Comparing Greenhouse Floor Heating Designs Using CFD

Abstract

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