Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis
A green roof can modify the roof outer surface temperature (Tr) to influence indoor air temperature (Ti). Green roof design and roof-slab thermal insulation jointly determine the coupled-roof system’s thermal performance. This study investigated their joint effects on subtropical winter warming, whi...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2022-11-01
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| Series: | Energy Reports |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2352484722024076 |
| _version_ | 1828010924158484480 |
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| author | Taibing Wei C.Y. Jim Yuxin Chen Anqi Chen Xiaojuan Li |
| author_facet | Taibing Wei C.Y. Jim Yuxin Chen Anqi Chen Xiaojuan Li |
| author_sort | Taibing Wei |
| collection | DOAJ |
| description | A green roof can modify the roof outer surface temperature (Tr) to influence indoor air temperature (Ti). Green roof design and roof-slab thermal insulation jointly determine the coupled-roof system’s thermal performance. This study investigated their joint effects on subtropical winter warming, which were seldom investigated. Custom-built houses without (bare roof) and with a 20-cm soil layer at circa 20% moisture content (soil roof) provided experiment plots to collect field data. The measured data tested the corrected finite element analysis model and simulated the combined influence of soil cover (properties kept constant) and a gradation of roof-slab thermal insulation on Tiin the unsteady heat transfer mode. Such multiple-factor and complex spatiotemporal studies are difficult using only field experiments and measurements. Average Tiwas raised by 0.44 °C on a typical winter day, bringing 4.55% energy saving to indoor-heating budget. With poor roof-slab insulation, the soil roof significantly retained indoor warmth. With improved roof-slab insulation, the soil roof’s influence on Tiwaned. A tipping point at 0.95 W/(m K) thermal conductivity signified a maximum threshold above which the green roof would not retain additional indoor heat. An upper threshold of thermal insulation at 0.35–0.05 W/(m K) was found, above which further insulation increase would not keep additional indoor warmth. Subtropical winter indoor warming by green roof was verified via two heat preservation mechanisms: retaining indoor heat to bring passive warming and delivering heat indoors to bring active warming. They were triggered by slightly warmed and notably warmed green-roof soil, respectively. The results ascertained quantitatively the complementary thermal role of green roof and roof slab. The findings can optimize the subtropical green-roof design and achieve winter indoor warming and thermal comfort. |
| first_indexed | 2024-04-10T09:08:37Z |
| format | Article |
| id | doaj.art-41545891c0c5471cb472a4e534c8a30e |
| institution | Directory Open Access Journal |
| issn | 2352-4847 |
| language | English |
| last_indexed | 2024-04-10T09:08:37Z |
| publishDate | 2022-11-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Energy Reports |
| spelling | doaj.art-41545891c0c5471cb472a4e534c8a30e2023-02-21T05:14:32ZengElsevierEnergy Reports2352-48472022-11-0181485214864Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysisTaibing Wei0C.Y. Jim1Yuxin Chen2Anqi Chen3Xiaojuan Li4Department of Civil Engineering and Architecture, Wuyi University, Wuyishan City, Fujian, ChinaDepartment of Social Sciences, Education University of Hong Kong, Lo Ping Road, Tai Po, Hong Kong, China; Corresponding author.Department of Computer Engineering, Wuyishan Vocational College, Wuyishan City, Fujian, ChinaDepartment of Civil Engineering and Architecture, Wuyi University, Wuyishan City, Fujian, ChinaCollege of Transportation and Civil Engineering, Fujian Agriculture and Forestry University, Fuzhou, Fujian, ChinaA green roof can modify the roof outer surface temperature (Tr) to influence indoor air temperature (Ti). Green roof design and roof-slab thermal insulation jointly determine the coupled-roof system’s thermal performance. This study investigated their joint effects on subtropical winter warming, which were seldom investigated. Custom-built houses without (bare roof) and with a 20-cm soil layer at circa 20% moisture content (soil roof) provided experiment plots to collect field data. The measured data tested the corrected finite element analysis model and simulated the combined influence of soil cover (properties kept constant) and a gradation of roof-slab thermal insulation on Tiin the unsteady heat transfer mode. Such multiple-factor and complex spatiotemporal studies are difficult using only field experiments and measurements. Average Tiwas raised by 0.44 °C on a typical winter day, bringing 4.55% energy saving to indoor-heating budget. With poor roof-slab insulation, the soil roof significantly retained indoor warmth. With improved roof-slab insulation, the soil roof’s influence on Tiwaned. A tipping point at 0.95 W/(m K) thermal conductivity signified a maximum threshold above which the green roof would not retain additional indoor heat. An upper threshold of thermal insulation at 0.35–0.05 W/(m K) was found, above which further insulation increase would not keep additional indoor warmth. Subtropical winter indoor warming by green roof was verified via two heat preservation mechanisms: retaining indoor heat to bring passive warming and delivering heat indoors to bring active warming. They were triggered by slightly warmed and notably warmed green-roof soil, respectively. The results ascertained quantitatively the complementary thermal role of green roof and roof slab. The findings can optimize the subtropical green-roof design and achieve winter indoor warming and thermal comfort.http://www.sciencedirect.com/science/article/pii/S2352484722024076Green roof designCoupled-roof systemRoof-slab thermal insulationPassive and active warmingIndoor heat preservationFinite element analysis |
| spellingShingle | Taibing Wei C.Y. Jim Yuxin Chen Anqi Chen Xiaojuan Li Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis Energy Reports Green roof design Coupled-roof system Roof-slab thermal insulation Passive and active warming Indoor heat preservation Finite element analysis |
| title | Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| title_full | Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| title_fullStr | Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| title_full_unstemmed | Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| title_short | Complementary influence of green-roof and roof-slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| title_sort | complementary influence of green roof and roof slab thermal conductivity on winter indoor warming assessed by finite element analysis |
| topic | Green roof design Coupled-roof system Roof-slab thermal insulation Passive and active warming Indoor heat preservation Finite element analysis |
| url | http://www.sciencedirect.com/science/article/pii/S2352484722024076 |
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