©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 8, August 2014.
By Darren Dageforde, P.E., Member ASHRAE
About the Author
Darren Dageforde is director of utilities and energy engineering at University of Nebraska Medical Center in Omaha, Neb.
In the rolling hills near Omaha, Neb., a new house demonstrates how to reset the bar in residential energy efficiency. This unassuming home operates at an annual energy use intensity of 13.2 kBtu/ft2 (0.046 kWh/m2), not including the effect of site-generated electricity. Contrary to conventional wisdom that higher efficiency costs more money, this home was actually constructed at a cost 16% less than an average custom-built home of comparable size in the area as predicted by nationally accepted cost estimating guides. This estimate and costs includes appropriate corrections for self-performed work as well as site-generation electrical equipment.
The actual cost of the energy to cool this home for the entire summer of 2012, the hottest summer on record in Nebraska, was $3.72. This performance is a reduction of more than 95% from an average regional house, not including the energy benefit of site-generated energy. The summer of 2013 produced results that were 3% better than the previous year.
Technologies proven in the industrial, institutional, and commercial sectors have been brought together to take residential energy efficiency to a new level. In the 30 years of the award program, this is the only single-family residence ever awarded a First Place ASHRAE Technology Award.
A husband/wife team acting as the owner, designer, general contractor, mechanical subcontractor, and accountant ensured that every major detail was installed and constructed as the design intended. This singular authority made decision-making and quality accountability clear and concise while allowing the house to be built by traditional residential subcontractors using standard commercial materials.
The vision of the project was simple: create an extremely energy-efficient home with minimal maintenance and low utility costs at a reasonable budget. It had to look, feel, and function like a traditional residential home.
The goal was net zero; however, unreasonable financial commitments simply to achieve this goal needed to be avoided. The resulting design was an “A/C-less” (no traditional air-based furnace/cooling system), raised ranch home design. The basic home is a 36 ft × 60 ft (11 m × 18.3 m) rectangular floorplate, with 9 ft (2.7 m) ceiling height and a full walkout basement. Half of the basement is semi-finished living space and half is a four-stall (small standard car) garage and work area. Thirteen standard fiberglass frame, U = 0.29 Btu/ft2·°F·h (1.64 W/K·m2) low-E glass windows comprise 11% of the exposed wall area.
The skeleton of the structure consists of insulated concrete form walls (R-22, code minimum = R-19), flat ceilings (R-48 attic insulation, code minimum = R-39) with a standard wood truss rafter system. This construction is extremely tight with minimal air infiltration. The upper floor is a pan and joist reinforced concrete monolithic pour insulated concrete form system (R-26) comprised of a 4 in. (100 mm) slab, with radiant tubing, over 6 in. wide × 10 in. (150 mm × 250 mm) deep joists, 24 in. (610 mm) center to center. The basement floor is a 4 in. (100 mm) concrete slab on grade with radiant tubing over R-10 insulation. Installed on the south-facing roof is a total of 4.1 kW of photovoltaic panels.
Environmental conditioning is provided by hydronic radiant heated and cooled floor slabs. The radiant system uses the large mass of the insulated concrete flooring deck system (>110,000 lbs [50,000 kg] of concrete for the upper floor) to store and continuously distribute thermal energy to the occupied environment. The floor is topped with ceramic tile instead of traditional carpet to reduce any insulating effects of the flooring, minimizing the required temperature differential between the floor and the living environment.
Read the Full Article
Return to Featured Article Excerpts