Energy and Economic Analysis for Greenhouse Envelope Design

The energy consumption of a building is significantly impacted by its envelope design, particularly for greenhouses where coverings typically provide high heat and daylight transmission. Energy and life cycle cost (LCC) analysis were used to identify the most cost-effective cladding design for a greenhouse located in Ottawa, Ontario, Canada (45.4° N) that employs supplemental lighting. The base case envelope design uses single glazing, whereas the two alternative designs consist of replacing the glass with twin-wall polycarbonate and adding foil-faced rigid insulation (permanent or movable) on the interior surface of the glass. All the alternative envelope designs increased electricity consumption for lighting and decreased heating energy use except when permanent or movable insulation was applied to the north wall and in the case of permanent insulation on the north wall plus polycarbonate on the east wall. This demonstrates how the use of reflective opaque insulation on the north wall can be beneficial for redirecting light onto the crops to achieve simultaneous reductions in electricity and heating energy costs. A maximum reduction in LCC of 5.5% (net savings of approximately $130,000) was achieved when permanent insulation was applied to the north and east walls plus polycarbonate on the west wall. This alternative envelope design increased electricity consumption for horticultural lighting by 4.3%, reduced heating energy use by 15.6%, and caused greenhouse gas emissions related to energy consumption to decrease by 14.7%. This analysis demonstrates how energy and economic analysis can be employed to determine the most suitable envelope design based on local climate and economic conditions. Keywords: Artificial lighting, Consistent daily light integral, Energy modeling, Envelope design, Greenhouse, Life cycle cost analysis, Light emitting diode, Local agriculture.