External Wall System Research Articles

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/m 2 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/m 2 to 130 W/m 2. 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.

TIM–PCM external wall system for solar space heating and daylighting

An external wall system for solar space heating and daylighting composed of transparent insulation material (TIM) and translucent phase change material (PCM) is presented. This system enables selective optical transmittance of solar radiation. Visible light is mainly transmitted and invisible radiation is mainly absorbed and converted to heat, causing in particular phase change. The storage medium is also the absorber. The concept of the system is presented in detail together with the investigations carried out, including a brief outline of modeling, optical experiments on PCM samples and long-term experiments on a prototype wall as well as numerical simulations. The results indicate a promising thermal–optical behavior of the system. For instance in a Swiss lowland climate (Zurich-airport) a mean energy flux of 13 W m −2 (system efficiency 0.27) was calculated through a south facing TIM–PCM wall into the building during the month with the lowest irradiation (December). The parameters of the prototype wall with a mean melting temperature of the PCM of 26.5°C were assumed. When considering the percentage of time in which the building does not lose energy through the south facing TIM–PCM wall, a maximum can be reached with a mean melting temperature of approximately 20 to 21°C. In this case energy losses through the façade occur only during 1% of the time. With regard to the practical application of the system in buildings, aspects of reliability and durability have to be further investigated.

The performance of external wall systems in tropical climates

Early failure in external wall systems of multi-storey buildings can incur high costs of maintenance and repair works. The prevention of rain penetration, the control of temperature changes, and resistance to pollution and climatic effects are vital requirements for achieving better performance. Imported technologies and materials are partially responsible for problems occurring but design, construction and maintenance processes also contribute. This paper presents a number of case studies specific to tropical climates to define common problems, determine particular causes and recommend suitable solutions.