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Minnesota Students Win ‘Race to Zero’ Title

Now in its second year, the design competition attracted teams from 33 U.S. and Canadian universities

Posted on Jun 1 2015 by Scott Gibson

A team of students from the University of Minnesota came up with the winning entry in this year's Race to Zero competition with a 2,544-square-foot two-story house designed to be affordable as well as energy-efficient.

The OptiMN Impact Home was designed specifically for infill lots in North Minneapolis and meets both the Department of Energy's Zero Energy Ready Home criteria and a program established by the city of Minneapolis called Green Homes North. The project was a collaboration between the university and Urban Homeworks, a neighborhood development program in Minneapolis.

According to the DOEUnited States Department of Energy., the aim of the competition, now in its second year, is to produce affordable, zero-energy homes that can be built by mainstream builders. The competition drew 33 teams from 27 different universities in Canada and the U.S., with winners announced last month at the National Renewable Energy Laboratory in Golden, Colorado.

DOE has posted a full list of entries and details about the houses at its website.

Housing for a hard-hit part of town

The university team targeted a vacant lot in a section of North Minneapolis that was struck by tornados in 2011 and also affected by the foreclosure crisis a few years earlier, according to a fact sheet distributed by the team. There are many vacant lots in the area where Green Homes North plans to build 100 energy-efficient homes.

The house is designed for a 40-foot-wide lot with its long axis aligned east-to-west, to make the most of solar gain. With most Minneapolis house lots running east-to-west, the team said, the design would be well suited to the area.

Among the features of the winning design are Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. appliances and windows, WaterSenseProgram developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures. low-flow plumbing fixtures, rainwater storage, LED lights, photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. panels, low-VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production. paints and finishes, and concrete made with fly ashFine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Flyash is employed as a substitute for some of the portland cement used in the making of concrete, producing a denser, stronger, and slower-setting material while eliminating a portion of the energy-intensive cement required. More info.

The total finished floor area is 1,696 square feet with another 848 square feet in a lower level that also could be finished. The design includes three bedrooms and 1 1/2 bathroom (plus another in the lower level).

Some of the details:

  • Foundation: The slab and footings are insulated to R-10, foundation walls to R-15. Moisture control comes with capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. breaks, a waterproof membrane, perimeter drainage, and a sealed sump.
  • Exterior walls: The 2x4 stud walls are sheathed with Zip System sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , insulated between the studs with fiberglass batts, and insulated on the outside with 3 inches of extruded polystyrene insulation, for a total R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of R-32.
  • Windows: Double-pane, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. units with a U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of 0.27 and a solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.20.
  • Roof: Vented truss construction with a clerestory; insulated to R-53 with a combination of rigid polyisocyanurate and fiberglass batts.
  • Mechanicals: For combined space and water heating, a Polaris condensing water heater plus a SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. 14 air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.. Heating and cooling distribution via forced-air ductwork.
  • Whole-house ventilation: Venmar energy-recovery ventilator(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV..
  • Photovoltaic system: Twenty 410-watt PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. panels for a total rated capacity of 8.2 kW, with an estimated annual output of 10,337 kWh. With PV, the house has a HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. score of 0.

Students estimated that the house would cost $226,797 to build, well within reach for a family of four with a median income of about $64,000.

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  1. DOE

Jun 2, 2015 10:45 AM ET

Well done. XPS?
by Charlie Sullivan

This is a nice design. It's great that this competition aims for cost effectiveness and good design as well as energy efficiency, and it seems like a good design that balances the different objectives well.

It's a little ironic that this design, using XPS, appears on the same day as an article telling us about how the XPS industry is dragging their feet, opposing efforts to reduce the global warming impact of their product. It's unfortunate that the design criteria for the competition were not broad enough to require considering that impact.

I'm also curious about the choice of low SHGC windows. Was that really the best choice for this climate, or was it driven by the fact that the low-cost window manufacturer chosen doesn't offer a high SHGC option?

Congratulations to the students. The building industry will be improved as people like them go into the field.

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