Hartley Nature Center
3001 Woodland Ave, Duluth, MN 56207
We were able to integrate a number of sustainable design features, including: renewable energy, energy conservation, use of recycled and non-toxic materials, and construction using Forest Stewardship Council certified wood.
Hartley has the capability to produce up to 13.1 kilowatts of electricity on a sunny summer day.. We have two solar arrays, one stationary mounted on our roof and a tracking system next to the parking lot. The panels are manufactured by RWE-Schott Solar, and are rated at 165 watts each. Our system is grid-tied, meaning that when we produce more electricity than we are using it flows back into the electrical grid and we are credited for it on our bill. The power that is produced by the panels is Direct Current, so it has to be converted to Alternating Current before it can be used. We have six Sunny Boy inverters that convert it to AC and also keep track of our power production.
The earth beneath us is a giant heat sink, absorbing and storing energy from the sun all summer long. That latent heat along with heat generated by the earth's core is then very slowly released throughout the winter months. As a result, the temperature of the soil ten feet below the surface stays at a fairly constant 50 degrees all year long. That heat can be extracted and used to help heat a building. Here is how we do it.
An anti-freeze type fluid flowing through one mile of coiled plastic tubing buried eight to ten feet under our butterfly garden in front of the building collects that heat and transports it inside. The heat pump compresses the liquid to extract the heat and then a heat exchanger transfers it to a fluid flowing through more plastic coils set into our concrete floors. Our system utlizes an Econar Energy Systems Geosource 2000 heat pump. The end result? Toasty warm floors and much lower heating costs.