Lighting and cooling energy consumption in an open-plan office using solar film coating

In subtropical Hong Kong, solar heat gain via glazing contributes to a significant proportion of the building envelope cooling load. The principal fenestration design includes eliminating direct sunlight and reducing cooling requirements. Daylighting is an effective approach to allow a flexible building façade design strategy, and to enhance an energy-efficient and green building development. This paper studies the lighting and cooling energy performances for a fully air-conditioned open-plan office when solar control films together with daylight-linked lighting controls are being used. Measurements were undertaken at two stages including the electricity expenditures for the office using photoelectric dimming controls only (first stage) and together with the solar control film coatings on the windows (second stage). Electric lighting and cooling energy consumption, transmitted daylight illuminance and solar radiation were systematically recorded and analysed. The measured data were also used for conducting and validating the building energy simulations. The findings showed that the solar film coatings coupled with lighting dimming controls cut down 21.2% electric lighting and 6.9% cooling energy consumption for the open-plan office.     

Solar XXI building: Proof of concept or a concept to be proved?

Solar XXI building is a low energy office building where passive and active solar strategies have been applied to reduce the use of energy for heating, cooling and lighting, combining also an extensive photovoltaic façade for electricity production. Solar XXI opened in 2006 and is considered a high efficient building, close to a net zero energy building (NZEB), where the difference between the energy consumed and that produced is 1/10^th of the energy consumed by a Portuguese standard new office building. Its design includes many energy efficiency concepts, such as a high insulated envelope, south sun exposure, windows external shading, photovoltaic panels heat recovery, ground-cooling system, daylighting, stack effect and cross ventilation. The solar gains of the windows and the effectiveness of shading devices were evaluated in order to correlate solar radiation, external and indoor air temperatures. It was also verified that amplitude-dampening of ground-cooled air ranged between 5 and 8 °C, following the trend of the analytical solution for heat diffusion of a cylindrical air/soil heat-exchanger.     

Reversible low solar heat gain windows for energy savings

Summer cooling loads in buildings can be reduced with windows of low solar heat gain coefficients (SHGC). Such windows are often double glazed with the exterior pane tinted or selectively absorbing. They reject part of the absorbed solar radiation to the environment, reducing the solar heat gain. This effect is undesirable in the cold season. However, the same window installed in reverse, i.e. turned by 180°, has a significantly higher SHGC. Thus, windows that can be reversed according to the season will both reduce summer heat gains and collect much of the beneficial solar radiation in winter. This paper investigates the energy savings achievable by reversing equator-facing windows for the duration of the cold season as opposed to leaving them in the “summer position”. Candidate climates in which these savings may be significant are identified. By means of a computer simulation, seasonal energy savings are predicted for a model room with reversible, low SHGC, windows. The results indicate that for suitable climates, significant savings are achievable.     

Optimization of building window system in Asian regions by analyzing solar heat gain and daylighting elements

This paper presents and optimizes the annual heating, cooling and lighting energy consumption associated with applying different types and properties of window systems in a building envelope. Through using building simulation modeling, various window properties such as U-value, solar heat gain coefficient (SHGC), and visible transmittance (Tvis) are evaluated with different window wall ratios (WWRs) and orientations in five typical Asian climates: Manila, Taipei, Shanghai, Seoul and Sapporo. By means of a regression analysis, simple charts for the relationship between window properties and building energy performance are presented as a function of U-value, SHGC, Tvis, WWR, solar aperture, effective aperture, and orientation. As a design guideline in selecting energy saving windows, an optimized window system for each climate is plotted in detailed charts and tables.     

Energy savings of office buildings by the use of semi-transparent solar cells for windows

The study investigated a PV window that consists of a double glazed window with semi-transparent solar cells. The window provides natural light transmission as well as electricity production. The effect of the PV window on energy consumption of office buildings was analyzed in terms of heating and cooling loads, daylighting, and electricity production. The purposes of the study were to find the optimum solar cell transmittance and window to wall ratio (WWR), and to estimate energy savings of the building. A standard floor of an office building was modeled to run computer simulation, and annual energy simulation was performed with EnergyPlus. The results showed that the solar cell transmittance of 40% and WWR of 50% achieved the minimum electricity consumption in the building when artificial lighting was controlled with daylighting. The optimum solar cell transmittance for PV windows in different orientation was also presented. By using the optimum PV window, the electricity consumption was reduced by 55% compared to the single glazed window with WWR of 30% and no lighting control.     

Evaluation of electrochromic windows impact in the energy performance of buildings in Mediterranean climates

Old buildings refurbishment is essential for the global improvement of building energy indicators. Within this context, the paper focuses on the energy savings that may occur when using electrochromic (EC) windows, an interesting emerging technology alternative to shading devices to control solar gain in buildings located in Mediterranean climates. The EC windows technology is briefly presented and the optical properties adjustments of the glasses are discussed according to the operated range. The EC window dynamic behavior and the different control strategies are modeled and implemented in the ESP-r building simulation program. The EC window impact in the energy needs for heating and cooling is studied, considering different ambient parameters (exterior dry bulb temperature, interior dry bulb temperature and incident radiation) and set points for the EC control. A comparison of several windows solutions (single, double-glazing and EC windows), the type of building, internal gains from occupancy, lighting and equipment and the orientation of windows are considered for discussion through the analysis of the energy needs for heating and cooling. It is concluded that for this climate the best positive results are obtained when the EC are used in the west façade. For the south façade the results show no significant advantages in using EC windows.     

Artificial neural networks for energy analysis of office buildings with daylighting

An artificial neural network (ANN) model was developed for office buildings with daylighting for subtropical climates. A total of nine variables were used as the input parameters – four variables were related to the external weather conditions (daily average dry-bulb temperature, daily average wet-bulb temperature, daily global solar radiation and daily average clearness index), four for the building envelope designs (solar aperture, daylight aperture, overhang and side-fins projections), and the last variable was day type (i.e. weekdays, Saturdays and Sundays). There were four nodes at the output layer with the estimated daily electricity use for cooling, heating, electric lighting and total building as the output. Building energy simulation using EnergyPlus was conducted to generate daily building energy use database for the training and testing of ANNs. The Nash–Sutcliffe efficiency coefficient for the ANN modelled cooling, heating, electric lighting and total building electricity use was 0.994, 0.940, 0.993, and 0.996, respectively, indicating excellent predictive power. Error analysis showed that lighting electricity use had the smallest errors, from 0.2% under-estimation to 3.6% over-estimation, with the coefficient of variation of the root mean square error ranging from 3% to 5.6%.     

Low exergy (LowEx) heating and cooling systems for sustainable buildings and societies

Heating, cooling and lighting appliances in buildings account for more than one third of the world's primary energy demand and there are great potentials, which can be obtained through better applications of the energy use in buildings. In this regard, the building sector has a high potential for improving the quality match between energy supply and demand because high temperature sources are used to meet low-temperature heating needs. Low exergy (or LowEx) systems are defined as heating or cooling systems that allow the use of low valued energy, which is delivered by sustainable energy sources (i.e., through heat pumps, solar collectors, either separate or linked to waste heat, energy storage) as the energy source. These systems practically provide heating and cooling energy at a temperature close to room temperature while the so-called LowEx approach, which has been and still being successfully used in sustainable buildings design.The present study comprehensively reviews the studies conducted on LowEx heating and cooling systems for establishing the sustainable buildings. In this context, an introductory information is given first. Next, energy utilization and demand in buildings are summarized while various exergy definitions and sustainability aspects along with dead (reference) state are described. LowEx heating and cooling systems are then introduced. After that, LowEx relations used to estimate energy and exergy demand in buildings and key parameters for performance assessment and comparison purposes are presented. Finally, LowEx studies and applications conducted are reviewed while the last section concludes. The exergy efficiency values of the LowEx heating and cooling systems for buildings are obtained to range from 0.40% to 25.3% while those for greenhouses vary between 0.11% and 11.5%. The majority of analyses and assessments of LowEx systems are based on heating of buildings.     

A passive solar building for ecological research in Argentina: the first two years experience

An energy-efficient building, featuring energy conservation, passive solar heating, and natural cooling strategies, was designed and built in La Pampa, a province in the temperate semi-arid region of central Argentina. Of compact design, it houses 350 m² of useful floor area in a roughly linear scheme, with the main spaces facing north and ancillary spaces (services) facing south. Solar windows running from above spandrel and up to ceiling height are provided for all the main spaces, and clerestory windows are provided for the solar gain to the south-facing spaces. An integrated sunspace is incorporated into the centre bay of the north facade, providing additional heat to inner spaces as well as functional and visual expansion. In the design stage, a simulation analysis was performed to assess the environmental and energy performance of the alternatives. The main energy features of the resulting building are a volumetric loss coefficient of 1.09 W m⁻³ °C⁻¹, and a predicted solar savings fraction of 70%. The summer cooling strategy includes the passive induction of exterior air into the building through earth-coupled ducts. Cooling by cross-ventilation is made possible during the night, but to preserve the security of the building from sudden storms, this occurs only when the building is occupied. Shading devices protect all windows in summer. Provisional monitoring, started during the 1995 winter period, showed encouraging possibilities of energy savings with adequate comfort conditions, demonstrating the technical feasibility of the scheme.     

Design and construction of a residential solar heating and cooling system

The first integrated system providing heating and cooling to a building by use of solar energy has been designed and installed in a residential-type building at Colorado State University. Solar heated liquid supplies heat to air circulating in the building and to a lithium bromide absorption air conditioner. Service hot water is also provided. Approximately two-thirds of the heating and cooling loads are expected to be met by solar energy, the balance by natural gas. The paper contains details of design and principles of operation. A breakdown of actual costs of the equipment and its installation is also provided.     

Design of a solar heating and cooling system for CSU solar house II

This paper describes the design of a solar air heating and night/day exchange cooling system with emphasis on the operational modes. In this type of system the collector absorbs solar energy and converts it to heat for space heating and domestic water heating. Cooling is accomplished by using the cool night air available in dry climates) to cool a pebble-bed storage unit and subsequently using the cool pebbles to lower the air temperature in the building during the day. Circulation is from the solar system to the building in the same manner as most modern heating and air conditioning units but uses air as the medium for heat transfer. The air system is particularly suited for climatic regions where heating loads are high and cooling requirements are moderate. The system utilized in Solar House II operates in either the heating or cooling mode as selected through a seasonable change-over switch. Solar preheated hot water is furnished for domestic use in either mode.     

Simple tool to evaluate energy demand and indoor environment in the early stages of building design

A simplified building simulation tool to evaluate energy demand and thermal indoor environment in the early stages of building design is presented. Simulation is performed based on few input data describing the building design, HVAC systems and control strategies. Hourly values for energy demand and indoor temperature are calculated based on hourly weather data. Calculation of the solar energy transmitted through windows takes into account the dependency of the total solar energy transmittances on the incidence angle, shades from far objects and shades from the window recess and overhangs. Several systems including heating, cooling, solar shading, venting, ventilation with heat recovery and variable insulation can be activated to control the indoor temperature and energy demand. Predicted percentages of dissatisfied occupants are calculated for a given time period to support decisions concerning the thermal indoor environment. The simplified building simulation tool gives reliable results compared to detailed tools and needs only few input data to perform a simulation. The tool is therefore useful for preliminary design tasks in the early design stages where rough estimates of the building design are given and rough estimates of energy use and thermal indoor environment are needed for decision support.     

建筑形式对太阳能热利用的影响研究

以上海地区的住宅建筑为研究对象,通过模拟分析的方法,采用DeST软件计算确定建筑逐时的采暖、空调能耗,研究分析窗墙比对建筑全年采暖能耗、全年空调能耗以及全年采暖、空调总能耗的影响规律,研究分析太阳辐射热增加所导致采暖能耗的降低幅度与外围护结构保温性能两者之间的定量关系。计算结果表示在夏季外窗遮阳和夜间通风的条件下,加大南向窗墙比可增强太阳能的热利用效率,降低建筑全年的采暖、空调总能耗;而外围护结构保温性能的增强则可降低室内向室外散热的程度,相应提高对冬季太阳辐射的热利用程度,从而达到降低采暖能耗的目的。     

Cooling potential of ventilated PV façade and solar air heaters combined with a desiccant cooling machine

Thermal energy collected from a PV-solar air heating system is being used to provide cooling for the Mataro Library, near Barcelona. The system is designed to utilise surplus heat available from the ventilated PV facade and PV shed elements during the summer season to provide building cooling. A desiccant cooling machine was installed on the library roof with an additional solar air collector and connected to the existing ventilated PV façade and PV sheds. The desiccant cooling cycle is a novel open heat driven system that can be used to condition the air supplied to the building interior. Cooling power is supplied to the room space within the building by evaporative cooling of the fresh air supply, and the solar heat from the PV-solar air heating system provides the necessary regeneration air temperature for the desiccant machine. This paper describes the system and gives the main technical details. The cooling performance of the solar powered desiccant cooling system is evaluated by the detailed modelling of the complete cooling process. It is shown that air temperature level of the PV-solar air heating system of 70 °C or more can be efficiently used to regenerate the sorption wheel in the desiccant cooling machine. A solar fraction of 75% can be achieved by such an innovative system and the average COP of the cooling machine over the summer season is approximate 0.518.     

Evaluation of control strategies for different smart window combinations using computer simulations

Several studies have shown that the use of switchable windows could lower the energy consumption of buildings. Since the main function of windows is to provide daylight and visual contact with the external world, high visible transmittance is needed. From an energy perspective it is always best to have the windows in their low-transparent state whenever there are cooling needs, but this is generally not preferable from a daylight and visual contact point of view. Therefore a control system, which can be based on user presence, is needed in connection with switchable windows. In this study the heating and cooling needs of the building, using different control mechanisms were evaluated. This was done for different locations and for different combinations of switchable windows, using electrochromic glazing in combination with either low-e or solar control glazing. Four control mechanisms were investigated; one that only optimizes the window to lower the need for heating and cooling, one that assumes that the office is in use during the daytime, one based on user presence and one limiting the perpendicular component of the incident solar irradiation to avoid glare and too strong daylight. The control mechanisms were compared using computer simulations. A simplified approach based on the balance temperature concept was used instead of performing complete building simulations. The results show that an occupancy-based control system is clearly beneficial and also that the best way to combine the panes in the switchable window differs depending on the balance temperature of the building and on the climate. It is also shown that it can be beneficial to have different window combinations for different orientations.     

An investigation of the potential for natural ventilation and building orientation to achieve thermal comfort in warm and humid climates

The aim of this study was to analyze the most important factor, the climatic conditions with respect to thermal comfort in buildings. The impact of building location and climate and orientation on thermal comfort were investigated.With the help of dynamic computer simulations the different hourly weather data were analyzed. First of all the climate determines the amount of solar radiation and mean outside temperature that a building is exposed to. The climate also influences the amount of energy that is used for heating and cooling but also the amount of energy that is used for lighting. There is solar excess which determines the amount of solar energy that is unwanted in the building. With growing amounts of glass and a glazing system that allows large solar heat gains,the impact of orientation is substantial. A detailed analysis was conducted to evaluate the potentials for improving thermal comfort. Detailed results are given in sample graphics and tables in the study. In a tropical climate the improvement in comfort by NV range between 9% and 41% (Kuala Lumpur in April). For a subtropical climate the improvements vary between 3% and 14%. In a temperate climate the improvements vary between 8% and 56%. The results showed that NV has a good potential in tropical and temperate climates but not in subtropical climates. Especially in Hong Kong it seems to be very difficult to apply NV. The results showed that in particular in the hottest period (summer) the potential for comfort improvements is rather small. The design of climate responsive building envelopes should take this into consideration.     

Photovoltaic system assessment for a school building

The installation of photovoltaic panels (PVs) on the roof of residential and commercial buildings is getting widespread as these areas stand normally idle and can be used for another purpose without losing an inhabited space. Considering the solar potential of Turkey, a significant amount of electricity generation is possible using current PV technology. For this reason, a two-story detached school building located in ?zmir, Turkey was taken into consideration and monthly as well as annual coverage ratio of an on-grid PV system for its entire energy requirement (including heating, cooling and lighting) was investigated. The PVs were installed on the south face of the school building roof. A heat pump, with a typical coefficient of performance (COP) value of 2.5, was used for supplying required cooling and heating. The heating, cooling and lighting loads were determined on a monthly basis. The average monthly electrical energy generation of the mounted PVs was calculated using a written code in Energy Equation Solver (EES) software. As a result, the monthly as well as yearly electrical energy demand coverage ratio values for the school using the installed PVs were revealed. Since the school building has a large south faced roof, the installation of PVs is very suitable to meet the cumulative electrical energy need of the heat pump and the lighting load. For Case 1, 180 PVs, which supply the entire yearly demand (with a 110% coverage ratio), were taken into consideration, while for Case 2, 265 PVs, which cover 75% of the roof area, were evaluated. The results showed that between November and March, PV electrical energy generation is not sufficient to meet all energy need of the school for both cases. However, significant coverage ratio values were observed for the rest of the year. In a yearly basis, the PV generation exceeded the building demand by 62% for the Case 2. This conclusion points out that the school can meet its yearly electricity need with the considered PV system and can even have an additional financial profit by selling its surplus PV electricity to the grid. Economic and environmental payback time values as well as simple payback time value were also computed for both investigated cases. The results pointed out a simple payback time of 7.9 years for Case 1 and 7.6 years for Case 2. Energy payback time was determined as 5 years for both systems. The greenhouse gas payback time of 2.7 years and 5.9 years was encountered for coal based and natural gas based calculations.     

Energy conservation measures in an institutional building in sub-tropical climate in Australia

In this study, various energy conservation measures (ECMs) on heating, ventilating and air conditioning (HVAC) and lighting systems for a four-storied institutional building in sub-tropical (hot and humid climate) Queensland, Australia are evaluated using the simulation software called DesignBuilder (DB). Base case scenario of energy consumption profiles of existing systems are analysed and simulated first then, the simulated results are verified by on-site measured data. Three categories of ECMs, namely major investment ECMs (variable air volume (VAV) systems against constant air volume (CAV); and low coefficient of performance (COP) chillers against high COP chillers); minor investment ECMs (photo electric dimming control system against general lighting, and double glazed low emittance windows against single-glazed windows) and zero investment ECMs (reset heating and cooling set point temperatures) are evaluated. It is found that the building considered in this study can save up to 41.87% energy without compromising occupancies thermal comfort by implementing the above mentioned ECMs into the existing system.     

Effect of fixed horizontal louver shading devices on thermal perfomance of building by TRNSYS simulation

Buildings in most countries around the world require large amounts of energy both for cooling and heating. In fact cooling loads due to solar gains represent about half of global cooling loads for residential as well as non-residential buildings. While solar gains through windows contribute largely to these loads, any method of decreasing these gains through shading should be applied with caution, since a balance is required; decreasing cooling loads by shading may increase heating loads drastically and vice versa. So the overall energy requirements both for heating and cooling should be considered. With this in mind a study was done on the thermal performance of a building by TRNSYS simulation, and a shading model for windows was incorporated in it. The shading devices adopted were external fixed horizontal louvers with different slat lengths and tilts. The study was conducted for four different cities in Italy. The optimization of the shading devices was done with respect to primary energy loads for the whole year, and the optimum design was found to depend on location and weather conditions. It was also found that shading factor varies with time of day and is different for summer and winter. For example, for Milan it was found that 70% of gain is cut off in summer, while only 40% is cut off in winter by using optimum shading, which is desirable.     

Reducing energy use in the buildings sector: measures, costs, and examples

This paper reviews the literature concerning the energy savings that can be achieved through optimized building shape and form, improved building envelopes, improved efficiencies of individual energy-using devices, alternative energy using systems in buildings, and through enlightened occupant behavior and operation of building systems. Cost information is also provided. Both new buildings and retrofits are discussed. Energy-relevant characteristics of the building envelope include window-to-wall ratios, insulation levels of the walls and roof, thermal resistance and solar heat gain coefficient of windows, degree of air tightness to prevent unwanted exchange of air between the inside and outside, and presence or absence of operable windows that connect to pathways for passive ventilation. Provision of a high-performance envelope is the single most important factor in the design of low-energy buildings, not only because it reduces the heating and cooling loads that the mechanical system must satisfy but also because it permits alternative (and low-energy) systems for meeting the reduced loads. In many cases, equipment with significantly greater efficiency than is currently used is available. However, the savings available through better and alternative energy-using systems (such as alternative heating, ventilation, cooling, and lighting systems) are generally much larger than the savings that can be achieved by using more efficient devices (such as boilers, fans, chillers, and lamps). Because improved building envelopes and improved building systems reduce the need for mechanical heating and cooling equipment, buildings with dramatically lower energy use (50–75% savings) often entail no greater construction cost than conventional design while yielding significant annual energy-cost savings.