Greenhouses are generally built to extend the growing season by avoiding extremes in temperature. Heating and cooling demands, however, lead to high energy consumption, correlating to high energy costs and reduced profits for businesses. Difficulties also exist in the control of the internal environment to optimize growth conditions for crops. In order to reduce heating and cooling costs, and to more efficiently maintain thermal equilibrium within a greenhouse, “Removable Foam Insulation” (RFI) technology is being developed. RFI involves generating liquid foam or bubbles using a foaming device that aerates a foaming solution. The resulting bubbles are distributed to fill a transparent roof cavity, and a collection system returns the liquid drainage when the bubbles collapse back to a holding tank for reuse. The foaming cycle is repeated as needed for either night time energy savings (insulation), or for day time solar shading. An 8m by 8m research greenhouse was designed and built for technology development and evaluation. A double poly separation wall divides the structure internally into two halves, permitting comparison between the RFI technology and the control zone. Measured energy savings of 52% to 87%, depending on outside climate conditions and foam characteristics, were achieved over the control greenhouse. Overall, RFI technology will typically save between 45% and 65% of annual energy requirements. The technology costs about $3.00/ft2 CND (preliminary installed price) and the payback period, depending on energy savings achieved and on energy costs, is 3 to 5 years. These initial results show excellent potential for energy savings. There is a need to investigate the addition of foam stabilizers to foam formulations to achieve better control of the bubble collapse rate. Additionally, cost reductions are needed to effectively scale up the RFI system to larger greenhouses. Future studies will focus on the shading and ventilation reduction capacity, as these aspects were not assessed.
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