UC Davis designed a CoolBot cool room (excellent project for homesteaders!) using rice hull concrete for insulation and a CoolBot controller to keep farm produce fresher. The cool room paid for itself the first year and even helped make a good profit for local farmers. The rice hull concrete was poured into forms to make insulating wall boards. This blog post will briefly summarize the outcome of their project. The full report is available online for free and can be found by searching for the title of the report: Cool room insulation – UC Davis D-Lab
Design considerations for the cool room:
1. Insulation material has to have a high R-value, better than EPS foam.
2. In order to increase the R-value, the insulation material has to be able to trap air in as part of its structure.
3. Insulation material has to be water resistant.
4. Insulation material has to be able to avoid air moisture condensation.
5. Insulation material has to be non-flammable.
6. Insulation material has to be wind resistance.
7. Insulation material has to be locally available.
8. Insulation material, if not commercially available, has to be made out of local resources.
9. Insulation material, if not commercially available, has to be made by local inhabitants according to their technical skills training.
10. Insulation material has to be low cost as possible.
11. Insulation material has to be malleable as possible to adjust to the different building options.
Summary of the mixing process: soak the whole rice hulls in equal volume of water for 30 minutes, mix cement separately, drain the rice hulls and slowly add them to the cement and then mix until uniform in consistency. A cement mixer speeds the process. Ratio of rice hulls to cement is between 3:1 to 4:1, so only minimal cement is needed.
Rice hulls are typically very low cost and sometimes even available for free. Over 100 million tonnes of rice hulls are generated each year throughout the world. Rice hulls are naturally fire resistant due to the silica coating on the hulls and therefore meet fire code requirements untreated. The insulation value of whole rice hulls is over 3.0/inch. Using this abundant, low cost, highly insulating agro waste to build affordable homes and other structures has lots of potential. There are numerous rice hull homes around the world that you can read about on our blog.