Envelope Evolution of Tall Buildings, an energy performance comparison

Tall buildings have recently spread widely but since early Fifties some questions about their energy consumptions and impact on the environment were asked. The most important issues were about the introduction of new envelope system, namely Curtain Wall, and its influence on tall buildings conditioning energy consumption. New wide glass openings on the building envelope led to high conditioning loads with additional costs of the Hvac systems. The question asked by Henry Wright in 1956 was about the opportunity to invest in new envelope systems reducing opening area and improving thermal features of glass and opaque wall as well. After sixty years the aim of this article is to answer to this interesting question by means of recent energy simulation tools which can provide useful informations about energy consumptions and thermal balance of buildings. A comparison between different typologies of tall buildings has been performed considering the historical evolution of the envelope. One hundred of tall buildings has been analysed in order to identify three envelope classes: massive curtain wall, simple curtain wall and advanced curtain wall. These classes have been simulated with Energy Plus under the same climatic conditions with the aim to provide a more precise comparison of the envelope characteristics. Three climates were considered: temperate, cold and arid. Interesting considerations came out after the simulation analysis. The cooling and heating energy consumptions are mainly in dependence of openings area and internal loads which are usually very strong in office buildings. In temperate climates, the cooling load is more influenced than the heating load from glass opening area because of high solar gains which during winter are balanced from internal gains. This condition changes in cold climates in which heating load is more influenced by the envelope curtain wall and by the opening area because of very low ambient temperatures. In general the simulation analysis shows that the envelope evolution from massive to advanced curtain wall is characterized from a reduction of heating and cooling loads due to improvement in thermal properties of envelope components and airtightness as well