Active solar heating system design options:

This article discusses the design specifications for rock-bed heat storage systems and floor designs for heat storage and heat retrieval such as n radiant heated floor active solar applications.

We discuss design rules of thumb for rock-bed floor airflow, air inlets and air outlets.

Active Solar Heat Storage Using Rock Bed Storage Systems

Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Our page top photograph shows a ceramic tile floor installed in Buenos Aires. Using ceramic tile finish flooring over a rock bed heat storage system is one method of design for a solar-heated radiant heat floor system.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Rock-bed or Stone-Bed Design for Solar Heat Storage and Radiant Heated Solar Floors

Question: Where can I find information on rock-bed or stone-bed heat storage system design?

I'm curious about rock-bed heat storage systems such as those used with active or even passive solar heating systems for homes. Have any tests been done to determine the optimum size of the rocks (or stones) for these heat storage systems? How can I assure good circulation of the air through the heat-storing stone?

Where can I find information on rock-bed heat storage design? - Kenneth Leifheit, Batavia IL

Answer: rock sizes, rock size consistency, air inlet and outlet specifications for rock bed heat storage systems:

Proper rock sizes and rock size consistency for heat storage systems

Rocks used in a rock-bed heat storage system can be anywhere from 1/2 to 6-inches in diameter. The standard stone size seem sto be 3/4" to 1 1/2" in size.

It is not a good idea to mix widely divergent rock sizes. The largest rocks (or stones) should be no more than twice the smallest rocks. Holding to this rule may require some screening after the rocks are delivered.

Relationship of rock or stone size to heat storage system operation

Large rocks in a heat storage system heat up slowly and cool off slowly.

Small rocks both heat up and cool off more rapidly.

Air resistance and rock size in heat storage systems

The smaller the rocks in your heat storage system design, the greater will be the resistance to the flow of air, meaning that a larger, more powerful fan is required unless the air path is very short.

Air inlets and outlets design for rock-bed heat storage systems

Air inlets and outlets for a stone-bed heat storage system must be designed to channel the air so that it wends its way through the rocks. This can be done by placing the air inlet to the rock bed heat storage system higher than the air outlet, forcing the warm air to "drop".

Alternatively you can build vertical baffles within the rock bed.

Avoid Air Flow Short Circuits in Rock Bed Heat Storage Systems

A sand-covered sheet of polyethylene plastic on top of the rocks will prevent an air gap from forming should any rock settling occur. This detail is important because an air gap over the rocks will "short circuit" the airflow that should be moving through the rock-bed and thus reduce its ability to both store and return heat to the building.

For an alternative design approach to storing heat in solar heating designs
see BLOCKBED RADIANT FLOORS - SOLAR DESIGN, and

for solar designs that combine greenhouse solar heat gain and trombe wall designs
see GREENHOUSE DESIGN for SOLAR HEATING.

For more on radiant slab floors see "Radiant Floors", Solar Age 5/82, and the following articles online:

RADIANT HEAT
RADIANT HEAT FLOOR MISTAKES
RADIANT HEAT TEMPERATURES
RADIANT SLAB FLOORING CHOICES
RADIANT SLAB TUBING & FLUID CHOICES

Other articles you'll want to see on passive solar floors, ceilings, and walls, include

• FLOOR, CONCRETE SLAB CHOICES
• SLAB INSULATION, RADIANT / PASSIVE SOLAR
• THERMAL MASS in BUILDINGS
• PASSIVE SOLAR PERFORMANCE PROBE - a case study of a home using a rockbed storage system

The question-and-answer article above, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

The link to the original Q&A article in PDF form immediately below is preceded (above) by an expanded/updated online version of this article.

• Q&A on Rock-bed Floor Design Specifications for Heat Storage- PDF version, use your browser's back button to return to this page. Original article, Solar Age Magazine, November, 1985, adapted and updated for InspectAPedia.com December 2010.

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Continue reading at SLATE THERMAL MASS for SOLAR HEAT STORAGE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BLOCKBED RADIANT FLOORS - SOLAR DESIGN for an alternative to block bed solar heat storage,
• FLOOR, CONCRETE SLAB CHOICES for supporting heat storage design details

Suggested citation for this web page

ROCK-BED SOLAR HEAT STORAGE DESIGN at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to SOLAR ENERGY

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Citations & References

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