Low Energy Office Building Research Articles

The Impact of an Ideal Dynamic Building Envelope on the Energy Performance of Low Energy Office Buildings

This paper shows the results of a research activity aimed at assessing the advantages of an ideal adaptive building skin over conventional building envelope systems.The basic idea underlying the research consists in imagining an ideal building envelope system characterised by the capability of continuously changing (within a certain range) some of its thermo-physical and optical properties. The reason for the continuous tuning of thermo-physical and optical properties lies in the assumption that an optimised (fixed) configuration, where the properties do not change over time, is not able to minimise the total energy demand of the building at each moment.For the sake of this purpose, an ideal dynamic WWR (Window-to-Wall Ratio) building envelope system for low energy office buildings was modelled and simulated. An integrated, commercial thermal-lighting building simulation tool (EnergyPlus) was used to perform the calculation. The energy performance of such a system was then analysed and compared against the performance of a conventional façade realised with best-available technologies.The results of the investigation demonstrated the advantages of a dynamic WWR configuration over a static one. However, the improvements achieved in energy demand were lower than expected. This behaviour is strictly related to the configuration of the building used as a reference, which already showed a very high energy performance.Limitations presented by the research method are also briefly pointed out and discussed.

Post Occupancy Evaluation Assessment Model for Low Energy Office Buildings

Preliminary research has indicated that Low Energy Office (LEO) problematic areas have not been thoroughly investigated. Many researchers have confirmed the lack of comprehensive Post Occupancy Evaluation (POE) in LEO buildings. The focus of this study is to develop a POE assessment model which comprehensively covers the building performance criteria compatible for LEO buildings. The research was conducted in two phases. The first phase was to identify the comprehensive POE criteria and its parameters. In this phase a qualitative survey data was analyzed using content analysis and subsequently validated in close-group discussion with professionals (33 performance parameters corresponding to 10 assessment criteria). The second phase was to develop a POE assessment model compatible for LEO buildings. To pilot test the model, a LEO building in Putrajaya, Malaysia was selected. The survey data was analyzed using Average Index and Frequency Analysis methods. The result showed that the 'economics' and 'culture' performance criteria were determined as the most problematic building performance areas. 'Functionality' and 'flexibility' were found to be the most expensive criteria in terms of cost of quality. The overall level of user satisfaction was verified as high with slight exception for 'safety' and 'aesthetics'. © 2013 American Scientific Publishers All rights reserved.

Optimizing the configuration of a façade module for office buildings by means of integrated thermal and lighting simulations in a total energy perspective

The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of solar energy at a building scale. An optimized configuration of the façade can contribute to reduce the total energy demand of the building.Traditionally, the search for the optimal façade configuration is obtained by analyzing the heating demand and/or the cooling demand only, while the implication of the façade configuration on artificial lighting energy demand is often not addressed.A comprehensive approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building and the optimization of the façade configuration becomes no longer straightforward, because non-linear relationships are often disclosed.The paper presents a methodology and the results of the search for the optimal transparent percentage in a façade module for low energy office buildings. The investigation is carried out in a temperate oceanic climate, on the four main orientations, on three versions of the office building and with different HVAC system’s efficiency. The results show that, regardless of the orientations and of the façade area of the building, the optimal configuration is achieved when the transparent percentage is between 35% and 45% of the total façade module area. The highest difference between the optimal configuration and the worst one occurs in the north-exposed façade, while the south-exposed façade is the one that shows the smallest difference between the optimal and the worst configuration.

Progress on single-sided ventilation techniques for buildings

Single-sided natural ventilation is a free cooling solution which accommodates readily to most office building layouts. However, this technique is often ruled out by building designers since its ability to maintain comfort conditions is difficult to assess. Indeed, the cooling effect of this technique driven by wind and stack effects is highly dependent on outdoor conditions. This article intends to review the techniques of single-sided natural ventilation and the tools available to assess the performance of this technique. Then, the performance of single-sided natural ventilation is assessed for low-energy office buildings in two European climates. The methodology is based on the use of a building energy simulation program coupled with a recently developed correlation for single-sided ventilation. Several cases of office buildings are assessed, taking into account the main factors influencing the natural ventilation potential such as building loads, thermal inertia and orientation. For each building case, the energy-saving potential of a mixed-mode cooling system is analysed compared with the same building case with a full air-conditioning system. The comfort level of non-air-conditioned buildings is then studied for each building case. Finally, the impact of the window type on the performance of single-sided natural ventilation is assessed.

Thermal Comfort Assessment-A Study Toward Workers’ Satisfaction in a Low Energy Office Building

Problem statement: The government of Malaysia has raised their concerns towards the issue of workers comfort and workspace quality in a Low Energy Office (LEO) building. New energy efficient building concepts and technologies require a revision of comfort standards, to create a suitable thermal condition in avoiding occupant dissatisfaction, adverse effect on their productivity and overall building performance. Approach: Assessment was conducted using Babuc-A (Portable air quality monitor) and sets of questionnaire adapted from ASHRAE-2004 were 99 respondents selected using a stratified random sampling. Results: This study shows that the thermal comfort zone temperature was identified to be within the range of 21.6-23.6°C and relative humidity of 42-54%. Conclusion: The results suggested that the thermal condition was in the acceptable range of ISO7730 and a lower room temperature was preferred by Malaysian in an office environment compared with the temperature criteria cited in ASHRAE-55. To create an optimum comfortable workplace, temperature between 20-26°C and relative humidity between 40-60% must be maintained. Adequate ventilation must be provided at the minimum rate of 10 l/s of fresh air per person for general office space or every 10 m2 of floor space.

Thermal comfort field studies in two certified energy efficient office buildings in a tropical climate

There has been a growing awareness to include passive design concepts in buildings as a design strategy for achieving energy efficiency and optimum indoor thermal comfort in workspaces as well. The challenging task for the building designers in the hot-humid tropics is the provision of indoor environmental thermal comfort for the occupants of the building while controlling energy use for the office space. This study has been conducted to investigate the post occupancy evaluation of occupants’ satisfaction in the working-spaces of two energy-efficient office buildings in a tropical country viz., Malaysia. Two office buildings, which have been classified as energy efficient buildings, in Malaysia were selected for the case study. One of them is a Low Energy Office (LEO) building, designed for low energy consumption and the second one is a Zero Energy Office (ZEO) building which was designed for demonstration of renewable energy applications. From the research it is seen that the thermal comfort parameters l...

Energy Consumption Level of Low-Energy Buildings among Different Climate Zones in China: Case Studies

According to statistics and field investigation, analyses of the energy consumption (EC) level are on the basis of three low-energy office building cases. These cases locate in three typical cities of different climate zones (North China region-Cold zone, East China region-Hot summer and cold winter zone, South China region-Hot summer and warm winter zone) in China. In conclusions, the energy consumption index (ECI) of these three cases is between 41.06~65.7 kWh/(m2•a). The percentage of EC used for cooling is more than 26.43%, and the outdoor climate conditions influence the total EC level of the whole building.

Geocooling potential of borehole heat exchangers' systems applied to low energy office buildings

Abstract The potentiality of geocooling (i.e. free cooling) with borehole heat exchangers is analysed for low energy office buildings. The borehole heat exchanger field is coupled to a heat pump in winter and to the cold distribution system in summer through a flat plate heat exchanger. The cooling requirement satisfied by a direct heat transfer into the ground through the borehole heat exchangers is so-called geocooling. A dynamic system model has been developed to simulate the building, the emission of thermal energy through thermally activated building systems, the technical installation including the borehole heat exchanger field and the interconnected thermal interactions. Thermal comfort requirements determine the building energy needs and the size of the ground coupled system. A methodology is presented for best system design. Building design, system technical feasibility and limits of the ground coupled system are discussed and result from the analysis of the numerous system simulations. Geocooling potential depends on the quality of the building design and its heat emission. The importance of the ground thermal conductivity and the ground recharge ratio on the system design are highlighted. Simple design sizing keys are proposed for a fast pre-sizing of a borehole field.

Low-energy office buildings using existing technology: simulations with low internal heat gains

Although low-energy and nearly zero-energy residential houses have been built in Sweden in the past decade, there are very few examples of low-energy office buildings. This paper investigates the design features affecting energy use in office buildings and suggests the optimal low-energy design from a Swedish perspective. Dynamic simulations have been carried out with IDA ICE 4 on a typical narrow office building with perimeter cell rooms. The results from the parametric study reveal that the most important design features for energy saving are demand-controlled ventilation as well as limited glazing on the facade. Further energy-saving features are efficient lighting and office equipment which strongly reduce user-related electricity and cooling energy. Together, the simulation results suggest that about 48% energy can be saved compared to a new office building built according to the Swedish building code. Thus, it is possible, using a combination of simple and well-known building technologies and configurations, to have very low energy use in new office buildings. If renewable energy sources, such as solar energy and wind power, are added, there is a potential for the annual energy production to exceed the annual energy consumption and a net zero-energy building can be reached. One aspect of the results concerns user-related electricity, which becomes a major energy post in very low-energy offices and which is rarely regulated in building codes today. This results not only in high electricity use, but also in large internal heat gains and unnecessary high cooling loads given the high latitude and cold climate.

Identifying important variables of energy use in low energy office building by using multivariate analysis

The aim of the study was to identify driving variables of energy use in a low energy office building by integrating building energy management system (BEMS) and energy use data. To take a further step towards zero emission buildings, it is necessary to identify what contributes the most to building energy use. Further, the idea was to encourage a smart use of BEMS data for energy use analysis. Multivariable analysis was used for the data analysis. Databases of 76 and 41 variables respectively, which included occupancy level, control signals, and water and air temperatures, were used to explain heating, electricity, and fan energy use. The results showed that important variables were different for different months in the case of heating energy use. The total electricity and fan electricity use could be defined with the same variables in different months. The total electricity use could be defined by using occupancy level and input fan signals. The suggested approach could be used by building operators to identify opportunities for decreasing energy use and for energy use estimation when data are lost due to data transmission issues or other problems. A relationship between building information and energy use was established.

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.

Thermal comfort and workplace occupant satisfaction—Results of field studies in German low energy office buildings

The issues of comfort and workspace quality in buildings have gained much importance with the European “Energy Performance of Buildings Directive” of 2001. New energy efficient building concepts and technologies require a revision of comfort standards, which were developed for air-conditioned buildings only. Particularly, the question of recommendable upper indoor temperature limits needs further investigation. In addition, a broader approach to occupant satisfaction in buildings is necessary with respect to overall building performance. The results of a 4-week summer field study on thermal comfort with 50 subjects in a naturally ventilated office building in Karlsruhe, Germany, show that thermal sensation votes do not correspond to calculated predicted mean votes, but a very good agreement can be seen with adaptive comfort models. The dependence between thermal comfort and the outdoor temperature in naturally ventilated buildings could therefore be confirmed. A survey on workplace occupant satisfaction in 16 office buildings in Germany revealed that the occupants’ control of the indoor climate and moreover the perceived effect of their intervention strongly influence their satisfaction with thermal indoor conditions. The paper also introduces a method for assessing the building performance by occupant surveys calculating the weighted importance of every satisfaction parameter in relation to the general acceptance of the workplace and then ranking the different satisfaction parameters.

Comparison of low-energy office buildings in summer using different thermal comfort criteria

Sustainable low-energy office buildings attempt to harness the buildings architecture and physics to provide a high quality working environment with the least possible primary energy consumption. A promising approach to condition those buildings in summer employs the utilization of the building's thermal storage activated by natural heat sinks (e.g., ambient air, ground water or soil) through night ventilation or thermally activated building systems (TABS). However, a certain room temperature cannot be guaranteed as occupants may influence the room energy balance by window opening, internal heat gains or sun shading control. Between 2001 and 2005, monitoring campaigns were carried out over 2 or 3 years in 12 low-energy office buildings which are located in three different summer climate zones in Germany. These climate zones are defined as summer-cool, moderate and summer-hot. The weather at the building site and the room temperatures in several office rooms were monitored by different scientific teams. The raw data are processed for data evaluation using a sophisticated method to remove errors and outliers from the database and to identify the time of occupancy. The comfort in all office rooms in each building is evaluated separately. For data presentation, these separate comfort votes per office room are averaged using the median instead of the arithmetic mean in order not to overestimate extremely cold or hot room temperatures. A comfort evaluation in these 12 low-energy office buildings indicates clearly, that buildings which use only natural heat sinks for cooling provide good thermal comfort during typical and warm summer periods in Germany. However, long heat waves such as during the extreme European summer of 2003 overstrain passively cooled buildings with air-driven cooling concepts in terms of thermal comfort.

Statistical simulation of user behaviour in low-energy office buildings

A large number of design guidelines and tools are available for the design of passive cooling systems. Using the underlying thermodynamic models, a certain input (e.g. air change rate, internal heat gains or sun control) results in a certain output (i.e. room temperature). However, in real buildings the room temperature at a given outdoor temperature is a distribution rather than a single value. Therefore, the building engineer should take uncertainties into account, since the actual use of the building, the building physical properties or the user behaviour are statistically distributed. One promising approach to include these uncertainties in the design procedure is the use of statistical models: the design parameter is defined by a mean value and its deviation. From a control theoretical point of view, the deterministic controlled system responds to random disturbance variables by a statistically distributed response function. Considering the institute building of Fraunhofer ISE as example, this study shows how statistical simulations can be applied to the design process of passive cooling in low-energy office buildings.

Passive and Low Energy Cooling of Office Buildings

In this work, the cooling performance of night ventilation systems and different earth heat exchange technologies were experimentally analysed in three office buildings in Southern Germany. One of the first passive energy standard office buildings in Europe was extensively monitored over a three year period to analyse the summer performance of a highly insulated and well shaded building in which night cooling ventilation was based on stack effect and cross ventilation. This was combined with a mechanical ventilation system incorporating a ground coupled heat exchanger to supply daytime fresh air.For comparison, an energy analysis was made of a mechanically driven exhaust air night ventilation system and a supply and exhaust air system in the other two buildings. The first of these was a passively cooled refurbished building in Tübingen which utilises mechanical night ventilation to effectively discharge ceilings with phase change material. In addition, fresh air cooling is achieved using a horizontal brine-earth heat exchanger. The second comparison building was a low energy office building in Freiburg which uses water based ground coupled heat exchangers for fresh air cooling and an exhaust air ventilation system for night cooling.During a typical German summer, in which the number of hours that the ambient air temperature exceeds 25°C is less than 160, the passively ventilated building performed excellently, even with relatively high internal heat loads of 200 to 400 Wh.m−2.day−1. However, when the ambient air temperature was significantly higher, such as in the summer of 2003 (i.e. 3 K higher than the average summer temperature), nearly 10% of all office hours recorded room air temperatures above 26 °C. In the case of the two buildings that were night cooled by mechanical ventilation, cooling performance was limited by the rather low air exchange rate of 2 h−1. This resulted in overnight room temperature reductions of just 2–3 K during hot summer nights. Also the coefficient of performance (COP) was relatively low for this approach at between 4 to 6.All the earth heat exchangers showed excellent energy performances with COP's between 20 and 50. However, due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removed a small part of the total load.

Passive cooling in a low-energy office building

In office buildings, the use of passive cooling techniques combined with a reduced cooling load may result in a good thermal summer comfort and therefore save cooling energy consumption. This is shown in the low-energy office building ‘SD Worx’ in Kortrijk (Belgium), in which natural night ventilation and an earth-to-air heat exchanger are applied. In winter, the supply air is successively heated by the earth-to-air heat exchanger and the regenerative heat exchanger, which recovers the heat from the exhaust air. In summer, the earth-to-air heat exchanger cools the ventilation air by day. In addition, natural night ventilation cools down the exposed structure which has accumulated the heat of the previous day. In this article the overall thermal comfort in the office building is evaluated by means of measuring and simulation results. Measurements of summer 2002 are discussed and compared to simulations with a coupled thermal and ventilation simulation model TRNSYS-COMIS. The simulations are used to estimate the relative importance of the different techniques. The evaluation shows that passive cooling has an important impact on the thermal summer comfort in the building. Furthermore, natural night ventilation appears to be much more effective than an earth-to-air heat exchanger to improve comfort.

Design, monitoring and evaluation of a low energy office building with passive cooling by night ventilation

In moderate climates, one promising approach to reduce the energy demand of office buildings for air conditioning without reducing comfort is passive cooling by night ventilation. The office building of DB Netz AG in Hamm (Germany) has been designed, constructed and monitored for a long period in the framework of the German research programme, “Solar Optimised Buildings”, SolarBau for short. Monitored data of room and ceiling temperatures in 12 office rooms, supply air flow rate and temperature in these office rooms, electricity consumption for each office room, climate and air temperatures in an adjacent atrium are evaluated by a new method for analysis which deals with short-term and long-term measurements and building simulation. The monitored data from the office building, which is used as such, are complemented by information from the building management system about the position of louvers and the shading devices. The contribution of simulation tools to the design of buildings with passive cooling by night ventilation is evaluated by a comparison between monitored data and simulation for a long period.

03/02540 Design of low energy office buildings: Gratia, E. and De Herde, A. Energy and Buildings, 2003, 35, (5), 473–491

03/02540 Design of low energy office buildings: Gratia, E. and De Herde, A. Energy and Buildings, 2003, 35, (5), 473–491

Design of low energy office buildings

There is an increasing demand for higher quality office buildings. Occupants and developers of office buildings ask for a healthy and stimulating working environment. The advent of computers and other office equipment increased the internal heat gains in most offices. Highly glazed facades, often with poor shading, have become very common. This, together with the extra heat gains from the electric lighting made necessary by deep floor plans, and the wider use of false ceilings, increased the risk of overheating. Decisions taken rapidly in the early stages of design can have a large impact on the performance of the finished building. For example, choices of the overall form of the building, the depth and height of rooms, and the size of windows can together double the eventual energy consumption of the finished building. They can also halve the daylight levels, and increase summer temperatures to levels which affect the occupants’ productivity. Later in the design process, radical design changes are rarely made. The paper uses data from practice and meteorological data for Belgium (northern part of Europe) to determine directions which should be used in practice. So, this research represents a help for architects to design energy efficient buildings with a good thermal interior climate.

Cooling-energy reduction in air-conditioned offices by using night ventilation

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper investigates the applicability of night ventilation in air-conditioned office buildings. A thermal and ventilation simulation model, together with suitable weather data were used to examine the potential for energy savings and/or improved internal comfort conditions by applying night ventilation cooling. It was found that natural ventilation strategies could save cooling energy in typical air-conditioned offices. However, the use of mechanical ventilation could lead to increased energy-consumption. If typical offices are modified to incorporate features assisting the application of night ventilation, then cooling energy could be saved when mechanical ventilation is used and further reduced in the case of natural ventilation. Such features would include exposed thermal mass or offices designed to ‘best practice’ guidelines, such as airtight construction and minimisation of internal and solar heat gains.