Urban Design to Reduce building energy use: Using CFD to inform better placement of buildings.

Transcription

1 Urban Design to Reduce building energy use: Using CFD to inform better placement of buildings. By Nicola Hurst

2 Background UHI Air conditioning Aims Method Results Conclusions Further Work Overview

3 UHI Urban Heat Island (UHI) is defined as an area which has consistently higher temperatures than surrounding areas. London surbanheatislandintensityis~9 C [1] Causes Change in properties of materials Lack of evapotranspiration Decreased wind velocities. Waste heat from energy consumption Effects Changes in weather patterns. Health risks due to increased pollution and high temperatures. Increased energy consumption.

4 Air conditioning Increased local temperatures Increased Air con use Increased global temperatures Increased CO 2 production through fossil fuel use Waste heat expelled into local environment

5 Aim To use Computational fluid dynamics (CFD) to compare how air flow may be affected by three potential building geometries on the banks of the river Don in Sheffield city centre. Predict the natural cooling potential the river has on the local environment.

6 Wicker riverside area Wicker is an area of Sheffield City Centre Currently undergoing regeneration works. Redevelopment by Sheffield City council. Picture shows area to be modelled using CFD Google Earth

7 Model Geometry All models consisted of basic shapes of the 3 buildings on the South bank. Differed in geometry of building on the North bank. 3 different geometries were made. block, split, fivebuild. Building 3 W Building 2 Building 1 block geometry split geometry fivebuild geometry

8 CFD CFD is used to solve equations on fluid flow. The two programmes used were GAMBIT and Fluent. Geometry built in GAMBIT. Placed inside domains to allow the solutions to be solved. Fluent used to simulate airflow patterns around the buildings. Model conditions K εmodel used. Inlet set as a power law. Reference wind-8 knots (4.12ms -1 ). Outlet 0 gauge pressure outlet Remaining walls symmetry Roughness constant 0.5 Geometry of model showing outer domain and meshing.

9 Results Average and maximum velocities are very similar. Velocity (ms -1 ) Volume Average Maximum Building Layout Inner domain Inner & Outer domain Inner domain Inner & Outer domain Layout 1 block Layout 2 split Layout 3 fivebuild Similarities between air movement and velocities in all models.

10 Air travels parallel across the whole of the windward facade. Backflow onto all buildings on the South bank. Circulation of air around the back of the building, causing back flow perpendicular to the facade. Though very low velocities. Taking only velocities into consideration, this layout is likely to receive greatest cooling. Results

11 Less flow along the Windward facade than block. Low velocities and little air movement in the building indents. Backflow onto buildings on South bank. Circulation of air around the back of the building, causing back flow perpendicular to the facade. Higher velocities than block. Taking air movement into consideration, this layout is likely to receive the least natural cooling. Results

12 Higher velocities seen between buildings. Less back flow onto buildings 1 and2. Circulation causing backflow onto the back of buildings. Though less uniform movement than other models because of air moving between buildings. High surface area: volume ratio may lead to greatest natural cooling. Results

13 Path lines show the movement of the air originating above the river. This air is predicted to be cooler than surrounding air. Evaporation of water from the surface of river is an enthalpy reaction. Path lines show that the air above river moves directly to the North facing facades ofthebuildingsonthesouthbank. Assume dominant cooling from the river will occur on the South bank buildings. Results

14 Conclusions Cooling effects of the river and building geometry can not be fully understood. Need to factor temperature into models. From velocity alone, can assume the geometry of buildings have no effect on the potential cooling of the river. Considering air movement; can assume least cooling will occur in the split building. This layout may prove the best geometry to have when taking into consideration recreational activities and pedestrian comfort. Unsure which geometry will experience the greatest cooling. In all cases the greatest cooling should occur in South bank buildings.

15 Further work Two main areas for further work: Firstly need to incorporate temperature into models. Secondly incorporate further buildings behind river front, to see how far the rivers cooling effect can travel.

16 Thank you to Dr. Abigail Hathway. Acknowledgements

17 References [1] Kolokotroni, M. & Giridharan, R Urban heat island intensity in London: An investigation of the impact of physical characteristics on change in outdoor air temperature during summer. Solar Energy, 82,