Inexpensive, Multiple-Unit Environmental Chambers with Temperature and Humidity Control1

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Abstract
A system is described that has eight independently controlled environmental chambers with a single electric resistance heat source and a medium-temperature 0.5-ton (100 Btu/min) refrigeration unit to provide warm and cold forced air through ducts to each of the units (90 by 60 by 60 cm). A thermostat in each chamber controls a pair of solenoid-actuated warm and cold air ports. Its design is simple and reliable, using integrated circuits for easy repair and high-current switching transistors instead of relays for increased longevity, Temperature control is ± 0.5°C, and humidity control has been added. The cost of all materials and equipment can be kept under 2,000 if the thermostats are assembled from component parts.

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