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Insulating a radiant slab (C) Daniel FriedmanSlate Thermal Mass for Heat Storage - Design Details for Passive Solar Heating Systems

Thermal mass effects of slate:

This article discusses the properties of slate as a medium for thermal mass in passive solar heating system design and greenhouse or sunspace thermal mass material.

Our page top photograph shows a ceramic tile floor installed in Buenos Aires, Argentina. 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.

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Active Solar Heat Storage Using Rock Bed Storage Systems

Photos of red slate roofing material in good condition

[Click to enlarge any image]

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

Thermal Properties of Slate for Solar Heat Storage and Radiant Heated Solar Floors

Question: how to install slate for use as thermal mass for sunspace or greenhouse passive solar heat storage

A client of mine has a unique storage material to use in his solarium - 30 one-inch thick slate pool table tops.

Will the thermal expansion and contraction affect the thermal bond to the concrete slab below?

Should we buffer the joints between the slabs of slate to prevent damage to the edges? - Tom Deal, alternative energy consultant, San Francisco CA

Answer:

Slate's coefficient of expansion is 0.0000058, meaning that for every foot of length slate will expand 0.0000058 feet, or about 0.00007 inches for every degree Farenheit of temperature rise.

A 60 degF temperature rise will cause an 8-foot long slate slab to increase in length by 0.0336 inches - roughly 1/32 inch.

If the sunspace experiences wider swings in temperature, the expansion and contraction of the slate will of course be greater.

Kevin Callahan at the National Concrete Masonry Association recommended using Type M mortar, which has a higher compressive strength than mortar normally used for concrete blocks. He commented, though, that the mortar might not bond very well to the slate, which does not have a very porous surface.

Bedding the slate in mortar should, however, create a fine thermal bond.

Gray roofing slates © D Friedman at InspectApedia.com

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

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

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 by an expanded/updated online version of this article.

Readers should also

see BLOCKBED RADIANT FLOORS - SOLAR DESIGN for an alternative to block bed solar heat storage

For supporting heat storage design details

see FLOOR, CONCRETE SLAB CHOICES and PASSIVE SOLAR FLOOR TILES, PHASE CHANGE.

Also see PASSIVE SOLAR FLOOR TILES, PHASE CHANGE

And at FLOOR CHOICES OVER CONCRETE SLABS we illustrate a floor slab (with incomplete under-slab insulation) that provides thermal mass helping to stabilize temperatures in a cabin in torthern Minnesota.


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