Radiant floor heating

12 Nov 07 | Conservation, Environment, Geothermal, Solar Hot Water

Buildings use a lot of energy. Heating, cooling, hot water supply, lighting, and appliances can use lots of electricity, oil, gas, etc. Each BTU that is used requires that something be converted from fuel to energy and by products. The by products in question depend on the type of fuel, but they can be anything from CO₂ to NO_x, SO_x, and mercury to name but a few. As you can see, the more energy efficient our homes become, the less it will cost to energize them and the better off it will be for the environment.

I spoke with somebody on the phone this morning about solar space heating. This is a topic of conversation I had with my brother in law last year at some point. Basically, in this climate, effective solar space heating consists of passive solar design and or radiant floor heating.

Conventional hydronic heating equipment e.g., radiators and base board convectors, requires water temperatures above 140 degrees Fahrenheit (60 C). During the coldest months of the year, December and January, a flat plate collector would not be able to collect enough energy to heat the water to that temperature. Evacuated tube collector may be able to, but the volume of water would not be enough. Most HVAC professionals agree that solar coupled with a radiant floor heating system, where water temperatures only need to be about 85 degrees, works the best.

Radiant floor heating is a really cool idea. These systems work great when a house is built on a concrete slab. Several inches of rigid foam installation is used to insulate the concrete slab from the earth. The heating loops are embedded in the concrete slab and the entire system can be broken up into one room zones. The heating loops use low cost PEX (Cross-linked polyethylene) pipe, which is easy to work with. With a solar system, a small conventionally fired (oil or gas) furnace is required in case there are several days of cloudy weather that prevent the solar collectors from working.

Obviously this type of installation requires a great deal of pre-planing in order to work right. House siting, orientation, solar panel positioning, tilt angles, and heat storage tank options all need to be worked out before the house is built. A new house needs to be designed from the bottom up to accommodate solar radiant floor heating, passive solar design can also be incorporated to enhance the thermal design.

In addition to solar, radiant floor heating works will with ground source geothermal heat pumps. These systems can supply a good deal of heat to larger structures that may be too large to heat with solar collectors alone.

Retro-fitting older houses with radiant floor heating is also possible. Older homes with wood floors require a number of compromises to get the system to work efficiently. In addition to that, before a radiant heating system is installed in an older home, the structure should have a complete energy audit done. This will ensure that the building envelope is where it should be regarding insulation, weather stripping, windows, etc. It makes no real sense to install an energy efficient system if all that energy is going to go out the window anyway.

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