Green Roof Heat Transfer

Ashrae energy modeling conference.

Green roof heat transfer.

The allegheny county office building green roof. An experimental study was conducted on green roofs under the semiarid summer climatic conditions of west texas to investigate the effect of soil type moisture content and the presence of a top soil grass layer on the conductive heat transfer through the roof. Uniform sand and local silt clay. Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect particularly during the day.

A green roof also known as a rooftop garden or a living roof is a vegetative layer grown on a rooftop. Two soil types were investigated. April 4 2011. 10 q s r q s q e t q c v 0 where q e t is the heat flux caused by the evapotranspiration rate in the plants and the substrate.

Foliage height leaf area index lai fractional vegetation coverage albedo stomatal resistance etc. For this particular study a downward heat transfer was analyzed for predicting the possible damages to a roof deck caused by a fire on the roof. Estimating heat and mass transfer processes in green roof systems. Proposed a heat transfer model developed from experimental data obtained on a green roof placed in a controlled environment laboratory considering the following heat fluxes.

Green roofs not only help reduce the urban heat island effect by covering conventional dark roofing surfaces with vegetation which absorbs less heat but they also use solar radiation to evaporate water from the growing media and transpire the absorption of water through a plants roots and release of it through its leaves as a vapor moisture. Green roof s response to fire in the most severe conditions. Building science group. National renewable energy laboratory.

Current modeling capabilities and limitations paulo césar tabares velasco ph d. This would demonstrate the potential fire hazard that a green roof could pose to a building. Unlike traditional black tar roofs green roofs reduce energy costs by absorbing heat instead of attracting it and. How heat doesn t move through a green roof cooler than cool roofs.

Cooler than cool roofs. Tests were also conducted on a control roof. Green roofs provide shade remove heat from the air and reduce temperatures of the roof surface and surrounding air. Parameters that affect heat transfer for a green roof were consid ered.

The hamerschlag hall green roof was found to lose 26 less heat than the control roof in heating months. Transfer through conventional layers in the green roof and a control roof at each location the effect that the green roof media has on the thermal performance of the roof system was evaluated.