Greenhouse Floor Heating, Preliminary Results from the 2003-2004 Heating Season

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 the typical design and control strategies that are implemented for these systems work well, they still may not be optimized for energy efficiency or crop benefit. 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. This paper describes the first attempt to develop and verify a model of a floor heating system that is installed in a research greenhouse located at Cook College, Rutgers University in New Brunswick, NJ. This model considers the simple case of a heated ebb and flood floor without a crop, and will be used to develop more complex models. The model’s output under predicted the average floor surface temperature measured in the greenhouse by an average of 3.20 o C (5.76 o F), for eight combinations of pipe water temperature and greenhouse air temperature considered, with a standard deviation of 0.28 o C (0.49 o F). By raising the external radiation temperature used as input to the model by an average of 8.63 o C (15.53 o F), the models predicted average surface temperature matched the measured average surface temperatures for all eight cases considered. In order to confidently verify the model’s output, a better method for determining the external radiation environment is necessary. More complete models need to be developed that include the soil below, the crop above, and all the thermal relationships that exist between them and the greenhouse. With such models, the thermal performance of these systems can be better understood, and the effects of changing design parameters as well as control strategies can be determined.