The Sustainability Workshop collects box/lid combinations made from Expanded Polystyrene for re-use as egg incubators. Based on the traditional farmer method, using a cardboard box and a light bulb vs. the modern thermostat-driven equivelent, the shop is closing-in on the high-performance incubator for $10 or less. Performance of the incubator is dependent on a stable room temperature, which is not uncommon on the exterior wall of most buildings.
The limiting factors in making an incubator from waste and cheap materials are the same as for most commercial still-air incubators. If room temperature is stable to within a few degrees, the added thermal mass of the box and the insulating qualities of the box combine to produce a consistent internal temperature requiring limited user maintenance. For most box sizes, a constant input wattage of 20-35 watts is common. The addition of the plexiglass window contributes greatly to heat loss and is responsible for creating the higher-wattage incubators.
Though this model shown below uses a watt meter to help the user stabilize internal temperature, one is not required. One expensive component is suggested: a good thermometer/hygrometer combination. For about $25 or less, the addition of such a meter greatly increases accuracy in maintaing temperature and humidity. It's worth noting that use of the commercial still-air incubator that inspired this design was somewhat flawed in terms of humidity control. After purchase of a hygrometer, problems in humidity control in the commercial unit were evident immediately.
The Sustainability Workshop currently collects materials on a weekly basis and can produce 1-5 incubators per week. Labor time required to collect these boxes, purchase additional components, waterproof the bottom and install the rotary dimmer/bulb combination is approximately 1-2 hours per incubator. With the addition of a good thermometer/hygrometer combination, costs can begin to equal the cost of commercial units. However, the benefits include the hygrometer, a larger capacity and more options for user-customization.
In practice, the egg incubators using the dimmer and lightbulb combination have provided internal temperature control similar, if not better, than the commercial unit tested in the Sustainability Workshop. The key to this performance is based on the idea of constant heat loss through the exterior of the box. While commercial still-air incubators also use expanded polystyrene boxes which are inherently insulated, they do not incorporate thermal mass and use thermostats in a slightly non-ideal way. Through observation, it was noticed that the thermostats in such units cycle on/off at a high rate while maintaining a stable internal temperature. By adding a constant lower wattage, the incubators from the Workshop keep temperatures just as stable through constant heat loss in proportion to the box size and insulating capacity.
My first chicken: I love her. Her name is Danielle.