Effect of substrate depth, vegetation type, and season on green roof thermal properties

Abstract

Effect of substrate depth, vegetation type, and season on green roof thermal properties 17 18 19 20 21 22 23 24 25 26 Abstract 27 28It is generally accepted that green roofs can influence thermal properties of a building, but 29 there is some disagreement on the role that substrate depth and plant species plays in this equation. 30A study was conducted over a second floor roof in East Lansing, MI, comparing prevegetated mats of 31 a mixture of sedum (depth = 5 cm) to a deeper roof (depth = 20 cm) planted with a mixture of 17 32 herbaceous perennials and grasses. Both roof sections were instrumented with heat flux sensors, 33 thermocouples, moisture sensors, and infrared sensors, and ambient weather conditions were also 34 continuously recorded by a weather station located on the roof. Data were collected for the period of 35almost a year to cover all four seasons. Also, the roofs were well established and had reached near 36 100% plant coverage by the time data collection commenced two years after planting. Most of the 37 differences in temperatures and heat flux through the roof occurred during the summer or winter. 38During summer, the shallow sedum roof experienced more extreme fluctuations in diurnal substrate 39 temperatures which tended to be warmer during the day, but cooler at night. Heat penetrating into the 40 building on the sedum portion of the roof was consistently greater than the herbaceous section during 41 the afternoon. However, during the night and early morning, heat gain into the building was greater on 42 the herbaceous roof, especially on cloudy and rainy days. During winter, heat transfer through the 43 sedum portion of the roof was affected more by outside environmental conditions, whereas the 44 herbaceous portion of the roof was stable. Although, the sedum roof exhibited more extremes, when 45 daily heat flux values were totaled for each month and each season, the herbaceous roof actually 46 3 experienced more heat entering the building during the summer, but less heat escaping the building 47 during the winter. This is an advantage during the winter months as the herbaceous roof would reduce 48 heating costs. However, contrary to conventional logic that plants with high transpiration rates are 49 superior, during the summer months the sedum roof outperformed the herbaceous roof. 50 51

A New Method to Determine How Compaction Affects Water and Heat Transport in Green Roof Substrates

“…A systematic comprehension of the processes occurring in every component of a green roof, under site-specific conditions, is required to understand the benefits described above. This systematic comprehension is extremely important in arid and semi-arid areas, where construction materials may be different and meteorological conditions significantly differ from humid climates, where majority of green roof investigations have been carried out to date [1,2,[10][11][12].…”

“…The vegetation and substrate layers are the central components that determine water and heat fluxes on green roofs [2,3,12,13]. This work focuses on green roof substrates, even when it is known that vegetation is relevant on green roof hydraulic and thermal performance.…”

Análise térmica de coberturas verdes aplicadas em contêineres

“…comportamento térmico dos componentes das coberturas vegetadas, a fim de avaliar a contribuição de cada elemento frente à transferência de calor. Eksi et al (2017), em seu trabalho, verificaram comportamentos térmicos distintos quando compararam dois tipos de coberturas verdes, cujas configurações se diferenciavam pela espessura dos substratos (camada de terra onde se desenvolvem as plantas) e a vegetação empregada em cada um, porém, sendo inconclusivos em relação à parcela de contribuição de cada camada (substrato ou vegetação).…”

“…Foram utilizadas 17 diferentes espécies de gramíneas e herbáceas cultivadas em profundidades de 5 cm e 20 cm de solo, respectivamente, sobre um telhado verde instalado no segundo andar de uma edificação local, cujo esquema pode ser visualizado na figura 22. Os dados foram coletados a partir de sensores de fluxo de calor, termopares, sensoresde umidade e infravermelho medindo as variações das propriedades das camadas das coberturas e também foi utilizada estação meteorológica para monitoração das condições climáticas do ambiente externo(EKSI et al, 2017). Mesmo apresentando maiores flutuações, a cobertura verde sedimentar, mais rasa, demonstrou melhor comportamento para o verão, onde a taxa de calor saindo da edificação foi mais significativa do que a herbácea mais profunda.…”

“…Mesmo apresentando maiores flutuações, a cobertura verde sedimentar, mais rasa, demonstrou melhor comportamento para o verão, onde a taxa de calor saindo da edificação foi mais significativa do que a herbácea mais profunda. Desta forma, pôde-se concluir que, para climas semelhantes aos de Michigan, o telhado verde herbáceo (20 cm de profundidade) contribui para economia nas contas com aquecimento nos períodos frios e a cobertura sedimentar (5 cm de profundidade) reduz as contas com resfriamento nos períodos quentes(EKSI et al, 2017). superfície vegetação cujas propriedades relacionadas à emissividade e refletância térmicas sejam significativas quando comparadas a de uma cobertura verde com outros tipos de vegetação ou coberturas convencionais.…”