TY - JOUR
T1 - To irrigate or not to irrigate
T2 - Analysis of green roof performance via a vertically-resolved hygrothermal model
AU - Sun, Ting
AU - Bou-Zeid, Elie R.
AU - Ni, Guang Heng
N1 - Funding Information:
This work is supported by the National Science Foundation of China under Grant No. NSFC-51190092. Elie Bou-Zeid is supported by US National Science Foundation under grant No. CBET-1058027 and by the US Department of Energy through Pennsylvania State University's Energy Efficiency Building Hub under grant No. DE-EE0004261. We are grateful to Tsinghua Property Management Center for the assistance in field measurement campaign. We also appreciate Dr. Zhi-Hua Wang for his constructive comments at the planning stage of this work. We thank the two reviewers for their insightful and constructive comments that significantly improve the quality of this work.
PY - 2014/3
Y1 - 2014/3
N2 - In this study, the performance of an irrigation-integrated green roof (GR) system is analyzed through numerical simulations using the vertically-resolved Princeton ROof Model (PROM). The simulations are driven by a 63-day series of summertime meteorological forcing measured at a GR site in Beijing, China. Due to the importance of the medium layer depth of GR systems, its effect on the dynamics of heat and moisture transports and consequently on the thermal performance is first examined under a no-irrigation scenario. The results confirm that the medium layer depth affects heat and moisture transports significantly, but non-monotonic trends emerge. A deeper layer is found to redistribute more water into the bottom section, thus limiting surface evaporation, while a thin layer does not store enough water, dries up fast, and decreases performance too. This indicates that an optimal layer thickness exists somewhere in the middle. Given a fixed medium layer depth, different irrigation scenarios are then investigated. Higher irrigation control limits (i.e. the soil moisture at which irrigation is initiated) enhance the thermal performance of the GR, but this enhancement plateaus at high limits. Based on these findings, a GR (constructed over an un-insulated concrete slab roof in Beijing) is simulated and a simplified operational cost-benefit analysis is performed by comparing the cost of irrigation to that of the energy saved due to lower air-conditioning (AC) requirement when the GR is wetted. The analysis indicates that the irrigated GR system costs are lower than the AC costs for an unirrigated GR. For instance, an irrigated GR system with an area of 100m2 under an irrigation control limit of 0.3m3m-3 will save [U+FFE5]110 (18 USD) for the chosen 63-day simulation period in Beijing. Therefore, irrigation-integrated GR systems emerge as potentially viable solutions for improving building energy efficiency in a temperate climate.
AB - In this study, the performance of an irrigation-integrated green roof (GR) system is analyzed through numerical simulations using the vertically-resolved Princeton ROof Model (PROM). The simulations are driven by a 63-day series of summertime meteorological forcing measured at a GR site in Beijing, China. Due to the importance of the medium layer depth of GR systems, its effect on the dynamics of heat and moisture transports and consequently on the thermal performance is first examined under a no-irrigation scenario. The results confirm that the medium layer depth affects heat and moisture transports significantly, but non-monotonic trends emerge. A deeper layer is found to redistribute more water into the bottom section, thus limiting surface evaporation, while a thin layer does not store enough water, dries up fast, and decreases performance too. This indicates that an optimal layer thickness exists somewhere in the middle. Given a fixed medium layer depth, different irrigation scenarios are then investigated. Higher irrigation control limits (i.e. the soil moisture at which irrigation is initiated) enhance the thermal performance of the GR, but this enhancement plateaus at high limits. Based on these findings, a GR (constructed over an un-insulated concrete slab roof in Beijing) is simulated and a simplified operational cost-benefit analysis is performed by comparing the cost of irrigation to that of the energy saved due to lower air-conditioning (AC) requirement when the GR is wetted. The analysis indicates that the irrigated GR system costs are lower than the AC costs for an unirrigated GR. For instance, an irrigated GR system with an area of 100m2 under an irrigation control limit of 0.3m3m-3 will save [U+FFE5]110 (18 USD) for the chosen 63-day simulation period in Beijing. Therefore, irrigation-integrated GR systems emerge as potentially viable solutions for improving building energy efficiency in a temperate climate.
KW - Green roof
KW - Irrigation strategy
KW - Thermal performance
KW - Urban Canopy Model
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U2 - 10.1016/j.buildenv.2013.12.004
DO - 10.1016/j.buildenv.2013.12.004
M3 - Article
AN - SCOPUS:84891375243
SN - 0360-1323
VL - 73
SP - 127
EP - 137
JO - Building and Environment
JF - Building and Environment
ER -