Templates for Modeling Temperature Response of Passive Greenhouses

ABSTRACT

A previous publication [1] introduced a model of interior air temperature response to exterior temperature for a single-zone structure with no active heating, ventilation, or cooling. The model was based on a simple exponential step response function relating the two temperatures. Results were sufficiently encouraging to apply the model to other simple passive structures. This article applies the model to two cases of passive greenhouses. One of the greenhouses is a rudimentary plastic-covered hoop house. The other is a super-insulated net-zero structure that grows summer crops in cold climates using sunlight as the source of heating. A model for the interior air temperature of both of these structures was developed using two time-series templates. The first template is an exponential step response function of outdoor air temperature. This template synchronizes the model to the actual interior temperature but does not match its amplitude. A second template was developed by subtracting the model using the first template from the actual interior air temperature data. The second template scaled according to available sunlight as measured by an inexpensive photometric sensor. The superposition of the two templates tracks the actual interior temperature reasonably well given the limitations described in this article. Average difference between actual and modeled data for both structures was within 2°F, although maximum deviations ranged up to 30°F. This article concludes with a discussion of refinements to the model and of its commercial deployment should it prove generally applicable to passive greenhouses.

Acknowledgements

The author thanks Synergistic Building Technologies for sharing the greenhouse data and Dr. Marc Plinke (now at Ceres Greenhouse Solutions, www.ceresgs.com) for his ongoing support and encouragement. Dr. Plinke may be contacted at [email protected]. Special appreciation extends to Dr. Larry Kinney for his vision that led to the creation of the SBT prototype. Michael Stiles may be contacted via email at [email protected].

Additional information

Notes on contributors

Michael R. Stiles

ABOUT THE AUTHOR

Michael R. Stiles, PhD, CEM, is a senior energy engineer at L&S Energy Services where he develops energy audits, feasibility studies for combined heat and power (CHP) projects, building energy models, and other activities in the commercial, industrial, and agricultural sectors. Dr. Stiles has 30 years' experience in energy analysis and technology and holds three US patents. The present article results from his ongoing interest in the potential of passive greenhouses for growing crops locally with a minimal energy footprint.