Greenhouses have the potential to be extremely nutrient and energy efficient, capturing heat, ammonia and carbon dioxide coming off of compost for soil and plant growth. Composting is an aerobic process, and especially at northern latitudes there is a balance between adding air and losing heat by convection. The New Alchemy Institute composting greenhouse was designed to address this problem by creating a partially closed nutrient cycle. Air inside the greenhouse was exchanged between the compost and a biofilter/ plant beds, exchanging CO2 for oxygen. Despite some difficulties balancing ammonia and heat generation, the greenhouse was able to raise plants and maintain thermophilic composting through a New England winter. Milwaukee’s Growing Power sees improved winter plant growth with simple piles on the inside of their hoophouses, but they are not focused on thermophilic composting.
Why composting greenhouses could save us: 30 residential units could have all of their excrement and organic wastes composted in a 12' by 20' greenhouse year round. Imagine every neighborhood running their own composting greenhouse and cutting off from the sewer.