ASHRAE Journal - August 2014 - 63

2014 ASHRAE TEcHnology AwARd cASE STudiES
nology

Above The living room entry has an abun-

dance of natural lighting and dark tile to
absorb the solar radiation.

Left The mechanical system is piped with

PEX tubing. To minimize pressure losses, the
tubing was installed with long sweeping bends
instead of abrupt square fittings giving it the
"tangled spaghetti" appearance.

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 singlefamily 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.
Due to the continuous and even heat flow of the large
mass floor system, the floor temperature is typically in
the 72°F to 77°F (22°C to 25°C) range, requiring a supply water temperature in the 77°F to 86°F (25°C to 30°C)
range for heating. This supply temperature is ideal for
heat pumps, especially geothermally coupled systems.
The radiant heating system is driven from a two-speed, 5
ton (17.8 kW) water-to-water heat pump (operating only
as a 2.5 ton [8.9 kW] unit) connected to five 200 ft (61 m)
deep closed loop geothermal wells as the heat source.
This water-to-water geothermally coupled system is
approximately 40% more efficient than traditional residential water-to-air geothermally coupled systems that
Au g ust 2014

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