1. The thermal effects of green roofs and walls : experimentation on the performance of vegetated building envelopes in the UK
- Author
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Yoshimi, Juri and Kang, Jian
- Subjects
720 - Abstract
Despite a number of previous studies investigating the thermal benefits of green roofs and walls, results were not applicable to all types of climate as the focus was predominantly based on the reduction of cooling loads. Therefore, two separate field experimentations were conducted on green roofs and walls in Meltham and Sheffield to evaluate the thermal effects of vegetation cover on buildings within the UK climate. Temperature measurements of building surfaces and interior space were recorded throughout four seasons, and observation results demonstrated that vegetation reduced daily temperature fluctuations occurring on the building's exterior surfaces. Vegetation was particularly effective in mitigating the influence of solar radiation; both green roofs and walls reduced daily peak temperatures of the building surface by approximately 12°C during the warmest month. This study also look ed at factors that could influence the performance of vegetation. Increased substrate mass in the green roof improved insulating performance to increase indoor air temperature, meaning that intensive green roofs with a substrate thickness of over 200mm would be suitable in cooler climates, and shallower green roofs with less negative insulating impacts during summer in warmer climates. Only a marginal difference in thermal performance was observed among all tested green walls including three modular living walls and a climber screen, suggesting that choosing systems with the lowest initial costs and maintenance would be beneficial from an economic perspective. Numerical analysis conducted using recorded temperatures found that green walls were more effective in reducing daily heat gain through the wall than heat loss. Although adding a layer of insulation improved the thermal resistance of the existing green wall systems, the comparison against a conventional external insulation material revealed that it was more effective in reducing heat loss through the wall and would be a better solution in heating load dominated climates such as the UK. The study proved that the true potential of green walls lies in the variable characteristics of such materials in reducing radiation gain during the day but having minimum insulation effects at night. Thus, the greatest thermal benefits of green walls can be achieved in cooling load dominated regions.
- Published
- 2016