Overall energy performance of semi-transparent single-glazed photovoltaic (PV) window for a typical office in Hong Kong

This paper develops an overall methodology for investigating the thermal and power behaviors of semi-transparent single-glazed photovoltaic window for office buildings in Hong Kong. In order to estimate its overall energy performance, this study is conducted in terms of total heat gain, output power and daylight illuminance. Three simulation models are established, including one-dimensional transient heat transfer model, power generation model and indoor daylight illuminance model. A typical office room reference is chosen as case study, and the weather data from 2003 to 2007 from the Hong Kong Observatory are used as the simulation inputs. By incorporating the simulation results, the overall energy performance can be evaluated in terms of electricity benefits corresponding to five orientations of the studied typical office. The priority of office orientation considering overall energy performance is: south-east, south, east, south-west and west. The findings show that thermal performance is the primary consideration of energy saving in the entire system whereas electricity consumption of artificial lighting is the secondary one. The overall annual electricity benefits are about 900 kWh and 1300 kWh for water-cooled and air-cooled air-conditioning systems respectively. The application of semi-transparent PV glazed window can not only produce clean energy, but also reduce building energy use by reducing the cooling load and electrical lighting requirements, which definitely benefits our environmental and economic aspects.     

A test method to evaluate the thermal performance of window glazings

An apparatus and a methodology to evaluate the thermal performance of window glazing are presented. Single glazings commercially available in Mexico are currently tested. During the test sequence, the glass samples are mounted in a specially designed calorimeter apparatus. The test is conducted in controlled laboratory conditions at the National Centre for Research and Technology Development in Mexico using a solar simulator test lamp. The calorimeter apparatus and the solar simulator test lamp were characterised and the overall heat loss coefficient U_c measured was of 1.7±0.1 W/m²°C. Overall heat transfer and shading coefficients are derived from the experimental results. The test method described allows the testing of practically any kind of glazing array. Glasses under investigation were of the reflective, absorbing coloured and common ones. This test method can be adequate to evaluate film coating glazing or multiple solar control coating glazing. Also, it can be of assistance to researchers, glass manufacturers and building designers in the development of rating and comparing of glazing options.     

Design and performance evaluation of a pump-as-turbine micro-hydro test facility with incorporated inlet flow control

In the context of micro-hydro power schemes the initial cost of conventional Francis turbine units is often prohibitive. As such there is growing interest in pump-as-turbine (PAT) technology offering a more cost effective, yet still highly efficient, power generating alternative, finding uses in remote area power supply and energy recovery systems. However, the implementation of a PAT is highly problematic in terms of predicting the installed best operating point coupled with poor off-design performance due to the fixed geometry and absence of inlet flow control. In the current work a micro-hydro test facility and turbine unit is developed utilising a commercially available pump impeller together with a customised housing for incorporation of inlet flow control. Working initially from established PAT theory, this paper presents the design and performance testing of a hydraulic turbine unit suitable for use in rural micro-hydro, and energy recovery installations. Maximum efficiency of the unit was found to be 79%, marginally higher than that of the parent pump, while the off-design efficiency offered considerable improvement over previously published data of traditional PAT systems. The design provides a cost effective power generator in comparison to small scale Francis turbines, while providing a greater operational range than traditional PAT units.     

Seasonal thermal performance analysis of glazed window filled with paraffin including various nanoparticles

A two-dimensional heat transfer model was proposed to numerically investigate the effect of enriching phase change material (PCM) with different kinds of nanoparticles on thermal performance of glazing windows in different seasons of the year. The results were presented in terms of liquid fraction of PCM, inner surface temperature and temperature difference between interior and exterior surfaces of glass window, and their occurrence times. The results showed that adding nanoparticles into PCM can promote the melting and solidification processes, extend the total time of PCM being in the liquid state, and raise the internal surface temperature of glass. However, in summer season, the internal surface temperature decreases and the total melting time respectively reduces by 7 and 1.5 minutes by introducing TiO₂ and ZnO nanoparticles into PCM. Furthermore, the introduced nanoparticles do not have the same effect on the thermal performance of the window unit. While the inner surface temperature decreases by 0.82 K in summer by addition of TiO₂ to PCM, it increases by 0.84 K in transition season and 0.89 K in winter season by utilizing ZnO nanoparticles. Although the nano-PCM remains in the solid state in winter, the existence of nanoparticles can still increase the inner surface temperature.     

The effect of a ventilated interior courtyard on the thermal performance of a house in a hot–arid region

This study describes an experiment to investigate the effect of a ventilated interior courtyard on the thermal performance of a house in a hot–arid region. The site of the experiment is Al-Oyyena village, situated in the countryside around Riyadh, Saudi Arabia. Statistical analysis of data recorded during the summer of 1997 was carried out. The results indicate that the courtyard gives high efficiency in providing cool indoor air through cross-ventilation. A statistical module and its validation for natural ventilation are presented. The aim is to estimate the indoor daily average dry-bulb temperature as a function of outdoor temperature and wind speed.     

浅谈家用太阳热水器热性能测试

如何评价与检测家用太阳热水器的热性能呢？国家质量监督检验检疫总局于2002年4月28日发布了国标GB／T 18708—2002《家用太阳热水系统热性能试验方法》，通过此试验方法可得到太阳热水器能量输入一输出曲线图，它全面系统地反映了在不同的季节、不同的太阳辐照量条件下的太阳热水器能量输入一输出特性，实现了我国太阳热水器产品的热性能试验与国际接轨。     

Experimental study on the thermal performance of a traditional house with one-sided wind catcher during summer and winter

The Nagapattinam district lies on the east coast to the south of Cuddalore and is bordered by the Bay of Bengal. The general geological formation of the district is plain and coastal. Energy conservation issues and environmental problems in recent years have increased interest in traditional architecture which is well known for its energy saving designs. This paper presents the quantitative evaluation of traditional buildings in the coastal region of Nagappattinam during summer and winter periods with the custom-made instrument called Mini-meteorological station to understand the various solar passive elements used in the traditional buildings that provide thermal comfort. In this paper, the comparison of thermal performance during winter and summer is explained.     

On a solar collector thermal performance test method for use in variable conditions

The transient collector performance test method defined in the British Standards Institution Draft for Development DD77: 1982 is discussed in the light of experience in its implementation. With care in its use and in the interpretation of its results the method is shown to be effective in determining the steady-state characteristics of flat-plate collectors from measurements taken variable conditions.     

A simplified method for modelling the effect of blinds on window thermal performance

An approximate method is presented for predicting the effect of a louvered blind on the centre‐glass thermal performance of a fenestration. The method combines a one‐dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U‐value of a standard double‐glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade‐off between U‐value and occupant comfort; placing the blind closer to the window improves the U‐value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two‐dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd.     

Evaluation of the thermal performance indices of a ventilated double window through experimental and analytical procedures: Uw-values

Simulations to evaluate energy demand for heating and cooling and thermal comfort are becoming more and more common place in the building design process, at least in the most complex cases. In all detailed or simplified calculations, to analyse heat transfer to and from a building, several input parameters are needed. The inputs for the simulation of a whole building are at least the building geometry, the building envelope thermal indices (like thermal transmittance or the solar heat gain coefficient) and typical local climatic data. In a ventilated double window, the air flow through the channel between the two windows makes its thermal performance highly dynamic and dependent on the air flow characteristics. For a whole building simulation, single coefficients or easily calculated coefficients are needed for each facade system, including ventilated systems. In this paper, equivalent thermal transmittance coefficients for a ventilated double window are assessed and presented. For that, experimental measurements in the absence of solar radiation (night period) were used to identify tendencies and validate calculations. Furthermore, simulations were done in order to estimate the U_w-values of the ventilated double window under different windows configuration and different air flow rates. These values can then be used in whole building simulation programmes.     

Data analysis on solar irradiance and performance characteristics of solar modules with a test facility of various tilted angles and directions

We examined and evaluated the output characteristics and the deterioration lowering factors of modules installed under various conditions (module directions and tilted angles) based on the data collected at the multi-position test facility, which was produced and installed in order to conduct evaluation using design parameters (correction coefficient). This report introduces example data and the results of our evaluation.     

Optical and thermal characterization of multiple glazed windows with low U-values

The optical reflectance and transmittance spectra of complete windows for near normal and oblique angles of incidence are calculated from spectra of the individual panes taking multiple reflections into account. Calculated and experimental spectra are compared for triple and quadruple glazed windows with different combinations of low-e coatings. For the annual energy balance of a window the total solar transmission at oblique incidence is more relevant than the near normal performance. It is shown that, owing to the experimental difficulties involved in optical measurements at oblique incidence, great care must be taken when evaluating the annual performance. A simple equation for the annual energy balance of the window taking solar radiation and thermal heat losses into consideration is presented. Annual meteorological data for the insolation and outside temperature are used together with the optical performance to evaluate the net energy heat flow through a window. This can be performed for the complete heating season to evaluate the heat load needed for the building as well as for the warm season to evaluate the cooling load needed owing to solar overheating. This model provides a simple way of comparing the thermal performance of windows with different combinations of advanced glazings in both cold and hot climates, and makes it possible to estimate the cost efficiency of such windows.     

Visual and energy performance of switchable windows with antireflection coatings

The aim of this project was to investigate how the visual appearance and energy performance of switchable or smart windows can be improved by using antireflective coatings. For this study clear float glass, low-e glass and electrochromic glass were treated with antireflection (AR) coatings. Such a coating considerably increases the transmittance of solar radiation in general and the visible transmittance in particular. For switchable glazing based on absorptive electrochromic layers in their dark state it is necessary to use a low-emissivity coating on the inner pane of a double glazed window in order to reject the absorbed heat. In principle all surfaces can be coated with AR coatings, and it was shown that a thin AR coating on the low-e surface neither influences the thermal emissivity nor the U-value of the glazing. The study showed that the use of AR coatings in switchable glazing significantly increases the light transmittance in the transparent state. It is believed that this is important for a high level of user acceptance of such windows.     

700MW机组检修节能诊断试验分析

通过热力试验确定机组在给定负荷下的运行特性,计算机组大修前后的热耗率等技术指标;对机组主辅机和热力系统的运行经济性能进行大修前后的节能诊断;分析大修前效率低、煤耗高的原因,并进行相应的技术和设备改造,保证大修后机组安全经济运行。     

Experimental investigation of performance of a multi-purpose PV-slat window

This paper reports on experimental investigation of performance of a new type of PV-slat window (PV-SW). The main functions of this PV-SW are as follows: to admit sufficient daylight, to act as a shading device for decreasing direct heat gain through window glazing and to ensure indoor air movement, which improves resident's thermal comfort. To assess the performance of this PV-SW, two test rooms of 1×1×1.5 m³ (H:W:L) volume were built using plywood and gypsum boards. At the first, the PV-SW of 0.5×0.6 m² surface area was located at the south-facing wall whereas the other room was equipped with a commercial transparent slat window of the same size.The PV-SW consists of six PV slats. The photovoltaic cells were connected in series giving a maximum electrical power output of 36 W (12 V×3 A). The circuit was connected to a direct current axial fan, located inside the room, that requires a maximum power of 43 W. The analysis of performance of this PV-SW was investigated based on power output, daylight factor and temperature difference between indoor and ambient.The experimental results showed that this multi-purpose PV-SW is extremely interesting as it can produce power up to 15 W, decrease indoor temperature and provide sufficient light for housing. The maximum indoor illumination was about 750 lx with slats angle of 68°. The room temperature was about 2–3^oC lower than that of room equipped with transparent slats.     

Daylighting performance of an electrochromic window in a small scale test-cell

In this paper, the results of an experimental investigation aimed at assessing the performance of electrochromic (EC) windows with respect to daylighting control in buildings are presented. The research is performed under real weather conditions by a small scale test-cell equipped with a small area double glazing unit (DGU) where one pane consists of an EC device with visible transmittance τ_v ranging from 6.2 to 68.1% and the other of an ordinary clear float glass (τ_v ≈90%). Experimental tests are carried out as a function of time, weather conditions, test-cell orientation and switching strategies. These data are integrated with spectrophotometric measurements. Results show that the angle selectivity of the glazing combined with its active switching effect allows a wide range of selectable transmission states to suit the latitude and orientation of a building in relation to the local climatic conditions. For south facing windows and under the involved climatic conditions EC glazing driven by a dynamic control strategy can be very effective in reducing discomfort glare caused by high window brightness. Glare reduction can be realized contemporarily maintaining the work plane illuminance to adequate level for computer based office tasks so without compromising much of the available daylight. Furthermore, since EC glazing is never switched to heavily darkened states (τ_v >20%), colour rendering of inside objects should be always acceptable, although internal illuminance level could be slightly lower than to what users prefer in relation to the correlated colour temperature of the incoming light. These results change when considering west orientation for which high-luminance direct sunlight patches are registered on the work-plane even for EC glazing switched to its lowest transmitting state letting suppose that EC windows cannot provide full control of uncomfortable direct sunlight effects without integration of additional shading devices.     

Performance of a low-energy house in a mild cooling season. Part 1: Thermal performance of the house

A low-energy house located in Halifax, Canada, was monitored for a year using a computerized data acquisition system. Data on indoor and outdoor temperatures, relative humidities, and power consumption were collected for a whole year. The results of the analysis of cooling season data are presented. It was found that indoor temperature variations in the house were generally small, indicating a high level of comfort. The cooling load, and the cooling energy requirement of the house were low owing to the high level of insulation, and could further be reduced by increasing the thermostat setting. This however would reduce the comfort level in the house. Temperature set-up during unoccupied periods did not reduce daily cooling energy requirement, and addition of an economizer control would not be feasible owing to the small magnitude of potential savings.     

Development of a test facility for photovoltaic-diesel hybrid energy systems

To quantify the potential for performance improvements of photovoltaic-diesel (PV-diesel) hybrid energy systems, a test facility has been installed at the Centre for Renewable Energy Systems Technology. The research facility is part of the cooperative program to develop improved power conditioning systems for the provision of electricity in remote areas (ACRE Project 4.1). A customised control interface has been developed using the control and data acquisition software, LabVIEW. The graphical user-interface supports the automatic or manual definition of control parameters, which allows the system designer to apply optimal control methods for the management of PV-diesel hybrid energy systems. Continuously monitored weather data supports the integration of photovoltaic resource and load demand forecasts as part of the control strategy. The paper describes the developed test facility and discusses the potential for performance improvements of stand-alone renewable energy systems, which can be achieved through the application of “intelligent” energy management strategies.     

Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 1, BIPV/T system and house energy concept

This paper is the first of two papers that describe the modeling, design, and performance assessment based on monitored data of a building-integrated photovoltaic-thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) in a prefabricated, two-storey detached, low energy solar house. This house, with a design goal of near net-zero annual energy consumption, was constructed in 2007 in Eastman, Québec, Canada - a cold climate area. Several novel solar technologies are integrated into the house and with passive solar design to reach this goal. An air-based open-loop BIPV/T system produces electricity and collects heat simultaneously. Building-integrated thermal mass is utilized both in passive and active forms. Distributed thermal mass in the direct gain area and relatively large south facing triple-glazed windows (about 9% of floor area) are employed to collect and store passive solar gains. An active thermal energy storage system (TES) stores part of the collected thermal energy from the BIPV/T system, thus reducing the energy consumption of the house ground source heat pump heating system. This paper focuses on the BIPV/T system and the integrated energy concept of the house. Monitored data indicate that the BIPV/T system has a typical efficiency of about 20% for thermal energy collection, and the annual space heating energy consumption of the house is about 5% of the national average. A thermal model of the BIPV/T system suitable for preliminary design and control of the airflow is developed and verified with monitored data.