Study on the thermal performance of the Chinese traditional vernacular dwellings in Summer

Based on the field measurements of the thermal environment parameters and a long-term auto-recorder of the indoor and outdoor temperature at four typical traditional vernacular dwellings at Wannan area in summer, some wrong viewpoints about Chinese traditional vernacular dwellings are clarified. Also, with the analysis of the fine structures design such as the dooryard, the structure of the double-pitched roof and the eaves by the measurements of temperature, wind velocity, etc. some design principles of the traditional vernacular dwellings in Wannan area are revealed, of which sun shading and insulation are of great importance while the natural ventilation is just considered as an auxiliary approach. So the strategy of ventilation design is to restrain the natural ventilation at daytime and to boost it at night. Moreover, the thermal sensation votes (TSV) of the occupants and the predicted mean votes (PMV) are compared and the evaluation standard in a naturally ventilated environment is also discussed.     

The influence of the envelope on the thermal performance of ventilated and occupied houses

The main objective of this article is to investigate the influence of the thermal properties of the envelope on the thermal performance of occupied and naturally ventilated houses. A naturally ventilated house built in Southern Brazil was modelled and calibrated in the EnergyPlus computer programme. Based on this calibrated model, a reference model for computer simulations was defined, and variations in the materials of the envelope, occupation patterns and ventilation were carried out. Hourly air temperature and relative air humidity were the output data for the thermal zones of each model. By inputting such data in the Analysis Bio computer programme, the percentage of discomfort hours in the models was obtained. Correlations between the percentage of discomfort hours and the equivalent thermal transmittance, thermal capacity and thermal delay values of the components of the envelope were investigated. Such analysis made clear that there is an influence of the envelope on the thermal performance of the occupied and ventilated house, and that the number of discomfort hours is lower in the models with higher thermal capacity and thermal delay envelope values. It was also observed that thermal capacity was the thermal property with the best correlation to discomfort hours.     

Frequency- and time-domain thermal response of dwellings

A system of algorithms is developed for calculation of the frequency- and time-domain responses of the heat transfer equations for a dwelling. Conduction through the walls, considered as multi-layered slabs, as well as convection to the inside air, infiltration, solar radiation deposition in the space, and radiative interaction between the walls is included in the calculation. The first part of this system of algorithms provides a means whereby a set of frequency responses of the dwelling as a whole may be calculated, one frequency response for each input-output pair, considering internal temperature or heat flow as the output, and the sol-air temperatures on each surface, infiltration, and the solar heat gain to the interior as inputs. The second part of the system of algorithms is then used to obtain from these frequency responses sets of digital transfer function coefficients of the type presented in the ASHRAE Handbook of Fundamentals, but relating the total dwelling heat gain, rather than that for a single wall, with specified internal temperatures, or internal temperature with specified heat gains, to the sol-air temperatures on each surface, infiltration, and solar heat deposited in the interior. The method is shown to produce rapidly calculatable, accurate results in the time-domain. Further the plots of the frequency responses themselves are expected to prove useful in seeking optimal thermal designs.     

Energy performance assessment of existing dwellings

The existing buildings stock in European countries accounts for over 40% of final energy consumption in the European Union (EU) member states, of which residential use represents 63% of total energy consumption in the buildings sector. Consequently, an increase of building energy performance can constitute an important instrument in the efforts to alleviate the EU energy import dependency and comply with the Kyoto Protocol to reduce carbon dioxide emissions. This is also in accordance to the European Directive on the energy performance of buildings (EPBD), which has come to effect on 4 January 2006. The energy performance assessment for existing dwellings (EPA-ED) is a new methodology supported by software, developed in the framework of a European project that focuses on energy related issues for existing residential buildings, in line with the EPBD. This paper presents an overview of the method and software that can be used to perform building energy audits and assess buildings in a uniform way, perform demand and savings calculations, provide owners with specific advice for measures to improve energy performance, issue an energy performance certificate for existing buildings, and include some representative results from the pilot studies performed in several European countries. Also the sister-method EPA-NR, on non-residential buildings, currently under construction, is introduced.     

Probabilistic climate projections with dynamic building simulation: Predicting overheating in dwellings

This study, as part of the Low Carbon Futures project, proposes a methodology to incorporate probabilistic climate projections into dynamic building simulation analyses of overheating in dwellings. Using a large climate projection database, suitable building software and statistical techniques (focussing on principal component analysis), output is presented that demonstrates the future overheating risk of a building in the form of a probability curve. Such output could be used by building engineers and architects to design a building to an acceptable future overheating risk level, i.e. providing evidence that the building, with specific adaptation measures to prevent overheating, should achieve thermal comfort for the majority of future climate projections. This methodology is overviewed and the use of the algorithm proposed in relation to existing building practices. While the methodology is being applied to a range of buildings and scenarios, this study concentrates on night-time overheating in UK dwellings with simple and achievable adaptation measures investigated.     

Field assessment of thermal behaviour of historical dwellings in France

In many countries, there is a great number of old buildings with local architectural, patrimonial, aesthetic and historic interest. They are the products of the vernacular traditional architecture fully integrating the environmental, social and economic local constraints.Moreover, this built inheritance is more heterogeneous than the modern stock of existing buildings. The historical buildings were built with different architectural designs featuring local styles of construction, different techniques and historical expertise.By experience, the actors of the building sector know that the thermal behaviour of historical buildings are not those of modern buildings set up at the time of the industrial period. However, they do not have assessed these specific thermal characteristics of historical buildings.This paper describes the complexity of architectural designs of historical dwellings in France. A field investigation during one year highlights various thermal characteristics of 11 dwellings. It provides a new understanding of thermal behaviour of these historical dwellings. The results show the thermal characteristics of historical dwellings and their differences with modern architecture.     

玉树灾后重建民居热环境研究

对玉树灾后重建民居的热工性能进行了分析,其围护结构满足严寒地区节能标准要求.分别选取玉树县禅古村重建的1栋无人居住建筑和1栋有人居住建筑进行了室内外热环境测试.重建民居在室外平均温度-12.5℃条件下单纯依靠建筑围护结构本身可提高室内温度9.4℃.重建民居相对震前民居节能率为60％.分析了重建民居室内热环境的成因,并提出了改进建议.     

Establishing the zero-carbon performance of compact urban dwellings

This paper presents an analysis of the zero-carbon performance of a case-study building which is representative of a growing number of new buildings that are being built on redevelopment sites in inner-city areas in the UK. Compact urban dwellings are apartment style buildings with a floor area of ～50 m² per dwelling, often based over two floors. The constraints of this type of building on achieving zero-carbon performance in the context of the Code for Sustainable Homes is discussed and the shortcomings of the code are demonstrated in terms of the target heat and electricity demand targets for the design of the building systems. A graphical representation of the simulation results is used to present the findings. It has been demonstrated that in specific urban contexts, zero-carbon performance as defined within the current UK compliance framework may be very difficult to achieve in practice given the assumptions used in the simulation here. Therefore, it is very likely that zero-carbon compact urban dwellings may require a net off-site import of electrical and/or thermal energy.     

巴渝地区夯土民居室内热环境

传统民居的传统生态建造经验与价值已得到广泛认可,巴渝地区因特殊的地形与气候,传统民居在热环境的营造上有自身的特点。以重庆江津区龙塘村夯土民居为研究对象,以实地测量的冬季室内热工参数为基础,运用软件模拟分析,对民居全年室内热环境进行评价,发现夯土墙对改善夏季热环境更为有利,夯土民居冬季室内热环境远比夏季差;民居建筑中阁楼空间在调节室内热环境方面作用显著,具有冬季保温,夏季隔热的作用。     

中国供暖临界地区居住建筑热环境分析

采用有效传热系数方法分析了中国供暖临界地区的居住建筑室内热环境，结果表明：现有形式的住宅仅靠围护结构的保温作用和室内余热不能保证１０℃的室内温度；降低换气次数和改善窗的保温性能是提高室温的有效方法。建议分步实现该地区居住室内环境指标。     

A simple design tool for the thermal study of dwellings

The objective of the OPTI program (the dwellings module) is to help architects to take into account the impact of design choices on energy consumption designing a dwelling project.In order to do so, the program must:

• •be highly user-friendly (language based on drawings);
• •need a minimum of data and
• •be very fast.

The computation of energy needs and overheating estimation require dynamic thermal programs. These are often slow and need a large amount of data.The use of many parametric studies realized with a dynamic thermal program allowed us to create software providing the user instantaneously with results from a dynamic thermal program without subjecting architects to the disadvantages of this type of program.Indeed, the program provides annual thermal needs and thermal comfort (winter and summer) in relation with orientation, building footprint, window area and type, insulation level, presence of external or internal shading devices, ventilation strategy applied and thermal mass.This design tool is based on Belgian climatic weather data but the same step could be transposed to other climatic data.     

A pseudo dynamic analysis tool for thermal certification of dwellings

The determination of a normalised heating energy consumption of dwellings can be achieved in different ways: basic and complex calculation methods, as well as experimental procedures can be considered. This paper deals with a certification method based on a limited monitoring of the dwelling coupled with a pseudo dynamic analysis tool. Firstly, the energy performance of a monitored dwelling (a modern single family dwelling and situated in a mild climate) is estimated on the basis of previous energy bills and the application of the prEN832 calculation method; secondly, the obtained figures are compared with those resulting from the pseudo dynamic analysis of the monitoring results.One of the goals of the developed experimental method was to set-up a test procedure that would not disturb the regular life of the dwelling occupants. Therefore, extensive use was made of wireless technology and passive tracer gas techniques have been used to derive an integrated ventilation rate for the house.The background of the pseudo dynamic technique, monitoring disturbances due to building occupation and the overall accuracy of the method are presented. The impact of parameters used for normalising the consumption, such as degree-days or test reference years climatic data (TRY) is discussed. The aim of this paper is, however, not to come up with a well defined standard procedure for determining the normalised heating energy consumption of dwellings but rather to confront the developed method results with those of other procedures and to identify critical limitations routes for possible improvements.     

Predicting thermal and energy performance of mixed-mode ventilation using an integrated simulation approach

Mixed-mode ventilation can effectively reduce energy consumption in buildings, as well as improve thermal comfort and productivity of occupants. This study predicts thermal and energy performance of mixed-mode ventilation by integrating computational fluid dynamics (CFD) with energy simulation. In the simulation of change-over mixed-mode ventilation, it is critical to determine whether outdoor conditions are suitable for natural ventilation at each time step. This study uses CFD simulations to search for the outdoor temperature thresholds when natural ventilation alone is adequate for thermal comfort. The temperature thresholds for wind-driven natural ventilation are identified by a heat balance model, in which air change rate (ACH) is explicitly computed by CFD considering the influence of the surrounding buildings. In buoyancy-driven natural ventilation, the outdoor temperature thresholds are obtained directly from CFD-based parametric analysis. The integrated approach takes advantage of both the CFD algorithm and energy simulation while maintaining low levels of complexity, enabling building designers to utilize this method for early-stage decisionmaking. This paper first describes the workflow of the proposed integrated approach, followed by two case studies, which are presented using a three-floor office building in an urban context. The results are compared with those using an energy simulation program with built-in multizone modules for natural ventilation. Additionally, adaptive thermal comfort models are applied in these case studies, which shows the possibility of further reducing the electricity used for cooling.     

Energy performance assessment of occupied buildings using model identification techniques

Model identification allows the assessment of energy performance of buildings based on measured data. However, model identification of occupied buildings is difficult because the disturbances introduced by the occupants are usually not measured. For office buildings, we propose a method to estimate the occupancy in function of electrical energy consumption. To determine the complexity of the model, SVD is used for the number of thermal zones and statistical analysis is used for the model order. The estimated model was evaluated by simulation, consistency of input–output behaviour and uncertainty analysis. The RMS of the simulation error is less than 0.7 °C for the training data set. The proposed method allows calculating macroscopic parameters of the building (such as thermal loss and time constants), showing the relative weights for heat losses and estimation of energy savings by heating control.     

Predicting integrated thermal and acoustic performance in naturally ventilated high-rise buildings using CFD and FEM simulation

The study of ventilation windows for both natural ventilation and noise mitigation has drawn significant attention recently. This paper presents the numerical approaches to analyse the integrated thermal and acoustical performance of ventilation windows, for a residential building in tropical climate which employs double-layer noise mitigation window for natural ventilation. Given a set of outdoor wind conditions, the distributions of indoor flow and temperature fields are simulated using Computational Fluid Dynamics (CFD) model. The thermal comfort is evaluated using statistical Predicted Mean Vote (PMV) method. For the acoustic performance, noise radiation from road traffic is assumed as the noise source, and the sound insulation of building façade is simulated using Finite Element Method (FEM). From the simulation results, it is found that the thermal satisfaction response is closely related to the inlet wind temperature and speed, and the window opening size greatly affects the ventilation performance. From the case study in Singapore, during certain season, day/night time and with sufficient wind flow, the ventilation window can provide enough fresh air, maintain adequate thermal comfort and quiet acoustic environment for the occupants. The numerical approaches presented in this paper are applicable to general window design studies, and the simulation findings can be incorporated into green building planning. The advantages of using simulation approaches are highlighted and their limitations are discussed.     

The thermal mechanism of warm in winter and cool in summer in China traditional vernacular dwellings

Yaodong is one representative of western China vernacular dwellings. Its indoor thermal environment is cool in summer and warm in winter. This study interprets the characteristic of warm in winter and cool in summer in such a dwelling by measuring the indoor, outdoor and wall’s temperatures in winter and summer. The human thermal comfort theory is used to evaluate thermal environment, and the periodic heat transfer mechanism is used to analyze the thermal transfer through the wall. The results show that the Yaodong thick wall effectively damping external temperature wave and keeping steady inner surface temperature are the chief causes of warm in winter and cool in summer in Yaodong, which lays a scientific basis for low energy building design.     

Radiation performance index for Dutch dwellings: consequences for some typical situations

This paper describes the new approach to control radiation exposure from natural sources to inhabitants of dwellings that is presently being considered in the Netherlands. The goal of this approach is to uphold the current rather favorable situation (average annual effective dose due to indoor radon and external radiation in dwellings is approx. 1 mSv). To achieve this goal a model is foreseen to predict the potential effective dose an inhabitant may receive from a dwelling on basis of its building plan. A scheme to calculate this dose is proposed in this paper. In future, such a scheme will be included in the Dutch Building Codes and houses to be built will be evaluated by using this scheme and comparing the results with, yet to be posed, limits to the potential effective dose.     

Comparison between measured and calculated energy performance for dwellings in a summer dominant environment

The objective of this study is to present a comparison between the measured and the calculated energy performance of dwellings. For this purpose, the energy consumption of ten dwellings is measured for one year. The added value of this work is that it is performed in a summer dominant environment. The energy needs of the same dwellings are also calculated by means of the methodology based on European Standards described in the CEN/TR 15615:2008 technical report. According to the findings of this study, a large gap exists between the calculated and the measured energy consumption of the examined dwellings. In order to evaluate the reasons for this deviation, a detailed analysis of the heating and cooling loads of the dwellings is performed. The intermittent heating of the building is found to be simulated accurately by the employed methodology, whereas the comparison between the calculated and the measured cooling loads reveals a large deviation of about 150%. Based on the findings of this study, a factor of 0.6 should be adopted in the case of cooling schedule, compared to the heating operation of the building.