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Interlock House

Solar Thermal Collection

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Adobe Flash Video: This video demonstrates how hot water collected from the Interlock House's array of evacuated tubes is used to provide domestic hot water, radiant floor heating, and power our liquid desiccant dehumidifier.

This presentation contains no sound.

While photovoltaics (i.e., solar panels) can convert sunlight into electricity, it it is also possible to collect heat from the sun and put it to work inside a home. Solar thermal collectors come in two types: flat plate and evacuated tubes.

To collect thermal energy, the Interlock House utilizes evacuated tube collectors. Evacuated tube systems work by passing water though a black pipe that is contained in a larger, vacuum-sealed glass tube. Sunlight passes through the glass tube and strikes the piping, thereby heating the water. While radiant heat from the sun can pass through a vacuum, conducted heat cannot. This means that upwards of 90 percent of the sunlight captured is converted to usable heat. Although more expensive than flat plate collectors, evacuated tubes are more efficient and produce water at much higher temperatures (above 170°F [77°C]). Because they are also much more efficient than photovoltaic panels, evacuated tubes have a much shorter period for return of investment—typically only three to five years.

The Interlock House features a bank of 60 Apricus evacuated tube thermal collectors. After running through a series of heat exchangers, the collected thermal energy is used to power our domestic hot water, radiant floor heating system, and liquid desiccant dehumidification system.

Radiant Floor Heating

During the winter, the Interlock House is heated using a three-zone radiant floor heating system. The hot water powering the system comes entirely from the evacuated tube array mounted on the roof of our house.

The radiant floor system we are using was manufactured by Warmboard. The highly efficient system routes hot water through tubing that rests in channels of aluminum. The thermal conductivity of aluminum ensures uniform heat distribution throughout each room. Moreover, while forced air systems do not move heat when they are not running, radiant systems continue to give off heat for a period of time after they have been shut off.

For more information on radiant heating in your house and the system we used in ours:

Cooling / Liquid Desiccant Dehumidifier

Download Adobe Flash

Adobe Flash is required to view the videos on this page. If you do not have Adobe Flash you can download a free copy from Adobe. If you already have Adobe Flash Player installed, you must also enable JavaScript.

Adobe Flash Video: This video demonstrates how the Interlock House's forced air conditioning system integrates with the liquid desiccant dehumidifier.

This presentation contains no sound.

Cooling in the Interlock House is provided by a highly efficient traditional air conditioning system. When running an air conditioning system, more than half of the energy expenditure is dedicated to removing moisture from the air before cooling it to the desired temperature. To reduce the amount of energy our air conditioner uses, incoming air is first passed over a student—designed, prototype liquid desiccant dehumidifier.

A desiccant is a substance that pulls moisture out of the air. For the prototype, we are using calcium chloride (common road salt). Incoming air is passed though a duct and runs over several metal plates. Above the plates is a reservoir that allows the liquid desiccant to slowly run downwards and pull moisture out of the passing air. At the bottom of the plates, a second reservoir collects the desiccant liquid so that a series of pumps can send it to a recharger. At the recharger, the liquid desiccant is heated by hot water from the evacuated tube array. Tthis causes the collected moisture to evaporate, and the evaporated moisture is vented outside the house.

Using the desiccant dehumidifier to reduce the total cooling load will result in significant energy savings.

Major sponsors Iowa State University U.S. Department of Energy Solar Decathlon U.S. Department of Energy National Renewable Energy Laboratory