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Abstract The albedo of a roof determines the fraction of incoming sunlight that is reflected, which affects heat transfer into the building and exchange of energy between the built environment and the atmosphere. While the albedo of individual roofs can be easily measured, roof albedo at the city scale is unknown. In this paper we characterize the albedos of roofs in seven cities in California: Los Angeles, Long Beach, Bakersfield, San Francisco, San Jose, Sacramento, and San Diego. The fraction of urban area covered by roofs ranged by city from 10% to 25%. City-wide average roof albedo ranged from 0.17 ± 0.08 to 0.20 ± 0.11 (mean ± standard deviation) for five of the cities; values were higher in Sacramento (0.24 ± 0.11) and San Diego (0.29 ± 0.15). Buildings with small roofs were found to constitute a large fraction of city roof area and to have low mean albedos. This suggests that efforts to increase urban albedo through the use of reflective roofs should include small roofs, which are presumably mostly residential. Roof albedos derived for Bakersfield were used in a regional climate model (Weather Research and Forecasting Model) to estimate temperature changes attainable by converting the current stock of roofs to “cool” high albedo roofs. It was found that seasonal mean afternoon (15:00 LST) temperatures could be reduced by up to 0.2 °C during both the summer and winter. Changes in precipitation were not significant at the 95% confidence level.

A linear correlation between UV-A and 380 nm was developed by means of the TUV 4.1 radiative transfer model. The prediction error of the correlation was evaluated with data from Buenos Aires, Argentina, 2001, and from 2006, Almeria, Spain. Percent random mean square error (RMSE%) was calculated for intervals of 10° of solar zenith angles, ranging 4.75% at 20° to 37.70% at 90° in clear days and 22.16% at 20° to 26.17% at 90° for cloudy days in Buenos Aires Argentina, and 1.27% at 20° to 11.27% at 90° for clear days in Almeria, Spain. Clouded days were not assessed with the data from Spain. In Argentina, the UV-A radiometer is located in a rural area and the 380 nm radiometer is located in an urban area 6 km away. Hence the real error of the proposed model is closer to that found in Spain were both measurements were performed at the same site. The objective of the work is to achieve a simple and precise method to assess UV-A availability for environmental applications of solar energy, particularly for solar water treatment, at any desired latitude.

Abstract Conventional jaggery making process utilizes the bagasse for boiling of sugar cane juice which releases pollutants into the atmosphere and high particulate matter from these emissions causes air pollution. In this article, solar powered jaggery industry with freeze pre-concentration is proposed with conventional and modified heating pans. The system performance, environmental impacts and economic feasibility were assessed by carrying out 4E (Energy-Exergy-Environment-Economic) analyses using the developed mathematical model. These systems were designed to produce 300 kg of jaggery per day when operated for 7.5 h in 3 batches with average solar direct normal irradation of 662 W/m2 and 343 °C. These systems are integrated with auxiliary heating for uninterrupted production in the absence of sunlight. These systems can mitigate nearly 2015.95 to 3062.15 tons of CO2 emission during its 25 years of lifespan under 300 clear days of operation each year. Jaggery produced by this technique is rich in its colour and completely safe for human consumption as no artificial clarificants are used. Amount invested in these systems can be recovered in a span of 12.03 to 13.45 years for jaggery selling price of USD.0.514/kg or INR.36/kg.

This paper provides a simplified analysis tool to assess the energy saving potential of daylighting for commercial buildings through skylights. Specifically, the impact of daylighting is investigated for various fenestration opening sizes, glazing types, control strategies, and geographic locations. A top floor of a prototypical office building has been considered in the analysis. The results obtained for the office building can be applied to other types of buildings such as retails stores, schools, and warehouses. Based on the simulation analysis results, it was determined that skylight to floor ratio more than 0.3 does not affect significantly the lighting energy savings. An optimum value of skylight to floor area ratio was found to be 0.2 to minimize the annual total building energy use.

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.

Abstract The aim of this paper is to examine the energy consumption of and determine energy-efficient design strategies for mid-rise and high-rise office buildings in composite climate. For this purpose, a comparative study is performed of six energy-efficient office buildings in composite climate in India. The selected energy-efficient office buildings are situated in the major cities (Delhi, Gurgaon, and Hyderabad) of India with a composite climate. This study investigates the effectiveness of different design strategies for reducing the heating, ventilation, and air-conditioning (HVAC) and lighting loads of the six buildings. The effect of factors such as the building form, envelope configuration, placement of the service core, window-to-wall ratio (WWR), and percentage of air-conditioned space on the HVAC load are analyzed. Similarly, the effect of the plan depth and WWR on the lighting load is also determined. Finally, the findings of the study are used to recommend effective design strategies for high-rise office buildings in composite climate. Moreover, the energy performance data are compared with the national energy consumption benchmarks for composite climate. The comparison indicates the design strategies performed well, that lead to a decrease in the energy consumption of high-rise office buildings in composite climate.

The objective of the present project is to develop a software simulation tool to accurately estimate the power generated from solar energy absorbed by photovoltaic panels mounted on the fac¸ade of a building in an urban environment, taking into account shading and reflection from neighboring buildings. The software tool has been designed and modeled in AutoCAD, with the help of AccuRender/Ecotect. We have previously presented the modeling approach [1]. We have recently established a test facility in which a 50W BP Solar module surrounded by several glass panels in wood frames has been used to simulate a BIPV system with neighboring buildings. Current-voltage characteristics at different times of day for different months are in the process of being recorded together with solar insolation data. These data will be used to perform preliminary validation of the simulation software. A preliminary comparison of the collected experimental solar module performance data with the computer simulated data will be presented.

The concept of reducing the cooling load of airconditioned building by maintaining a water film spray over the roof is a well known proposition in the literature and has been exploited both experimentally and theoretically by several workers. The conscious scientific application of air ventilation in summer has also been suggested for passive space airconditioning. Since the ventilation is controlled by opening windows/door and hence depends on ventilation timings or its duration, a periodic analysis for variable ventilation is also desirable if the window on south-facing wall is opened/closed on daily cycle. In this communication the authors have developed a periodic heat transfer model which incorporates the effects of furnishings (assumed isothermal mass), air ventilation through window/door (assumed time dependent) and the basement ground heat storage. Explicit expression for the indoor air temperature as a function of time in a building with a water film over the roof and controlled ventilation has been obtained. Numerical calculations for a typical hot summer day in Delhi using the relevant parameters have been made to study the feasibility of the proposed model. The effects of the presence/absence of water spray over the roof, continuous and intermittent ventilation rates and timings on the indoor air temperature have been examined. It is found that the maintenance of a water film spray over the roof and the ventilation control systems in a building in hot sunny climates significantly reduces the indoor air temperature.

Even though PV technology is new and expensive for the building industry today, and regardless of market development and technology advancement, a BIPV system cost can actually be reduced and its application can spread further into the building industry as this paper will manage to show. However, PV systems still have not been accepted by the building industry and consumers yet. According to the results of a survey by the workshop of Building Integrated Photovoltaic for Design Professionals which was sponsored by the National Energy Laboratory (NREL) and the American Institute of Architects (AIA), “a major barrier to analyzing renewable energy systems is assembling and presenting the technical and financial data to persuade a client that a BIPV would make economic sense.” [Wenger and Eiffert, 1996] This paper uses Life Cycle Cost Analysis (LCCA) for identifying BIPV system cost components and makes the connection between the findings of LCCA and the design process. It identifies specific quantifiable measures/variables that will be compared with a non-PV integrated building or different PV system applications by using the LCCA method that confirms cost related issues. Calculations of payback period as a result of LCCA gauge the sensitivity of these variables and show how some of them are significantly more important than others in reducing the pay back period. Offering an efficient approach for integration of PV into curtain wall also meets the long-term objective of the satisfaction of the building user.

Abstract This paper is the second of two papers that describe the modeling and design of a building-integrated photovoltaic–thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) adopted in a prefabricated, two-storey detached, low energy solar house and their performance assessment based on monitored data. The VCS concept is based on an integrated thermal–structural design with active storage of solar thermal energy while serving as a structural component – the basement floor slab (∼33 m2). This paper describes the numerical modeling, design, and thermal performance assessment of the VCS. The thermal performance of the VCS during the commissioning of the unoccupied house is presented. Analysis of the monitored data shows that the VCS can store 9–12 kWh of heat from the total thermal energy collected by the BIPV/T system, on a typical clear sunny day with an outdoor temperature of about 0 °C. It can also accumulate thermal energy during a series of clear sunny days without overheating the slab surface or the living space. This research shows that coupling the VCS with the BIPV/T system is a viable method to enhance the utilization of collected solar thermal energy. A method is presented for creating a simplified three-dimensional, control volume finite difference, explicit thermal model of the VCS. The model is created and validated using monitored data. The modeling method is suitable for detailed parametric study of the thermal behavior of the VCS without excessive computational effort.