Effect of densification and compactness on urban building energy consumption: Case of a Transit-Oriented Development in Dallas, TX

Highlights

• A unique approach is proposed to quantify the impact of compactness and densification on urban energy consumption.

• It is illustrated and validated via a case study of a transit-oriented development, the Mockingbird Station in Dallas, TX.

• Urban building energy models are developed for base case (business-as-usual), compactness, and densification scenarios.

• The energy intensity per unit of area increased with compactness and densification while it decreased per unit of dwelling.

• The proposed approach successfully bridged the gap between the ‘macro’ urban planning and ‘micro’ building energy scales.

Abstract

Transit-Oriented Development (TOD) and energy-efficient buildings have gained significant attention in recent years as promising approaches for a sustainable urban future. However, research efforts that aim to assess both approaches and integrate them remain very scarce in the literature, leaving potential relationships or synergies between the two approaches underexplored. The goal of this research is to evaluate the impact of two sustainable urban planning principles of TODs, namely compactness sand densification, on the energy performance of the urban built environment. Using Urban Building Energy Modeling (UBEM), an analysis of the Mockingbird Station in Dallas, TX, shows that compactness and densification lead to unexpected increases in the energy intensity of the built environment.

Introduction

Cities today, owing to the rapid urbanization and population increase, are grappling with several urban issues such as pollution, congestion, personal health, and safety. Sustainable urban development is seen as a possible solution to mitigate these adverse effects on the overall livability of the urban area. Good urban mobility, moderate to high density and diversity of land uses, energy conservation, quality of life, and air quality are some of the characteristics of sustainable urban development. In particular, Transit-Oriented Development (TOD) has gained interest over the last two decades as a model of sustainable development to mitigate urban sprawl. A TOD is a mixed-use urban environment that is medium to highly dense, compact, mixed-use, multi-modal, walkable, and typically centered around public transit (Calthorpe, 2004; Calthorpe, 1993).

In parallel to sustainable urban development approaches, there is increasing pressure and need to increase the efficiency of the built environment (Azar & Menassa, 2014). It is estimated that buildings and construction account for more than 35 % of the global energy demand (UN Environment Report, 2017). As a result, governments are setting energy efficiency targets to improve the efficiency of their building sector. One such example is the case of the European Union, which has set a target of 20 % energy efficiency improvement by 2020 through the Energy Efficiency Directive (Directive 2012/27/EU of the European Parliament and of the Council, 2019), while New York City (NYC) aims at reducing their building energy consumption as a step towards climate change action (Hsu, Meng, Han, & Suh, 2019).

Both TOD and energy-efficient buildings have gained significant attention in recent years as part of possibilities for charting a more sustainable urban future. However, despite the increasing number of studies on both approaches, most research efforts remain segregated, rarely integrating them to identify potential relationships or synergies between the two approaches. A lack of research investigating energy consumption in buildings in an urban setting using a broader and data-driven approach has been highlighted by recent studies (Hsu et al., 2019; Hamilton et al., 2013). Conversely, TODs are often proposed as a viable and sustainable planning solution that can mitigate the impact of sprawled urban development through dense and compact development. While most studies have assessed the impacts of TOD-type development to have a positive impact, recent studies have reported negative impacts with an increase in urban heat index (Kamruzzaman et al., 2018). Also, there is a particular lack of quantitative research on how the morphology of sustainable urban planning approaches, such as TOD, impacts the energy performance of the urban built environment. This can be in part attributed to the lack of detailed energy models that predict the performance of groups of buildings at the urban scale, as opposed to the abundance of models that study individual buildings’ performance. As a result, it is challenging to numerically and objectively assess how energy-efficient a sustainably-built urban environment truly is.

The goal of this paper is to propose an Urban Building Energy Modeling (UBEM) framework to quantify the effect of urban densification and compactness on building energy performance at an urban scale. While any urban development can be assessed using the methodology proposed in the study, to our knowledge, this study is the first that applies UBEM to investigate whether TODs are likely to reduce or increase energy efficiency.

As detailed in the upcoming section, the proposed methodology consists of (1) developing an UBEM of the buildings in an existing transit station, namely the Mockingbird rail station in Dallas, TX, (2) simulating alternative scenarios of sustainable best planning practices such as urban compactness and densification, and (3) quantifying the impact of such changes on the energy performance of the urban building stock.

This study does not examine the effect or efficiency of the development (e.g., access to transit options and walkability) nor the attributes that make an urban environment a TOD; these have been investigated by several studies in the last decade (Cervero, 2006; Maghelal, Natesan, Naderi, & Kweon, 2011). Instead, the focus is on the less evaluated premise of a TOD to be energy efficient. Beyond the findings of the case study, there are two important contributions of the proposed method, starting with its ability to bridge the gap between the ‘macro’ urban planning scale on the one hand and the ‘micro’ building energy scale, on the other. Such an integrated approach is essential to provide a holistic assessment of the sustainability of TOD. Another significant contribution is the generalizability of the UBEM approach, which can be applied to any urban development worldwide. The approach is particularly valuable when there is a scarcity of actual energy performance data on the studied building stock, which makes “bottom-up” modeling approaches (as proposed in this study) advantageous compared to “top-down” statistical approaches.