Solar Thermal Radiant Flooring

Solar thermal radiant floor heating is an old idea that has been made new again. Many years ago, both the Greeks and Romans heated the floors of baths with wood fires. The concept makes perfect sense - heat rises, after all. Today, solar energy is used to heat water that runs through piping in the flooring. Floors have a thermal mass, so they act as a sort of battery, storing heat for long periods of time.

The following information is adapted from the Energy Efficiency and Renewable Energy fact sheet put out by the US Department of Energy:

In many areas of the country, the amount of solar heat gain from solar thermal radiant flooring is not enough to heat a house by itself, but it can supplement a conventional furnace or boiler and reduce heating fuel consumption from 10 percent to as much as 90 percent.

Types of Solar Radiant Floor Heating

Solar heat collectors can be used with two types of radiant floor heating systems. Both systems use the sun to heat the fluid (air or a liquid) in the collectors. The thermal mass of the floor (the fact that it is 'solid' and 'deep') acts as both a storage battery and a heat sink. The latter function helps keep the room air from overheating.

Solar Radiant Air Floors

In solar radiant air floor systems the sun warms air from the collectors or a sunspace. Air passages might be made out of any of the following materials: plastic drain pipe, concrete block laid on its side, hollow-core concrete panels or layers of corrugated steel deck. In most cases, radiant air floors are not cost-effective because air does not retain much heat. Radiant air floors are used in some cases because they are relatively easy to install.

Solar Hydronic Radiant Floors

Hydronic radiant floor systems pump heated water from a storage tank through tubing laid in a pattern underneath the floor. An individual thermostat regulates the flow of heated water through a solenoid valve and manifold to each room in the house.

There are a number of ways you can use active solar collector systems with hydronic radiant floors.

Back-Up Heating Systems

On cloudy days, when the sun is not bright enough to heat the home by itself, a back-up heating system is necessary. Back-up heating may be one of several heat sources: a wood stove, gas or oil-fired burners, or electric heating elements in the boiler. A conventional domestic water heater may be sufficient as a backup heater.

Cost of Solar Radiant Floor Heating

Whole-house solar heating systems initially cost $14,000 or more. In contrast, a conventional heating system might cost $4,000 to $8,000 for the same size house. The cost of installation often depends on the availability of materials and labor costs. The cost also fluctuates depending on the size, type of house, and amount of solar fraction available.

Bibliography

"Design and Monitored Performance Review of a Solar Heated Home (in Minnesota) with Radiant Floor System," D. Thayer, M.J. Heinen, and M. Monesterio, pp. 327-332, Solar 2000 Conference Proceedings, American Solar Energy Society, 2000.
"Gimme Shelter," M. Klein, J. McKneight, R. Reser, D. Shantz, Home Power, (No. 46) pp. 37-42, April/May 1995.
"Gimme Shelter: Solar Hydronic Space Heating," M. Klein, J. McKneight, R. Reser, D. Shantz, Home Power, (No. 49) pp. 43-47, October/November 1995.
"Hybrid Solar System Supplies Radiant Heat," W. Johnson, Solar Engineering and Construction, (3:5) pp. 27-29, September/October 1984.
"Hydronic Heating on Renewable Energy," R. Hyatt, Home Power, (No. 79) pp. 36-42, October/November 2000.
"Hydronic Radiant Heat for Wood-Framed Floors," J. Siegenthaler, The Journal of Light Construction, (11:11) pp. 34-37, August 1993.
"Life Cycle of a 100% Solar House," Robert K. Multer, Solar Today, (8:3) pp. 27-29, May/June 1994.
"Premium Heating with Radiant Slabs," M. Friedlander, Solar Age, (11:4) pp. 66-71, April 1986.
"Radiant-Floor Heating: When It Does-And Doesn't-Make Sense," A. Wilson, Environmental Building News, (11:1) pp. 1, 9-14, January 2002.
"Radiant Slab Techniques," J. Siegenthaler, The Journal of Light Construction, (10:11) pp. 21-24, August 1992.
"Solar Energy and Radiant Floors," A. Wilson, New England Builder, (4:4) p. 15, January 1986.
"Solar Heat for My Maine Workshop," G. Marsden, Home Power, (No. 89) pp. 34-43, June/July 2002.
"A Solar Heated Greenhouse," R. Lane and C. Marken, Home Power, (No. 96) pp. 48-54, Aug/Sep 2003.
"Solar Shines Again," S. Spaulding, Radiant Living, (published by The Radiant Panel Association, see below) pp. 45-48 &50.
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