density, carbon emissions, transportation and energy ......density, carbon emissions, transportation...

csdCenter for Sustainable Development

Density, Carbon Emissions,

Transportation and Energy Efficiency

Dana Flatow

Werner LangInstructor

UTSoA - Seminar in Sustainable Architecture

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Density, Carbon Emissions, Transportation and Energy Efficiency

Dana Flatow

Introduction

There are many factors involved with the effects of density in an environ-ment. This paper explores the more general effects of energy use and greenhouse (GHG) gas emissions in both low and high-density develop-ments. Over the past 10 years there have been a handful of studies that look closely at the role that density plays in energy efficiency and GHG emissions. This paper will examine these studies and provide a compari-son of the metrics and hypotheses that are used to evaluate the role of urban development in the reduction of GHG emissions and energy use.

All studies reviewed for this paper show a strong inverse correlation between the density of a community, energy use and greenhouse gas emissions produced. Common to each study is the understanding that higher density developments result in both the reduction of greenhouse gas emissions and energy use. Of

this overall reduction, the studies agree that 45 to 50 percent of this re-duction would be the result of energy efficiencies (such as district heating of buildings in both the residential and commercial sectors), another 45 to 50 percent would be the result of the reduction of vehicular travel, and the last 3 to 5 percent would be the result of the reduction of municipal infrastructure support.

The studies generally indicate that transportation is the leading factor of GHG emissions, while building maintenance and operations de-mand higher energy usage. Overall, the studies show that a low-density development is less energy efficient and produces more greenhouse gases than a high-density environ-ment.

The studies use data collected from case studies and research con-ducted in North America. Density is assessed as high density or low den-sity, and each study compares the

Fig. 01 Mapping Carbondale, CO. www.pedbikeimages.org/danburden.


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various communities on three similar fronts: infrastructure, transportation and energy use. This paper looks specifically at the effects of trans-portation on GHG emissions and the amount of energy use in low and high density developments.

Greenhouse Gas Emissions and Transportation

A study done at the University of Toronto, by Norman, MacLean and Kennedy study, shows that GHG emissions and energy use of low density developments are 3.7 times higher than those found in high density developments. The study also shows that whether or not the data is examined by per person or per square unit, this trend remains consistent. When analyzing GHG in both high and low density environ-ments, transportation is the main contributing factor of GHG emis-sions. See figure 2.

The most common form of transpor-tation regardless of type of density is light-duty transportation, consisting of private automobiles and public transportation. These two forms of transportation are closely linked to two types of users, those relying on private transportation and those rely-ing on public transportation. Automo-biles (running primarily on gasoline and diesel) are fossil fuel dependent and are thus high producers of GHG emissions (Norman, MacLean, Ken-nedy). See figure 3.

A study done at the Oak Ridge National Laboratory by Brown and Southworth, states that a suburban environment of 4 homes per acre produces 25 percent more CO2 emissions than that of an urban envi-

Figure 03 Transportation Emissions. Sightline Institurte

7%

32%

61%

Low Density

45%

12%

43%

High Density

Transportation Building Operations Materials

Figure 02 Anual GHG emissions associated with low and high-density deveopment. Norman, MacLean, Kennedy.

GHG Emissions

Transportation Emissions


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ronment of 20 homes per acre.

It is important to note the overall significance of transportation when it comes to GHG emissions in a low-density development. The Norman, MacLean, Kennedy study shows that while transportation is a significant cause of GHG emissions for both low and high density development, the amount of GHG emissions produced are significantly different. Probable causes of this difference are due to the distances needed to travel in the two development types.

Figure 4 shows the difference be-tween two neighborhoods, one in Seattle, WA and the other a suburb of that city. The image illustrates the difference of density in a one-mile radius, considered to be a walkable distance. When identifying attri-butes of a walkable (and/or bike-able) neighborhood, access to both residences and business alike as well as services, shops, restaurants, public parks, schools and public transit stops become the key factors in community planning and smart growth development. In this type of development, when people do opt for vehicular travel, the trips driven become shorter, resulting in fewer miles traveled and a reduction of GHG emissions.

A study by the Urban Land Institute (ULI) validates the benefits to having alternatives to driving. By structur-ing a community specifically so that reliance on automobile usage is reduced, GHG emissions can be curbed. A 20 to 40 percent reduc-tion of vehicle miles traveled (VMT) can be achieved in a more compact development. The study found that residents of the most walkable neigh-borhoods drive 26 percent less than

Neighborhoods with cul-de-sacs and winding streets, such as this one in Bellevue, WA, have few shops and services within walking distance.

A one-mile walk in this urban neighborhood, Seattle's Phinney Ridge, takes you through a gridlike street network with a mix of residences and businesses. This walkable design puts stores and services within a short walk of many homes.

Figure 04 Map of a Compact Community: Walkability within One Mile. Where you can go: Seattle’s Phinney Ridge neighborhood and Bellevue, WA’s Eastgate neighborhood. Sightline Institute.


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those living in the developments of greater sprawl, and estimates that a 30 percent reduction of VMT is a realistic assumption for a compact development. See figure 5.

The ULI study goes further, hypoth-esizing that smart growth alone could be responsible for reducing transpor-tation-related CO2 emissions, reduc-ing current trends by 7 to 10 percent by 2050. This is attributed solely to changing land use patterns, and does not include the potential energy saving that are attributed to the build-ings within compact developments.

The Frank, Pivo study finds that as density increases, single occupancy vehicles (SOV) usage drops and other forms of transportation (notably walking and public transit) begin to increase. This study examines mul-tiple forms of density (employment, population and land-mix) as well as two forms of trips most frequently made (work and shopping). The study found that the type of transpor-tation used is related to employee density per acre. At 20 to 30 em-ployees per acre, 90 percent of the employees use SOV as the main source of transportation. At 50 to 75 employees per acre, 60 percent rely on SOVs. Once employment density reaches 125 employees per acre, the reliance on SOVs diminishes and 65 percent of employees rely on public transit and walking.

While VMT changes depending on density, the studies find that shop-ping trips are most greatly influenced by increased density. When looking at population density, a similar shift in mode of transportation from SOV to public transportation and walking begins to occur at a density of 13 residents per acre.

Energy Efficiency

While transportation is the main source of energy use and GHG emissions for low-density devel-opments, the energy required to operate a building becomes the main source of energy use and GHG emissions for a high-density environ-ment.

The energy efficiency of buildings, for the purpose of this paper, is directly related to the operational and maintenance use of energy. This is comprised of the energy needed to heat and cool a single building as well as an individual unit within a larger dwelling. See figure 6.

The Brown Southworth study indi-cates that emissions from electricity consumption dominate in the resi-dential sector, where it accounts for 76 percent of CO2 emissions, and in the commercial sector, where it accounts for 67 percent. The domi-nance of electric services in these sectors underscores the important

role that low-carbon electricity generation could play as an ad-ditional means of reducing CO2 emissions from the energy used in buildings. In the residential sector, most notably single family dwellings, improvements would best be made by increasing the end-use efficiency of space heating and water heating. In the commercial sector, specifically office buildings, improvements in air conditioning and lighting provide the greatest advantage for reductions.

The amount of VMT per household is a predictor of energy efficiency. VMT per household is greatly ef-fected by density and access to public transportation. However the strongest predictors of energy ef-ficiency are residential density and public transit. Single-family de-tached homes comprise 63 percent of all housing units, accounting for 73 percent of residential energy con-sumption. This is the second largest building type in terms of energy consumption.

0

7.5

15.0

22.5

30.0

Avg. Daily VMT per Capita

10 Most Sprawl-ing Metropolitan Areas

10 Least Sprawl-ing Metropolitan Areas

Figure 05 Avg. Daily VMT per Capita, Urban Land Institute.

Daily VMT per Capita


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The Norman, MacLean, Kennedy study shows that when evaluated per capita, single-family houses, com-mon to low-density developments, use approximately twice as much energy as buildings which house multiple living units, common to high-density developments. One prob-able cause for the increased energy use in single-family dwellings is the increased exterior wall surface area, which in turn creates the demand for greater heating and cooling loads. However, when energy use is evalu-ated per square meter, the same study shows that the annual energy use for low and high density building is the same.1

The size of the dwelling needing to be heated and cooled remains the biggest factor of energy consump-tion. When single-family detached homes are compared with similar household living in multifamily hous-ing it is found that 35 percent more energy for space heating and 21 per-cent more energy for space cooling is used in the single-family detached home. Similarly, when a 1,000 square foot house is compared to a 2,000 square foot house of similar traits, the larger of the two consumes 16 percent more energy for space heating and 13 percent more energy for space cooling (ULI).

Unlike the energy used to fuel automobiles, the energy consumed in buildings has a smaller impact on total GHG emissions. This is be-cause buildings rely mostly on natu-ral gas which has a lower carbon to hydrogen ratio than the gasoline and diesel used to fuel cars (Norman, MacLean, Kennedy). See Figure 6.

Conclusion

9%

60%

31%

Low Density

12%

70%

18%

High Density

Transportation Building Operations Materials

Figure 06 Anual energy use associated with low and high-density development. Norman, MacLean, Kennedy.

Figure 07 GHG emissions for direct combustion and elecricity by end-use sector. Pew Center on Global Climate Change.

Energy Use

Emissions by Sector


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The studies evaluated in this paper illustrate the connection between density, GHG emissions and energy use. The established understand-ing is that GHG emissions and energy use can be greatly reduced by increasing the energy efficiency of buildings and reducing vehicular travel.

A decrease in energy consumption can occur foremost in the reduction of the amount of energy needed to operate a building (energy related to heating and cooling). District heat-ing and cooling projects may be appropriate to reduce operational energy for high density and high-rise developments. Existing structures can achieve energy savings when retrofitted and also benefit with upgraded appliances and systems. Upgrading heating, ventilation and air-conditioning (HVAC) systems is a short-term solution for reducing both GHG emissions and increasing energy efficiency as related to both residential and commercial struc-tures (Brown et al.).

When considering density, much can be done to decrease GHG emis-sions within existing communities. The largest changes that effect GHG emissions are those that reduce automotive transportation. It is necessary to specifically reduce the distances required to travel between work, home and basic services, specifically in suburban areas (Nor-man et al.). Effective changes might included encouraging urban infill and mixed-use developments. This would significantly reduce vehicular travel and encourage alternative modes of transportation by develop-ing pedestrian and bicycle paths in urban areas. Additionally, moving

high density developments closer to the major employment areas of a city will affect GHG emissions as vehicu-lar travel is reduced.

This information generates an under-standing of the differences between high and low density developments as related to known environmental impacts. However, it also poses a challenge to those that can inform how cities are developed. For the most part, these changes require transformations in local zoning policies (Brown et al.). The changes necessary to reduce GHG emis-sions and energy use in high and low density areas are, to a very large degree, possible.Glossary


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High Density: Also known as compact devel-opment. Factors used to asses high density are: apartment dwellings, considered to be 20 living units per acre, greater than 12,500 persons per square mile.

Low Density: Types of low density housing includes single family detached and single family attached dwellings. Housing typically found in a suburban development.. Factors used to asses low density are: 4 homes per acre, a density less than 1,500 persons per square mile

Mixed Use: A type of development that integrates a variety of businesses, services and housing.

Smart Growth: A form of urban planning where growth and transportation occur towards the center of a city. The aim is to avoid sprawl and the creation of a network of suburbs. Development tends to be of mixed-use and alternative forms of transportation (walking, bicycling, public transportation) are encouraged. ...

Notes

1: It appears that the authors are saying that any given livable space can house more or less occupants. When looking at the space per capita there is an opportunity to increase energy efficiency by increasing the number of occupants. However, when comparing solely the square footage of a living unit in a high density or a low density development, the energy use is the same....

Figures

Figure 01: Mapping Carbondale, Colorado, 2006, www.pedbikeimages.org/danburden.

Figure 02: “Anual GHG emissions associated with low- and high-density development”, Norman J., MacLean H. L., Kennedy C. A., 2006, “Comparing High and Low Residential Density: Life-Cycle Analysis of Energy Use and Greenhouse Gas Emissions” Journal of Urban Planning and Development Volume 132, Issue 1, pp. 10-21.

Figure 03: Transportation Emissions, “How Low-Carbon Can You Go: The Green Travel

Ranking, The Long Version”, Sightline Insti-tute, http://www.sightline.org/maps/charts/climate-CO2byMode.

Figure 04: “Map of a Compact Community: Walkability within One Mile. Where you can go: Seattle’s Phinney Ridge neighborhood and Bellevue, WA’s Eastgate neighborhood.”, Sightline Institute, http://www.sightline.org/maps/maps/Sprawl-SuburbWalk-CS06m.

Figure 05: “Avg. Daily VMT per Capita”, Ewing R., Bartholomew K., Winkelman S., Walters J., Chen D.,2008, “Growing Cooler: The Evidence on Urban Development and Climate Change”, Urban land Institute.

Figure 06: “Anual energy use associated with low- and high-density development”, Norman J., MacLean H. L., Kennedy C. A., 2006, “Comparing High and Low Residential Density: Life-Cycle Analysis of Energy Use and Greenhouse Gas Emissions” Journal of Urban Planning and Development Volume 132, Issue 1, pp. 10-21.

Figure 07: “GHG Emissions from Direct Combustion and Electricy by End-Use Sec-tor”, Pew Center on Global Climate Change, Residential and Commercial Overview, http://www.pewclimate.org/technology/overview/res-comm....

References

Brown M. A., Southworth F., 2008, “Mitigating climate change through green buildings and smart growth” Environment and Planning A 40(3) 653 – 675.

Ewing R., Bartholomew K., Winkelman S., Walters J., Chen D., 2008, “Growing Cooler: The Evidence on Urban Development and Climate Change”, Urban land Institute.

Frank L. D., Pivo G., 1994, “Impacts of Mixed Use and Density on Utilization of Three Modes of Travel: Single-Occupant Vehicle, Transit, and Walking”, Transportation Research Re-cord, Issue Number 1466.

Norman J., MacLean H. L., Kennedy C. A., 2006, “Comparing High and Low Residential Density: Life-Cycle Analysis of Energy Use and Greenhouse Gas Emissions”, Journal of Urban Planning and Development Volume 132, Issue 1, pp. 10-21....

Furthur Reading

Golob T. F., Brownstone D., 2005, “The Impact of Residential Density on Vehicle Usage and Energy Consumption”, University of California Energy Institute, Policy and Economics, Paper EP-011...

density, carbon emissions, transportation and energy ......density, carbon emissions, transportation...

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