Solar Thermal Heating, Cooling and Ventilation System For Shipping Containers
A guiding principle for us is that the technologies and processes we create should allow for the production of food year-round. With indoor production facilities, such as our re-purposed shipping containers, keeping the indoor temperature at a level ideal for plant growth can be a challenge, especially in winter months.
In central Ohio, where the hapi project was created, we have 4 distinct seasons. Our winters last from December through February, during which outside air temperatures average around 20°F with a record low of -28°F. Sub-zero colds snaps are not uncommon. Some season extension techniques, such as hoop houses and cold frames, can allow for growing cold-weather crops late into the winter. Similarly these technologies can effectively move spring a few weeks sooner. However, a cold snap can quickly stunt winter growing activities for all except heated greenhouses.
A key goal for all of our products is to evolve urban agriculture technologies along multiple, separate but interrelated axis'. First and foremost of these is energy. While it is certainly feasible to burn fossil fuels to heat a grow container, it goes against our commitment to make food production carbon neutral. Solar thermal is not a new technology. It is often employed to heat water (solar water heaters) and, less commonly/commercially, air. In either case, the units function as follows (example is with air).
A heat absorber is placed in a box with a transparent top/face. The box has an inlet at its lower end and an outlet at its upper end. When sunlight strikes the absorber, the air that is in contact with it warms. This warm air rises and exits through the outlet. This upward air movement creates a convection current. Cooler air moves into the unit from the inlet. This air is in turn warmed and the process continues while sunlight remains.
Our needs and constraints are a bit different from most of what we found online. We needed to mount the unit on the end of a corrugated box made of thick steel, with insulation on the inside. The unit is mounted completely vertical and must help us exceed our daily operational needs during the winter, in order to make up for the short days of January.
To learn more about this and other projects, visit us at hapihq.com.
We started with a sheet of 11/32" plywood, standard size 4' x 8'. Then we made a box frame out of three 1" x 6" x 8' planks. The outer edges of the box frame fits exactly to the outer edges of the plywood. We set the plywood on the frame, aligned the edges and screwed it to the frame with 1 1/4” wood screws. The total cost for this step was about $38.