Friday, October 23, 2009

It's Getting Cold Outside...But Not Below the Frost Line

The San Juan Channel House employs a geothermal system connected to a hydronic radiant floor heat, which sounds intimidating, but is a great way to reduce fossil fuel usage by relying on a renewable energy source: the ground.

The installation of geothermal heat for the SJCH includes a trench 5' deep, 65' long, and 15' wide (the frost line on the island is 12"). Three layers of coils are laid on top of each other in the trench, with 2' between each coil. All feed into a main line. The water is kept at a fairly constant temperature, about 54 to 56 degrees. Less energy is then required to get the water to a suitable temperature for heating in the hydro
nic system. The system is zoned for different areas of the house.

Hydronic floor heat pipes before the slab pour

One of the great advantages of hydronic floor heat from an energy use stand point is that is constant and cannot be quickly adjusted, therefore, when someone is cold they can bundle up instead of just cranking the thermostat. This leads to lifelong habits of adjusting yourself to the climate as opposed to having the climate adjust to you. Radiant floor heat allows for a constant temperature between the zone 1' below the ceiling and 1' above the floor.

The up-front cost is about $5,000 more than a traditional forced air system (using the trenching system outlined above, going deeper adds to the cost), but should pay for itself in 5-10 years, depending on local energy costs. Some of this up-front cost is made up for in the lack of duct work, including the improved air quality and ease of not accommodating duct work in the framing.

The geothermal heat is augmented by additional energy saving moves. The wood-burning fireplace is by Bodart & Gonay, a Belgian brand, and has an 88% efficiency rating. The fireplace is connected to a fan vent feeding outlets to the master bedroom above, allowing heat from the fireplace to naturally rise and heat the second floor as well as the first floor living area.

One disadvantage of the geothermal system is that the heat pump loses efficiency when the temperature dips below 25 degrees, which is very uncommon for our region. When this happens, or whenever the temperature drops suddenly, the residents use the wood fireplace. The wood stove heats the entire house with less wood and lost heat than a traditional open fireplace.

The geothermal heat system for the San Juan Channel house is also discussed in Seattle Magazine
and At Home Magazine.

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