Novel approaches to improve energy efficiency in northern New England greenhouses
Growers are using greenhouses more than ever to reduce loss due to unpredictable weather and extend the growing season. Hoop houses are inexpensive to erect, but require a lot of energy, especially in northern New England. This project builds on our greenhouse network in Maine, New Hampshire and Vermont, partnering with growers to increase their sustainability through improved energy conservation in hoop houses. Two energy conservation systems, a soap bubble insulation system developed in Canada, and a thermal curtain, have been retrofitted into separate gable-style 88 ft. greenhouses at a large Vermont greenhouse ornamentals operation. Monitoring equipment was installed to quantify energy savings relative to ambient temperature. A greenhouse grower survey was conducted on energy use in the tri-state region. Most responding growers spent less than $10,000 annually on electricity and over half spent less than $10,000 on propane or oil for heating. Twenty-four percent of the respondents used $10,000-25,000 on fuel. The expense of implementing energy saving measures was identified as the most limiting factor, and providing tax incentives for energy conservation was cited as the most helpful to encourage adoption of conservation practices. Energy audits were completed at four Vermont commercial greenhouse operations in 2011, and feedback from growers indicated that the information received from the audits was useful. One of the growers was so enthusiastic about what he learned that he hosted a workshop to encourage other growers to arrange for audits. Another grower receiving an audit has replaced the boilers in six of his greenhouses because he recognizes the savings he will ultimately realize from these improvements. He also has installed digital thermostats to enhance his energy savings. He is considering installing an energy curtain in one of his greenhouses because of the energy benefits he observed in the test greenhouses at his operation.
1. Assess two innovative energy-saving devices retrofitted into a greenhouse: a bubble insulation system and an energy/shade screen system.
2. Conduct comprehensive energy audits before and after retrofitting the greenhouses to quantify the benefits of both devices.
3. Determine cost of greenhouse retrofitting, energy savings and potential tax incentives from which to assess the costs and benefits of both systems compared to an unimproved greenhouse.
4. Conduct a survey to generate baseline data on current energy consumption and conservation used by greenhouse growers in the tri-state region.
5. Conduct energy audits at 9 greenhouse operations to provide quantitative information about trends in current energy consumption and identify the most significant measures that would improve conservation.
6. Conduct workshops in each state to present information on energy conservation and federal and state incentive opportunities, and host an open house to demonstrate the innovative energy conservation systems tested.
7. Produce a grower-friendly guide entitled How to Retrofit a Greenhouse for Energy Conservation. Cost of retrofitting, energy savings and potential tax incentives will be determined from the data, from which an accurate assessment of the benefits of these systems will be made.
8. Develop a web-based program enabling growers to calculate cost savings from energy conservation activities.
Over 1,650 growers will receive information about energy conservation in greenhouses. Of the total growers receiving information, 5% (~80 growers) will implement at least one recommended tactic in one 2,000 sq ft greenhouse (total 160,000 sq ft), resulting in an annual reduction of energy cost of $500 per greenhouse grower operation. One grower per state (3 growers) will retrofit at least one greenhouse with either a bubble or thermal blanket insulation system, resulting in a yearly cost savings in fuel use of $1,000.
Obj. 1. Many problems with the operation of the bubble insulation system occurred over the first two years that required innovative solutions for repair. In 2012, the system was in continuous operation from mid-January through March, which was longer than the previous year. While it was encouraging to correct these major problems, the following new problems surfaced in the fall that needed attention: a) many leaks of the soap solution occurred because of small tears in the plastic; b) an O-ring in a critical valve failed due to high temperatures in the greenhouse during a hot spell this summer; c) the soap solution did not drain back properly into the tank because the greenhouse plastic was tighter than last year; and d) the bubbles produced were of poor quality due to changes in the soap solution. The following adjustments were made to correct these problems: a) the plastic covering the greenhouse was replaced and care was taken to make it tighter than in previous years to reduce flapping; b) the valve was replaced and care will be taken in the future to ensure that the exhaust fan remains on during the summer to keep internal ambient temperatures below damaging levels; c) special tubes were installed between the two layers of plastic to permit the unrestricted flow of the solution to the collecting tanks; d) experimental devices were designed to allow for extensive testing of the soap solution to determine the best soap and carbowax (antifreeze) concentrations to use to maximize freeze protection and bubble quality in terms of insulation. This year reminded us that the bubble system is clearly in an experimental phase and was not originally designed for a single gable-style greenhouse. While it shows potential in terms of energy conservation, further research and development is needed before it is ready for widespread use by growers. See Appendix 1 for images of work done on the bubble system in 2012.
Obj. 2. Collection of assorted energy consumption and weather data continued to be done by EnSave, a local energy analysis company. We also recorded gas usage daily during the period of operation of the systems. The bottom line for growers is dollars saved by reduced gas use. Based on the amount of gas used in each greenhouse during the period of operation, and the cost of the gas, we determined that the cost of gas used was $742 less in the bubble house than the control house and $193 less than in the curtain house. The cost of gas was $549 less in the curtain house than the control house. We could see clearly that greater gas savings was realized in the bubble system house when temperatures were lowest. The 2012 winter was unusually mild, which reduced the impact of energy savings from the two energy conservation systems compared to the control house. Digital thermostats were installed in the three greenhouses and an automatic opener for the curtain this fall. These improvements are expected to enhance energy conservation and provide more meaningful data on differences among the three treatments. The greenhouse operations manager and owner were trained on how to operate these devices. See Appendix 1 for graphs and tables of the results from 2012.
Obj. 3. Because issues continue to surface with the bubble system that require additional redesign, it is not yet feasible to determine the cost of retrofitting a hoop greenhouse for that system. However, information continues to be compiled on costs for both energy systems as the project progresses. These data will be used in the future to determine the expenses associated with actual retrofitting the structures for energy conservation and included in final calculations relevant to cost-benefit of the systems for growers.
Obj. 4. The grower survey was conducted in 2011 and results were compiled and reported on in the last report. The bottom line for growers is money; it is the cost of improvements that was identified as the primary barrier preventing them from upgrading their structures. Plans are underway to prepare an article reporting the results of this survey.
Obj. 5. Energy audits were completed at four Vermont commercial greenhouse operations in late 2011 by Dr. John Bartok. Feedback from the growers receiving audits indicated that the information received was very useful. One of the growers was so enthusiastic about what he learned that he hosted a workshop to encourage other growers to arrange for audits. Another grower receiving an audit has replaced the boilers in six of his greenhouses because he recognizes the savings he will ultimately realize from these improvements. He also has installed digital thermostats to enhance his energy savings. He is considering installing an energy curtain in one of his greenhouses because of the energy benefits he observed in the test greenhouses at his operation. Efforts are underway to identify growers who will receive audits in New Hampshire and Maine in early 2013.
Obj. 6. Workshops were held in ME, NH and VT in January 2012 where growers received handouts on energy conservation and a short presentation of the scope of this project. A short video of the bubble insulation system in operation was shown. Growers were very interested in the option. In the workshop evaluation, energy conservation was listed as a topic growers wanted to learn more about in the future. Several opportunities occurred to demonstrate the bubble and curtain systems for growers and regional specialists. We hosted a tour of the site for a group of approximately 10 members of the Northeast Horticulture Inspection Society in mid-April. All of the people to whom we demonstrated the bubble system were very intrigued by it. We also collaborated with a Univ. of Vermont student to prepare an amateur video describing the system for Vermont Independence Day. This video can be viewed at the following URL: http://www.youtube.com/watch?v=W9lOxF_jOZE See Appendix 1 for images of some of the visitors to the test site.
Obj. 7. The guide is scheduled for production in the final year of the project after compiling data from the previous years of work. Because of the ongoing challenges associated with the operation of the bubble system, we intend to request an extension on the project to allow us to further improve on the system. It is unrealistic at this time to prepare this guide.
Obj. 8. The web-based program is scheduled for development in the final year of the project based on data we collected in previous years.
Impacts and Contributions/Outcomes
Despite the additional cost and various problems associated with retrofitting the greenhouses, the cooperating grower has already noticed a significant reduction in gas consumption in the greenhouses with the thermal curtain and bubble system compared with the unimproved greenhouse. The growers who received energy audits were highly satisfied with the information they received and several have already invested in the recommended changes. One grower at his personal initiative hosted a demonstration to show other growers the benefits of an audit.
The collaborating grower, Mr. Chris Conant, continues to be an incredible cooperator. He has assigned his personnel to assist us with various aspects of retrofitting the bubble system at no cost to us. He has been involved in all phases of the retrofitting process. He and his staff have provided critical expertise relevant to greenhouse construction that has contributed to developing an effective bubble system. He has shared information about the project with other growers and industry representatives. We also continue to receive technical support from several specialists from Canada involved in the original development of the bubble insulation system. Specifically, Mr. Joey Villenueve, greenhouse engineer and president of the consulting company Environment – MJ, has provided ongoing advice to get the bubble system into operation. We also continue to interact with Mr. Ilan Sadon, IGOS.MN LTD., Engineering Products Management, from Israel, who holds the rights to the bubble system. Redesigns and adjustments to the bubble insulation system were made with assistance from Peter Skinner, engineer and owner of E2G Solar.
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