October 3, 2012 by benchapman4
In the summer of 2010, I had the opportunity to be part of the team that designed and built the first passive freezer that we’d ever heard of. The idea was simple, we create a well-insulated room and stack several thousand 2-liter bottles full of salt water along the walls. In the winter, we open hatches in the ceiling and everything freezes. At the end of the winter, we close the hatches and it stays at about 25°F for the whole year.
The team of students, led by physics teacher Tom Tailer ran some calculations to make sure the physics added up and calculated that we needed about 3000 bottles and about 18 inches of foam insulation on the walls and ceiling for good performance. We built the structure and insulated it using waste styrofoam, ground-up using a modified leaf shredder.
The passive freezer has no moving parts and only uses electricity to turn on the lights. It has 3 rooms that work like an airlock. When you enter, the first room is very small and is about the same temperature as the air outside. Continue through the second door and you are in the refrigerator room, which tends to be around 40°F. The third door leads to the freezer, the biggest room, which keeps itself at about 25°F.
The freezer is built on a community scale and would be perfect for a farm as well. Tom and Beth Tailer use it to freeze meat from the chickens and sheep that they raise. They’re also exploring freezer jams, kimchee, and other ways to prepare food for cold storage. Their neighbors use the cool entrance chamber to brew beer!
Vermont Public Radio Story (Audio only)
Here’s the transcript from a local news story about the freezer, filmed October 2010, after we built the structure, but while it was still being bottled and insulated.
“We are constructing eco freeze, which is a passive refrigerator freezer,” explained Elizabeth Tailer.
A community sized freezer which is completely sustainable on it’s own. They’re using thousands of soda bottles filled with a salt-water mixture and ground up Styrofoam to insulate the structure which optimizes heat loss and updating an ancient idea. “We put 200 grams of salt in it which in a 2 liter bottle will produce a 10 percent by weight salt solution,” Tailer said.
“Ancestors would use an ice house to keep their produce cold throughout the whole year however we don’t have an ice house here. We don’t have a lake that freezes all year so we decided to utilize recyclables,” Elizabeth Tailer said.
“Instead of NIMBY, what people talk about — Not In My Backyard, it’s WIMBY – What’s In My Back Yard,” Tailer said.
The refrigerator-freezer system is built into the side of a hill so that when the earth freezes it will minimize heat loss. The freezer is in the basement of a building which will have multiple purposes from educational to drying foods. “The idea is to develop then educate around sustainable food, harvesting, storage and culinary delights,” Tailer said.
“So much of our resources are utilized keeping our food fresh and we wanted to do it without using any energy at all,” Elizabeth Tailer said.
The soda bottles are going to be stacked in a hexagonal pattern like that of honey bees to maximize space which they hope will keep the bottles frozen year round. “The beautiful thing with soda bottles is that the plastic can take 2-thousand pounds per square inch of pressure — there are very few things that can do that,” Tailer said.
But making this massive size of a freezer doesn’t come easy. The Tailer’s, plus countless others are working on filling thousands of water bottles with the salt and water mixture. “The purpose of the salt is to depress the freezing temp. If you store food at 0 degrees Celsius you’ll still get some bacterial growth. Commercial freezers try to get down to 0 degrees Fahrenheit. What we’re looking at is about a 20 degree freezer which will stop most bacterial growth,” Tailer said.
The structure was built in five short weeks last summer with the help of ten interns, and they hope it will be filled with all 3-thousand bottles before winter. “I think it’s going to open my heart even larger because what we want to do with it is spread it throughout the planet and not do it for making money but to take people off the grid and bring them back to their ancestral roots where we use our resources wisely and walk gently on the planet,” Elizabeth Tailer said.
“I wont be around to see it, but my hope is that in 100 years this will still be a functional system,” Tailer said.
Dawn Danby and Jeremy Fadouli on the Autodesk Sustainability Workshop team wrote about our freezer in their article in Develop 3D on whole systems thinking.
An even more radical refrigerator design harks back to the era of the root cellar. Olin College of Engineering undergraduate students Ben Chapman and Cory Dolphin worked with a family in Vermont to capture and store the cold of winter weather. They built a large walk-in refrigerator-freezer with roof vents that open to the outside cold in winter.
Thick insulated walls are lined with thousands of re-used 2-litre bottles, each filled with saltwater to freeze and store the cold. The saltwater freezes at a lower temperature than plain water, thus keeping the unit cooler in the summer. For communities with northern climates, this kind of passive technology can cut the environmental impacts of refrigeration to nearly zero.