Green facades and Building structures

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Abstract

Plants can fulfil various functions. Plants provide places for playing, sports and recreation, establishing social contacts, isolation and escape from urban life, aesthetic enjoyment, viewing buildings from a distance and so on. Vegetation and plants on roofs and façades is one of the functions of plants most with respect to the built environment and horticulture. The presented report contains a general description of vertical greening systems (plants or vegetations against a façade) and their behaviour in relation to air quality improvement, aesthetics, energy saving, biodiversity, mitigation of the urban heat island effect and its social impact. Vegetation in relation to moisture transport and a life cycle analysis (LCA) for two living wall systems are particularly extensively explained. Vertical green or “green walls” is at the moment a popular item of sustainable development for a better environment related to dense urban areas. Vertical greening can be divided in three main branches, namely: - green façades; (traditional use of climbing plants against a façade from the ground or from planter boxes), are the easiest and cheapest manner to cover the vertical surfaces with vegetations. Green façades that are available until now can be classified in to two main categories, namely plants rooted into the ground and plants that are rooted in artificial substrate at grade with watering system. Green façades can be applied directly to the wall and also indirectly to the wall with a supporting structure such as net system or cable and wire net system. A large variety of plants can be used for making green façades. Especially Hedera plants (common ivy) are the most common ones. - wall vegetations; (spontaneous growing of plants on structures), are growing without any human intervention in a natural way with irregular patterns. This type of vegetation can be typically found on older buildings and monuments. Concrete panels with large pores variety are a new development to create green structures within a short period of time (1-2 years). These panels are also a type of façade which are suitable to plant vegetation on them. - living wall system (LWS); (pre-vegetated “prefabricated” modular panels or in situ applied panels), is a relative new application form of vertical green using modern technology. A watering system and nutrients distribution are always required and the modular panels are replaceable. There are various types of living wall systems which are already applied and applicable. Living walls are distinct from green façades in that they support vegetation that is rooted in substrate attached the wall itself, rather than being rooted at the base of the wall, and as a consequence have been likened more to vertical living systems. Living wall systems can be used either outdoor or indoor. A large verity of plants as herbs can be used on the living wall panels. A few examples of living wall systems that are described in this report are LWS based on planter boxes, LWS based on foam substrate, LWS based on mineral wool and LWS based on felt layers. Vertical greening systems have a range of advantages and disadvantages, which are summarized below. Advantages of vertical greening systems include: - filtering air particulates to improve air quality. - reducing (mitigate) the heat island effect (UHI). - providing sound insulation. - moderating a building's internal temperature via external shading. - creating a microclimate, which will help to alter the climate of a city as a whole. - providing biodiversity and a natural animal habitat. - protecting the wall against graffiti. - improving the insulation properties in summer and winter. Disadvantages of vertical greening systems include: - chance of damage on façade in case of green façade directly to the wall. - maintenance of vertical greening systems. - costs of vertical green systems, especially living wall systems. - irrigation systems. An experimental setup called ‘hotbox’ is made to test a number of vertical greening systems to determine the moisture transport through it. The hotbox is made of plywood (thickness 18 mm) and EPS-SE insulation material (thickness 200 mm). The hotbox has a dimension of (3000 mm x 1800 mm x 1800 mm) and has two compartments for indoor and outdoor climates. The principle of testing in the hotbox is to determine under steady state conditions (laboratory condition) moisture transport through a test specimen (bare wall) placed between a warm and a cold enclosed enclosure and to compare this with vertical greening systems hung on the wall under a variety of climate conditions (summer and winter). The test specimen used for the experiment consists of a wall with a surface of 1 m2 (made in Dutch building system). The test specimen has a (inner leaf + insulation + air cavity + masonry). The measurements are performed with thermocouples and hygrometers through the complete system of a bare wall with greening systems on it. As it is mentioned the behaviour of different vertical greening systems according to building physics and sustainability aspects are also discussed in this report. A start was made to determine the black spots within the thermal behaviour aspects of vertical greening systems. In a number of experiments some vertical greening systems (Hedera helix directly to the wall, Hedera helix, indirectly to the wall, LWS planter boxes system, LWS foam based system, LWS mineral wool based system and LWS felt layers system) have been tested in a test setup called ‘hotbox’. The results of the performed tests show that the vertical greening systems which are calculated for determining of moisture transport (Hedera helix directly to the wall, Hedera helix indirectly to the wall and LWS based on planter boxes) have no negative influence with respect to moisture transport and condensation on the surface of the wall. It became clear that vertical greening systems on the façades in the winter cause condensation. The summer measurements show that with a normal relative humidity of about 75% the condensation cannot take place in any layer of the structure. Condensation is occurred at all measured greening systems with freezing temperatures. According to Glaser method the condensation in all cases does not exceed the limitations. This means that the absorbed moisture by the structure in the winter (60 days) should evaporate back in the summer (90 days). There is not a vapour diffusion resistance figure (µ) for greening systems in the literature and therefore it is needed to assume a vapour diffusion resistance figure (µ) for vertical greening systems to calculate the condensation. For all condensation calculations a vapour diffusion resistance figure (µ) of 1.5 is assumed for vertical greening systems, which corresponds with the regulations that (µ?1). It is important to notice that the relative humidity outdoor and indoor, vertical greening system type, outdoor and indoor temperatures play a major role in determining of condensation and vapour diffusion. Living wall systems have a more or less airtight texture and they are protecting the façade better against direct sunshine and (heavy) rains. The materials used for living wall systems can ensure that the moisture transport does not take place easily. To realize vertical greened surfaces, it is necessary to take in to account that manufacturing of for example supporting structures can have a negative environmental effect, which is in struggle with sustainability. Sustainable construction could be described as a way of designing and constructing building that support human health (physical, psychological and social) and which is in harmony with nature, both animate and inanimate. A system is sustainable when the environmental burden is lower than the environmental benefit profile. The results from the conducted life cycle analysis for living wall system based on mineral wool and living wall system based on foam substrate provide insight in the environmental impact of the studied vertical greening systems. - the LWS based on mineral wool has one of the high environmental burdens due to the materials used. The aluminium supporting structure forms largely the effect since the materials affect positively the thermal resistance of the system. - the LWS based on foam substrate has also high influence on the total environmental burden, but the foam substrate (biodegrable) itself is a sustainable product. - for the living wall system based on mineral wool and living wall system based on foam substrate in both climate types (Mediterranean and temperate) the environmental burden profile is higher than the benefits gained for heating and cooling. - both LWS based on mineral wool and LWS based on foam substrate have almost the same contribution to the energy savings for heating but, for the Mediterranean climate, a higher influence was noted for the cooling properties of the plants which are to recognise for all 6 vertical greening system tested in hotbox.