The Project
Development of a single family residence on an in-fill lot in an urban area of Seattle. In order to design it in the most sustainable manner, a primary objective is to reduce the amount of energy this home will consume every day of every year for its expected lifetime of 50-100 years or more. The team is targeting an 80% reduction of energy use compared to current averages. To achieve this goal a number of factors must be considered prior to design: occupant needs; local climate; and local renewable resources. Only in that context can the building’s energy systems be appropriately designed.
Sustainable Energy Use
What quantity of energy consumption would be sustainable? US consumption rates are embarrassingly the highest in the world by any measure: five times global per capita, ten times the Chinese, and twenty times the Indian average consumption rates.[i] Residential buildings in the US are responsible for 1.2 Billion metric tons of CO2 emissions.[ii] Over the past 50 years in the US, home size per occupant has nearly tripled along with our energy consumption.
As a result, we find ourselves in a position where current consumption levels cannot be met without severely impacting future environmental conditions, namely climate change (among other negative impacts). Forecasting the current 1.9% annual CO2 output rate increases in to the future leads to what the UN International Panel on Climate Change (IPCC), the EU, and numerous scientific organizations around the globe believe will be uncontrollable and catastrophic climate change, unless we take dramatic action now. These reports represent current scientific consensus.
2030 Challenge
The thrust of the 2030 Challenge[iii] is to meaningfully reduce the carbon footprint of the built environment over the next 20 years such that all new building stock and rehab work is done to increasing levels of energy efficiency, eventually resulting in a zero energy standard. It is a high bar to be sure, but it is possible. The current 2030 Challenge requirement for new building stock is to reduce energy consumption by 50% relative to average consumption for that building type. That percentage ratchets up every five years until 2030 when zero energy is the requirement, adjusting to the 60% level in 2010.
Energy reduction target
One of the project team members has recently completed construction of a home that exceeds the 60% threshold, so the team decided to push that level up significantly while remaining realistic in the context of the market environment, and the methodology of incremental yet meaningful increases in energy performance. We selected an 80% reduction, which per the 2030 Challenge, equates to 7.7 KBtu/Sq. Ft./Yr[iv], and is required in 2020.
Methodology
How do we achieve an 80% reduction on a speculative housing product, selling into the general buying population, which is largely uneducated on this topic? By employing an integrated design process to engage the right resources early enough to optimize the project, our costs can stay reasonable by “tunneling through the cost barrier.” The problem with that concept in residential applications versus commercial is that productivity is not measurable in residential, and home owners are less sophisticated than company CFOs who have the resources to analyze costs and future benefits. So we have to be especially sensitive to first costs, and effectively communicate future savings to potential owners.
Heating & Cooling
The structure is a 3-story single residence, 600 SF per floor for a total of roughly 1600 SF of living space with 200 SF of conditioned garage. Heating & cooling is the largest user of energy in the home. Assume a typical residential family unit of 2-4 persons for living, and some home office use. The location, East-West orientation and solar access are sufficient for moderate passive solar heat gain with the current existing structures to the south. However, modeling all future potential allowable density and development would yield almost no solar access in the winter months across most of the south façade except the roof, therefore this must be the design baseline. Using a simple energy model to calculate heat losses, SIPs are selected for wall (10.25”) and roof (12.25”) construction, and ICFs (6.75” EPS) for below grade first floor, and 4-inch rigid foam under the slab. Triple glazed windows will be necessary to meet energy goals. Air sealing to achieve approximately 1 ACH at 50 Pascals will ensure tight envelope performance and use of an Energy Recovery Ventilator with a very high efficiency rating (90%+) will ensure that energy is not wasted thru infiltration or mechanical exhaust. Heating load is reduced by 80%.
Hot Water
Hot water is the second largest energy use in the home, so the house will utilize vacuum tube solar hot water collectors on the roof at a 65 degree pitch to optimize winter production, but still produce 100% in summer months. Load reductions such as very low flow fixtures will reduce this demand further. Hot water heating is reduced by 80%.
Lighting
Lighting is next: The Energy Star Advanced Lighting Package will guide the lighting selection and beyond that, natural daylighting can be utilized in the space thru design strategies such as open floorplan, using fewer walls and doors. All exterior and some interior fixtures will employ occupancy or photo controls to eliminate unnecessary use. Lighting energy will be reduced by approximately 75-80%.
Everything else
For the remaining energy draws, “best in class” methodologies will inform product selection. For example, the Department of Energy publishes a list of every make and model of refrigerator available in the US and its precise consumption level[v]. Surprisingly, some models of almost every type of appliance can be as much as three times as efficient as the common models for only a marginal additional cost.
Offsetting Electric load
Ideally we can get to 80% without the use of PV solar electric generation. This is an important point for this project as PV generally is considered cost-prohibitive, particularly in spec development projects. The house will be pre-wired so that occupants can add PV more readily in the future, and the cost to pre-wire for PV is nominal.
Measuring up
To confirm the analysis, the building energy use must be modeled and then tested and measured to generate a HERS index (nationally acceptable rating system) and compare this result with the goal of 80% reduction. This step has not been done yet (this calculation requires inputting results from the blower door test at the end of construction). Until this step is completed the actual performance will not be known, merely estimated.
Costs
This house will incur additional costs relative to a code-built home of similar size. The window package, ERV, SIPs, lighting, and appliance upgrades will cost into the low 5 digits, but probably not much beyond an estimated $15-20,000 extra. For a house of average size and priced in and around the $400,000-$500,000, this is a premium of 3-5%. For the typical mortgage of say $400,000, monthly payments of $2900 are typical. With average home energy bills at $2000/year, an 80% reduction will net enough savings to cover the costs of those energy performance improvements. It is imperative to think long-term in order to realize these efficiencies. If developers continue to only focus on first costs, and buyers zero in on cost alone, we all lose. Understanding cost is the key to this becoming a reality.
Result
For roughly no net cost it should be feasible to build a home that puts us on a path to sustainable buildings, at least as it relates to energy consumption. The envelope is one part of the house that can’t easily be retrofitted after construction, and energy consumption takes place every day over the 50-100 year life of the structure, so its environmental impact is very large in that context, and must be taken as a primary objective. You can always add rain barrels, solar panels, and faucet aerators later on, but you can’t re-insulate the slab after you move in.
[i] Making Better Energy Choices, Worldwatch, www.worldwatch.org/node/808#1
[iii] 2030 Challenge, http://architecture2030.org/2030_challenge/index.html
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