Effect of envelope colour and thermal mass on indoor temperatures in hot humid climate

Studies, around the world, have demonstrated that envelope colour has significant effect on building thermal performance and the use of thermal mass can usefully modify the thermo-physical signature of buildings. However, their influences under hot-humid climate have not been investigated in details. In view of the issue, a testing facility has been established in the Department of Architecture of the Chinese University of Hong Kong; the facility allows study of the effect of various building design features on indoor temperatures. This paper presents the results of investigation about the effect of envelope colour and thermal mass on indoor temperatures. The study reveals that the use of lighter surface colour and thermal mass can dramatically reduce maximum indoor temperatures. However, their applications in building design could be very different, and to a large extent, depend on the circumstance. Furthermore, the paper demonstrates the possibility to develop predictive formulas for daily maximum indoor air temperature.     

Numerical analysis and field measurements of the airflow patterns and thermal comfort in an indoor swimming pool: a case study

Public indoor swimming pools are a very popular type of sports facility. They need to ensure good indoor air quality and thermal comfort of the occupants (TCO) while reducing their energy consumption. The objectives of this study are to develop a numerical code, based on the zonal method; to investigate the indoor airflow patterns; and to determine the TCO in the indoor swimming pool. The numerical simulation, performed using the TRNSYS software (version 17), is validated against intensive field measurements, carried out in the public indoor swimming pool located at Bishop’s University (Sherbrooke, Quebec, Canada), of the temperature, velocity, and relative humidity of the air as well as the surface temperature of the walls, ceiling, and floor. The developed code is then used to study the indoor flow patterns and to evaluate the TCO using three indexes: the humidex chart, the predicted mean vote (PMV), and the predicted percentage of dissatisfied (PPD). The results show a hot-humid rather uncomfortable atmosphere is prevailing in the occupied parts of the studied indoor swimming pool. The calculated airflow rates show that, due to the position of the ventilation inlets and outlets, most of the ventilation air circulates in the upper part of the building causing an insufficient air renewal in the occupied parts of the studied indoor swimming pool.     

Variable air volume ventilation control strategies analysed in six climate zones

This paper presents eight ventilation control strategies and their annual energy and indoor air quality simulation results for an academic building as if it were situated in each of six geographic locations. The results show that without tempering at the terminal boxes, no ventilation strategy could satisfy the outdoor air requirements when the thermal loads are low. The fixed outdoor air percentage method is the worst one. From an economic perspective, strategies using optimization techniques minimize the operating energy demand and consumption. Supply air temperature (SAT) and primary airflow rate are the two proper optimization parameters on the air side of heating, ventilating, and air‐conditioning systems. In addition to control strategies, geographic locations or weather patterns influence the benefits of optimization. Generally, a mild‐dry climate intensifies the advantages of the SAT reset and encourages the primary airflow optimization. Inversely, hot‐humid weather minimizes the benefits. Copyright © 1999 John Wiley & Sons, Ltd.     

Analysis of design approaches to improve the comfort level of a small glazed-envelope building during summer

An architect applies glazing to a building envelope to express an expansiveness and hi-tech quality through transparency. However, in small over-glazed buildings, the glazed envelopes often lead to an inadequate comfort level in summer, when much cooling energy is needed to improve the comfort level and occupants are forced to avoid the use of glazed envelopes. This paper presents the results of comfort survey and measurements on the indoor environment of an architecturally significant small glazed-envelope building that has received many awards for its architectural design quality, and analyzes design approaches to improve the comfort level of its occupants. During the late summer of 2002, the comfort survey was conducted, polling responses from 57 office workers, while simultaneously measuring air/surface temperatures and daylight factors. Numerical simulations were performed to investigate 13 design approaches for the improvement of the comfort level. From the temperature/daylight factor measurements, the indoor air temperature did not maintain the set-point temperature of 24.0 °C even with the operation of the air-conditioning system. When using the roller shades, the intensities of illumination and luminance on each measured desk surface were unevenly distributed from 650 Lux and 51 cd/m² to 6291 Lux and 310 cd/m². From the survey, office workers suffered thermal discomfort and uncomfortable glare from high or non-uniform brightness distributions in the working areas. From the numerical analyses using computer simulations, the double-skin envelopes with the sufficient intermediate space and shading devices were suggested to improve the comfort level.     

分析商场中庭温度梯度对空调舒适度的影响

叙述了运用DEST对商场室内温度进行非空调开启期间模拟，利用计算流体力学（CFD）方法对商场中庭进行气流组织模拟以及使用标准κ-ζ模型，运用SIMPLE算法进行离散化的结果，得出，室内基础温度分布、商场中庭建筑的温度梯度及其对室内热环境的影响，旨在指导空调系统的设计。     

On the dynamic thermal behaviour of indoor spaces

A new model is presented for predicting the dynamic thermal response of indoor spaces to indoor heat pulses. The model is based on the concept of the “indoor surface thermal capacitance”, C_s, which characterizes the thermal inertia of an indoor space and expresses the heat stored within indoor air and surface layers of walls and furnishings, per degree of mean temperature difference between indoor air and building envelope. Extensive comparisons with measurements and rigorous finite-difference solutions show that the accuracy of the proposed model is satisfactory for a wide range of practical applications. Comparison with other indoor space simulations of the same class, characterized as “simplified approaches”, show that the present one may provide considerably increased accuracy.     

Shading effects on the winter thermal performance of the Trombe wall air gap: An experimental study in Dalian

There has been little research on the application of shading devices in the air gap of the Trombe wall in China. Experiments on the thermal performance of an advanced Trombe wall with shading in the air gap was conducted in a passive solar house in Dalian. The thermal performance was investigated with regard to the simultaneous temperatures, heat gain and their acquisition of the Trombe wall. By analyzing experimental data, an investigation was carried out on the heat preservation effect by the shading device on a winter night. The theoretical optimum fixed location of the shading in the air gap for minimizing the heat loss was also discussed. Finally, the influence of shading on improving indoor thermal comfort was discussed using the concept of the building envelope response factor (BER) presented earlier by Lukic [The transient house heating condition—the building envelope response factor (BER). Renewable Energy 2003;28(4):523–32].     

Application of terminal box optimization of single‐duct air‐handling units

Terminal boxes maintain room temperature by modulating supply air temperature and airflow in building heating, ventilation and air‐conditioning (HVAC) systems. Terminal boxes with conventional control sequences often supply inadequate airflow to a conditioned space, resulting in occupant discomfort, or provide excessive airflow that wastes significant reheat energy. In this study, the procedure for the optimal minimum airflow setpoint was developed to improve thermal comfort and reduce energy consumption. The determined minimum airflow setpoint was applied in an office building air‐conditioning system. Improvements in indoor thermal comfort and energy reduction were verified through measurement. The results show that the minimum airflow reset can stably maintain room temperature, satisfy comfort standards and reduce energy consumption compared with the conventional control. Copyright © 2009 John Wiley & Sons, Ltd.     

Using CFD to investigate ventilation characteristics of vaults as wind-inducing devices in buildings

This paper investigates the potential of the vaulted roofs for improving wind-induced natural ventilation, using computational fluid dynamics (CFD) three-dimensional modelling. This has been carried out in a parametric study considering different climatic and geometrical parameters. Using Fluent 5.5 program, natural ventilation performance has been modelled and assessed according to the value of airflow rate, and the quality of internal airflow distribution. It has been concluded that utilisation of vaulted roofs for natural ventilation increases inflow rate of the building, and re-distribute internal airflow currents by attracting some of the air to leave through roof openings instead of walls openings. This has improved ventilation conditions in the upstream and central zones of the building, but not in the downstream zone. Natural ventilation performance of two equivalent domed and vaulted roofs has also been compared. Results showed that there are many similarities between domed and vaulted roofs in terms of their natural ventilation performance. The advantage of any roof shape in air suction is highly dependant on wind direction.     

Study of thermal comfort in courtyards in a hot arid climate

The outdoor thermal comfort in an enclosed courtyard has been studied numerically by the three dimensional prognostic microclimate model, Envi-met 3.1. The effect of wind, and shading by different means – galleries, horizontal shading or trees – has been examined. The effect of wind is evaluated by allowing cross-ventilation through openings at 3 and 5 m height above ground level, designed according to the prevalent wind direction. The study was conducted for the hours 11–17 LT during June assuming average climate conditions. The thermal comfort is evaluated by the Predicted Mean Vote (PMV) index.During hot summer days, outdoor comfort is mainly dependent on solar radiation; hence, shading is the best means to improve comfort, while the contribution of wind under all configurations studied was limited and much smaller than the shade contribution.The amount of shade is mainly determined by the courtyard orientation. Inspection of empty enclosed courtyards has shown that an elongated E–W rectangular courtyard has the least shade, and therefore it is the most uncomfortable.When the courtyard is ventilated by openings, hot air and radiation penetrate through them increasing the air temperature and the radiation temperature in the courtyard relative to the conditions obtained in a closed courtyard. Higher openings are less comfortable to stay under, and further decrease the comfort in the courtyard. The addition of trees or/and galleries to the closed courtyard significantly improves the outdoor comfort. Under the assumption of constant building temperature of 25°, the addition of galleries is the most efficient shading strategy.Quantitative results exhibiting these trends are presented for specific configurations and orientations of ventilated and/or shaded courtyards.     

Airflow in courtyard and atrium buildings in the urban environment: a wind tunnel study

A wind tunnel study was carried out to investigate the airflow through courtyard and atrium building models located within an urban setting and exposed to an urban atmospheric boundary layer. Ventilation strategies resulting from the use of different courtyard and atrium pressure regimes (positive pressure and suction) were examined. The model buildings were monitored both in isolation and in idealised urban environments of varying group layout densities. The effect of wind direction was also observed. The results from the study suggest that the open courtyard in an urban environment had a poor ventilation performance whilst an atrium roof with many openings operating under a negative (suction) pressure regime was the most effective. Changing the wind direction from perpendicular to the building façades to a 45° incidence angle had the effect of making the differences in the observed flows between all the models much smaller.     

Nonlinear coupling between thermal mass and natural ventilation in buildings

An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.     

Airpak软件在气流组织领域的应用

Airpak是用于模拟室内气流组织的CFD专用软件,用于工程领域和科学研究。介绍了Airpak软件的基本特点,并用该软件模拟了某办公室的气流组织和热舒适性,为改善室内热环境提供参考。     

Effect of ventilation strategies on air contaminant concentrations and energy consumption in buildings

Considering the diversity of indoor contaminant characteristics and generation patterns, finding an appropriate ventilation strategy that can secure acceptable indoor air quality with minimum energy consumption is a challenging task for HVAC system designers and operators. This study theoretically models and investigates the impact of various ventilation strategies on contaminant concentration behaviour and corresponding ventilation cooling energy requirements for a single‐zone enclosure. Two types of contaminants are considered; carbon dioxide as an occupancy dependent and formaldehyde, which is independent of occupancy. An airflow model is used to predict space pressure and air leakage rates across the enclosure envelope, and an air quality model is used to predict time‐varying contaminant concentrations. In addition, a building energy simulation model is utilized to predict the corresponding ventilation cooling energy requirements under hot climatic conditions. Results from this study show that acceptable contaminant concentrations during occupied periods can be achieved by different ventilation strategies but at substantially different ventilation energy requirements. More than 50 per cent reduction in ventilation energy requirements can be obtained while maintaining acceptable IAQ if proper ventilation strategy is employed. Copyright © 2001 John Wiley & Sons, Ltd.     

The application of dynamic insulation in buildings

Dynamic insulation, a form of ‘Breathing Wall’ construction which allows the movement of air and moisture through the external walls of a building, was seen as one possible method for reducing building envelope heat losses and achieving high indoor air quality. A research investigation was conducted to provide a firm scientific understanding of dynamic insulation. An important outcome of the work will be the development of building envelope designs which effectively and economically employ dynamic insulation in cold climates. This paper presents some general conclusions, confirming that the energy saving produced by dynamic insulation alone is small relative to that obtained in conjunction with conventional air heat recovery methods.     

室内动态热舒适的影响因素分析

析了室内动态热环境下人体热舒适的主要影响因素,并探讨了不同因素的影响程度,指出室内动态热环境下人体热舒适性是各种因素综合作用的结果,室内空气温度、气流速度、空气相对湿度、平均辐射温度、人体生理心理特点、人体活动量、服装参数等均对动态热舒适有影响,其中空气温度及气流速度的动态化是其影响的主要客观因素,人体条件及服装参数是主要主观因素。     

A grey‐box model of next‐day building thermal load prediction for energy‐efficient control

Accurate building thermal load prediction is essential to many building energy control strategies. To get reliable prediction of the hourly building load of the next day, air temperature/relative humidity and solar radiation prediction modules are integrated with a grey‐box model. The regressive solar radiation module predicts the solar radiation using the forecasted cloud amount, sky condition and extreme temperatures from on‐line weather stations, while the forecasted sky condition is used to correct the cloud amount forecast. The temperature/relative humidity prediction module uses a dynamic grey model (GM), which is specialized in the grey system with incomplete information. Both weather prediction modules are integrated into a building thermal load model for the on‐line prediction of the building thermal load in the next day. The validation of both weather prediction modules and the on‐line building thermal load prediction model are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Recommendation on modelling of solar energy incident on a building envelope

It is important to know how to design a building to meet seasonally varying energy needs. In high latitude countries in winter the demand for space heating is high and a building envelope should receive maximum incident solar energy. On the other hand, in summer, walls and roofs exposed to incident solar radiation usually require shading to avoid too much solar gain. Data on solar energy availability are crucial for good building design. However, it is important how the availability of solar radiation is determined. An important aim of the paper presented is to give some results of a comparative analysis of two basic sky models, isotropic: Hottel–Woertz–Liu–Jordan and anisotropic: the HDKR, Hay–Davies–Klucher–Reindl, to recommend one of these models for determination of solar energy availability on a building envelope and to formulate the energy balance of a building. Differences between results obtained from both models increase with the slope of exposed surfaces. The biggest differences (12–15%) are evident for vertical south surfaces, especially in summer. The simplified isotropic sky model is not recommended for evaluation of solar radiation availability on the building envelope. Underestimation of solar gains can lead to the selection of an unsuitable concept and construction of a building and result in poor indoor thermal comfort, i.e. overheating of rooms in 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.     

Integrated analysis of whole building heat,air and moisture transfer

There is a continuous dynamic heat, air and moisture (HAM) interaction between the indoor environment, building envelope and mechanical systems. In spite of these interdependences, the current indoor, building envelope and energy analysis tools are used independently. In this paper a holistic HAM model that integrates building envelope enclosures, indoor environment, HVAC systems, and indoor heat and moisture generation mechanisms, and solves simultaneously for the respective design parameters is developed. The model is benchmarked with internationally published test cases that require simultaneous prediction of indoor environmental conditions, building envelope moisture performance and energy efficiency of a building.