Comparing Greenhouse Floor Heating Designs Using CFD

Floor heating in greenhouses has become more and more popular over the past decades because of the considerable benefits warm floors can have on greenhouse crops. In addition, bottom watering is beneficial for many crops. Making use of the synergy of both bottom heat and bottom watering, many greenhouse growers are utilizing heated ebb and flood floors as their main plant productions system. While typical warm floor systems work well, they may not be fully optimized. Accurate and flexible computer models can be extremely valuable design tools when applied to the study of greenhouse environmental control systems and can answer many questions without the time and expense associated with experimental research. A model was developed and validated, using computational fluid dynamics (CFD) software, of a typically designed warm floor system. The model was then modified to investigate the effect of heating pipe diameter and spacing, vertical position in the floor slab, and soil thermal conductivity on heat flux through the floor and temperature uniformity at the floor surface for typically designed commercial greenhouse floor heating systems. Thirty two simulations were completed to compare the performance of two different pipe diameter/spacings, two pipe elevations in the floor slab, and two soil conductivity values, each with four pipe water and greenhouse air temperature combinations. The results showed that soil thermal conductivity had little effect on temperature, heat flux, or temperature uniformity on the surface of the floor. Raising the pipe position increased both the floor surface temperature and surface heat flux, but reduced the surface temperature uniformity and had little impact on reducing soil heat flux. Using a smaller diameter pipe with a closer spacing increased the temperature, heat flux, and temperature uniformity on the surface of the floor without increasing the percentage of the total heat input to the floor that was lost to the soil below the floor.