Energy and cost analysis of semi-transparent photovoltaic in office buildings

Solar energy conversion systems and daylighting schemes are important building energy strategies to produce clean energy, reduce the peak electrical and cooling demands and save the building electricity expenditures. A semi-transparent photovoltaic (PV) is a building component generating electricity via PV modules and allowing daylight entering into the interior spaces to facilitate daylighting designs. This paper studies the thermal and visual properties, energy performance and financial issue of such solar facades. Data measurements including solar irradiance, daylight illuminance and output power for a semi-transparent PV panel were undertaken. Using the recorded results, essential parameters pertaining to the power generation, thermal and optical characteristics of the PV system were determined. Case studies based on a generic reference office building were conducted to elaborate the energy and cooling requirements, and the cost implications when the PV facades together with the daylight-linked lighting controls were being used. The findings showed that such an integrated system could produce electricity and cut down electric lighting and cooling energy requirements to benefit the environmental, energy and economic aspects.     

Evaluation of a large dish‐type concentrator solar lighting system for underground car park

To utilize solar energy more efficiently and reduce lighting power consumption in underground public spaces such as car park, a large dish‐type concentrator solar lighting system is put forward along with its evaluation, which is a unique design to apply a laminated layer of beam split thin‐film coating and thin‐film solar cells onto the dish reflector. The collected sunlight is split into 2 parts, one being reflected into a fiber optical bundle and transmitted for daylighting, while the rest being absorbed by solar cells for electricity generation as the other way to replenish daylighting. A set of 4 solar lighting systems using 3.28‐m diameter dish are designed to meet the lighting requirement in a 1771‐m² underground car park. A mathematical model is adopted to calculate the output power and conversion efficiency of solar cells distributed on the parabolic dish surface. The indoor illuminance distribution is given by lighting simulation. The results indicate that the average daylight illuminance in the car park can vary between 62.7 and 284 lx on February 25, 2016 and between 62.7 and 353 lx on August 17, 2016 for 2 chosen days, respectively. For the presented design, the electricity produced by solar cells is just enough to power light‐emitting diodes for lighting meeting a criterion at night. Considering about 19% conversion efficiency of solar cells and the efficacy of 129.5 lm/W of light‐emitting diodes, the hybrid solar lighting system can have about 40% utilization ratio of solar energy, so it can be concluded that a sufficient lighting provision can be provided by the proposed large dish‐type concentrator solar lighting system for applications in underground car park.     

Daylighting and its effects on peak load determination

Daylighting is an important issue in modern architecture that has been characterized by the use of curtain walls in commercial buildings. In Hong Kong, the overall thermal transfer value (OTTV) calculations are mandatory requirements in the submission of building plans to control the building energy use, but daylighting credits are not included in calculating the OTTV of building envelope designs. Natural daylight helps reduce the electricity use and the associated sensible cooling load due to artificial lighting. Hence, proper daylighting designs can contribute to smaller air-conditioning system and lower the peak power demand of buildings. We use the computer simulation tool, DOE-2, to demonstrate the energy performance of a generic commercial building with different OTTV designs in terms of peak cooling plant requirement and peak building power demand due to various daylighting systems. The peak loads are determined from the simulation results. Regression techniques are conducted to correlate the incremental peak electricity use and incremental peak cooling capacity with OTTV and daylighting aperture (DA) (window-to-wall ratio (WWR) times light transmittance (LT)). Contours of equal incremental peak electricity use and incremental peak cooling plant demand for different building envelope parameters are developed. Important features for daylighting schemes are highlighted and implications for OTTV designs discussed.     

天然采光对建筑能耗影响的研究

在定性分析天然采光对建筑能耗影响的基础上,以一天窗建筑为研究对象,利用eQUEST能耗模拟软件为工具,分析了结合照明控制的天窗采光对夏季供冷峰值负荷及建筑各用能项如照明、供冷、供热的能耗影响,探讨了天窗透光率、照明密度、照明控制方式对建筑能耗的影响,并针对不同气候地区的典型城市探讨了昼光照明的气候差异性。     

The optimization of demand response programs in smart grids

The potential to schedule portion of the electricity demand in smart energy systems is clear as a significant opportunity to enhance the efficiency of the grids. Demand response is one of the new developments in the field of electricity which is meant to engage consumers in improving the energy consumption pattern. We used Teaching & Learning based Optimization (TLBO) and Shuffled Frog Leaping (SFL) algorithms to propose an optimization model for consumption scheduling in smart grid when payment costs of different periods are reduced. This study conducted on four types residential consumers obtained in the summer for some residential houses located in the centre of Tehran city in Iran: first with time of use pricing, second with real-time pricing, third one with critical peak pricing, and the last consumer had no tariff for pricing. The results demonstrate that the adoption of demand response programs can reduce total payment costs and determine a more efficient use of optimization techniques.     

Simulation of façade and envelope design options for a new institutional building

This paper presents a simulation case study of façade and envelope preliminary design options for the new Engineering building of Concordia University in Montreal. A major principle of the analysis was to create a high quality building envelope in order to optimally control solar gains, reduce heating and cooling energy demand and reduce electricity consumption for lighting, while at the same time maintain a comfortable and pleasant indoor environment. The stated approach of the design team was to aim for an energy-efficient building, employing innovative technologies and integrating concepts such as daylighting and natural ventilation. Detailed energy simulations were therefore performed from the early design stage, in order to present recommendations on the choice of façade, glazings, shading devices, lighting control options, and natural ventilation. Integrated thermal studies, a daylighting analysis and the impact of the above on HVAC system sizing were considered. Simulation results showed that, using an optimum combination of glazings, shading devices and controllable electric lighting systems, the energy savings in perimeter spaces can be substantial. Perimeter heating could be eliminated if a high performance envelope is used. The building is currently being commissioned.     

An analysis of lighting energy savings and switching frequency for a daylit corridor under various indoor design illuminance levels

Visual comfort and electric lighting energy issues are essential criteria to justify daylighting schemes. The evaluation of energy efficiency due to daylight linked lighting control systems is best demonstrated by case studies. This paper presents field measurements on daylighting for a fully air-conditioned daylit corridor. Artificial lighting load, brightness of the fluorescent luminaires, daylight availability for various switching illuminance levels were systematically recorded and analyzed. The general features and characteristics of the findings including the number of switching operations and electric-lighting energy savings are presented and discussed. Daylighting theories, using cumulative frequency distribution of outdoor illuminance and regression models based on brightness of light output, outdoor illuminance and electric light power to estimate daylight-linked lighting control savings, have been developed and assessed. It has been found that data from both approaches show reasonably good agreements with measured results. The findings from this study provide some operational and energy information, which would be useful and applicable to other interior spaces with similar architectural designs.     

基于分布式算法的实时电价策略研究

在智能电网中,实时电价(RTP)是解决智能电网供需平衡的理想手段。通过分析国内外实时电价机制发展现状,将家庭用户负荷分为四类,综合考虑用户间的不同用电特性,构建了相应的用电效益优化模型,采用分布式算法,结合某地区的具体数据,并针对不同的需求响应方案、蓄电池成本、系统大小对模型进行仿真。结果表明,基于分布式算法的需求响应实时电价策略可使社会用电效益最大化。     

A review of daylight illuminance determinations and energy implications

Daylighting is recognized as an important element in architecture and a useful strategy in energy-efficient building designs. Daylight gives a sense of cheeriness and brightness that can have a significant positive impact on the people. There is a scope for integrating daylight with electric light to reduce building energy use. The amount of daylight entering a building is mainly through window openings, which create in the indoor environment a more attractive and pleasing atmosphere, in addition to maximise visual access to the pleasant views of the outside world. Determinations of the exterior and interior daylight and lighting energy savings are key issues to demonstrate the benefits based on daylighting designs. This paper provides a review of daylight illuminance determinations and the lighting energy reductions due to daylighting schemes. The study includes daylight measurements, prediction of daylight illuminance under various sky conditions and potential electric lighting energy savings from daylight-linked lighting controls. The article aims at providing building professionals, practitioners and researchers more information and a better understanding of daylight for promoting effective daylighting designs and evaluations.     

An analysis of daylighting and solar heat for cooling-dominated office buildings

Computer simulation techniques were used to assess the energy performance of a generic commercial office building in Hong Kong. The simulation tool was DOE-2.1E. The thermal and energy performance of daylighting schemes were analysed in terms of the reduction in electric lighting requirement and the cooling penalty due to solar heat. Regression analysis was conducted to correlate the peak electricity demand and annual incremental electricity use with two fenestration variables, namely the solar aperture and the daylighting aperture. Contours of equal annual incremental electricity use were shown to be a function of the solar and daylighting apertures. It is envisaged that these simple charts can be a useful design tool for architects and engineers to assess the relative energy performance of different fenestration designs, particularly during the initial design stage when different building design schemes and concepts are being considered and developed.     

An analysis of energy-efficient light fittings and lighting controls

Electric lighting is one of the major energy consuming items in many non-domestic buildings. Using appropriate energy-efficient light fittings with dimming controls and proper daylighting schemes can help reduce the electrical demand and contribute to visual comfort and green building development. This paper presents a study on the energy and lighting performances for energy-efficient fluorescent lamps associated with electronic ballasts and high frequency photoelectric dimming controls installed in a school building. Electricity expenditures and indoor illuminance levels for a workshop and a classroom employing high frequency dimming controls were analyzed. Simple prediction methods were used to illustrate the lighting savings. The findings provide the operational and performance information, which would be applicable to other spaces with similar building layouts and lighting schemes.     

DAYLIGHTING TECHNOLOGIES IN NON-DOMESTIC BUILDINGS

Natural daylight is an inexpensive and very efficient light source provided that the amount of daylight entering a building is controlled according to demand. In commercial buildings electricity for lighting can be cut by 50-75% using daylighting design techniques in combination with efficient artificial lighting. New lighting control technologies and advanced computer simulation tools lo optimize large buildings makes it possible to exploit these energy savings.

Daylight is a very efficient light source, providing more light for less input of thermal energy than any other artificial light source. Efficient shading systems are now emerging systems that can control the admission of daylight to the room according to requirement, and avoid overheating. Some of these systems, such as reflective light shelves, will also contribute to a better distribution of the daylight available by redistributing some daylight to the back of the room. However, more work is needed to develop and test such combined daylight and shading systems.

The use of daylight to reduce electric lighting must be seen as an integrated part of the overall energy optimization of the building. An efficient control of the use of daylight and artificial lighting will not only reduce electricity use for lighting. Additionally, the use of electricity for ventilation and cooling can be reduced also, because the internal heat gains provocating these electricity uses are reduced. This calls for an integrated design approach to the overall energy design of the building, involving the architect and the engineer from the very beginning of the design phase.

Visual comfort of office buildings receives increasing attention, partially because of the VDU's (Visual Display Units) of the computers, that are now almost standard equipment of every work place. The performance requirements for both daylighting systems and artificial lighting systems have been sharpened, and the attention to this fact is crucial in future development of lighting systems.     

Daylighting and energy analysis for air-conditioned office buildings

We propose a simple method for estimating the likely energy savings in electric lighting due to daylighting and the possible cooling penalty. Fractions of the working year and cooling season when daylighting alone is adequate to provide the indoor design illuminance are presented for on-off and top-up controls. Based on the simple average daylight factor method, energy savings in electric lighting have been estimated for a generic office building using measured outdoor illuminance data in Hong Kong. The daylight-induced cooling penalty is estimated using average solar heat gain factors. Our case study suggests that daylighting schemes can result in substantial energy savings in air-conditioned office buildings in Hong Kong.     

Daylighting performance evaluation of a bottom-up motorized roller shade

This paper presents an experimental and simulation study for quantifying the daylighting performance of bottom-up roller shades installed in office spaces. The bottom-up shade is a motorized roller shade that opens from top to bottom operating in the opposite direction of a conventional roller shade, so as to cover the bottom part of the window, while allowing daylight to enter from the top part of the window, reaching deeper into the room. A daylighting simulation model, validated with full-scale experiments, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions. Then, a shading control algorithm was developed for application in any location and orientation. The validated model was employed for a sensitivity analysis of the impact of shade optical properties and control on the potential energy savings due to the use of daylighting. The results showed that Daylight Autonomy for the bottom-up shade is 8–58% higher compared to a conventional roller shade, with a difference of 46% further away from the façade, where the use of electric lighting is needed most of the time. The potential reduction in energy consumption for lighting is 21–41%.     

基于短期均衡模型的动态电价经济效率研究

针对动态电价是实现电力市场资源优化配置的重要途径问题,基于微观经济学理论建立了动态电价的短期均衡模型,通过实际算例分析了峰荷、用电总量、用户用电成本、消费者剩余、生产者剩余及社会剩余对动态电价的经济有效性。结果表明,动态电价能有效反映供电成本,引导用户有序用电,减少用电成本,具有良好的经济效率。     

Measurements of solar radiation and illuminance on vertical surfaces and daylighting implications

There is a growing concern about the rapid development of infrastructure and building projects and their likely impacts on the environment. Particular concerns have been raised about office building developments and energy consumption issues. In recent years, there has been increasing interest in using daylight to save energy in buildings. Lighting control integrated with daylighting is recognised as an important and useful strategy in terms of energy-efficient building design. It is believed that proper daylighting schemes can help reduce the electrical demand and contribute to achieving environmentally sustainable building developments. This paper presents a simple method for estimating the likely energy savings in electric lighting due to daylighting and the possible cooling penalty. Vertical solar radiation and illuminance data measurements are described. Cumulative frequency distributions of daylight availability are reported. The likely energy savings in office buildings are determined based on on–off and top-up controls, and the energy and environmental implications are discussed.     

An analysis of light-pipe system via full-scale measurements

Daylighting is an effective sustainable development strategy to alleviating the problems in energy and the environment, and improving the qualities for visual comfort and health. In Hong Kong, many buildings are high-rise blocks constructed close to each other resulting in severe sky obstructions. Recently, a great deal of attention has been paid to the development of natural daylight exploitation products. One invention is the light-pipe system that transports natural light efficiently from outdoor into rear part of a room. However, this innovative daylighting device is not popular in subtropical Hong Kong. The main reason for such unenthusiastic responses is the lack of local data to indicate the visual performance, energy savings and design implications. A research project was initiated to evaluate these issues. The study includes field measurements of daylight illuminance in a corridor installed a number of light pipes. The results demonstrate that the light-pipe system can provide sufficient illuminance, improve the daylight uniformity and have a high potential to reduce the electric lighting energy consumption.     

基于需求响应的居民可控能效负荷优化

为解决居民生活用电需求不断增加,居民生活用电方式不合理造成能源浪费越来越严重的问题,从居民用户的可控能效负荷入手,对典型可控能效负荷空调、热水器和照明负荷进行分析,建立负荷能耗数学模型,根据其运行特性,结合居民用户用电习惯和分时电价,制定居民可控能效负荷优化策略;建立以居民用户用电成本和用电满意度为目标的优化模型。为提高和声搜索算法的求解速度与计算精度,对其参数进行动态调整,并与差分进化算法进行融合,应用于可控能效负荷的优化求解。算例结果表明了改进算法具有较好的收敛性和较高的准确性,验证了居民可控能效负荷优化策略的可行性,实现了从需求响应的角度对可控能效负荷进行优化管理的思想。     

Cost-reflective electricity pricing: Consumer preferences and perceptions

In Australia, residential electricity peak demand has risen steeply in recent decades, leading to higher prices as new infrastructure was needed to satisfy demand. One way of limiting further infrastructure-induced retail price rises is via ‘cost-reflective’ electricity network pricing that incentivises users to shift their demand to non-peak periods. Empowering consumers with knowledge of their energy usage is critical to maximise the potential benefits of cost-reflective pricing. This research consulted residential electricity consumers in three Australian states on their perceptions and acceptance of two cost-reflective pricing scenarios (Time-of-Use and Peak Capacity pricing) and associated technologies to support such pricing (smart meters, in-home displays and direct load control devices). An energy economist presented information to focus groups on the merits and limitations of each scenario, and participants’ views were captured. Almost half of the 53 participants were agreeable to Time-of-Use pricing, but did not have a clear preference for Peak Capacity pricing, where the price was based on the daily maximum demand. Participants recommended further information to both understand and justify the potential benefits, and for technologies to be introduced to enhance the pricing options. The results have implications for utilities and providers who seek to reduce peak demand.     

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.