| 1. |
- Chen, L., et al.
(författare)
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Numerical investigations of wind and thermal environment in 2D scaled street canyons with various aspect ratios and solar wall heating
- 2021
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Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 190
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Tidskriftsartikel (refereegranskat)abstract
- Optimizing urban ventilation is an effective way to improve urban air quality and thermal environment. For this purpose, under the validation of wind-tunnel experiments, flow regimes and micro thermal environment in typical reduced-canyon models with aspect ratios (AR) of 1.1, 2.4, 4 and 5.67 were investigated by CFD simulations using periodic boundary condition. ANSYS Fluent 15.0 with a solar ray tracing model and radiation model was performed to numerically study turbulence characteristics with wind-driven force and solar-heating conditions. Results revealed that, with wind-driven condition, a clockwise vortex existed in normal and deep street canyon (AR = 1.1 and 2.4) while two counter-rotating vortices appeared in extremely deep canyon (AR = 4 and 5.67). Moreover, different turbulence structures and air temperature distribution existed in canyons with different solar-heating conditions. When the leeward wall or ground was heated, the pedestrian-level velocity increased and street ventilation was strengthened compared to wind-driven condition for all AR values. Particularly, the single main vortex was strengthened (AR = 1.1 and 2.4), and the two-vortex structure in extremely deep canyons (AR = 4 and 5.67) changed to single-vortex structure. When the windward wall was heated, the clockwise main vortex at AR = 1.1 and 2.4 was deformed, and a new sub vortex gradually appeared near street bottom. Furthermore, at AR = 4 and 5.67, windward solar heating destroyed the two-vortex structure and slightly improved pollutant dilution capacity. This work implied that extremely deep street design with weak pedestrian-level ventilation should be avoided. It also provides a meaningful reference for urban planning.
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| 2. |
- Jones, Kristine, et al.
(författare)
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Cost-effectiveness of critical time intervention to reduce homelessness among persons with mental illness
- 2003
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Ingår i: Psychiatric Services. - : American Psychiatric Association Publishing. - 1075-2730 .- 1557-9700. ; 54:6, s. 884-890
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Cost-effective programs are needed to assist homeless persons with severe mental illness in their transition from shelters to community living. The authors investigated the cost-effectiveness of the critical time intervention program, a time-limited adaptation of intensive case management, which has been shown to significantly reduce recurrent homelessness among men with severe mental illness. Methods: Ninety-six study participants recruited from a psychiatric program in a men's public shelter from 1991 to 1993 were randomly assigned to the critical time intervention program or to usual services. Costs and housing outcomes for the two groups were examined over 18 months. Results: Over the study period, the critical time intervention group and the usual services group incurred mean costs of $52,374 and $51,649, respectively, for acute care services, outpatient services, housing and shelter services, criminal justice services, and transfer income. During the same period, the critical time intervention group experienced significantly fewer homeless nights than the usual care group (32 nights versus 90 nights). For each willingness-to-pay value - the additional price society is willing to spend for an additional nonhomeless night - greater than $152, the critical time intervention group exhibited a significantly greater net housing stability benefit, indieating cost-effectiveness, compared with usual care. Conclusions: Although difficult to conduct, studies of the cost-effectiveness of community mental health programs can yield rich information for policy makers and program planners. The critical time intervention program is not only an effective method to reduce recurrent homelessness among persons with severe mental illness but also represents a cost-effective alternative to the status quo.
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| 3. |
- Yang, Bin, et al.
(författare)
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A review of advanced air distribution methods - theory, practice, limitations and solutions
- 2019
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788 .- 1872-6178. ; 202
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Tidskriftsartikel (refereegranskat)abstract
- Ventilation and air distribution methods are important for indoor thermal environments and air quality. Effective distribution of airflow for indoor built environments with the aim of simultaneously offsetting thermal and ventilation loads in an energy efficient manner has been the research focus in the past several decades. Based on airflow characteristics, ventilation methods can be categorized as fully mixed or non-uniform. Non-uniform methods can be further divided into piston, stratified and task zone ventilation. In this paper, the theory, performance, practical applications, limitations and solutions pertaining to ventilation and air distribution methods are critically reviewed. Since many ventilation methods are buoyancy driving that confines their use for heating mode, some methods suitable for heating are discussed. Furthermore, measuring and evaluating methods for ventilation and air distribution are also discussed to give a comprehensive framework of the review.
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| 4. |
- Yang, H., et al.
(författare)
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Numerical investigations of Re-independence and influence of wall heating on flow characteristics and ventilation in full-scale 2D street canyons
- 2021
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Ingår i: Building and Environment. - : IEEE. - 0360-1323 .- 1873-684X. ; 189
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Tidskriftsartikel (refereegranskat)abstract
- Validated by wind tunnel data, this study numerically investigates the integrated impacts of wind and thermal buoyancy on urban turbulence, ventilation and pollutant dispersion in full-scale 2D deep street canyons (aspect ratio AR = H/W = 3 and 5, W = 24 m). Isothermal urban airflows for such deep street canyons can be Reynolds-number-independent when reference Reynolds number (Re) exceeds the critical Re (Rec~106,107 when AR = 3, 5), i.e. AR = 5 experiences two main vortices and one-order smaller NEV* (~10−3, the normalized net escape velocity) than AR = 3 with a single main vortex (NEV*~10−2). With sufficiently large Re (Re > Rec) and the same air-wall temperature difference (Ri = 2.62, 4.36 when AR = 3, 5), four uniform wall heating patterns were considered, including leeward-wall heating (L-H), windward-wall heating (W–H), ground heating (G-H), and all-wall heating (A-H). Various indicators were adopted to evaluate street ventilation and pollutant dilution capacity (e.g. age of air (τ,s), NEV*, pollutant transport rates (PTR)). Full-scale wall heating produces a strong upward near-wall buoyancy force, which significantly influences flow patterns and improves street ventilation for most cases. When AR = 3, L-H strengthens the single-vortex airflow. When AR = 5, L-H converts the isothermal double vortices into a single-clockwise vortex. For both ARs, W–H reverses the main clockwise vortex to an enhanced counterclockwise one, moreover G-H and A-H cause a more complicated multi-vortex pattern than isothermal cases. Overall, when AR = 3, L-H and W–H increase NEV* by 68% and 40% than the isothermal case. When AR = 5, four wall heating patterns all raise NEV* considerably (by 150%–556%). For both ARs, the L-H, W–H and A-H amplify the contribution of mean flows on removing pollutants but reduce that by turbulent diffusion compared with isothermal cases.
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