developed for stand-alone hybrid wind/photovoltaic (PV) power systems, using multi-objective optimisation algorithms. Multi-objective particle swarm optimisation algorithm and non-dominated sorting genetic algorithm-II are selected related to their match with the nature of renewable energy sizing problem. A match evaluation method is developed based on renewable energy supply/demand match evaluation criteria, to size the proposed system in the lowest cost. As an example of application of this technique, six different wind turbines (WTs) and also six different PV modules have been considered. The sizing methodology determines a multi-objective design, obtaining the best solutions that the applied algorithm has found simultaneously considering three objectives: inequality coefficient, correlation coefficient, and annualised cost of system. The optimal number of WTs, PV modules, and batteries ensuring that the system total cost is minimised while guaranteeing a highly reliable source of load power is obtained. A management strategy has been designed to achieve higher electricity match rate. Based on the proposed technique, the algorithm developed for different cases, using the climatic condition data of the city Zabol, located in south-east of Iran. Additionally, a study of operating hours of diesel generator in optimal configuration is carried out.     

中国被动房外围护系统研究——以寒冷、严寒气候区被动房项目为例

德国的被动房是目前世界公认的具有超低能耗、超低碳排放量、超高室内舒适度等特点的建筑技术体系。德国的气候特征与中国华北地区的气候特征具有相似性,因此,研究并建造被动房对于我国建筑节能工作的发展具有重大的意义。外围护系统作为被动房设计的重点要素,对建筑的节能效率有重大的影响。以寒冷、严寒气候区的被动房项目为例,对被动房外围护系统进行分析与阐述,并以秦皇岛"在水一方"被动式住宅示范项目为例,进行能耗模拟与对比分析。提出适合我国寒冷、严寒气候区气候特点的被动式超低能耗建筑外围护系统的设计策略。     

A general methodology for optimal load management with distributed renewable energy generation and storage in residential housing

In the US, buildings represent around 40% of the primary energy consumption and 74% of the electrical energy consumption [U.S. Department of Energy (DOE). 2012. 2011 Buildings Energy Data Book. Energy Efficiency & Renewable Energy]. Incentives to promote the installation of on-site renewable energy sources have emerged in different states, including net metering programmes. The fast spread of such distributed power generation represents additional challenges for the management of the electricity grid and has led to increased interest in smart control of building loads and demand response programmes. This paper presents a general methodology for assessing opportunities associated with optimal load management in response to evolving utility incentives for residential buildings that employ renewable energy sources and energy storage. An optimal control problem is formulated for manipulating thermostatically controlled domestic loads and energy storage in response to the availability of renewable energy generation and utility net metering incentives. The methodology is demonstrated for a typical American house built in the 1990s and equipped with a single-speed air-to-air heat pump, an electric water heater and photovoltaic (PV) collectors. The additional potential associated with utilizing electrical batteries is also considered. Load matching performance for on-site renewable energy generation is characterized in terms of percentage of the electricity production consumed on-site and the proportion of the demand covered. For the purpose of assessing potential, simulations were performed assuming perfect predictions of the electrical load profiles. The method also allows determination of the optimal size of PV systems for a given net metering programme. Results of the case study showed significant benefits associated with control optimization including an increase of load matching between 3% and 28%, with the improvement dependent on the net metering tariff and available storage capacity. The estimated cost savings for the consumer ranged from 6.4% to 27.5% compared to no optimization with a unitary buy-back ratio, depending on the available storage capacity. Related reduction in CO₂ emissions were between 11% and 46%. Optimal load management of the home thermal systems allowed an increase in the optimal size of the PV system in the range of 13–21%.     

Study on thermal performance of semi-transparent building-integrated photovoltaic glazings

This paper presents a one-dimensional transient heat transfer model, the Semi-transparent Photovoltaic module Heat Gain (SPVHG) model, for evaluating the heat gain of semi-transparent photovoltaic modules for building-integrated applications. The energy that is transmitted, absorbed and reflected in each element of the building-integrated photovoltaic (BIPV) modules such as solar cells and glass layers were considered in detail in the SPVHG model. Solar radiation model for inclined surface has been incorporated into the SPVHG model. The model is applicable to photovoltaic (PV) modules that have different orientations and inclinations. The annual total heat gain was evaluated by using the SPVHG model. The impacts of different parameters of the PV module were investigated. It was found that solar heat gain is the major component of the total heat gain. The area of solar cell in the PV module has significant effect on the total heat gain. However, the solar cell energy efficiency and the PV module's thickness have only a little influence on the total heat gain. The model was also validated by laboratory tests by using a calorimeter box apparatus and an adjustable solar simulator. The test results showed that the simulation model predicts the actual situation well.