Energy and Economic Analysis for Greenhouse Ground Insulation Design

James Bambara,Andreas Athienitis

doi:10.3390/en11113218

Abstract

Energy and life cycle cost analysis were employed to identify the most-cost effective ground envelope design for a greenhouse that employs supplemental lighting located in Ottawa, Ontario, Canada (45.4° N). The envelope design alternatives that were investigated consist of installing insulation vertically around the perimeter and horizontally beneath the footprint of a greenhouse with a concrete slab and unfinished soil floor. Detailed thermal interaction between the greenhouse and the ground surface is achieved by considering 3-dimensional conduction heat transfer within the TRNSYS 17.2 simulation software. The portion of total heat loss that occurred through the ground was approximately 4% and permutations in ground insulation design reduced heating energy consumption by up to 1%. For the two floor designs, the highest net savings was achieved when perimeter and floor zone horizontal insulation was installed whereas a financial loss occurred when it was also placed beneath the crop zone. However, in all cases, the improvement in economic performance was small (net savings below $4000 and reduction in life cycle under 0.2%). Combined energy and life cycle cost analysis is valuable for selecting optimal envelope designs that are capable of lowering energy consumption, improving economics and enhancing greenhouse durability.

Highlights

Heating is a major operating expense for greenhouses that are located in mid-to-high latitude locations
Permutations in the ground envelope design will have a small impact on the overall greenhouse energy savings
The cost-effective ground insulation design forfor a Themethodology methodologywas wasapplied appliedtotodetermine determinethe themost most cost-effective ground insulation design greenhouse located in Ottawa, ON, Canada

Summary

Introduction

Heating is a major operating expense for greenhouses that are located in mid-to-high latitude locations. Much of the prior work regarding ground heat transfer has been performed for buildings [1,2,3]. Most studies have separated the ground into one or more relatively thin earth layer and energy transfer is solved using 1-dimensonal (1D) heat transfer equations [9,10,11]. The advantage of 2-dimensional (2D) heat transfer is that it enables interaction with the greenhouse edge/perimeter. The entire footprint (and interaction with the perimeter) can only be studied when 3-dimensional (3D) discretization of the ground is performed, whereby the ground is divided into control volumes so that overall heat transfer can be solved analytically or numerically. The only study that employed 3D analysis of ground heat

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