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Concentration of CO2 in the Atmosphere

Coming Attractions in Greenhouse Energy Efficiency

Greenhouse

Mike Stiles Ph.D.

Hello, greetings from the front lines of Green Greenhouses. By way of introduction, I’ve consulted with the electric and natural gas utility National Grid in upstate New York for the last several years. I’ve developed methods for quantifying the energy impacts of greenhouse efficiency measures for National Grid’s incentive programs.

This article covers very recent developments in energy-efficiency greenhouse design here in the Northeast U.S. But before we begin, I have to lay out some ground rules.

My work with National Grid is covered by confidentiality agreements, so I can’t name names or divulge proprietary details with which I’ve become familiar. This article is also vendor-neutral, and I’m not here to promote any specific products. I can however introduce up-and-coming greenhouse technologies and provide key words to get you started on your own research. For starters, do a web search on “large- scale winter greenhouses New York State.”

That said, here are some technologies and developments that may interest you if you’re looking to grow crops year-round while minimizing your energy and carbon footprint:

Thermal Curtains: These are made from specialized textile materials for the greenhouse environment. Mounted on motorized rollers, these curtains provide an extra thermal barrier over crops and are also useful for solar control in the summer. Although they are not a new technology, they haven’t been adopted very widely in the Northeast. They are prevalent in other parts of the country like California and Oregon where utility company incentives are already available.

In cold climates, thermal curtains save heating energy by about 10 to 30% annually, depending on the crop’s heating requirements. Paybacks are on the order of 10 years and will shorten as utility company incentives become available locally. Key words: Greenhouse thermal curtains; Energy Trust of Oregon; SoCalGas heat curtains; PG&E thermal curtains.

Greenhouse Foundations: Building your greenhouse with an insulated concrete block foundation will reduce your heating requirements by about 10%. Additionally, it establishes a “thermal bubble” that keeps soil temperatures above 50oF year-round. This is an important use of the soil as a thermal storage medium during the long winter months when the sun hardly shines in the Northeast.

There is a related technology that pumps warm, moist air from the peak of a greenhouse into the soil enclosed by the foundation via a network of ducts. It saves an additional 10% on annual heating. Key words: Greenhouse foundations; climate battery.

Lighting: Efficient LED grow lights have been the subject of much publicity so it isn’t difficult to get information about them. When placed under thermal curtain canopies, they synergistically contribute to heating the crops.

Controls, Controls, Controls: Automation and data logging are becoming increasingly important for integrating and running advanced greenhouse systems. Data records from electronic management systems are also becoming increasingly useful for documenting energy performance for utility incentive programs.

Hemp and Cannabis: They have been the focus of a boutique market that blew a bubble. Emphasis has been on large scale indoor industrial operations that do not take advantage of natural resources like sunlight. Some states have already experienced market saturation under these conditions – how much weed can people smoke, for crying out loud? The commercial future of these plants is in energy-efficient small-scale community greenhouses, depending, of course, on the chaotic legal and regulatory environments we’re experiencing. Key words: Evan Mills cannabis

The Future of Greenhouse Design: You’re sitting at your computer sipping a cup of locally grown Maghrebi mint tea. After entering your information into an app, you get a screen something like the one shown in the graphic.

In the upper left corner of the graphic is a visual of your selection and a summary of its energy performance – the more efficient it is, the less heating fuel you will need, but the more expensive its first cost will be. The graph in the lower left shows your energy savings compared to “business as usual” and is the basis for your utility incentives, rebates, and so on.

The upper right corner is a summary of your crop selections, your projected energy rates, and other operational metrics. The app has optimized your options given your growing requirements and geographic location. The bottom right panel shows your bottom line in a typical year of growing conditions.

OK, we’re not quite there yet, but you see where I’m going with this. As soon as you add a foundation to a greenhouse and stock it with efficient heating, ventilation, and lighting equipment, it starts acting much more like a building than a plastic wrapper out on the field. And we know from the last 50 years of building science how to design buildings for energy efficiency with materials you can buy commercially. Stay tuned folks!

Mike Stiles is a Senior Energy Engineer at L&S Energy Services Inc. and can be reached at mstiles@LS-energy.com. For additional technical information on advanced greenhouse designs visit

https://ls-energy.com/advanced-greenhouse-development/.

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