in pursuit of energy efficient minimalism
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.
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.
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!
- CSD meets Passivhaus standard
- Passivhaus site EUI is about 12.5kBTU/ft²a on all-electric supply
- CSD homes are 2,720 ft² (based on the 2005 RECS detached single family average)
- Urban TOD is energySTAR/LEED rated (aka ‘green’)
Here are the numbers from the Rose/EPA study for site energy:
Household Energy: 108MBTU
CSD built to Passivhaus
Next, we convert the CSD to a Passivhaus…
12.5kBTU x 2,720 ft² = 34MBTU
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.
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