Technical Topics Related to UC's Solar House Project

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

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-ε 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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