5. Solar Rooftop Test Cell—Experimental Methodology and Results of Multivariable Sensitivity Analysis

Existing greenhouse models in literature often use input parameters that are selected with little to no scientific explanation. To address this, a solar test cell was constructed and placed on the roof of the Albert A Thornborough building at the University of Guelph from June to August 2021. The test cell was built to allow controlled investigation of thermal properties of a simplified version of a greenhouse, with fewer unknown values and relationships. The experimental set-up included 6 mil polyethylene glazing above a 10 cm deep air layer, above 5 cm of sand. The structure was framed with dimensional lumber and particle board and included 2.5 cm of foam board insulation on side walls and below the sand layer to mitigate heat loss. Interior and exterior temperature and relative humidities, as well as wind speed and solar irradiance were recorded over the duration of the experiment. Heat transfer in the cell was simulated with a modified one-dimensional lumped capacitance model that tracked heat fluxes between discrete layers. Identifying the optimal parameters for this test cell allow for relevant findings to be transferred to more complex greenhouse models. Two multivariable sensitivity analyses were conducted on parameters and relationships used in the model, with the optimized configuration resulting in root mean squared errors for air temperature that were less than 5 °C, with a daily air temperature range of over 70 °C. Also included is a methodology for finding the thermal conductivity and specific heat capacity of the soil using measured temperatures.