Thermal network analysis of a conditioned building: The effect of location of insulation

Thermal network analysis has been applied to an air-conditioned enclosure to predict the daily variation of heat flux. The effect of putting the insulation on the concrete roof/wall has been analysed in detail. It is found that, when only the ceiling is insulated, the difference in concrete thickness, either on the top side or bottom side with a fixed thickness of insulation sandwiched in between, total concrete thickness remaining the same, does not affect the total heat flux appreciably. The contributions to the heat flux from the south and west walls are also found to be quite significant. The effect of putting the insulation on the south, as well as on the west, walls is also significant.     

Performance of trombe walls and roof pond systems

This paper describes an analysis of the periodic heat transfer through thermal storage walls and roof pond systems subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other. A one-dimensional heat conduction equation for temperature distribution in the walls and roof has been solved using the appropriate boundary conditions at the surfaces; explicit expressions for the periodic heat flux through storage walls and the roof have been derived. Numerical calculations for the periodic heat flux into the room have been made in order to assess the relative thermal performance of storage walls and roof pond systems in both winter and summer. It is found that a thermal storage mass wall is preferable for longer heat storage times while a water wall is suitable for rapid heat dissipation into the living space. For New Delhi, a roof pond system comprised of water-concrete-insulation, in ascending order of thickness, in the summer and in descending order of thickness in the winter, is found to be most desirable, whereas a combination with an ascending order of thickness is more appropriate for a typical cold climate like that of Boulder, Colorado, USA.     

Thermal performance of a non-air-conditioned building with PCCM thermal storage wall

This paper presents a time-dependent periodic heat transfer analysis of a non-air-conditioned building having a south-facing wall of phase-changing component material (PCCM). A rectangular room (6 × 5 × 4 m) based on the ground is considered. The effects of heat transfer through walls and roof, heat conduction to the basement ground and furnishings, heat gain through window and heat loss due to air ventilation have been incorporated in the periodic time-dependent heat transfer analysis. The time-dependent heat flux through the PCCM south-facing wall has been obtained by defining the effective thermal properties of the PCCM for a conduction process with no phase change. Numerical calculations are made for a typical mild winter day (7 March 1979) at New Delhi for heat flux entering through the wall and inside air temperature. Further, a PCCM wall of smaller thickness is more desirable, in comparison to an ordinary masonry concrete wall, for providing efficient thermal energy storage as well as excellent thermal comfort in buildings.     

Thermal load levelling of heat flux through an insulated thermal storage water wall

This communication presents an investigation of the thickness distribution of a given total thickness of the insulation inside and outside a thermal storage water wall for acheiving the maximum load levelling of the heat flux entering through the wall. Analysis is based on the solution of the heat conduction equation for the temperature distribution in the insulated wall subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other side. an explicit solution for a temperature distribution satisfying the apporpriate boundary conditions at the surface has been derived to obtaing a periodic heat flux through the storage water wall. It is found that for a given total thickness (cost) of insulation the thicknesses of outside and inside insulation must be equal for best load levelling. Moreover, more load levelling is achieved when the whole of the insulation is outside rather than inside the thermal storage water wall.     

Heating and cooling of a building by double hollow concrete slab

This paper presents the thermal performance, in the heating and cooling of a building, of a double hollow concrete slab, one of whose faces is exposed to solar radiation and ambient air while the other is in contact with room air at constant temperature. A blackwened network of pipes is laid on the top surface and glazed sutiably. the flow rate of water / air through pipes is kept constant. It is seen that there is a time difference of 10-12 h between the maximum/ minimum of the thermal flux extering the room and the solair temperature for any flow rate. the heat flux inside the room is reduced appreciably for higher infiltration when there is no water flow to heat the building. the effect of a water film on the performance of the wall/roof has also been discussed and found to be more effective for the reduction of the heat flux coming into the building.     

Optimum placement/distribution of insulation/concrete in a heavily insulated multilayered roof/wall for best load levelling

In this paper we investigate the optimum placement/distribution of insulation/concrete in a double hollow multilayered wall/roof for achieving the best load levelling in the thermal flux through the slab. It is seen that, of six possible configurations, for a given total thickness of insulation and given total thickness of concrete, the best load levelling is achieved when equal thicknesses of insulation are placed on outside and inside. Better load levelling is achieved in the insulation-air gap-concrete-air gap-concrete configuration when the thickness of the inner layer of concrete (facing room) is least, consistent with structural considerations. No, or the worst, load levelling is achieved in the concrete-air gap-insulation-air gap-insulation and insulation-air gap-insulation-air gap-concrete configurations.     

Maximum thermal load levelling in a double hollow wall/roof

The effect of a metal sheet in the middle of a hollow concrete slab, on the thermal performance of the concrete slab has been studied; one face of the wall/roof is exposed to solar radiation and ambient air and the other is in contact with room air at constant temperature. the optimum distribution of inside and outside concrete thicknesses for maximum thermal load levelling has been obtained; it is seen that this is achived when the outer concrete thickness is as small as possbile. These result have also been compared with the results corresponding to single hollow and double hollow concrete slabs.     

Effect of using a reflecting sheet in an air gap on the thermal performance of hollow walls and roofs

In this paper, the effect of placing a reflecting sheet in an air gap on the thermal performance of single hollow, double hollow and insulated hollow walls and roofs is studied. One face of the wall or roof is exposed to solar radiation and ambient air and the other is in contact with room air at constant temperature. These results are also compared with the predictions made in the case when a water film is maintained on the roof or wall. Numerical calculations are for a typical hot day (the 26th of May, 1979) in New Delhi. It is seen that the use of a reflecting sheet in single hollow and double hollow walls and roofs is more economical—and gives a better performance—than the water film system.     

Solar thermal modelling of a non-airconditioned building: Evaluation of overall heat flux

This paper presents an investigation of the thermal behaviour of a non-airconditioned building with walls/roof being exposed to periodic solar radiation and atmospheric air while the inside air temperature is controlled by an isothermal mass, window and door in the walls of the room. The effects of air ventilation and infiltration, the heat capacities of the isothermal storage mass inside air and walls/roof, heat loss into the ground, and the presence/absence of the window/door have been incorporated in the realistic time dependent periodic heat transfer analysis to evaluate the overall heat flux coming into the room and the inside air temperature. A numerical computer model using typical weather data for Delhi has been made to appreciate the analytical results quantitatively. It is found that the heat fluxes through different walls have different magnitudes and phase lags w.r.t. the corresponding solair temperatures. The overall heat flux coming into the room as well as the room air temperature are sensitive functions of the number of air changes per hour, closing/opening of the window and the door ventilation. The effects of the heat capacity of the isothermal mass and the basement ground are found to reduce the inside air temperature swing and the presence of a window is found to increase the inside air temperature even when the window area is much smaller than the wall/roof area. The model presented would be an aid to a building architect for good thermal design of non-airconditioned buildings.     

Thermal load levelling of heat flux in PCCM collection/storage walls/roof system

In this communication, a steady state analysis of a phase change component material (PCCM) collection-cum-storage walls/roof system has been presented by incorporating the effect of water flow through a parallel plate placed at the liquid and solid interface. The effect of various parameters, i.e. fraction of melted region, walls/roof thickness, flow rate and latent heat of fusion of PCCM on heat flux entering the air conditioned room has been studied in detail. Numerical calculations have been made for two typical days at Delhi (18 June 1983 and 18 January 1984). The following conclusions have been made: (i) thermal load levelling decreases with an increase of the fraction of melted region and vice versa for total thickness of walls/roof; and (ii) phase shift of 10 h is observed for 40–50% fraction of melted region for walls/roof thickness of 0.10 m.     

Periodic heat transfer through a hollow concrete slab: Optimum placement of the air gap

This paper describes an investigation of the periodic heat transfer and optimum placement of the air gap in a hollow concrete slab subjected to solar radiation and atmospheric air on one side and in contact with air at a fixed temperature on the other. The heat conduction equation has been solved using the appropriate boundary conditions at the interfaces. It is found that the presence of an air gap considerably reduces the heat flux through the slab; further, for a given total thickness of concrete the best load levelling is achieved when the thickness of the outer layer of the concrete is least, consistent with structural considerations.     

空调建筑外墙和屋顶经济绝热厚度的计算

该文介绍了种计算空调建筑外墙和屋顶经济绝热厚度的模型。该模型根据热流通过不同组件时间的相关分析并运用Lagrange乘子法，计算了不同增初投资额条件下外墙和屋顶的经济绝热厚度。运用该模型，依据上海、南京、武汉和重庆的气候参数对一典型住宅建筑进行了数值计算。计算结果表明，从经济评价角度来看，外墙保温隔热宜采用各热材料价格和气候因素对外墙和屋顶绝热材料厚度取值的影响。     

Comparison of experimental and theoretical results for the transient heat flow through multilayer walls and flat roofs

This study deals with comparison of experimental and theoretical results of transient temperature variations in multilayered building walls and flat roofs, and heat flow through the building structures. Experimental and theoretical models are presented to find the transient temperature variations in these structures and heat flow through these elements, which depends on inside surface and room air temperatures. Instantaneous inside and outside air temperatures, and surface temperatures of each wall and roof layers are measured by using the experimental model consisted of two rooms, cooling units, measuring devices and computers. A computer program based on the theoretical model is developed to perform numerical calculations. Hourly temperature variations of the nodal points are computed numerically over a period of 24 h by using the hourly measured ambient air temperatures and solar radiation flux on a horizontal surface for the city of Gaziantep (37.1°N), Turkey, and also by using thermophysical properties of the structures. Results obtained from the experimental and theoretical models are compared with each other, and validation of the theoretical model is verified in this paper. Computations for various multilayer building walls of briquette, brick, blokbims, and autoclaved aerated concrete (AAC), which are commonly used in Turkey are repeated for finding heat gain through these structures, and results are compared to determine suitable wall material. It is observed that AAC and blokbims are more suitable wall materials than briquette and brick due to heat flow through these elements.     

Enhancement of solar gains through a roof using a thermal trap

This paper investigates the viability of increasing solar gains through the roof of an air-conditioned room using the thermal trap effect. In solving the heat conduction equations through the thermal trap and the concrete slab, the finite difference method has been employed and the initial conditions are derived from the assumption that, initially, the ceiling of the room and the top of the trap material are in equilibrium with constant room air temperature and the ambient air temperature, respectively. The effect of the thickness of the thermal trap and that of the concrete slab on the thermal flux transferred through the roof have been studied.     

Effect of the absorption coefficient of a transparent outer layer on the thermal flux transmitted through a roof/wall

This paper examines the effect of the absorption coefficient of a transparent slab, which forms the outer layer of a roof/wall, on such factors as average thermal flux passing/through/a roof/wall, maximum and minimum values of this thermal flux and the thermal load levelling. It is seen that a non-completely transparent slab (non-zero absorption coefficient) performs slightly better than a completely transparent slab (zero absorption coefficient) for small thicknesses, as far as the average thermal flux through a roof/wall is concerned. A non-completely transparent slab with an absorption coefficient greater than 3 m^?1 is as effective as a completely transparent slab in introducing thermal load levelling. For both a non-completely transparent slab and a completely transparent slab, maximum, minimum and average values of the thermal flux increase with increasing thickness.     

Thermal behavior of buildings with curved roofs as compared with flat roofs

In this paper, a detailed finite element model dealing with heat transfer through a domed or vaulted roof is suggested based on a three-dimensional heat transfer equation and solar geometry. This model allows a comparison of the thermal behavior of curved and flat roofs in terms of heat flux and daily heat flow through them into an air-conditioned building under different climatic conditions. The results of numerical calculations show that the ratio of daily heat flow through curved roofs to that through flat ones is not affected by the curve radius, thickness and construction material of the roof, but is significantly influenced by the half rim angle θ₀ of the roofs and the ambient temperature. Compared to a flat roof, under typical hot dry climatic conditions, the daily heat flow through a domed roof of θ₀=90° is about 40% higher, whereas the daily heat flow through a south–north oriented and an east–west oriented vault of θ₀=90° is about 20 and 27% higher, respectively. The reason for this is mainly attributed to the convective heat transfer between the enlarged curved roof and ambient air. However, when θ₀<50°, heat flux and daily heat flow through a curved roof is close to that through a flat roof. The results also confirm that curved roofs are not suitable for areas with higher air temperature and intense sky diffuse radiation typical of hot humid areas.     

Thermal performance of double hollow wall/roof

This paper presents an investigation of the periodic heat transfer through a double hollow concrete block, one face of which is exposed to solar radiation and atmospheric air while the other is in contact with room air at constant temperature. It is seen that maximum load levelling occurs when the thickness of the two air gaps is the same (5 cm); for typical parameters a time difference of 12 h between maximum/minimum of the thermal flux and solair temperature is also obtained.     

Passive cooling of building using multi air gaps

In this paper the thermal performance of an air space in an inclined roof and the optimum number of air spaces are discussed. One face of the roof is exposed to solar radiation and ambient air and the other is in contact with room air at a constant temperature. It is found that, for the desired thermal performance, the roof should always be horizontal. It is also inferred that dividing an air gap into a number of gaps reduces the heat flux coming into the room. At most, one may effectively use only four air gaps. The effect of using reflecting sheets in the air spaces has also been investigated. To achieve the best thermal load levelling, the outer concrete leaf should be of least thickness.     

Effect of phase change material on passive thermal heating of a greenhouse

In this study, a periodic analysis of a greenhouse with combination of phase change material (PCM) and insulation as a north wall has been developed for thermal heating. The thermal model is based on Fourier analysis. Effect of distribution of PCM thickness on plant and room air temperature has been studied in detail. The plant and room air temperature have been evaluated with and without north wall. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of numerical results, it is inferred that (i) there is a significant effect of PCM north wall and heat capacity of plant temperature during off‐sunshine hour due to storage effect and (ii) the rate of heat flux inside greenhouse from north wall is maximum for least thickness of PCM. Copyright © 2005 John Wiley & Sons, Ltd.     

Optimum distribution of insulation and concrete in a multilayered wall of roof

In this paper we investigate the optimum distribution of insulation and concrete in an insulation/air/concrete/air/insulation slab (referred to as IACAI) and in a concrete/air/insulation/air/concrete slab (referred to as CAIAC) (which may be used for either a wall or a roof) in order to achieve the best levelling in the thermal flux through the slab. It is seen that, for given total thicknesses of insulation and concrete, the best load levelling is obtained (i) in IACAI, when the thicknesses of the insulation inside and outside are equal and (ii) in CAIAC when the thickness of the outer layer of concrete is least, but nevertheless consistent with structural considerations.