Place Value Wiki - D1. Urban form, density and energy use

D1. Urban form, density and energy use

Sprawl and energy use

Aims and method:

Uses several national databases in the USA to link urban form to residential energy consumption. The analytical structure consisted of six models, estimated with different data sets but linked conceptually through common variables. 400 counties are included ranging from compact (New York City) to sprawl (Goochland County in the Richmond, Virginia) were examined.

Key findings:

· All end-use energy demands increase with increasing annual household income (although vary by race / ethnicity)

· The amounts of delivered energy use for space heating, cooling, and all other uses are strongly related to the physical characteristics of housing units. Old houses are less energy efficient than new ones. Detached houses require more energy than attached ones.

· Compared with households living in multifamily units, otherwise comparable households living in single-family detached units consume 54% more energy for space heating and 26% more energy for space cooling.

· Residential energy use varies with house type and house size and these vary with the degree of urban sprawl.

· The average household would be expected to consume 17.9 million fewer BTUs of primary energy annually (about 20% less) living in a compact county than in a sprawling county (respectively one standard deviation above and below the mean index).

· Energy conservation, and the associated reduction in greenhouse gases, can be thought of as just one more reason to encourage compact development and discourage sprawl.

Reference:

Ewing, R. & Rong, F. (2008) The impact of urban form on U.S. residential energy use, Housing Policy Debate, 19:1, 1-30

http://www.tandfonline.com/doi/abs/10.1080/10511482.2008.9521624

Energy consumption and urban texture

Aims and method:

Explores the effects of urban texture on building energy consumption. The study is based on an analysis of digital elevation models (DEMs) for London, Berlin and Toulouse. Different algorithms are proposed and discussed, including the calculation of the urban surface-to-volume ratio and the identification of all building areas that are within 6m from a façade (passive areas). An established computer model to calculate energy consumption in buildings, the Lighting and Thermal (LT) model, is coupled with the analysis of DEMs, providing energy simulations over extensive urban areas.

Key findings:

· Surface-to-volume ratio does not describe the total energy consumption in urban areas. A better indicator is the ratio of passive to non-passive zones, although accurate energy consumption values can only be derived from an integrated simulation such as LT.

· The results of the LT simulation show an integrating and smoothing effect, so that the sensitivity of energy consumption on urban form is reduced.

· The variation of energy consumption relating to urban geometry (or texture) is relatively small at 10% when compared with the potential impact of systems efficiency or occupant behaviour

· But values of this order of magnitude could have a tremendous impact on the energy budget of cities and would justify careful thought in urban planning.

· In hotter climates the relative importance of exposure of the building envelope versus the danger of heat losses is likely to be greater.

Reference

Ratti, C., Baker, N., & Steemers, K. (2005). Energy consumption and urban texture. Energy and buildings, 37(7), 762-776.

http://www.sciencedirect.com/science/article/pii/S0378778804003391

Urban form and energy consumption

Aims and method:

Empirically estimates the relationship between urban forms and energy consumption from the perspective of spatial patterns of urban land use. Using quantitative panel data of urban changes across five cities in the Chinese Pearl River Delta (Guangzhou, Dongguan, Shenzhen, Foshan and Zhongshan) between 2005-2008, the study explores how changes in built form affect energy consumption.

Key Findings:

· As urban size increases energy consumption increases.

· Fragmented urban land use patterns are correlated with increased energy consumption.

· The dominance of the largest urban patch is negatively correlated with energy consumption.

· Compact city design may result in reduced energy consumption.

Reference:

Chen, Y., Li, X., Zheng, Y., Guan, Y., & Liu, X. (2011). Estimating the relationship between urban forms and energy consumption: A case study in the Pearl River Delta, 2005–2008. Landscape and Urban Planning, 102(1), 33-42.

http://www.sciencedirect.com/science/article/pii/S0169204611001381

Residential density and energy consumption

Aims and method:

Using quantitative analysis, this study examines two questions: 1) is there a relationship between urban form and electricity consumption for single-family homes in Illinois after controlling for differences in household characteristics, structural characteristics, weather, and other mitigating factors? 2) what are the implications of these findings for how residential subdivisions are designed and built?

Key Findings:

· Urban form characteristics matter at the micro-scale: compact residential development provides opportunities to manage residential electricity consumption, and by extension, greenhouse gas emissions.

· Homes in higher density residential subdivisions are associated with lower rates of summer electricity consumption

· Homes located in subdivisions adjacent to less developed properties are associated with higher electricity consumption during the winter, which suggests an insulating effect of density in that neighbouring structures may act as windbreaks.

Reference:

Wilson, B. (2013). Urban form and residential electricity consumption: Evidence from Illinois, USA. Landscape and Urban Planning, 115, 62-71.

http://www.sciencedirect.com/science/article/pii/S0169204613000601

Carbon release and urbanisation

Aims and method:

Examines the way in which urban development affects carbon dioxide exchanges by comparing three different sites (central London, Swindon and on the Alice Holt nature reserve). Using contemporaneous measures of carbon dioxide exchange across the three sites, the role of surface cover is quantitatively evaluated to better understand the role urban development has on carbon capture.

Key Findings:

· Variation in annual CO2 exchange among urbanised study sites is approximately ten times that observed among vegetated ecosystems.

· Urban and suburban patterns of CO2 fluxes at the sub-daily, weekly and seasonal cycles can be directly attributed to patterns in human behaviour.

· The major difference between CO2 release on working days and non-working days illustrates the potential impact that reducing anthropogenic activities (or cutting emissions by improving efficiency) could have.

· Reductions in traffic intensity, improved energy efficiency in buildings, and preferential use of electricity over combustion of fossil fuels could make a significant impact in limiting carbon release from towns and cities.

Reference:

Ward, H. C., S. Kotthaus, C. S. B. Grimmond, A. Bjorkegren, M. Wilkinson, W. T. J. Morrison, J. G. Evans, J. I. L. Morison, and M. Iamarino (2015). Effects of urban density on carbon dioxide exchanges: Observations of dense urban, suburban and woodland areas of southern England. Environmental Pollution, 198, 186-200.

http://www.sciencedirect.com/science/article/pii/S0269749114005314

Urban form and carbon emissions

Aims and method:

Examines the effect of urban form at the urbanised area level on individual household level carbon dioxide emissions, accounting for both transportation and residential energy uses. Using multi-level structural equation modelling the study evaluates the 125 largest urban areas in the United States.

Key Findings:

· More compact, mixed-use urban forms dramatically reduce CO2 emissions and energy consumption.

· Increased transport subsidies are positively related with a reduction in vehicle miles travelled and CO2 emissions.

· With 42% of US greenhouse gas emissions coming from household travel and residential energy use, strategic efforts at reducing emissions would benefit from land use policies favouring compact urban design.

Reference:

Lee, S., & Lee, B. (2014). The influence of urban form on GHG emissions in the US household sector. Energy Policy, 68, 534-549.

http://www.sciencedirect.com/science/article/pii/S0301421514000299

Compactness and carbon emissions

Aims and method:

Develops and examines spatial indices to characterise urban form and its relationship to CO2 emissions in 50 Japanese cities. Using quantitative analysis, the study evaluates the relationship between compactness and the complexity of urban settlements (shape, density, extent of irregularity and ruggedness of urban settlement patches), and the extent of centrality and population density and CO2 emissions.

Key Findings:

· Greater compactness and less irregularity correlated with lower CO2 emissions.

· Extreme density and mono-centrism lead to higher CO2 emissions.

· Need to balance density and diversity of use to achieve greatest reduction on CO2 emissions.

Reference:

Makido, Y., Dhakal, S., & Yamagata, Y. (2012). Relationship between urban form and CO2 emissions: evidence from fifty Japanese cities. Urban Climate, 2, 55-67.

http://www.sciencedirect.com/science/article/pii/S2212095512000132

City size, density and carbon emissions

Aims and method:

Develops a quantitative model that characterises the size and composition of household carbon footprints for every U.S. zip code, city, county, and U.S. state. This information is used to develop high geospatial resolution household carbon profiles of each location and to analyse the effect of population density and level of urbanisation on full life cycle green house gas emissions.

Key Findings:

· The relationship between population density and urbanisation is size dependent.

· Consistently lower household carbon footprints are found in urban core cities (∼40 tCO2e) and higher carbon footprints in outlying suburbs (∼50 tCO2e), with a range from ∼25 to >80 tCO2e in the 50 largest metropolitan areas.

· Population density exhibits a weak but positive correlation with carbon footprints until a density threshold is met, after which range, mean, and standard deviation of household carbon footprints decline.

· While population density contributes to relatively low household carbon footprints in the central cities of large metropolitan areas, the more extensive suburbanisation in these regions contributes to an overall net increase compared to smaller metropolitan areas.

· Suburbs alone account for ∼50% of total U.S. household carbon footprints.

Reference:

Jones, C., & Kammen, D. (2014) "Spatial distribution of US household carbon footprints reveals suburbanization undermines greenhouse gas benefits of urban population density." Environmental science & Technology 48(2): 895-902.

http://pubs.acs.org/doi/abs/10.1021/es4034364

The shape of cities and greenhouse gas emissions

Aims and method:

Evaluates the spatial and temporal characteristics of CO2 emissions across different built-up areas and urban forms using quantitative panel data (covering 1990-2010) from China’s provincial capitals. Econometric models were used to quantitatively evaluate the relationship between estimated CO2 related energy emissions and urban form.

Key Findings:

· Integrated (compact) urban forms with regular shapes lowered greenhouse gas emissions.

· Reducing shape complexity of cities (perimeter-to-area ratios) is positively related to reducing emissions.

Reference:

Fang, C., Wang, S., & Li, G. (2015). Changing urban forms and carbon dioxide emissions in China: A case study of 30 provincial capital cities. Applied Energy, 158, 519-531.

http://www.sciencedirect.com/science/article/pii/S0306261915010314

Compactness and CO2 emissions efficiency

Aims and method:

Examines the relationship between urban compactness and urban CO2 efficiency in 30 Chinese provincial capitals. Develops quantitative metrics for urban compactness and urban CO2 efficiency indicators and evaluates them using panel data covering 1985, 1996 and 2007.

Key Findings:

· CO2 economic efficiency (which aims to minimise CO2 emissions while maximising the efficiency of urban economic processes) is increased by increasing urban compactness.

· In China where social infrastructure is not always well developed, CO2 social efficiency (which aims to minimise CO2 emissions while maximising urban social welfare) is reduced by increased urban compactness.

· Optimising efficiency requires a balance between compactness and investment in public services to manage the resulting high population density.

Reference:

Liu, Y., Song, Y., & Song, X. (2014). An empirical study on the relationship between urban compactness and CO2 efficiency in China. Habitat International, 41, 92-98.

http://www.sciencedirect.com/science/article/pii/S0197397513000684

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