UBC Theses and Dissertations
Light transmissive variable thermal insulator based on nonimaging optics with potential application in cold climate greenhouses. Valerio, Angel
Greenhouse structures have demonstrated success enhancing crop yields in farmlands, but the energy for thermal control and lighting make them impractical in cold weather locations because traditional greenhouse construction techniques result in a trade-off between light transmission and thermal insulation. The objective of the project described in this dissertation was to conceptualize, design and test a practical solution to the light transmission and thermal insulation trade-off challenge. The system that was developed is a variable light valve system that can be switched between two states – in one state the system acts as a sunlight transparent window and the other state the system acts as a highly thermally insulated ceiling capable of keeping the structure warm in cold weather conditions. Switching between the two states requires only a simple, low-cost rotation mechanism. The possibility of extending the hours of operation for the light valve system by adjusting the angular position of its light valve elements was also explored. The light valve system when in its highly thermally insulated state, demonstrated a thermal insulation value above 3.33 m²K/W and 70% light transmittance when in its light transmissive state. In order to achieve this thermal insulation value, air mass transfer losses through the light valve structure were reduced by the implementation of low pressure seal. The experimental devices used to test the light valve system demonstrated it can be constructed using inexpensive and readily available materials. The project described in this dissertation has successfully confirmed a practical solution to reduce the energy use for heating in cold climate greenhouses while maintaining appropriate sunlight transmittance through their structure. The light valve system may represent a practical alternative for cold climate greenhouse horticulture.
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