Natural Home Show House 2009 | Tapping Into Mother Nature: Geothermal From the Ground Up
By Karen Adams
Workers drill three small geothermal “wells” on-site of the Natural Home Show House 2009 that reach a depth of 250 feet. A hose-like uni-coil is inserted down each hole of the three to form a loop, which will transport water down to either cool it or warm it as part of the geothermal system at the Adams’ house.
When building any house, including a green one, the vision usually is of what the house will look like when it is finished—you know, nice rock, pretty landscaping and stout chimney, but the Natural Home Show House 2009 project actually began underground via geothermal energy and will work its way up. That is to say we tapped into mother nature to help us using passive solar principles in combination with our geothermal unit. Our architect, Ben Adam, AIA, designed the house using a few simple strategies:
• Orient the house to face south to limit harsh western sunlight, capture solar and prevailing breezes for natural ventilation, and provide daylighting with windows on north and south faces.
• Minimize glazing on east and west exposures to reduce heat gain.
• Specify a “cool” roof that provides low heat absorption and has high reflectivity at the proper angle to maximize solar absorption for solar hot water heating and future photovoltaics.
• Use roof overhangs and structures over windows and shading where needed.
• Specify a super efficient insulation package, such as Optima, a loose fill fiberglass insulation for closed cavity applications.
• Use energy-efficient, low e-glass windows.
• Use landscaping to help with windbreaks.
The design captured these elements, and it makes a real difference when you send the plans over to the geothermal expert and he factors in all of this to determine how much air conditioning is required. His recommendation: 3 tons of air conditioning for 3,500 square feet. He said that he had another house, virtually the same size, that required 5 tons of air conditioning because the house wasn't designed with passive solar principles. The real kicker is the energy analysis; ours energy bills will be about $1,500 for 12 months. The other house? About $2,675 to heat and cool for 12 months.
So, what is geothermal and how does it work? Geothermal is a term that describes Geoexchange (ground source heating and cooling). Geoexchange is the process of using the renewable energy from the earth to heat and cool a building by means of heat transfer. There are several different methods, but for our house, three small yet deep (250-feet) wells were drilled to capture the earth’s stable temperature. A long, closed-loop uni-coil was inserted into each hole forming an eventual closed loop reverse return loop field.
To cool a home, the WaterFurnace geothermal system pulls heat from your home and either moves it back into the earth loop or goes to a make a deposit in your hot water tank. Then the cooled air is distributed via the duct system in the home. During the heating cycle, the WaterFurnace system uses the earth loop to extract heat from the ground. As the system pulls heat from the loop it distributes it through a conventional duct system as warm air. The same heat energy can also be used for a radiant floor system or domestic hot water heating. I’ve heard that this air feels very comfortable—just the right temperature and humidity—great for this 40 something’s skin!
The whole drilling process on-site took less than half of a day. The crew from Zavala Drilling said the ground was softer than they anticipated. Raul Zavala said the first 20 or so feet was hard rock but after that it was soft. In fact, talcum-like dirt came out as they drilled. The drilling cost about $5,000. If we made it work on a half-acre lot, most anyone can make it work.
We believe both the payback in terms of reduced energy bills and the fact that it is a quiet, clean, renewable source of energy will pay dividends for us and our children.