Building A Passive Refrigerator
The 8th grade physics class came to our site to build a small passive refrigerator. Since throughput (refer to articles on throughput) is front and center on any of the projects designed we wanted to access available free energy as much as possible thus in the winter months the refrigerator would use the cold air from the outside to keep our food cold. The students were all familiar with the basic idea on how the fridge operates; hot air rises and cold air sinks. What they needed was to have a fuller picture of the principles involved such as Newton’s law of gravity, density, and molecular energy in regards to temperature.
As the diagram demonstrates the refrigerator is simply a box with an insulated two inch plastic pipe (blue) that allows the cool air under the north side of the house to flow into the bottom of the box. Since cold air sinks, with only an incoming pipe the cold air will not flow into the refigerator. Another two inch pipe (red) enters the top of the box and leads to the outside through the roof. This pipe is not insulated and warms to the temperature that is inside the house. Since hot air rises the air in this pipe moves upward and pulls the cooler air from under the house and through the fridge.
The days began in the same way as previous educational blocks. We started with Bothmer exercises and then went over the academic portion of the lessons inside the house (refer to Waldorf School – Eighth Grade of 2014 – Building a Hot Water Solar Panel) followed by lunch . After lunch we develop practical skills while building the refrigerator.
The days began in the same way as previous educational blocks. We started with Bothmer exercises and then went over the academic portion of the lessons inside the house (refer to Waldorf School – Eighth Grade of 2014 – Building a Hot Water Solar Panel) followed by lunch . After lunch we develop practical skills while building the refrigerator.
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At the end of the week we moved inside to review what we did. For the summer months the refrigerator was to use excess electricity to power Peltier elements which make use of a bimetal in which a 12 volt DC current is passed creating a cold side and a hot side. These elements have no moving parts, last a long time, and are easy to install. There was a challenge in removing the heat from the hot side and the project needed further thought; perhaps it will become another project for another class. Since our house is powered by the sun and we have enough electricity to power a freezer, we will continue to freeze water and use the ice in the refrigerator in the summer months until the challenges can be solved.
A passive refrigerator addresses the “Law of Diminishing Returns”. (refer to The Law of Diminishing Returns). When an object such as a refrigerator wears out it can take more money and energy to fix it rather than to just obtain a new one. Right now our country is facing the reality of fixing our aging infrastructure such as our roads, bridges, water and sewage pipes, and the electrical grid. We are realizing that the costs of the resources to accomplish this are rising. Because most household furniture has no moving parts nor is it subjected to weather, we are all familiar with tables, chairs and chests of drawers that are very old. When furniture does need repair usually a local person can be found to fix the antique or perhaps it can be fixed by the owner. However, when a conventional refrigerator becomes old and needs repair there is a point when the choice to buy a new one makes more sense. This passive refrigerator, with no moving parts or refrigerant, is more like a piece of furniture that can keep food cold for decades and decades without the need for major repairs. It can be built and maintained locally and blend in with the kitchen cabinets.