Variable thermal cell array greenhouse envelope for energy-efficient food production

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It is widely accepted that the global food supply problem can be alleviated by building greenhouses on non-arable land near the communities where the food is needed. Traditional transparent greenhouse structures, however, are not practical in hot or cold climates, because the energy required to provide thermal control is prohibitive and it is economically unfeasible to electrically illuminate crops inside non-transparent insulated structures. To address this problem, we have developed a high-performance variable insulation system that can be switched from a daylight transparent window to a highly thermally insulated panel, making greenhouses practical in most climates and seasons. The high insulation characteristic of our system arises from our novel thermal cell array system, a construction of highly compressible gas-filled pockets contained within a stack of lightweight polymer film layers contained within a sealed window panel. In its expanded state, the thermal cell array has the same insulation value as a solid Styrofoam wall, and in its compressed state, the insulation material virtually disappears and the panels essentially act as a traditional transparent greenhouse wall. While the method of expanding and compressing the array can easily be done using a motor, this design also lends itself to a new form of electrostatic actuation, whereby the array can be compressed simply by applying a voltage to inexpensive, vacuum-deposited thin films, thus eliminating mechanical motor parts. In this project, we will demonstrate and quantify the performance of this system to manage the internal temperature of a greenhouse within a range that is desirable for plant growth, without the use of energy for heating or lighting. The development work described in this proposal is required to prove this potential to prospective commercialization partners within the Canadian greenhouse industry.