Warm season cooling requirements for passive buildings in Southeastern Europe (Romania)

The first Romanian passive office building has been constructed by the AMVIC Company in Bragadiru, 10 km south of Bucharest. The overheating rate and the cooling load are higher for a passive building than for a standard building. The internal heat sources and the maximum allowed indoor temperature do markedly affect the cooling load. A time-dependent model shows that cooling is necessary during April-September. The ground heat exchanger is an effective system for cooling-down the fresh air inlet temperature. Also, the Venetian blinds prove to be efficient in diminishing the building heat input. However, these two systems are not able to ensure a controlled thermal comfort during summer. This suggests that an active cooling system should be used when passive buildings are implemented in the Romanian climate. The standard configuration of the passive buildings ventilation system (which is usually designed for heating purposes), must be changed in case cooling becomes necessary during the warm season. The results are of interest for other countries in Southeastern Europe.     

Development of feasibility approaches for studying the behavior of passive cooling systems in buildings

This study is a contribution to European projects Pascool/Joule II and Altener/Sink that deals with feasibility of passive cooling systems in Europe. The first aim of this work was to define a design methodology to evaluate natural cooling potential according to the climatic quantification criteria of the site, the cooling system performance, and comfort criteria defined by the couple of temperature and relative humidity set points. A simplified approach, based on climatic potential criteria as theoretical cooling potential index, the available potential index, the cooling need index, and the natural cooling normalized capacity, was developed. It was applied to 105 European sites for different types of evaporative cooling systems (direct and indirect), and for various temperature and relative humidity set points. During the second stage, a refined approach taking into account building characteristics and the cooling system performance, was developed. This method is based on the integration of numerical models of passive cooling systems in a thermal building software in order to consider interaction phenomena between cooling system and building. Application of this approach to one building has been done in order to assess energy consumption gain achieved by using passive cooling systems. These two complementary approaches provide helpful information dealing with the feasibility of a passive cooling technique based on comfort and energy saving criteria. They could be used by architects and building designers as helpful decision making tools during the different stages of building design.     

FUTURE RESEARCH ACTIONS IN PASSIVE COOLING

The PASCOOL program was the most important European project on passive cooling of buildings. The project addressed topics included solar control, the combined effect of ventilation and thermal mass, thermal comfort during summer and the potential of natural cooling techniques. PASCOOL put in evidence also the axes towards which future research on passive cooling should be oriented. This research, giving the continuously increasing trend of energy consumption for cooling purposes, is absolutely necessary in order to take advantage of the complete potential that passive cooling can offer to buildings while maintaining the living standards, health and comfort of the occupants. This paper presents these future issues that comprise (a) research on the microclimatic scale in order to address the impact of outdoor environment on the cooling load of buildings, (b) investigation of comfort requirements under transient conditions during summer, (c) research on natural ventilation in urban environments and the impact of outdoor pollution on indoor air quality, (d) development of alternative cooling systems and techniques, (e) development of integrating design concepts optimising the use of solar heating, passive cooling and natural light in buildings.     

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.     

Path Analysis of Energy-Saving Technology in Yangtze River Basin Based on Multi-Objective and Multi-Parameter Optimisation

The Yangtze River Basin in China is characterised by hot-and cold-humid climates in summer and winter, respectively. Thus, increased demand for heating and cooling energy according to the season, as well as poor indoor thermal comfort, are inevitable. To overcome this problem, this study focused on the influence of passive design and heating, ventilation, and air conditioning equipment performance on the energy performance of residential buildings, and explored potential energy-saving technology paths involving passive design and improved coefficient of performance through a multi-objective and multi-parameter optimisation technique. A large-scale questionnaire survey covering a typical city was first conducted to identify family lifestyle patterns regarding time spent at home, family type, air conditioner use habits, indoor thermal comfort, etc. Then, the actual heating and cooling energy consumption and information of model building were determined for this region. Subsequently, the design parameters of an individual building were simulated using Energyplus to investigate the cooling and heating energy consumption for a typical residential building with an air conditioner. The results indicated an improvement of approximately 30% in energy efficiency through optimisation of the external-wall insulation thickness and the external-window and shading performance, and through use of appropriate ventilation technology. Thus, a multi-objective and multi-parameter optimisation model was developed to achieve comprehensive optimisation of several design parameters. Experimental results showed that comprehensive optimisation could not only reduce cooling and heating energy consumption, but also improve the thermal comfort level achieved with a non-artificial cooling and heating source. Finally, three energy-saving technology paths were formulated to achieve a balance between indoor thermal comfort improvement and the target energy efficiency(20 kWh/(m2?a)). The findings of this study have implications for the future design of buildings in the Yangtze River Basin, and for modification of existing buildings for improved energy efficiency.     

Thermal and environmental assessment of a passive building equipped with an earth-to-air heat exchanger in France

In France, where a division by 4 of the greenhouse gases emissions is aimed from 1990 to 2050, technical solutions are studied in order to reduce energy consumption while providing a satisfactory thermal comfort level in buildings. A two-dwelling passive building has been carried out in Formerie (North-West of France), complying the “Passivhaus” standard. This building, not yet monitored, has been modeled using the dynamic simulation software COMFIE, which is dedicated to building eco-design. In order to account for the implemented ventilation system, including a heat recovery unit and an earth-to-air heat exchanger, a specific model has been developed and integrated to COMFIE as a new module. In this article, this model is described first. In order to quantify the benefits brought by a passive design, the simulation results are presented for the passive house and a reference house complying with the French thermal regulation for buildings. The heating load and thermal comfort level of both houses are compared, showing for the passive design a tenfold reduction of the heating load and a clear reduction of summer discomfort. Finally, the environmental assessment – carried out with the life cycle assessment tool EQUER – shows the reduction in primary energy consumption, global warming potential and other impacts brought by the passive house design. Passive house appears to be an adequate solution to improve the environmental performances of buildings in the French context.     

Low energy ventilation and cooling within an urban heat island

More recent UK climatic data for use in the design of naturally ventilated buildings show that passive stack ventilation alone is unlikely to maintain summertime comfort in a new University College London building within the London city heat island. A stack ventilation strategy developed by the design team was evolved by the introduction of passive downdraught cooling (PDC). PDC enables cooled air to be distributed throughout the building without fan assistance. The underlying principles of the technique were explored using computational and physical models. The architectural integration and seasonal control modes are described. Predicted performance of PDC is compared with actual measurements.     

The bioclimatic design approach to low-energy buildings in the Klang Valley, Malaysia

Formulating passive energy design strategies require an understanding of the climatic influence on buildings and the thermal comfort of their occupants. This paper presents the bioclimatic approach in building design as well as the techniques which are applied to formulate various strategies in order to achieve indoor comfort conditions. The paper deals with the Bioclimatic Chart, the Building Psychrometric Chart, Mahoney Tables and the Control Potential Zones which utilise the thermal neutrality concept. Regional climatic data from the Klang Valley area in Malaysia were utilised in formulating the design strategies. The most appropriate design strategies for hot, humid regions were then deduced. The most preferred strategies found were the use of ventilation, dehumidification and shading. Consequently, a full recommendation for the integral use of these three passive methods are suggested to be used in all buildings in Malaysia.     

Optimizing opening dimensions for naturally ventilated buildings

Since naturally ventilated buildings respond to site conditions and microclimate, we cannot establish a “one set of criteria” for every naturally ventilated building. So natural ventilation should be optimized to deal with thermal comfort in passive buildings during summer. A survey of existing tools for natural ventilation simulation shows the dominance of so-called “analysis” tools over “design” tools. In this present work, we will propose a new method to size natural ventilation openings based on inverse calculation, reduction of the number of independent parameters and optimization of occupants thermal comfort.     

基于性别的严寒地区高校教学楼自然通风热舒适性研究

严寒地区夏季采用自然通风作为被动式降温手段,改善空气品质的同时减少能耗,其热舒适性会受到多因素影响。对严寒地区夏季自然通风条件下两种建筑布局的高校教学楼热环境进行实测,对影响热舒适的三种因素,温度、湿度以及受试者体重指数(bady mass index,BMI)进行调查研究,基于在室人员不同性别,进行差异性、相关性和显著性对比分析。结果表明:内廊式教学楼较中庭式教学楼有更好的热舒适性;操作温度与热舒适性密切相关,中性温度为27.96℃,其中男性为27.51℃,女性为28.26℃;相对湿度与操作温度负相关,且对热舒适性有较大影响;BMI与热舒适性呈现较低的相关性,其并不能明显影响热舒适性,但相同BMI下,男性热感觉略高于女性;利用Griffiths评价模型能准确预测严寒地区夏季舒适温度。     

On the use of sunspace for space heating/cooling in Europe

The heating/cooling potential of a typical sunspace has been investigated in the present study as a function of different climatic conditions in several locations throughout Europe. Passive solar design is mainly concentrated on providing space heating during winter as well as on avoiding overheating during the summer period. In the present paper the feasibility of a sunspace as a heating system was studied taking into account the climatic conditions. Simultaneously, various passive cooling techniques are proposed and examined in order to avoid overheating during summer. For this reason, a representative case study is presented and simulated for several climatic conditions. The simulated results showed that sunspaces can be an appropriate and effective system all over Europe during the cold period of the year. Thermal mass within buildings, shading devices, buried pipes and night ventilation techniques can be essential and effective methods to control overheating during summer.     

Earth-to-air heat exchangers for Italian climates

The European Energy Efficiency Building Directive 2002/91/CE, as well as other acts and funding programs, strongly promotes the adoption of passive strategies for buildings, in order to achieve indoor thermal comfort conditions above all in summer, so reducing or avoiding the use of air conditioning systems.In this paper, the energy performances achievable using an earth-to-air heat exchanger for an air-conditioned building have been evaluated for both winter and summer. By means of dynamic building energy performance simulation codes, the energy requirements of the systems have been analysed for different Italian climates, as a function of the main boundary conditions (such as the typology of soil, tube material, tube length and depth, velocity of the air crossing the tube, ventilation airflow rates, control modes). The earth-to-air heat exchanger has shown the highest efficiency for cold climates both in winter and summer.The possible coupling of this technology with other passive strategies has been also examined. Then, a technical-economic analysis has been carried out: this technology is economically acceptable (simple payback of 5–9 years) only in the cases of easy and cheap moving earth works; moreover, metallic tubes are not suitable.Finally, considering in summer a not fully air-conditioned building, only provided with diurnal ventilation coupled to an earth-to-air heat exchanger plus night-time ventilation, the possible indoor thermal comfort conditions have been evaluated.     

Energy efficiency of small buildings with smart cooling system in the summer

In this paper, a novel cooling control strategy as part of the smart energy system that can balance thermal comfort against building energy consumption by using the sensing and machine programming technology was investigated. For this goal, a general form of a building was coupled by the smart cooling system (SCS) and the consumption of energy with thermal comfort cooling of persons simulated by using the EnergyPlus software and compared with similar buildings without SCS. At the beginning of the research, using the data from a survey in a randomly selected group of hundreds and by analyzing and verifying the results of the specific relationship between the different groups of people in the statistical society, the body mass index (BMI) and their thermal comfort temperature were obtained, and the sample building was modeled using the EnergyPlus software. The result show that if an intelligent ventilation system that can calculate the thermal comfort temperature was used in accordance with the BMI of persons, it can save up to 35% of the cooling load of the building yearly.     

Solar passive features in vernacular architecture of North-East India

Energy consumption in the buildings sector is very high and is expected to increase further due to improvements in living standard and increase in the world’s population. Incorporating appropriate solar passive features in climate responsive buildings are good options for energy conservation. This kind of building design integrates the micro-climate and architecture with human thermal comfort conditions and improves the building energy efficiency. From ancient times, people have used solar passive techniques in vernacular architectures throughout the world. However, still there is a lack of understanding, both in qualitative and quantitative aspects of solar passive techniques in vernacular architectures of North-Eastern India. A field study has been carried out to find out the various solar passive features in these naturally ventilated vernacular buildings in different bioclimatic zones of the region. The methodology of this work consists of survey of 150 households (50 houses in each bioclimatic zone) and, interacting with 300 occupants in each zone. The photographic evidences of solar passive features in these buildings are also collected. In this paper, the solar passive features related to building form and orientation, envelope design, shading, use of natural ventilation, internal space arrangements and activities of the habitants are explained for all the climatic zone of the region.     

Potential for free-cooling by ventilation

Natural ventilation is one of the most effective techniques for cooling. Its potential for cooling may be assessed by using a method based on the indoor–outdoor temperature difference of the free-running building, the adaptive comfort criteria and the outdoor temperature. It is demonstrated that the free-running temperature may be used instead of the balance temperature in energy estimation methods. The indoor–outdoor temperature difference of the free-running building becomes a characteristic of the thermal behavior of the building which is decoupled from comfort range and outdoor temperature. A measure related to the energy saved and the applicability of free-cooling is given by the probabilistic distribution of the degree-hours as a function of the outdoor temperature and time. Weather data for this method are available in public domain from satellite investigation. The method can be applied when buildings similar to existing ones are constructed in a new location, when existing buildings are retrofitted or when completely new buildings are designed. The method may be used to interpret the results of building simulation software or of the field measurements.     

Bringing simulation to implementation: presentation of a global approach in the design of passive solar buildings under humid tropical climates

In early 1995, a DSM pilot initiative was launched in the French islands of Guadeloupe and La Reunion through a partnership between several public and private partners (the French Public Utility EDF, the University of Reunion Island, low cost housing companies, architects, energy consultants, etc…) to set up standards to improve thermal design of new residential buildings in tropical climates. This partnership led to defining optimized bio-climatic urban planning and architectural designs featuring the use of passive cooling architectural principles (solar shading, natural ventilation) and components, as well as energy efficient systems and technologies. The design and size of each architectural component with regard to internal thermal comfort in buildings has been assessed with validated thermal and airflow building simulation software (CODYRUN). These technical specifications have been edited in a reference document which has been used to build over 800 new pilot dwellings through the years 1996–2000 in Reunion Island and in Guadeloupe. Monitoring experiments were held in these first ECODOM dwellings in 1998 and 1999. This resulted in experimental validation of the impact of the passive cooling strategies on the thermal comfort of occupants leading to the modification of specifications when necessary. The paper presents all the methodology used for the application of ECODOM, from the simulations to the experimental results. This follow up is important, as the setting up of the ECODOM standard will be the first step towards the introduction of thermal regulations in the French overseas territories, by the year 2002.     

Performance evaluation of passive cooling in office buildings based on uncertainty and sensitivity analysis

Natural night ventilation is an interesting passive cooling method in moderate climates. Driven by wind and stack generated pressures, it cools down the exposed building structure at night, in which the heat of the previous day is accumulated. The performance of natural night ventilation highly depends on the external weather conditions and especially on the outdoor temperature. An increase of this outdoor temperature is noticed over the last century and the IPCC predicts an additional rise to the end of this century. A methodology is needed to evaluate the reliable operation of the indoor climate of buildings in case of warmer and uncertain summer conditions. The uncertainty on the climate and on other design data can be very important in the decision process of a building project.The aim of this research is to develop a methodology to predict the performance of natural night ventilation using building energy simulation taking into account the uncertainties in the input. The performance evaluation of natural night ventilation is based on uncertainty and sensitivity analysis.The results of the uncertainty analysis showed that thermal comfort in a single office cooled with single-sided night ventilation had the largest uncertainty. The uncertainties on thermal comfort in case of passive stack and cross ventilation were substantially smaller. However, since wind, as the main driving force for cross ventilation, is highly variable, the cross ventilation strategy required larger louvre areas than the stack ventilation strategy to achieve a similar performance. The differences in uncertainty between the orientations were small.Sensitivity analysis was used to determine the most dominant set of input parameters causing the uncertainty on thermal comfort. The internal heat gains, solar heat gain coefficient of the sunblinds, internal convective heat transfer coefficient, thermophysical properties related to thermal mass, set-point temperatures controlling the natural night ventilation, the discharge coefficient C_d of the night ventilation opening and the wind pressure coefficients C_p were identified to have the largest impact on the uncertainty of thermal comfort.The impact of the warming climate on the uncertainty of thermal comfort was determined. The uncertainty on thermal comfort appeared to increase significantly when a weather data set with recurrence time of 10 years (warm weather) was applied in the transient simulations in stead of a standard weather data set. Natural night ventilation, designed for normal weather conditions, was clearly not able to ensure a high probability of good thermal comfort in warm weather. To ensure a high probability of good thermal comfort and to reduce the performance uncertainty in a warming climate, natural night ventilation has to be combined with additional measures. Different measures were analysed, based on the results of the sensitivity analysis. All the measures were shown to significantly decrease the uncertainty of thermal comfort in warm weather. The study showed the importance to carry out simulations with a warm weather data set together with the analysis under typical conditions. This approach allows to gain a better understanding of the performance of a natural night ventilation design, and to optimize the design to a robust solution.     

Novel heating and cooling concept employing rainwater cisterns and thermo-active building systems for a residential building

This paper introduces and evaluates a novel heating and cooling concept employing thermo-active building systems and environmental energy, harnessed from two 11-m³ rainwater cisterns for a 285-m² residential building in passive house standard in Germany. The building strives for a significantly reduced primary energy use with carefully coordinated measures, such as high quality building envelope, by means of vacuum insulated panels, supply and exhaust air system with heat recovery, reduced solar heat gains (solar shading), and the integration of thermal solar collectors and photovoltaic in the plant system. On this premise, a comprehensive long-term monitoring in high time-resolution was carried out for the building for two years with an accompanying commissioning of the building performance. Measurements comprise the energy use for heating, cooling, and ventilation, as well as the auxiliary equipment, the performance of the environmental heat source and sink (rainwater cistern), thermal comfort, and local climatic site conditions.     

Impact of passive cooling techniques on energy demand for residential buildings in a Mediterranean climate

This study presents the thermal analysis of a building prototype, which was designed and built in accordance with energy efficiency measures to improve indoor thermal comfort, particularly in summer. The building prototype is located in Souidania (20 km southwest of Algiers, latitude 36°7N, Longitude 03°2E). The location is characterized by a temperate Mediterranean climate. In order to perform this analysis, various activities are carried out: a series of monitoring campaigns; dynamic simulations with TRNSYS software, calibration of the model with experimental data and comparative study with buildings that use different wall constructions. Based on a validated building thermal model, dynamic analysis is carried out in order to evaluate the impact of thermal mass and of eaves and night ventilation. The results demonstrate that cooling energy demand is more affected by thermal transmittance values than by the envelope thermal mass. A recommended guideline for the optimum overhang length for south-facing windows is proposed. Ultimately, it is found that the combination of both natural ventilation and horizontal shading devices improves thermal comfort for occupants and significantly reduces cooling energy demand.     

Thermal-comfort analysis and simulation for various low-energy cooling-technologies applied to an office building in a subtropical climate

Simulation of buildings’ thermal-performances is necessary to predict comfort of the occupants in buildings and to identify alternate cooling control-systems for achieving better indoor thermal environments. An analysis and prediction of thermal-comfort using DesignBuilder, based on the state-of-the-art building performance simulation software EnergyPlus, is carried out in an air-conditioned multi-storeyed building in the city of Rockhampton in Central Queensland, Australia. Rockhampton is located in a hot humid-region; therefore, indoor thermal-comfort is strongly affected by the outdoor climate. This study evaluates the actual thermal conditions of the Information Technology Division (ITD) building at Central Queensland University during winter and summer seasons and identifies the thermal comfort level of the occupants using low-energy cooling technologies namely, chilled ceiling (CC), economiser usages and pre-cooling. The Fanger comfort-model, Pierce two-node model and KSU two-node model were used to predict thermal performance of the building. A sophisticated building-analysis tool was integrated with the thermal comfort models for determining appropriate cooling-technologies for the occupants to be thermally comfortable while achieving sufficient energy savings. This study compares the predicted mean-vote (PMV) index on a seven-point thermal-sensation scale, calculated using the effective temperature and relative humidity for those cooling techniques. Simulated results show that systems using a chilled ceiling offer the best thermal comfort for the occupants during summer and winter in subtropical climates. The validity of the simulation results was checked with measured values of temperature and humidity for typical days in both summer and winter. The predicted results show a reasonable agreement with the measured data.