On-site wood production. A single crate can handily heat two large buildings (21k square feet) over three 20-degree days.
In Vermont 28% of our annual carbon emissions come from combusting fuel in our homes and businesses, primarily for heating and cooling. Clearly, heating the structures we live and work in is an energy-intensive task. In contrast to conventional approaches, Teal Farm is heating its buildings with clean renewable resources that expel minimal carbon and achieve an ideal heating goal: to run a perpetually-generating system on the sun's immense energy.
Integration is essential to our heating system and we take advantage of seasonally abundant renewables while incorporating wood as a perennially available resource. This approach, coupled with innovative storage, succeeds in accomplishing what no other farm in the northeast has done–heating with renewable energy and minimal combustion.
Our heating system is experimental and therefore best completed in phases. This gives us the opportunity to study and quantify the successes and pitfalls of our
design, making it more effective and relevant when it is applied elsewhere. As of winter 2008, Phase I includes:
- 300 square feet of solar thermal arrays
- 3 Tarm® boilers
- 6 super-insulated 600 gallon water tanks
- Radiant flooring throughout 30,000 sq ft of conditioned space
- 4 masonry heaters
- Solar greenhouse with passive vents into house
- Highly sophisticated control system
building envelopes (R-40,R-60) on all new construction
Radiant tubing runs through all barn and farmhouse floors in concrete or adobe. Their mass acts as a heat sink.
Abundant greenhouse heat enters house through passive vents on the second floor.
In Phase II (to be installed in 2009-2010) we will add the following:
- 600 square feet of solar thermal arrays
- Additional boilers and water storage tanks (if necessary)
- Heat pumps
When Phase II is finished, our goal of perpetual heat production at Teal Farm will be realized.
We are confident that other enterprises–farms, schools, businesses, colleges and universities–will benefit from the valuable lessons of our pioneering design, as heating becomes an increasing environmental and economic challenge.
By taking advantage of renewable resources close-at-hand and matching their availability with state-of-the art technology and storage mechanisms, the heating system at Teal Farm typifies the necessary elements of true green energy design.
Super-insulated water pipes feed into farmhouse from the Energy Barn with zero heating loss.
Solar thermal arrays
These function by capturing the sun's radiant energy via a set of evacuated heat pipes arranged in a solar collector array. Evacuation of the heat pipes results in decreased air pressure; similar to the way water boils at low temperature when air pressure is reduced, water inside the heat pipes boil and vaporizes well below 212°F, as low as 86°F. As the sun's heat causes the water to boil, vapor rises from the water in the pipes and transfers its heat to glycol, a liquid with excellent heat storage capacities. Glycol then circulates first through the domestic hot water storage tank and then to storage tanks reserved for radiant heating.
Near-complete combustion produces almost no particulate emissions, and uses astounding 85% of the wood's energy.
Tarm boilers can use multiple fuels but at Teal Farm we have chosen the most renewable fuel given our 1200 acres of forest–cordwood. Chosen for their near-complete combustion, Tarm boilers burn largely unprocessed wood at super high temperatures–1800°F–achieving efficiencies of 80-85% of the energy stored in the biomass. Boilers are fired one to three times a day, depending on demand and outside temperatures. After a boiler is fired, heat exchangers within the boilers heat water that is directed to immediate heating demands (in the energy barn and farmhouse) or to water tank storage if no present demand exists. This allows us to maximize the efficiency of each firing and to store any “excess” heat in the system for later use.
One daily firing of the 3 boilers (about a 3 x 4-foot stack of wood) currently heats the farmhouse, the energy barn, and provides domestic hot water during 20-degree winter days.
Insulated water tanks
Six 600 gallon super-insulated water tanks store large amounts of energy allowing us to take advantage of sunny days and accumulate sufficient reserves when there is little sun. A large tank of heated water is one of the best mediums in which to store energy; its slow release of heat over time rivals that of stone. Each storage tank contains two copper coil heat exchangers that are fed by solar hot water panels, heat pumps, or wood-fired boilers (see below). No matter which renewable energy source is used, the tanks' water medium and super-insulated nature ensures minimal loss of temperature over time–less than 0.3°F per day.
Copper heat-exhange coils inside the insulated water tanks.
Web controls for heating system
Heat pumps, which will be installed during Phase II, will be used during the winter months, from October to March, when the outdoor air temperature is above 25º F and when there is available electricity. Heat pumps work by drawing energy from 50ºF spring water via a 2,500 gallon tank; heat is extracted via electricity and sent to hot water storage tanks. This supplementary system works when Teal Farm has abundant electricity and the outside temperatures are not very cold, i.e., during the fall and spring shoulder seasons.
Four masonry heaters provide supplementary heat during the winter months. The stone and brick mass captures the heat from a single firing and radiates a soft warmth over 24-hours at near constant temperatures. The flue system in a masonry heater extends throughout the stone mass, expanding the surface area across which heat can be absorbed and radiated into the room. The heater in the farmhouse's main room also incorporates a natural convection loop that supplies hot water to a bathtub on the
Main heating loop circulates solar and wood-heated water through Energy Barn and to farmhouse.