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Res: [EnergyPlus_Support] Greenroof
"Observation from the Field Roofing Facility showed that a generic extensive green roof with 150 mm (6 in.) of growing medium could reduce the temperature of the roof membrane significantly in the summer. The exposed roof membrane on the Reference Roof was recorded to reach over 70°C (158°F) in the summer but that under the Green Roof rarely reached over 30°C (86°F). Also the Green Roof modified the temperature fluctuations the roof membrane experienced, especially in the warmer months. The median daily temperature fluctuation of the membrane on the Reference Roof in spring and summer ranged from 42 to 47°C (76 to 85°F), however, the Green Roof reduced the temperature fluctuation to 5-7°C (9-11°F). The Green Roof also significantly moderated the heat flow through the roofing system in the warmer months. The average daily energy demand for space conditioning due to the heat flow through the roof was reduced from 6.0-7.5 kWh/day (20,500-25,600 BTU/day) to less than 1.5
kWh/day (5,100 BTU/day) as measured on the Reference Roof and the Green Roof, respectively. This corresponded to a reduction of over 75%" (Liu & Baskaran, 2003).
"To explore the thermal benefits of green roofs, a before and after measurement and an experiment were carried out. Maximally, over 60% of heat gain was stopped by the system. The impact of different types of vegetation may vary as well. Those with relatively extensive greenery coverage led to better thermal performance" (Wong et al, 2005).
"Although cooling effects are clearly site specific, there have been attempts to generalize the energy cost savings from a green roof. The private cooling cost in Acks (2003) for a standard roof was estimated at $0.16 per square foot through five independent calculations, and a green roof was assumed to reduce cooling costs by approximately 15%. In Wong et al. (2004) energy costs were estimated using the energy model based on the Power DOE program, yielding annual energy savings of between 5,000 and 29,000 kWh. An extensive green roof under these conditions would result in cost savings of $4,773.40 each year, and these energy cost savings could significantly decreased costs of installing both extensive and intensive green roofs. England et al. (2004) estimated green roof annual energy savings at a value between $2,500 and
$12,500" (Report on the thermal environmental benefits and costs of green roof technology for the city of Toronto, 2005).
----- Mensagem original ----
De: "Drury.Crawley@xxxxxxxxxx" <Drury.Crawley@xxxxxxxxxx>
Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
Enviadas: Quinta-feira, 26 de Abril de 2007 9:25:00
Assunto: Re: [EnergyPlus_Support] Greenroof
The energy impacts of green roofs are VERY small. The detailed
measurements
have shown the energy savings to be similar to adding a small amount of
insulation
to an already insulated roof. Some of the studies were showing a energy
difference
of only 10 kWh/m2 on an annual basic.
The real benefits of green roofs are reduced stormwater runoff, reduced
roof surface
temperatures (roofs last longer), and reduced heat island contributions.
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