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 relatively 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. 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. In 2011, energy audits were completed at four Vermont commercial greenhouse operations. In 2013 support was provided to several New Hampshire growers to arrange audits, and several were completed. Feedback from growers indicated that the information received from the audits was useful and led to adoption of many of the recommended adaptations.
Research into the comparative energy efficiency of the bubble insulation system, the thermal curtain and an unimproved hoop greenhouse continued. The greenhouse with a curtain used less gas than the unimproved house, and efficiency was enhanced with installation of an automatic operating system. This allowed the curtain to be opened and closed to maximize gas savings. It was also used for shade to keep the greenhouse cool in the spring and summer, thereby reducing electric use by cooling fans. The bubble insulation system operated continually through the 2013 winter/spring and fall growing seasons. This is the longest period of operation for the system since it was installed in Vermont, and most likely the longest ever since it was first designed in Canada. However, several mechanical issues have surfaced requiring continual attention and repairs.
Despite these problems, gas usage was consistently less in the greenhouse with the bubble system than in the curtain and unimproved houses. Growers and industry representatives continue to express interest in the bubble system, but until its operation is more reliable, it is unlikely to become a standard for the industry.
- Assess two innovative energy-saving devices retrofitted into a greenhouse: a bubble insulation system and an energy/shade screen system.
- Conduct comprehensive energy audits before and after retrofitting the greenhouses to quantify the benefits of both devices.
- 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.
- Conduct a survey to generate baseline data on current energy consumption and conservation used by greenhouse growers in the tri-state region.
- 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.
- 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.
- 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.
- Develop a web-based program enabling growers to calculate cost savings from energy conservation activities.
- Performance Target:
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.The bubble system ran continuously from December 2012 until warm weather arrived in late April 2013, the longest period of operation since it was installed. After shutdown several cracked schedule 40 PVC elbows and couplers were discovered. These and several others were replaced with schedule 80 PVC, which is thicker and more heat resistant. Previously we found that the soap solution breaks down if left in the hot greenhouse over the summer. To remedy this, the soap solution was transferred to a 350 gallon tank located in a cool location for the summer months. In early September, the system was operated initially with water to identify leaks. Several were located and repaired mostly by taking the unions apart and re-applying plumbers tape and re-tightening the joints.
Making these system repairs required removal and re-installation of the inner and outer plastic layers several times which resulted in holes and slit-type cuts which, based on past experience, are areas prone to leaks of the soap solution. Consequently, both inner and outer plastic layers were replaced with new UV-resistant greenhouse plastic in late September in preparation for the upcoming greenhouse season. Several of the bubble generators and other plumbing parts were also inspected and repaired.
Soon after installation of the new plastic layers in late September, the area experienced a wind event with sustained 50 mph winds for several hours. The new plastic had been installed very tightly which had been determined through previous experience to be necessary for proper inflation and operation of the bubble system. The raised tubing and bubble generator structure located along the peak of the greenhouse between the two plastic layers, tipped over, breaking several generators and ripping holes in the outer layer of the new plastic. The system was inspected and it was found that the heavy duty cable ties anchoring the tubing and bubble generators structure had stretched, allowing the high winds to push on the plastic and knock over the tubing structure. Extensive repairs to the system were made, including replacement of numerous generators and the cable ties. The outer plastic layer also had to be replaced. It was observed that the current bubble generators are cracking in one consistent place (see Appendix). This appears to be a weak link in the original system that needs to be redesigned. A new schedule 80 PVC reducer was sourced that could remedy this problem and work has begun on developing the new much sturdier generator assembly (See Appendix).
In addition to devising a sturdier generator, discussion is underway to design a new approach to generating the bubbles. Currently, whenever generators become clogged, the plastic must be detached to allow access to the generator. This results in small punctures in the plastic. We envision designing the system so that the generator assembly with all of the air and solution tubes is outside the two layers of plastic rather than between them. This will allow for servicing the generator nozzles without having to remove the inner plastic layer.
Another problem experienced during the fall of 2013 was the plugging of spray nozzles with fine particulates requiring removal of each affected generator to access and remove the plugged spray nozzle. It was found that the 43 micron stainless steel filter which is meant to prevent particles from reaching the generators had begun to come apart, though it was installed only 16 months ago. This will be replaced (under warranty), and an additional internal brace was installed to prevent it from recurring.
We speculate the strong backwash of soap solution that occurs when the system shuts off may push too hard on the filter, causing the filter failure. In spite of these problems, the system ran dependably from early October 2013 until it was shut down in mid December at the end of the poinsettia season. This was the first time since the beginning of the project that we were able to run the system continually throughout the fall season.
Obj. 2. Collection of assorted energy consumption and weather data continued over the past year. Natural gas usage was also recorded daily during the period of operation of the systems. The bottom line for growers is dollars saved by reduced natural gas use. Based on the amount of natural gas used in each greenhouse during the period of operation, and the cost of the gas, the following energy savings was observed:
Soap bubble system: in 2012: 43% less gas and $946.00 lower cost than control; in 2013: 38% less gas and $727.00 lower cost than control;
Thermal energy curtain: in 2012: 31% less gas and $682.00 lower cost than control; in 2013: 31% less gas and $593.00 lower cost than control. The 2013 figures are for the late winter-spring period only and do not include the fall 2013 data as of yet. We could see clearly that greater gas savings was realized in the bubble system house when temperatures were lowest. Both the 2012 and 2013 winters were unusually mild, which reduced the impact of energy savings from the two energy conservation systems compared to the control house. Another important point to be made is that the greenhouses used for this study are heated with natural gas which at this time is a relatively inexpensive fuel source. Propane users would see roughly four times the savings as those stated above and fuel oil users would see roughly twice the savings stated above.
In 2012 digital thermostats were installed in the three greenhouses and an automatic opener for the curtain which improved reliability considerably making our data more rigorous. 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.
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. Currently only preliminary figures could be determined excluding the ongoing cost of servicing the bubble system. The cost of the purchase and installation of the systems are estimated to be $16,200 for the bubble system, and $10,800 for the thermal curtain. These values are based on the cost of the curtain in 2010, and an estimate of the cost of parts for the bubble system. The cost of the bubble system would definitely be less if a standard commercial system was developed. The cost of the curtain would also be less if it was installed at the time the greenhouse was erected rather than as a retrofit. 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. In 2013, several New Hampshire growers were contacted to enquire about their interest to receive audits. The PIs assisted them with making contact with NRCS to arrange for support for the audits. At least one grower received an audit through NRCS. Without assistance through UVM personnel, it is doubtful whether this would have taken place due to the complexity of the application process.
Obj. 6. Workshops were held in ME, NH and VT in January 2013 where growers received handouts on energy conservation and a short presentation of the scope on this project. 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 in 2013. In July, the Board of Directors of the American Floral Endowment, a leading national greenhouse/floriculture industry association, received a tour of the research site at Claussen’s. This group of over 20 leaders in the industry was fascinated with the project and impressed by the grower involvement in the research. In addition a presentation was given to over 45 greenhouse growers from New Hampshire for the annual meeting of the New Hampshire Horticulture Association. The growers were interested in the technology, and look forward to an on-site demonstration in the coming year. A grower workshop at Claussen’s to demonstrate the bubble system and other energy conservation options is anticipated for later in 2014.
Obj. 7. The guide is scheduled for production in the final year of the project after compiling data from the previous years of work. It is unrealistic at this time to prepare this guide. However, we have initiated filming of the greenhouse in operation for production of an educational video. A 3D schematic animated drawing of the bubble greenhouse and all of its mechanical components was produced using a CAD program to be used as part of the video. An outline and first draft of a script has also been done and is a work in progress at the time of this report. Discussions with Dr. John Bartok have begun to develop the guide to ensure it is applicable yet not redundant.
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.
To date, approximately 530 growers and greenhouse specialists have received information about energy conservation in greenhouses. We have also interacted with several local growers, and others who are located outside the region and overseas, who are specifically interested in the bubble system. At least 5 growers in Vermont and New Hampshire have received energy audits since the start of the project, and all of them have made major changes to their operation as a result of information learned, and reduced energy consumption as a result. Though the bubble system continues to generate interest, challenges associated with its operation prevent us from fully realizing its energy conservation benefits. Until major design changes are made, we feel these difficulties will limit its implementation by growers in the future.
Impacts and Contributions/Outcomes
This project continues to serve as a catalyst for discussion about greenhouse energy conservation among growers, though the potential of the bubble system remains to be realized. It should be noted that the goal of the research component of this project was to assess the suitability of the bubble system. The continued problems associated with keeping the bubble insulation system operating proves that it is not ready for general use or commercialization. In fact, it would need major redesigning to be suitable for installation into any greenhouse operation. However, the system never ceases to intrigue growers, engineers and greenhouse specialists of all types. 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, Dr. John Bartok has interacted with growers through energy audits, which growers have found very informative. He continues to express his willingness to assist with producing a guide on energy conservation. 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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