CO2 Enrichment and Hot Water Heat in a Greenhouse as a Mean of Recovering Bioresources From Swine Waste

Abstract

Predictions of heating and cooling requirements of a greenhouse located at the Barham Farm, Zebulon, N.C. were made via computer simulation. Kimball's Modular Energy Balance Model (MEB) was used to simulate thermal behavior of the greenhouse. The weather inputs to the model were provided by data collected at the greenhouse and a Typical Meteorological Year (TMY2) data file for Raleigh, NC. Greenhouse air temperature (Tai), inside CO2 concentration (CO2) and inside relative humidity (RH) levels were used to validate the accuracy of the model. Absolute percentage differences ranging from 5.92% to 10.67% for Tai were observed. CO2 levels showed the biggest differences between observed and predicted data, from 14.93% to 42.33%, and RH showed a difference of 9.79% to 19.41%. Heating times were under-predicted, showing percentage difference between observed and predicted periods from -3.01% to -34.87%. On the other hand, cooling periods were over-predicted. With the exception of the month of February were cooling periods were under-predicted. Percentage difference for cooling periods ranged from -3.59% to 27.80%. The use of supplemental heat using a 10,000 gallon hot water tank serving as a waste heat collector was simulated. No data was available on its operation. Based on specific operating assumptions, it is expected that heat from the hot water will supply approximately 35% of the total energy demand of the greenhouse in a typical meteorological year. It was observed that the use of supplemental heat is most sensitive to its initial water temperature and the cutoff temperature. Outside weather conditions to which the use of hot water is most sensitive are solar radiation and wind speed.