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Concentration of CO2 in the Atmosphere

A Net-Zero Solar Challenge at Walden Pond

“I found myself in a schoolroom where I could not fail to see and hear things worth seeing and hearing.” Henry David Thoreau, speaking of being in nature.

Rendering of the Walden Pond Visitors’ Center. Photo courtesy of Maryann Thompson Architects

Rendering of the Walden Pond Visitors’ Center. Photo courtesy of Maryann Thompson Architects

By Emma Rumple

There was a time when people in this country were taught that air pollution was the “smell of progress,” and buying disposable products was beneficial because it meant more things would be made, creating more jobs. The message was still spread when I was a child, though some were already seeing through it.

A whole generation of us came alive when we discovered Henry David Thoreau’s Walden. It showed us that there was a path out of that morass, and we felt refreshed by its vision. It was our environmental guide, showing us a clear way to a better life and a better world, in which human beings once more integrated themselves with nature, to their own greater joy.

The Commonwealth of Massachusetts Department of Conservation and Recreation (DCR) administers Walden Pond State Reservation in memory of Thoreau and his simple, happy life in the woods. Walden is appreciated by hundreds of thousands of visitors each year. Now, the state is providing a new facility where they can learn about Thoreau’s intentional self-reliance.

We might be tempted to reflect on the incongruity in a picture of people arriving in cars to learn, under electric lights, in comfortably heated space, about Thoreau’s rustic life, lighted by his “japanned lamp” and heated by wood. But the picture comes to a wonderful resolution in the new Walden Pond Visitors’ Center. It provides an immediate view of the environment and is marvelously sustainable. Much to the point, it is engineered to be a net-positive energy producer, not only providing for its own lighting and heating, but supplying power to charge visitors’ electric vehicles while they park. There is even a reasonable hope that the center will have extra power to share with the town of Concord.

The historic nature of the site and care for the environment shaped the architect’s design response. The DCR asked that only trees necessary to accommodate the new building be removed with all others surrounding left standing. The 80-foot tall trees limit the potential for passive solar heating but provide welcome shade for the summer visitors reducing climate- conditioning energy use during the busiest season.

Maryann Thompson Architects, a Boston-area firm well known for sustainable design, kept year-round energy use at the visitors’ center to a minimum by applying Passive House building standards. Insulation is R-60 in the roof and R-30 in the walls. The large windows, which provide wonderful views of Walden Pond and its surroundings, are to be triple-glazed. Air sealing will be done with the greatest possible care. What climate-conditioning load remains will be satisfied by environmentally-friendly, high-efficiency air-source heat pumps. There will be no fossil fuels used on site.

The center’s siding is of locally harvested ash specially heat-treated to make it suitable for the purpose. DCR foresters carefully selected the ash trees from the woods surrounding the reservation, confirming them already dead before they were taken. Landscape architect Michael Van Valkenburgh provided gentle swales around the center to manage runoff and limit erosion in the vicinity of the pond.

The Walden Pond Visitors’ Center will be powered by a solar photovoltaic (PV) system designed by Solar Design Associates of Harvard, Massachusetts. Since the new building is surrounded by mature trees and thus not suitable for rooftop PVs, it was decided to field the solar as parking-lot canopies at an existing parking lot that already had good solar access.

Like the building, the parking lot canopy is unusual – very unlike a typical mall parking lot. Rows of cars on the edge of the lot are shaded by woods and there are eighteen feet of plated space between rows. The solar canopies were placed to span the median. The capacity of the overall system is 105 kilowatts, DC, and the expectation is that it will provide 120 megawatt-hours per year. The parking area will also feature four charging stations, each with hookups for two vehicles.

Another important project participant is the Town of Concord Municipal Light Plant. The MA DCR appreciates their cooperation in providing the proper service connection to connect the solar to the visitors’ center and the local utility distribution grid.

Given the great consideration for nature, we might think Thoreau would approve heartily.

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