A Perpetual Harvest Greenhouse System: Integrating Barn, Biofilter, and Greenhouse

A prototype was built to evaluate the performance of an integrated barn-biofilter-greenhouse system. The greenhouse floor in the integrated system consisted of a bed of gravel to store maximum solar energy. A vertical airflow biofilter (3.34 x 3.34 m) was constructed inside a solar energy greenhouse (floor area of 15 x 6.7 m); exhaust air from a barn was passed through the biofilter for odour treatment before being released into the greenhouse. A booster fan was used to provide a steady airflow rate of 1.4 m 3 /s to the biofilter. Data were collected from October 19 to December 6, 2007. The maximum temperature drop along the 15.5 m long, and insulated (R-20) duct carrying the exhaust air from the hog barn to the biofilter was 7°C. The lowest temperature recorded on top of the biofilter surface was 1.3°C when the biofilter booster fan was not working, while the lowest floor temperature was -3°C. On the coldest day in December, when the biofilter booster fan was not in service, the daily average temperature inside the greenhouse was 4.3°C, whereas the outdoor daily average temperature was -25°C. In order to keep the minimum greenhouse temperature at 10°C, the maximum required volumetric flow rate of barn exhaust air at 15°C was 1.60m 3 /s. Maximum hydrogen sulfide (H 2 S) removal efficiency was 55%. The weekly average concentration of carbon dioxide (CO 2 ) inside the greenhouse varied from 841 to 1536 ppm. The system has shown promise at creating an environment suitable for plant growth inside the greenhouse using a waste gas stream from a hog barn to provide both auxiliary heat and enhanced CO 2 levels.