Green Roof and Thermal Performance: Articles Review Example

Green roofs are quite effective in resolving environmental problems at both urban and building levels. There are various benefits of using green roofs rather than the conventional roofs. Some of the benefits include reducing air pollution, reduction of noise, and improvement of storm water management. Green roofs increase animal and vegetal biodiversity in urban areas. In addition to that, they reduce the areas carbon footprint through conversion of carbon dioxide to oxygen. In places where green roofs are used in buildings, the green house effect is reduced significantly (Jaffal, 2012). Due to that, most environmental agencies recommend the use of green roofs for construction of modern buildings.

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Green roofs also improve the energy efficiency of buildings through transfer of heat. (Heidrinejad et al., 2015) posit that reduction of temperature around such roofs improves the effectiveness of HVAC systems to a large extent through provision of a cooling effect to fluids before they get back to the chiller. The low temperature improves the working of the photovoltaic panels. Green roofs make the roofing membranes to last long because they limit the thermal stress that is subjected to them. It is also important to note that green roofs mitigate the urban heat island effect. Green roofs are generally categorized into extensive and intensive roofs depending on their thickness.

Jaffal, Issa et al. "A comprehensive study of the impact of green roofs on building energy performance." Renewable Energy 43 (2012): 157-164

Heidarinejad, Ghassem, and Arash Esmaili. "Numerical simulation of the dual effect of green roof thermal performance." Energy Conversion and Management 106 (2015): 1418-1425.

Due to low additional loads, retrofitting are mostly made using extensive green roofs because no extra strengthening is required. Green roofs are better than traditional roofs because they lead to a cost reduction of approximately 20%. Climate is the main determinant of the type of green roofs used (Jaffal, 2012). For instance, substrates and plants are used as green roofs in Australia. Different regions use different types of roofs.

The surface temperature, of roofs is usually high during summer. Green roofs have a significant effect on temperature. Some of the impacts of green roofs on temperature include soil thermal resistance, foliage shading, and evapotranspiration. Heat flux in the roofs is affected thus influencing the building energy, and indoor thermal conditions. The winter and summer temperatures on the outer part of the roofs are less extreme. The fluctuation amplitude on the outer part of green roofs is lower than that found on conventional roofs (Heidrinejad et at., 2015). As a result, the thermal stress that is applied on the roof membranes is reduced to a great extent thus increasing the longevity of the roofs.

Even though research has been conducted on the impacts of using green roofs in buildings, several aspects are not clearly understood. It, therefore, calls for other research activities. For example, no way of quantifying the effects of green roofs on air temperature inside buildings has been identified. In most cases, the indoor effects of green roofs are quantified using models that are not well detailed.

Heidarinejad, Ghassem, and Arash Esmaili. "Numerical simulation of the dual effect of green roof thermal performance." Energy Conversion and Management 106 (2015): 1418-1425.

Jaffal, Issa et al. "A comprehensive study of the impact of green roofs on building energy performance." Renewable Energy 43 (2012): 157-164

In addition to that, variations of indoor conditions and the building energy demand depend on key parameters such as climate, roof insulation, and green roof configuration (Jaffal, 2012). Further investigation should be conducted to find out what can be done to improve the efficiency of green roofs.

This paper is presents a detailed analysis of the significance of green roofs on thermal performance of structures. It includes consideration of green roof soil temperature, use of foliage, the energy demand, and indoor air temperature. Comparison between the conventional roofs and green roofs has been conducted so that a good understanding on the topic under discussion is attained. The setbacks of using green roofs have also been discussed so as to lead individuals to making well informed decisions.

Buildings in modern day are constructed after considering various actors, environmental issues, and financial abilities. In developed countries, consumption and release of energy is a major issue affecting individuals. The local authorities and governments in such regions are quite concerned about energy issues and how to reduce consumption of energy. In Europe, 40% of the energy consumed comes from buildings. Buildings in the same regions contribute to 36% of the total amount of carbon dioxide emitted. Such impacts therefore, call for measures that lead to efficient energy consumption strategies. To overcome energy issues, innovative construction solutions have been implemented and are still being employed in constructions. Research is still being conducted to find out the best ways of conserving energy.

Jaffal, Issa et al. "A comprehensive study of the impact of green roofs on building energy performance." Renewable Energy 43 (2012): 157-164

Application of vegetated land roofing is one of the most effective ways of conserving energy (Jaffal, 2012). The method is also associated with other benefits such as sustainability, improvement of energy performance, aesthetic purposes, improvement of air quality and urban heat islands.

Green roofs have an insulation role which leads to improved capturing of solar radiation, and the evaporative cooling. Inter-reflections in the foliage bring a cooling effect. Green roofs are associated with a lot of positive impacts on energy performance of structures. The other important thing to note is that green roofs increase durability of roofing membranes. The principle of green roofs is covering a low sloped roof or a flat roof using a vegetated substrate. The important components of a green roof include isolation, a roof support, vegetation or a growing media, and a drainage layer. Integration of green roofs in most buildings is usually, successful in the initial stages of constructions. However, the integration of green roofs on existing buildings is still feasible. People can benefit from the installation of green roofs especially if they were previously using conventional roofing (Heidrinejad et at., 2015). For people intending to conserve energy and going green, application of green roofs is quite economical.

Jaffal, Issa et al. "A comprehensive study of the impact of green roofs on building energy performance." Renewable Energy 43 (2012): 157-164

Heidarinejad, Ghassem, and Arash Esmaili. "Numerical simulation of the dual effect of green roof thermal performance." Energy Conversion and Management 106 (2015): 1418-1425.

As a result of benefits associated with green roofs, studies have been conducted to measure and model the impacts of green roofs in performance of energy in buildings. Vegetation can stop approximately 60% of energy contributions coming from external sources. About 40% of cooling is saved when green roofs are used in buildings. In places like Chicago, a high green roofs reduces the amount of energy consumed by cooling during summer (Ouldboukhitine et al., 2011). Energy is reduced due to the shading effect of the vegetative substrates.

The shading effect may increase heating consumption during winter since solar radiation is stopped when it arrives on the vegetations surface. In Toronto, the amount of energy consumed on buildings was reduced by 73% on the top floor by the use of green roofs. In Athens, green roofs green roofs are 39% effective in reducing cooling consumption by 58% for the floors top as compared to other conventional roof (Heidrinejad et at., 2015).

Green roofs are also studied by several authors from different parts of the world. Insulation plays a great thermal role when it comes to green roofs. It is also important to note that green roofs do not effectively replace the functions of the insulating layers. Green roofs containing water have an increased thermal conductivity which leads to the reduction of the buildings thermal performance. For frozen roofs, insulation is quite effective thus leading to conservation of energy (Ouldboukhitine et al., 2011). The performance of frozen roofs does not show a huge difference from conventional roofs when snow is present.

Heidarinejad, Ghassem, and Arash Esmaili. "Numerical simulation of the dual effect of green roof thermal performance." Energy Conversion and Management 106 (2015): 1418-1425.

Ouldboukhitine et al. "Assessment of green roof thermal behavior: A coupled heat and mass transfer model." Building and Environment 46, no. 12 (2011): 2624-2631.

For materials with high porosity including the substrates of green roofs, the transfer of moisture has a large impact. Jim and Lilliana (2012) assert that the effects of gravity on roofs have serious consequences on predictability of water exchange. In addition to that, balance of water fort the evaluation of water content in roof is helpful in assessing the vegetation thermal behavior. It is, therefore, important to consider the thermal behavior by coupling mass and heat transfer in models. In developing an approach that deals with assessment of thermal behavior of green roofs, a moisture transfer model and a green roof model help show the impacts on conservation of heat. The developed models coupled with urban and building climate simulation tools help the designers of buildings to assess the effect of green roofs as thermal comfort and energy demand in addition to weather experienced in developed regions.

While modeling the thermal activities of green roofs, it is important to study various interacting phenomena which include plant physiology, and mass and heat physiology. Green roof models vary depending on the type of studies being carried out. The usually range from detailed to simple models. The simplest green roof model considers a decrease on U-value of the roof. Other studies have shown detailed models with a significant heat balance which also considers cooling by evapotranspiration and shading by foliage. Del Barrio came up with a thermal model for investigating the impact of green roofs on the energy performance of buildings.

Jim and Lilliana. "Weather effect on thermal and energy performance of an extensive tropical green roof." Urban Forestry & Urban Greening 11, no. 1 (2012): 73-85.

Koenig and Frankenstein also came up with FASST (Fast All-Season Soil Strength) model that helped understand the impacts of green roofs on buildings. In the FASST, two balances of heat at the roof soil surface and the foliage surface are considered. Other considerations taken include the leaf are index (LAI), stomatal resistance, foliage height, fractional vegetation coverage, and albedo. Mass and heat transfer are also taken into consideration in the model (Jaffal, 2012). The above components are studied by assuming that the leaf is a body where air circulates in it.

Mass and heat transfer in green roofs is usually expressed by nonlinear differential equations. In most buildings, green roofs are made up of four different elements which include roof, air, soil, and plant structure. In each component of the systems, mass and heat transfer are solved depending on their relevance. Boundary conditions of the roofs match the problems encountered and also lead to conservation of mass and heat fluxes. Below are some of the assumptions taken when expressing the relationship between green roofs and conservation of energy (Jim and Lilliana, 2012).Jim and Lilliana. "Weather effect on t...