Suburban development can trump TOD on site energy…

There’s been an ongoing debate locally that density, specifically Transit Oriented Development (TOD), is always the ‘greener’ option. While we are definitely in favor of smart density and absolutely love the ‘feel’ of highly livable cities like Berlin, Copenhagen and Basel – we realize that will never be Seattle. That being said, Seattle’s downtown neighborhoods – including the I.D., Pioneer Square, Belltown, Capitol Hill, U-district, Queen Anne, Eastlake, South Lake Union, Fremont, Wallingford and yes, even most of Roosevelt – are already as dense as much of Copenhagen (Seattle density map).

This is a good thing. What isn’t so hot are attempts to make up for the vastness of Seattle’s single family zoning (nearly 60% of the city by area) through significant upzoning of neighborhoods outside the urban core (like Roosevelt) to include disproportionate towers 120’ tall or greater. We’ve always felt height limits of 65’-85’ in urban villages allow for livable density and, if done properly, can make for great places. I realize we’ve got a long way to go on the ‘done properly’ bit – but some developers are doing great things.

foto: dan bertolet

To make matters worse, the density uber alles crowd likes to harp on how much more energy efficient urban TOD always is compared to the suburbs. While we’re all for legitimate claims and reasoning on why urban living is better than suburban, energy efficiency could be the least accurate comparison, and here is why.

source: EPA

The recent Jonathan Rose/EPA study looked at the EIA’s 2005 Household residential energy consumption survey (RECS). I believe this study to have two flaws. First, it only looked at site energy usage. Second, the TOD looked at individual units instead of overall building performance, thereby underestimating the actual unit average. With multifamily housing, a significant percentage (roughly 40% on several Northwest buildings, according to a recent ECOTOPE study) of actual energy usage is devoted to garage, exterior and corridor lighting, common area heating and ventilation, and laundry usage.

Taking into account the source factors of operational energy (and ideally, CO2 emissions – a better metric for which is ‘greener’), would have provided a more accurate snapshot of actual energy usage by building type/location. With the understanding that the study only looked at site energy usage, we definitely know it’s possible to have a Conventional Suburban Development (CSD) without renewables that can actually be more energy efficient than an urban, ‘green’ TOD… Ready, steady, go!

Assumptions:

  1. CSD meets Passivhaus standard
  2. Passivhaus site EUI is about 12.5kBTU/ft²a on all-electric supply
  3. CSD homes are 2,720 ft² (based on the 2005 RECS detached single family average)
  4. Urban TOD is energySTAR/LEED rated (aka ‘green’)

Here are the numbers from the Rose/EPA study for site energy:

Typical CSD
Household Energy: 108MBTU

CSD built to Passivhaus
Next, we convert the CSD to a Passivhaus…

12.5kBTU x 2,720 ft² = 34MBTU

Green TOD:
Household Energy: 44MBTU

Green TOD w/ 40% common area usage:
Household Energy: 44MBTU + 29.3MBTU = 73.3MBTU

In actuality, achieving Passivhaus for any development is the game changer, and utilization of grid-tied renewables and electric vehicles even more so. Claims that urban TOD is always more energy efficient simply because it’s denser just isn’t necessarily true (especially if based on flawed studies) – though there are a number of beneficial reasons for urban development, including embodied energy of infrastructure, resource efficiency, etc.

  • http://www.markasaurus.com Mark Hogan

    It’s interesting to see the numbers you have run on this comparison because it’s a debate that seems to come up a lot. The one factor you haven’t included is transportation energy, and on that one item the increased car use that almost always accompanies suburban densities (even in cities) will probably negate any benefit derived from the increased efficiency of the buildings. The EPA included transportation energy use in the graphs but I didn’t see how this factored in your equations at the end. Additionally, I would guess that the EPA’s numbers for transport use in a TOD are actually more conservative that what could actually be achieved in a city like Seattle or San Francisco with decent public transportation since they are based on national TOD averages.

  • http://bruteforcecollaborative.com mike eliason

    Mark,

    Good point. I specifically didn’t look at transportation energy as it’s been building efficiency that TOD advocates of late have brought up. Completely agree that suburban transportation energy is far too high, but also is the place for largest potential improvement.

    This can be improved through two factors, electric vehicles – a passivhaus combined with electric vehicle(s) would use less total energy than the operational energy of a typical green TOD – and significant minimum MPG increases. One of the findings in the Swedish One Tonne Life experiment – that electric car usage for a house in suburban Stockholm was responsible for less CO2 emissions than busing. That’s not to say I think the ‘burbs are better, I just think claims for urbanity and density need to be accurate for stronger arguments.

  • Dan

    Nicely put. There was an attempt to do TOD in my town. It turned into how high can you go so the developer could maximize the profit and ultimately failed. During this exercise research showed that other TOD’s deliberately minimized parking spaces which later caused a lot of problems. The other issue for TOD is that you have to be sensitive to the existing neighborhoods and existing mass trans users.

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