The Solar Radiant Heat System

A solar radiant heat system is a modern age adaptation of an ancient radiant floor heating methods that were used by the Romans in their public baths.

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What is solar radiant floor heating?

Where does the solar radiant floor heating system make sense?

Advantages and disadvantages of solar radiant floor systems

What is the incremental cost of a solar radiant floor heating system?

History and background on radiant floor systems

What is solar radiant heating

There are three ways heat can be transferred: convection, conduction and heat radiation. Let us concentrate on heat radiation. Heat can be regarded as an Electromagnetic wave in the infrared band and as such the heat energy is radiated away from a hot object and it is absorbed by a nearby thermal mass that can store it. Any radiant heating system needs to have a heat source (a boiler or heater), a close loop of water pipes carrying hot water (radiating the heat energy) and a thermal mass such as floor slabs or wall radiators. According to the US Department of Energy fact sheet, the amount of solar heat in the cold regions is not sufficient to heat up a residential home, however it can pre-heat the water before it enters the heater. The estimated saving in fuel (or electricity bills, according to the US Department of Energy can be anywhere between 10% and 90%. Practically, an existing radiant system can be upgraded to be supplemented by a solar hot water system that includes a solar thermal collector and an optional additional solar water tank that stores the pre-heated water. It is recommended to have a thicker than usual floor slab that will act as a big thermal mass that will store the heat. A 4 to 6 inches concrete slab will gradually store up enough heat to keep the house comfort during the winter.

Where does the solar radiant heating system make sense?

If the homestead (or house) is already equipped with a radiant floor heating system, adding a solar thermal collector and if necessary a solar hot water storage tank is a very cost effective proposition.
For new homes, if all options are still open, electrically operated heat pumps might be a better solution, however heat pumps (an air conditioner in its heat mode) need to have an outside air temperature exceeding 42 degrees F (6 degrees C), a condition that is not met during the winter months of the cold regions. A careful tradeoff between hot air convection systems and radiant water heating is required, I’d recommend to consult with one of the companies that build green houses and zero energy houses. Whatever heating system is employed, the house insulation must be in a perfect condition and best way is to have to long walls perpendicular to the South with large energy efficient windows facing South.

Advantages and disadvantages of solar radiant floor systems

One advantage of the solar radiant floor systems is that the heat comes from the floor and rise by convection to the ceiling. Most people feel good with a warm floor under their feet. The supplemented solar heat energy comes free of charge, the winter heating energy bills are going to be smaller with the solar system installed.
Old timers remember the copper tubing under the floor that leaked and got corroded and floor cracks and humps with the water going through temperature variations. It is claimed by the industry that this disadvantage of radiant floor heaters has disappeared in the wake of the PEX tubing, PEX is a cross-linked polyethylene. It is flexible, it can withstand many temperature cycles, it doesn’t corrode and co-exist nicely with the concrete slabs.

Thermal Mass

Thermal mass (or heat capacity) is the heat storage capacity of an object. The thermal mass is in a direct proportion to the object mass and to its specific heat capacity (its heat capacity per a unit of mass)The specific heat capacity of water is about twice as good as that of concrete and sandstone and about three times better than that of a brick wall.

What is the incremental cost of a solar radiant heating system?

The incremental cost of a solar radiant heating, that is the cost of the solar collectors, preferably evacuated tubes solar collectors and the solar hot water tank and additional plumbing, valves, thermostats and control are in the $5,000 range, including installation. It is wise to use the solar system for hot water heating. The solar components are low maintenance components and the life expectancy can extend to over 10 years. With the provisions of the federal and states energy tax credits, the investment will pay itself within the first 5 years.

History and background on radiant floor systems

Ancient Greek and Roman public baths, called Thermae (from Greek thermos, "hot") used primarily the under floor radiant heating. Well preserved remainders of Roman baths are strewn all over the Mediterranean and Europe in places where the Roman ruled. Two rooms in particular, the Tepidarium (similar to a modern dry sauna) and the Caldarium (hot water bath) used the under floor heating.

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