Einstein Science Reporting for Kids
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31-May-2007

Contact: M.B. Reilly
mary-bridget.reilly@uc.edu
513-556-1824
University of Cincinnati

International solar house competition helps students see the light

Forget the bad-boy image of those SUVs. It's buildings that really pump energy from the planet.

After all, in the U.S., commercial and residential buildings guzzle 65-percent of all electricity, 40-percent of all raw materials and even 12-percent of drinkable water. And heating oil prospects for homes don't look any more promising. In mid-May, weekly stocks of heating oil were off 20 percent from last year. That means supplies could remain low and home heating prices could be on the rise entering the winter-heating season.

In recognition of buildings' energy dependency, 20 select universities from around the world housing the globe's best business, design and engineering programs are engaged in a pioneering competition, each vying to innovate, design and build the best solar house possible. (The competition is called the Solar Decathlon.)

The University of Cincinnati with its internationally recognized programs in design along with its nationally known business and engineering programs is one of those 20 schools and has mobilized more than 200 students in its on-campus construction effort. When that house is complete in October, it will travel (along with the 19 other houses) to Washington D.C.'s National Mall where hundreds of thousands of visitors are expected to walk through it.

Among those leading UC's effort are faculty and students from the College of Business, College of Engineering and College of Design, Architecture, Art, and Planning.

Architect Anton Harfmann, associate dean in UC's College of Design, Architecture, Art, and Planning, explained, "Up till now, the great majority of construction has treated energy issues as an after-thought, an add on. What we're doing here is using available technology in new ways to integrate energy solutions into a home that is 100-percent solar powered and still meets people's needs."

That's precisely the aim of the international Solar Decathlon competition: To promote research and development related to alternative energy, specifically solar energy, in a home that must function as a residence and as a home-based business.

Thus, ALL the house's needs must ultimately derive from the sun: Fully functioning appliances, mechanics like air conditioning and heating; as well as a commuter vehicle. In addition, the house must be constructed and designed using sustainable materials.

Within its 800-square-foot house, UC innovations include

  • Roofing advances that include a slightly sloping, south-facing roof sheathed by a grid of 36 photovoltaic (PV) solar-collecting panels. These panels alone will produce more than enough energy to power the house, energy that can be stored for a cloudy day, sold back to the grid or used to power the electric commuter vehicle.

  • Unusual utilization of evacuated tubes to create thermal energy to cool and dehumidify the house. (In other words, hot water is actually used to provide chill air or air conditioning.) As a result of the system, the UC team expects to generate four or five times as much hot water as other teams, and this places less reliance on the roof's PV panels in case of cloudy weather.

  • A unique thermo-electric heat pump that could also be used as a back up to cool and dehumidify the house.

Each of these innovations is important. For instance, the arrangement of the PV panels by UC's students resolves a number of challenges currently posed by their use. Said Harfmann, "Right now, PV technology is generally embedded in existing roofs made of shingles. That means the life span of the roof and the life span of the panels are interlocked. You can't change out the PV panels without replacing the roof. That means the rapidly improving effectiveness of PV technology does a current homeowner using PV-integrated materials no good. Second, and just as importantly, the roof commonly overheats and that actually reduces the effectiveness of the PV cells."

The simple solution posed by UC's Solar Decathlon team consists of a small space of separation between the conventional PV panels and the insulated, waterproof roof. This allows for air flow between roof and panels and actually means that the PV panels serve to shade the roof.

"It's light, not heat, that causes the PV panels to operate at peak efficiency. So, this helps us make maximum use of light while reducing heat (by encouraging air flow between the roof and the PV panels)," stated Harfmann, adding that the system would allow a home owner to replace PV panels at any point as panels improve in terms of technology and efficiency. And those panels are "getting better and more efficient all the time," he said.

The design and creation of this structure and its systems is providing a "power-full" challenge to students, but one that is worth it, according to engineering student Andy Schroder. "I want to have cheap electricity," he said.

The actual design of the house is that of a contemporary loft-style home, including a kitchen, living area and dining area. A continuous expanse of windows extends all around the perimeter of the house just under the roofline (and thus, serves as the top portion of the wall). This uninterrupted (and wide) expanse of windows not only makes the house seem larger but also, obviously, makes for maximum use of natural light vs. electrically powered luminescence.

The house design also incorporates a shaded, outdoor deck that extends from the living area, making the space appear even larger. The modular form of the house would allow for ease of expansion if required for a growing family. Finally, the skeleton of the house is comprised of recycled steel columns and beams.

Other aspects of the UC solar house made possible by sponsors:

  • Highly energy-efficient windows and glass doors (to allow the sun in by day) wherein the incorporated blinds serve as night insulation.

  • Soy-based double insulation in the Formica-paneled walls that serves as a rain screen.

The students' work will be showcased on the National Mall in Washington D.C. from Oct. 12-20. There, each house will be judged on 10 criteria related to energy creation and conservation by means of innovative architecture, engineering, communications and hot-water creation.

Said UC architecture student Matt Mutchler, "The standards for the future could be created here."

Technical Topics

  • Roofing advances

One means for converting the sun rays into electricity for the house is the use of photovoltaic panels integrated into the home's roof. Ideally, these panels would be angled to provide maximum exposure and maximum numbers of panels on the roof's surface. However, UC's use of these panels is restricted because the house must travel to Washington D.C. (We can't have low-clearance bridges knocking off our photovoltaic panels!) So, we had to place our photovoltaic panels at a lower pitch on the roof, which means less energy production that is optimally possible from these panels.

  • Water collection

The collection of filtered rainwater for gardening, use in the above-mentioned heating/cooling systems and other non-potable needs is enabled by the dramatically sloping roof which funnels rainwater into a collection gutter and then into a storage unit.

  • Getting into hot water to chill the house

Evacuated tubes (containing solar-heated water) will be placed on an exterior wall of the house and used as a patio fence. The energy from the hot water will cool the house.

In an attempt to maximize energy pulled from the sun, the use of evacuated tubes ("tubes within tubes" in which the innermost tube contains water) is proposed. These 120 tubes are actually used to form a patio fence on the south side of the house. When the sun hits the tubes and heats the water on the inside (even while the tube exteriors remain cool to the touch), it will produce enough energy to air condition the house and to produce all the home's hot-water needs for washing, dishes, laundry, etc. The tubes' hot water is then moved through a heat-exchange system where it would vaporize lithium bromide gas. The gas then moves into another chamber where it would become a cool liquid under high pressure that serves as something of an "aerosol can" that, when released from high pressure, would be used to create cold air to cool the house as necessary. The "battery" for storing all of this thermal energy consists of two cisterns (holding a collective 600 gallons of water) placed beneath the foundation of the house.

  • Radiant heating

Some of the solar-produced hot water runs through tubing embedded under the floors. Thus, it creates heat that radiates throughout the house.

  • A back-up heating/cooling system being developed (but not actually installed in the house)

A radiant panel system could be installed on the wall of a room or as a window unit. The temperature of the panel is controlled using thermoelectric (TE) modules sandwiched between two aluminum parallel plates. By applying DC voltage, thermal energy is absorbed from one plate surface and released to the other plate surface at the opposite side by the Peltier Effect. The direction of heat pumping in the system is fully reversible. Thus, the unit could be used to augment heat into a room in the winter or to augment chilling (air conditioning) of a room in summer.

The students are using 10 such pumps to create a water-to-water heat pump. The transfer of energy between the plates occurs as water is pumped along either side of the panels, heating the liquid up to about 140 degrees Fahrenheit (for household and personal use) or cooling the water to about 40 degrees Fahrenheit (for dehumidifying and chilling the air). The temperature of the water for household use is controlled by means of the velocity by which it passes along the series of plates. These thermoelectric heat pumps convert surplus electrical energy from the PV panels, and one of the devices can heat or cool up to 60 gallons of water per day.

  • Getting the air-flow right

Computer simulations have been conducted to optimally place duct outlets and radiant wall panels to provide the best possible airflow pattern within the house for maximum comfort. Initially a 2-D natural convection air-flow study, assuming Boussinesq approximation, was carried out with isothermal vertical walls and adiabatic top and bottom. This was then extended to 3-D natural convection models for square enclosures for both laminar and turbulent flows (k- model) for a range of Rayleigh numbers from 103 to 1012 and the results compared to previous publications (i.e. validation runs). Next, CFD (Computational Fluid Dynamics) simulations were carried out for the enclosure with typical building walls (U values) heat loss with a constant heat flux inlet source. The resulting temperature fields and velocity vectors, shown plotted in different planes, for the above sample cases are shown. Lastly a GAMBIT model for our specific UC solar house geometry design and duct arrangements has been developed and CFD runs are currently in progress for a range of environmental conditions.

  • The small touches

Everything within the house all furnishings and accessories is also sustainable right down to the low-flow shower head, the furniture and the cabinetry. For instance, the kitchen cabinets and counters will be constructed from "3 Form Eco-Resin," a translucent, sustainable material used to make surfaces. Chairs will be upholstered by recycling and reusing old sweaters.

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