Design of solar radiation and thermal capacity influence on the indoor climate of buildings

The influence of building design on indoor climate is studied using Hoffman and Feldman's Total Thermal Time Constant Method for simulation of the thermal response of a building.Comfort requirements in summer in residential buildings, and the manner in which they can be achieved by appropriate building design in order to improve indoor thermal conditions are discussed.The proper use of insulation and heat capacity properties (represented in this paper by the total thermal time constant of the external elements) and the use of light external colours are very important in eliminating or minimizing the need for air conditioning coolers. The correct design of insulation, and window areas permitting solar radiation penetration, can drastically reduce heating requirements in winter.The incomplete results reported are part of a research in progress on the calibration of ventilation as a source of cooling in summer and of window area (with solar radiation penetration) as a source of heating in winter.     

New concepts and approach for developing energy efficient buildings: Ideal specific heat for building internal thermal mass

The shortcomings or limitations of the traditional approach to developing energy efficient buildings are that they can not determine: (1) the ideal thermophysical properties of building envelope material, where “ideal” means that such material can use ambient air temperature variation and/or solar radiation efficiently to keep the indoor air temperature in the thermal comfort range with no additional space heating or cooling; (2) the best natural ventilation strategy; (3) the minimal additional energy consumption for space heating in winter or air-conditioning in summer. To overcome these problems, some new concepts for developing energy efficient buildings are put forward in this paper. They are the ideal thermophysical properties of the building envelope material, the ideal natural ventilation rate, and a minimal additional space heating or cooling energy consumption. A new approach for determining these properties is also developed. In contrast to the traditional approach (the thermophysical properties of building envelope material are known and constant so that the relating equations describing the indoor air temperature tend to be linear differential equations), the new approach solves the inverse problem (thermophysical properties, etc. of a buildings are unknown), whose solution can be a function instead of a value. As a first step, the ideal specific heat of the building envelope material for internal thermal mass is analyzed for buildings located in various cities in different climatic regions of China, such as Beijing, Shanghai, Harbin, Urumchi, Lhasa, Kunming and Guangzhou. We found that the ideal specific heat is composed of a basic value and an excessive one which is of δ function for the cases studied. Some limitations that would need further study are introduced in the end of the paper.     

Coupling of thermal mass and natural ventilation in buildings

The coupling of thermal mass and natural ventilation is important to passive building design. Thermal mass can be classified as external thermal mass and internal thermal mass. Due to great diurnal variation of ambient air temperature and solar radiation intensity, heat transfer through building envelopes, which is called external thermal mass, is a complex and unsteady process. Indoor furniture are internal thermal mass, affecting the indoor air temperature through the process of absorbing and releasing heat. In this paper, a heat balance model coupling the external and internal thermal mass, natural ventilation rate and indoor air temperature for naturally ventilated building is developed. In this model, the inner surface temperature of building envelopes is obtained based on the harmonic response method. The effect of external and internal thermal mass on indoor air temperature for six external walls is discussed of different configurations including lightweight and heavy structures with and without external/internal insulation. Based on this model, a simple tool is developed to estimate the indoor air temperature for certain external and internal thermal mass and to determine the internal thermal mass needed to maintain required indoor air temperature for certain external wall for naturally ventilated building.     

Ideal thermophysical properties for free-cooling (or heating) buildings with constant thermal physical property material

Free-cooling is understood as a means to store outdoors coolness during the night, to supply indoors cooling during the day in summer, while free-heating is understood as a means to store the solar radiation during daytime, to supply indoors heating during the night in winter. In principle, free-cooling or free-heating can make the indoor air temperature in the comfortable region all the year if the thermophysical properties of building envelope material are in the desired range (defined as ideal thermophysical properties in this paper). Those properties are obviously related to the outdoor climate condition, internal heat source intensity, building configuration, ventilation mode etc. For a given region and a given building, the critical values of those ideal thermal physical properties can be determined through modeling and simulation. Two parameters, I_win and I_sum, are defined to describe the overcool degree in winter and the overheat degree in summer, respectively. To illustrate, the critical values of thermophysical properties of building envelope of a building located in Beijing are obtained through modeling and simulation. The simulated results are validated with experiments. The model, the methodology and the results are helpful for selection of suitable building envelope materials and for design of energy efficient buildings.     

Application of latent heat thermal energy storage in buildings: State-of-the-art and outlook

Latent heat thermal energy storage (LHTES) is becoming more and more attractive for space heating and cooling of buildings. The application of LHTES in buildings has the following advantages: (1) the ability to narrow the gap between the peak and off-peak loads of electricity demand; (2) the ability to save operative fees by shifting the electrical consumption from peak periods to off-peak periods since the cost of electricity at night is 1/3–1/5 of that during the day; (3) the ability to utilize solar energy continuously, storing solar energy during the day, and releasing it at night, particularly for space heating in winter by reducing diurnal temperature fluctuation thus improving the degree of thermal comfort; (4) the ability to store the natural cooling by ventilation at night in summer and to release it to decrease the room temperature during the day, thus reducing the cooling load of air conditioning. This paper investigates previous work on thermal energy storage by incorporating phase change materials (PCMs) in the building envelope. The basic principle, candidate PCMs and their thermophysical properties, incorporation methods, thermal analyses of the use of PCMs in walls, floor, ceiling and window etc. and heat transfer enhancement are discussed. We show that with suitable PCMs and a suitable incorporation method with building material, LHTES can be economically efficient for heating and cooling buildings. However, several problems need to be tackled before LHTES can reliably and practically be applied. We conclude with some suggestions for future work.     

Climate change impacts on building heating and cooling energy demand in Switzerland

The potential impacts of climate change on heating and cooling energy demand were investigated by means of transient building energy simulations and hourly weather data scenarios for the Zurich–Kloten location, which is representative for the climatic situation in the Swiss Central Plateau. A multistory building with varying thermal insulation levels and internal heat gains, and a fixed window area fraction of 30% was considered. For the time horizon 2050–2100, a climatic warm reference year scenario was used that foresees a 4.4 °C rise in mean annual air temperature relative to the 1961–1990 climatological normals and is thereby roughly in line with the climate change predictions made by the Intergovernmental Panel on Climate Change (IPCC). The calculation results show a 33–44% decrease in the annual heating energy demand for Swiss residential buildings for the period 2050–2100. The annual cooling energy demand for office buildings with internal heat gains of 20–30 W/m² will increase by 223–1050% while the heating energy demand will fall by 36–58%. A shortening of the heating season by up to 53 days can be observed. The study shows that efficient solar protection and night ventilation strategies capable of keeping indoor air temperatures within an acceptable comfort range and obviating the need for cooling plant are set to become a crucial building design issue.     

Outdoor thermal environment for different urban forms under summer conditions

The present work investigated the outdoor thermal environment for different urban forms under the summer conditions of Sendai, Japan and Guangzhou, China. Sendai has a moderate humid subtropical climate, whereas Guangzhou has a humid subtropical climate. Numerical simulations were performed with a coupled simulation method of convection, radiation, and conduction. A cubic non-linear k–ε model proposed by Craft et al. was selected as the turbulence model and three-dimensional multireflections of shortwave and longwave radiations were considered in the radiation simulation. Seven urban forms (the ratios of building distance to building height were 0.24, 0.36, 0.48, 0.71, 0.95, 1.19, and 1.43.) were studied. The openness and compactness of the urban forms were compared by developing a new assessment system. The following results were obtained. (1) The distributions of wind velocity around the buildings became polarized as building distance decreased, and the proportion of low wind velocity grew large. These conditions mainly caused poor ventilation and thermal discomfort. (2) The cooling effects of building shade became increasingly significant as building distance decreased because of the low level of exposure to strong sunshine in compact forms. (3) Safe outdoor thermal conditions (standard effective temperature ≤37 °C) can be partially achieved in Sendai by decreasing building distance, whereas the same could not be achieved in Guangzhou. Further countermeasures are essential in Guangzhou.     

Modeling of a solar-assisted HVAC system with thermal storage

A numerical model of the solar-thermal-assisted heating, ventilation and air conditioning system in a 7000 m² educational building, situated in a high-desert climate, is used to predict performance and optimize control parameters. Heating, cooling and shoulder seasons are considered in the study. It is found that the solar assist can account for over 90% of the total heating requirements if certain energy conservation strategies are adopted. The solar cooling assist can reduce the total external cooling energy requirement by between 33% and 43%, the latter result achieved, surprisingly, at lower solar array operating temperatures. In the shoulder season, it is possible to operate the building without any external contribution, by heating the building in the coldest hours of the day, and using any excess heat to produce chilled water, to be stored and used when required. Operation of the solar-assisted system within a much larger district energy system makes it possible to achieve maximum performance.     

建筑环境设计模拟分析软件DeST第4讲建筑热过程中的太阳辐射相关模型

太阳辐射是影响建筑热状况的重要外扰，在建筑热过程分析时，必须加以准确的考虑。太阳辐射可以被不透明建筑围护结构表面吸收，也可以直接透过建筑的半透明围护结构进入室内，这就需要解决两个问题：有多少太阳辐射量能够到达建筑的表面；到达半透明围护结构表面的太阳辐射有多少能够穿过半透明围护结构直接进入室内。详细介绍了DeST在建筑动态热过程分析中，与建筑表面吸收太阳辐射情况密切相关的建筑表面阴影计算方法和散射辐射的考虑方法，并对半透明围护结构的辐射透过模型与传热模型进行了细致分析。     

Solar powered absorption air conditioning

The design of buildings to provide a suitable thermal environment is discussed and the reasons for artificial heating or cooling introduced. The problem of sizing a solar-powered cooling plant is investigated. An iterative method of estimating heat flow and resultant temperatures in buildings subject to fluctuating heat loads is described. A model is developed to allow investigation of the performance of a solar collector and thermal storage system and some of the basic relationships between performance and physical parameters are determined.

An iterative method of predicting the cooling output from a lithium bromide-water absorption refrigeration plant having variable heat input is described.

The design of a solar collector/thermal storage) absorption cooler system, its performance on a particular building and its fine tuning are examined.     

Solar radiation and cooling load calculation for radiant systems: Definition and evaluation of the Direct Solar Load

The study of the influence of solar radiation on the built environment is a basic issue in building physics and currently it is extremely important because glazed envelopes are widely used in contemporary architecture.In the present study, the removal of solar heat gains by radiant cooling systems is investigated. Particular attention is given to the portion of solar radiation converted to cooling load, without taking part in thermal absorption phenomena due to the thermal mass of the room. This specific component of the cooling load is defined as the Direct Solar Load.A simplified procedure to correctly calculate the magnitude of the Direct Solar Load in cooling load calculations is proposed and it is implemented with the Heat Balance method and the Radiant Time Series method.The F ratio of the solar heat gains directly converted to cooling load, in the case of a low thermal mass radiant ceiling, is calculated for different kinds of office rooms with a large glazed external surface. An example of cooling load calculation developed with the proposed procedure is given.     

A comparison of Mesua ferrea L. and Hura crepitans L. for shade creation and radiation modification in improving thermal comfort

Open spaces in tropical climates are highly exposed to solar radiation. These conditions will influence the outdoor energy budget, leading to an increased heat island effect and reduced human thermal comfort. Trees, however, can influence the microclimate through radiation control that indirectly reduces direct radiation uptake and glare by humans and buildings. This condition affects building energy budget and human thermal comfort. This study compares the effectiveness of Mesua ferrea L. and Hura crepitans L. in shade creation and radiation modification in improving human thermal comfort. The study employed two methods: (i) a field measurement procedure and (ii) a computer-based sun-shading analysis using ECOTECT. The results from this study indicate that both M. ferrea L. and H. crepitans L. contribute significantly to direct thermal radiation modification below their canopies. The average solar filtration under the tree canopy for M. ferrea L. was 93%, with 5% canopy transmissivity, 6.1% of leaf area index (LAI) and 35% of shade area. For H. crepitans L. the average heat filtration under the canopy was 79%, with transmissivity of 22%, LAI of 1.5 and 52% of shade area. Thus, the study found that M. ferrea L. was more significant as a thermal radiation filter than H. crepitans L., due to the former's denser foliage cover and branching habit. This significant filtration capability contributes to reduce more terrestrial radiation, cooling the ground surfaces by promoting more latent heat, reducing air temperature by promoting more evapotranspiration and effectively improves outdoor thermal comfort in tropical open spaces.     

Thermal characteristics of a double-glazed external wall system with roll screen in cooling season

A double-skin system (double-glazed external wall) is an effective passive system that can be used to decrease solar heat gain into buildings. Detailed information on the thermal distribution of double-skin facades is necessary to design better systems that can provide thermal comfort and conserve energy. In this study, the three-dimensional thermal characteristics of double-skin facades that had the ventilation opening installed partially and were screened partially by the adjacent buildings were investigated by field measurements. To that end, field measurements were carried out on the double-skin exterior wall (9.4 m high and 27.0 m wide) installed in an atrium located in the west of an existing building during cooling period for typical summer conditions. Maximum air change rate of natural ventilation through the bottom opening up to the top opening is about 20–25 [1/h], the reduction ratio of total solar heat gain compared with those of non-natural ventilation is about 25%. The exhaust solar heat gain is about 100 W/m² per inner glass surface area of the double-skin facades. Air temperature distribution of air space in the double skin was ranged from 30 °C to 44 °C, and heat gain difference ranged from 50 W/m² to 130 W/m². The influence of the ventilation openings and the shade conditions on temperature distribution of double skin is found to be significant and the double-skin system was verified to reduce the cooling loads effectively.     

Experimental approach to the contribution of plant-covered walls to the thermal behaviour of building envelopes

The use of vegetation has an important impact on the thermal performance of buildings and on the modification of the urban climate as well, both in winter and summer. Plants absorb a significant amount of solar radiation for their growth and biological functions, functioning as a solar barrier that prevents solar radiation absorption extensively. Their utilization is essential and can considerably improve the microclimate of the built environment. Vegetation planted to cover the external surface of a building is common practice in urban areas. However, up to now, it has not been fully approved as an energy-saving method. Climbers can provide a cooling potential on the building surface, which is very important during the hot periods of the year, especially in warm climates. Hence, the peak temperatures that appear are essentially lower, in addition to the decrease of heat flow losses. In this study the thermal analysis concerns two equivalent building floors that incorporate non-covered and covered with plants wall sections (insulated wall surfaces), respectively. The investigation is carried out during the cooling period in the Greek region. A comparison between the bare and plant-covered surface sections of the walls is conducted via an experimental setup (stationary method). Results are focused on the developed temperature variations and dynamic thermal characteristics of wall surfaces for both cases under investigation. As it is shown, the contribution of plant-covered wall sections is important so that the thermal behaviour of the building envelope can be improved.     

Five-year data of measured weather,energy consumption,and time-dependent temperature variations within different exterior wall structures

This paper presents coherent 5-year measured data that have been gathered for analyses of building energy consumption and thermal performance of exterior walls. The data is also very suitable for calculations and simulations of heating and cooling energy need of buildings. The data was collected from six identical test buildings, having exterior walls that are constructed of different building materials. The data include the following: indoor–outdoors temperatures; temperatures at various depths within the northern, southern, eastern, and western exterior wall facades; indoor–outdoors relative humidity, heating energy, wind speed and direction; air tightness, infiltration, and horizontal global solar radiation. A computer system (data logger) was used to monitor, check, calculate, integrate, and save the data acquired from approximately 520 sensors in each test building. Measurements were taken with a time interval of 20 s. The 20 s values were then integrated over a time interval of 30 min and the minimum, maximum, and mean values were subsequently stored to a computer database. Analyses of the results indicated that temperatures within the buildings’ exterior walls are constantly changing and, that occasionally the flow of conduction heat is reversed (i.e. outside–inside) due to solar radiation. For accurate results of temperature distribution and the actual heat losses through building envelopes, none steady-state calculations are essential. Depending on the intensity of solar radiation and the material characteristics of the walls, temperature gradient at the inner surfaces of exterior walls may become milder compared to that of the outer surfaces.     

Are the relative variation rates (RVRs) approximate in different cities for the same building with the same outer-window reform?

By analyzing and comparing hourly, monthly and classified cooling and heating energy consumption of Tampa and Guangzhou, it can be found that the reduction of heat transfer coefficient of outside window can obviously decrease annual heating need. Its effect is essentially similar to the reduction of outer-wall heat transfer coefficient. The reduction of outer-window heat transfer coefficient can significantly increase the heating or cooling RVRs of the hours without solar radiation (basic RVRs) and it can also increase the heating RVRs at the hours with solar radiation. However, it can just increase cooling RVRs at the hours with solar radiation limitedly. Only supplemented with restraining solar radiation effectively, it could raise the cooling RVRs significantly. Whatever any climatic conditions, the annual heating energy consumption is governed by the classification without solar radiation ($>80\%$) and annual cooling energy consumption is governed by the classification with solar radiation ($>90\%$). Therefore, in order to decrease heating energy consumption, the first choice is the improvement of envelope's thermal insulation performance while to decrease cooling need, the first measure is to restrain solar radiation and then supplemented with the improvement of envelope. It is shown by the research that under the same outer-window heat transfer coefficient (i.e., the same measure of outer-window thermal insulation is adopted for the same building), the heating RVRs are approximate and the cooling RVRs are also approximate in different cities. This paper proves at another angle the universalism of approximation of heating and cooling RVRs under different climatic conditions (or in different cities) for the same building with the same energy-efficient measure again.     

Further validation of a method aimed to estimate building performance parameters

A further validation of an earlier developed neural network method for estimating the total heat loss coefficient (K_tot), the total heat capacity (C_tot) and the gain factor (α) based on measured diurnal data of internal–external temperature difference, supplied heat for heating and “free heat” is presented. The validation was performed in laboratory scale, using a test cell, for three different cases of ventilation, without (constant)-, natural-, and forced ventilation. Earlier measurements from a building was also used in order to simulate a realistic energy use pattern and a rather stochastic behavior of α, which also was transformed to represent existing and future buildings in terms of the composition of their energy use. For all three types of ventilation and different types of buildings, the method was capable of estimating the three different performance parameters and their different dependencies. For K_tot, the RMSE was between 3 and 20% and for α, the deviation was between 9 and 19%.     

The impact of auxiliary energy on the efficiency of the heating and cooling system: Monitoring of low-energy buildings

This paper presents a detailed meta-analysis of end and primary energy use for heating, cooling and ventilation of 11 low-energy non-residential buildings and one residential building in Germany that belong to the EnOB research program launched by the German Federal Ministry for Economy. In particular, the analysis emphasizes the substantial impact of auxiliary energy use on the efficiency of heating and cooling performance. The investigated buildings employ environmental energy sources and sinks - such as the ground, ground water, rainwater and the ambient air - in combination with thermo-active building systems. These concepts are promising approaches for slashing the primary energy use of buildings without violating occupant thermal comfort. A limited primary energy use of about 100 kWh_prim/(m²_neta) as a target for the complete building service technology (HVAC and lighting) was postulated for all buildings presented. With respect to this premise, a comprehensive long-term monitoring in high time resolution was carried out over the course of two to five years, with an accompanying commissioning of the building performance. Measurements include the energy use for heating, cooling, and ventilation, as well as the auxiliary equipment, the performance of the environmental heat source and sink, and local climatic site conditions.     

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.     

Solar thermal modelling of a building with a roof pond and ventilation control systems

The paper proposes and presents thermal modelling of a ventilation-controlled, non-air-conditioned building with evaporative cooling (e.g. open water pond) over the roof for passive solar air conditioning. The ventilation rate, expressed in terms of number of air changes per hour, is assumed to be time-dependent, as should be the case in normal practice. A self-consistent periodic heat transfer analysis for a non-air-conditioned building with roof cooling and ventilation control systems, furnishing (assumed isothermal mass), windows, door and basement ground heat storage effects has been developed to assess the feasibility of the proposed passive space air-conditioning. It is shown that for no-ventilation summer nights the inside air temperature remains higher than the ambient air temperature even with an effective roof cooling system, and hence the windows should be opened to lose the internal heat and to introduce cool and fresh outside air. It is found that for a ventilation-controlled building with a roof pond the passive solar air conditioning can be achieved more effectively.