Thermal Storage Wall Research Articles

Utilization Of Solar Air Collectors For Heating Of Isfahan Buildings In IRAN

Energy supply to Iran requires the substitution of an energy model based on fossil by one based on renewable energy sources. The building sector, about 40% of total annual energy consumption, has an important share in energy demand in Iran. Iran as a Middle Eastern country has recently begun to use renewable energies. Solar energy, because of its availability and large number of sunny days in this country, is mostly concentrated. In this paper vented thermal storage wall that is used for heating of Isfahan buildings, Central of IRAN, are studied. The heating loads for a residential building which has about 800m2 floor area at four floor are calculated. Then the vented thermal storage wall are designed and the amount of annual energy saving is calculated. It is shown that more than 60 percent of winter energy consumption will saved by using this system.

A comparative performance study of some thermal storage materials used for solar space heating

One of the most common methods used in passive heating is the utilization of a massive wall for heat storage. Many factors affect the performance of the wall, such as the thickness and the media used for heat storage. A numerical study has been conducted on a zone heated by a thermal storage wall. Three different storage materials are examined, namely concrete, the hydrated salt CaCl 2·6H 2O and paraffin wax (N-eicosane). A numerical model is presented in this paper which judges the suitability of these materials as thermal storage mediums under the actual weather conditions of Iraq. For that purpose, the room temperature fluctuation in the zone is evaluated for each material using different thickness for each wall. The study concluded that an 8-cm-thick storage wall made from the hydrated salt is capable of maintaining the comfort temperature in the zone with the least room temperature fluctuation.

Modeling energy efficiency of bioclimatic buildings

The application of bioclimatic principles is a critical factor in reducing energy consumption and CO 2 emissions of the building sector. This paper develops a regression model of energy efficiency as a function of environmental conditions, building characteristics and passive solar technologies. A sample of 77 bioclimatic buildings (including 45 houses) was collected, covering Greece, other Mediterranean areas and the rest of Europe. Average energy efficiency varied from 19.6 to 100% with an average of about 68%. Environmental conditions included latitude, altitude, ambient temperature, degree days and sun hours; building characteristics consisted in building area and volume. Passive solar technologies included (among others) solar water heaters, shading, natural ventilation, greenhouses and thermal storage walls. Degree days and a dummy variable indicating location in the Mediterranean area were the strongest predictors of energy efficiency while taller and leaner buildings tended to be more energy efficient. Surprisingly, many passive technologies did not appear to make a difference on energy efficiency while thermal storage walls in fact seemed to decrease energy efficiency. The model developed may be of use to architects, engineers and policy makers. Suggestions for further research include obtaining more building information, investigating the effect of passive solar technologies and gathering information on the usage of building.

Computer Simulation of Transparently Insulated Buildings for Energy Evaluation

A dynamic computer simulation model has been developed to evaluate the energy performance of buildings cladded with Transparent Honeycomb Insulation (THI). U-value of THI is dependent upon the honeycomb cell dimensions, thermal characteristics of the material and temperatures encountered across the honeycomb insulation. Solar transmittance of THI is also angle-dependent. Two new modules for TRNSYS have been developed to incorporate these two special characteristics of honeycomb insulation in the simulation model. The simulation model not only confirms convection suppression capability of the insulation but also facilitates the change in the design and material of THI during simulation. As an example a room with a transparently insulated thermal storage wall has been simulated and results show minimizing heat loss and maximizing solar gain potential of THI.

Numerical study on a low energy architecture based upon distributed heat storage system

Basic performance of a hybrid heating system was investigated numerically through several case studies including examinations of effects of PCM as a heat storing materials. A simple test room assuming passive utilization of solar energy was used with a thermal storage wall (Trombe wall) inside it. Unsteady simulation was performed with a CFD code developed by authors. As the outdoor conditions, standardized weather data of Sapporo city, a cold climate district in Japan, were used. In the simulation, the room air was controlled with the heater operations setting the target air temperature at 18 degree Celsius. Simulated results indicate the effectiveness of PCM and suggest the possibility of developing low energy houses with hybrid system introduced in this study.

Computer simulation of transparently insulated buildings for energy evaluation

SYNOPSIS A dynamic computer simulation model has been developed to evaluate the energy performance of buildings cladded with Transparent Honeycomb Insulation (THI). The U-value of THI is dependent upon the honeycomb cell dimensions, thermal characteristics of the material and temperatures encountered across the honeycomb insulation. Solar transmittance of THI is also angle-dependent. Two new modules for TRNSYS have been developed to incorporate these two special characteristics of honeycomb insulation in the simulation model. The simulation model not only confirms convection suppression capability of the insulation but also facilitates the change in the design and material of THI during simulation. As an example a room with a transparently insulated thermal storage wall has been simulated and results show minimising the heat loss and maximising the solar gain potential of THI.

A study on a passively heated single-zone building using a thermal storage wall

The thermal performance of a passively heated zone is predicted by calculating the transient temperature variation of each node in the system using a finite-difference model. The sensitivity of the zone air temperature to the change in some of the zone features is examined. Some of these parameters included the thickness of the walls, using constant and variable heat transfer coefficients, having controlled and uncontrolled thermocirculation in a vented storage wall.

A study on a passively heated single-zone building using a thermal storage wall

The thermal performance of a passively heated zone is predicted by calculating the transient temperature variation of each node in the system using a finite-difference model. The sensitivity of the zone air temperature to the change in some of the zone features is examined. Some of these parameters included; the thickness of the walls, using constant and variable heat transfer coefficients, having controlled and uncontrolled thermocirculation in a vented storage wall.

水・煉瓦混成蓄熱壁を利用した試験模型の熱性能

This study aims at analyzing thermal Performance of the mixed water-brick walls as a thermal storage wall for Passive building to promote energy conservation and to maintain indoor comfort level by thermal design of buildings. The experiments were carried out by constructing a container (3m × 6m × 2.4m) with water and brick walls facing to the south. The computer simulation programs were used to analyze the thermal performance of the model for long-term base. The results show that the water wall performs well for high stable temperature variation and the brick wall works as an effective means of the thermal radiator for maintaining a better indoor condition.

Analysis of collector-storage building walls using phase-change materials

The use of thermal storage walls that serve both as solar collector and thermal storage is well known. The wall is usually composed of masonry or containers filled with water to provide sensible heat storage, i.e., storage resulting from the specific heat capacity of a material as it increases in temperature. An interesting alternative to the standard materials are phase-change materials (PCMs) which employ latent heat storage. Latent heat storage utilizes the energy associated with a change of state of a material such as the transition from a solid-to-liquid, or liquid-to-gas. The solid-to-liquid phase change is preferred for many applications because of the much smaller volume change resulting in this transition for a given amount of energy storage. This paper summarizes the results of a simulation study of the use of PCMs as a collector-storage wall.

Thermal comfort in buildings through a mixed water-mass thermal storage wall

This communication presents a time dependent periodic heat transfer analysis of a non-airconditioned building having south facing thermal storage mixed water-mass wall. The outer surfaces of walls/roof are exposed to periodic solar radiation and atmospheric air temperature while the inner surfaces are in contact with variable inside air temperature. The effects of heat transfer through walls and roof, heat conduction to the basement ground and furnishings as well as heat loss due to air ventilation have been incorporated into the building model. Explicit solution for the inside air temperature and periodic heat flux through the thermal storage mixed water-mass wall have been obtained. Numerical calculations show that a concrete-water concrete mixed thermal storage wall is more desirable than a pure water or pure concrete mass Trombe wall for providing excellent thermal comfort in buildings.

Transwall versus trombe wall: Relative performance studies

This paper compares the performance of two types of thermal storage wall, namely Transwall and Trombe wall. Both of them are located directly behind the south facing glazing of a wall. A Transwall is essentially a transparent modular wall. It consists of water in a container made of parallel glass walls and has a partially absorbing plate at the centre parallel to the glass wall. Thus, it partially absorbs and partially transmits solar energy. A Trombe wall consists of either masonry or water in opaque containers and does not transmit solar energy. The relative performance of these has been studied to find out their suitability for a cool climate of North India. Mathematical models have been developed to predict the thermal performance in terms of the heat flux entering the living space through these walls. Numerical calculations for Srinagar (India) climatic conditions show that the Transwall is more effective than the Trombe wall to meet the daytime heating load, but from load levelling and both day and night performance points of view, a water Trombe wall is better. The results are quite general and can be extended to any place having similar climatic behaviour.

Comparison of an analytical model with experimental results for a passive thermal storage wall

Comparison of an analytical model with experimental results for a passive thermal storage wall

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.

Proportioning composites for efficient thermal storage walls

Thermal storage walls for use in passive solar collectors are analyzed with the purpose of establishing guidelines for the design of low-mass, high-efficiency walls. Numerical results for the efficiency of thermal transfer are shown to be well approximated by a simple, stationary-state formula, with which general design objectives are identified, in particular the desirability of materials having prescribed thermal heat capacity and conductivity. The required proportioning of metals, masonry and phase change materials to yield materials with such properties is determined for the case of parallel layering. Illustrations of binary and ternary composites are presented. Compared with concrete, paraffin-metal mixtures are found to offer thermal storage walls having a 90 per cent reduction in storage mass and a 20 per cent relative increase in efficiency.

The performance results of Trombe-Wall passive systems under Aegean Sea climatic conditions

Since 1977, at the “Solar Energy Thermal Applications Laboratory of M.T.A.” in Marmaris, Turkey, an experimental study of a “Trombe Thermal Storage Wall” passive system continues in operation; two analogous houses have been built, one of which is serving as a reference system. The incident solar radiation on a vertical surface, the temperature changes of the internal and external surfaces of the wall, at interval of thirty minutes, and the convective flow through the “Trombe-Wall” have been measured in order to determine the solar fractions transmitted by the processes of radiation, convection and thermocirculation. In the present study, the variation of the “Trombe-Wall” efficiency has been calculated during the period of a year using a computer evaluation model in which the half hour measurement data have been introduced. The experimental results show that, according to the months, 15–35 per cent of the incident solar radiation over the south facade is transmitted to the interior through the “Trombe-Wall”, while the reference house transmits from the south facade 8–19 per cent of solar radiation received. Finally, it can now be confirmed that the results of the “Trombe-Wall” system without any special type insulation, contributes to practically the total heating load of the village houses under the sunny Aegean Sea Climatic conditions.

A Simple Tool for the Design of Passive Solar Buildings

The design tools that are presently available for use by designers of passive solar heating or cooling systems include detailed simulation codes, correlations derived from the detailed codes, and simulations that may be used for short-term analyses using programmable handheld calculators or desktop computers. An alternative method is based on classical frequency response techniques and yields results that are in close agreement with those that are obtained from detailed computer simulations. The method may be used to quickly determine the average temperature and the magnitude of the diurnal temperature variation in a passive solar building. The effects of parameter changes may also be quickly and easily determined by this method. The method is described in the paper and results are presented for a slab-on-grade building having a thermal storage wall and a thermal storage floor incorporating off-peak load management.

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.

Radiation and Free Convection Shield for Passive Thermal Control

A radiation and free convection shield (RFS), when used with a thermal storage wall, can enhance the thermal performance of the storage wall and provide passive thermal control. In order to optimize the performance of the RFS, it is desirable to know how the impedance provided by the use of an RFS varies with the thermophysical properties of materials used to construct it. A numerical nodal thermal model was constructed to evaluate the impedance as a function of the thermophysical properties of the RFS. Two RFS thermophysical properties are identified as the most important in controlling the impedance from the storage wall to the room: thermal conductivity and total surface emissivity. A decrease in the RFS surface-to-surface thermal conductance, a decrease in the RFS total surface emissivity, or both, substantially increases the impedance from the storage wall to the room.

Passive solar heating of buildings using a transwall structure

Passive solar heating systems can utilize a number of design approaches, but the most prominent ones are those employing “direct gain” or a “Trombe thermal storage wall”. In this work we propose a new passive system employing a “transwall”, which is a partially transparent thermal storage wall placed adjacent to a window admitting solar energy. Part of the solar energy is absorbed within the transwall, and the remaining part is transmitted to the interior of the room. The transwall is architecturally more attractive than the completely absorbing Trombe wall, since it admits light to the room and allows the occupants to see out through the window without glare and overheating problems of direct gain systems. Calculations using thermal network models and based on reasonable assumptions for relative comparisons have been used to compare thermal performance of transwall, Trombe wall, and direct gain systems. The analysis shows that the transwall system can be expected to have thermal performance very close to or exceeding the other systems, depending on how effectively convective heat transfer is quenched in the thermal storage medium. The important question of visual clarity for the transwall system has been evaluated for a prototype by photographing a scene with and without optical transmission through the structure. Optical distortion is minimal in the transwall transmission photograph.