5/24/2013
What's Behind Your Curtains?
Jennifer Zurko
Twenty-eight to 30 cents per gallon. That’s how much oil cost in 1974.
We look at that and scoff, but it was up from 12 to 13 cents per gallon in just one year. Today, according to the U.S. Energy Information Administration, heating oil is hovering at about $3.00 per gallon. We’ll never see oil under $1 again.
pictured: This retractable heat retention/shade screen systems uses Svensson FLS Reflective Shade and is installed on the roof along the rafters. Photo courtesy of Growers Supply
But the first major energy crisis in the mid-’70s opened the door to innovative products to help growers save on fuel. Vic Ball wrote in the August 1975 issue of
GrowerTalks, “We won’t see cheap fuel again in our lifetime … [so we] must rethink basic approaches to growing/marketing.”
Growers had already been using shade cloths to create short days, which also kept the greenhouse cool during certain months. When fuel skyrocketed in the ’70s, growers were rationing, using portable heaters (which posed a fire risk), looked into other fuel sources (like coal and propane) and turned to crops that required less fuel. Toward the later part of that decade, growers were erecting double-poly curtain systems—called “insulation sheets”—in their greenhouses to keep the heat in. It reduced the light levels, obviously, but it also saved on energy—reportedly 40% to 50% in fuel savings.
Now, you can find some type of energy curtain in almost every greenhouse. So, what is today’s grower looking for in energy curtains and what does the future hold? We asked a few manufacturers to tell us what they’re seeing out in the field.
What’s trending
Energy-to-crop focus
Kurt Parbst, president of Ludvig Svensson’s North and South American subsidiaries, said the original reason growers used energy curtains was to insulate the greenhouse during the night. But growers soon realized having a formal system gave them climate control along with ventilation, heating and cooling. The curtain also affects the quality of the plants by influencing temperature and quality of light.
“Understanding the impact means that a grower can use the curtain to better steer the climate to conditions in which the crop is more productive or a higher quality,” said Kurt. “Growers learned that they installed curtains to save energy, but found they could grow better crops.”
Multiple systems
Hans van der Spek, owner of J.C. van der Spek Greenhouse Services, said that he’s seen several growers installing multiple systems, one on top of the other, for different types of crops and needs.
“Each system provides its own benefit as a growing tool, as well as the energy savings that they create together,” said Hans.
Fire security
After the shift from glass to poly or fiberglass greenhouses during the ’60s and ’70s, many growers were faced with sleepless nights because they realized the risk of a fire was greater with plastic houses and it’s been a consistent worry ever since. But now, companies that make energy curtains are using flame-retardant materials.
Kurt said this is determined by assessing the flammability of the glazing, the type of equipment that’s present that could potentially be a point of ignition, the value of the crop and the facilities.
“Originally, it was thought that there was not much to burn in a greenhouse and the perceived risk was low. Now there are petrochemical-based plastics in glazings, curtains, plant containers and, perhaps, even benches,” explained Kurt. “Today’s crops, especially in high-density areas like plugs, are extremely valuable. Motors, pumps and lamps are operating automatically and often without the presence of a night watchman. Installing a curtain with no fire security is a thing of the past. Since about 2003, the commercial-grade energy curtain had at least a fire break safety measure in every panel.”
More competition
In the world of energy curtains, there are more cooks in the kitchen. Energy curtains have been used for nearly 40 years and new suppliers have realized the benefits. Zachery Carr, greenhouse specialist for Growers Supply, said the market has become more competitive as more manufacturers vie for growers’ business by specializing in energy conservation. And, during the last decade, automatic systems have replaced exterior, stationary shade panels and spray-on shade, said Zachery.
What’s changed
Adaptability
Since the energy crisis of the 1970s, energy curtains have come a long way. The first ones looked simple, but really complicated things—especially when it came to light and humidity levels.
“Early curtains were films that did not transport water or humidity,” said Kurt. “They transitioned from films with perforations to textile products to catch condensation and transport excess growing zone humidity to the attic.”
Plus, today’s curtains can be customized to fit any type of greenhouse, said Hans. The use of seals (or skirting) around the perimeter of the curtain system along with an aluminum edge and rubber closure provides almost a completely airtight system with little or no heat loss, he said.
More options
In the age of disco, growers would create makeshift shade curtains with what they could get their hands on—like a foil or aluminum sheet that would reflect light. Now, there are a multiple suppliers who specialize in energy curtains who will help you decide what’s best for your greenhouse environment.
Longer lifespan
Through the years, manufacturers have made energy curtains so growers could get more for their money. Many of the makeshift curtains only lasted through one season. Hans said that systems can last up to 20 years with proper maintenance and all of our sources agreed on a typical lifespan of the curtain to be around seven to 10 years.
“Most curtains are warranted against premature UV degradation and excess shrinkage for a period of five years,” said Kurt. “The longevity over the North American region is typically eight years, but may extend up to 10 or 12 years, depending on the UV exposure and frequency of opening and closing. With the expense of replacement, long service life is likely to remain the requirement.”
What’s important
Is it in the budget? Can I trust my vendors?
As with most major greenhouse investments, cost is the primary concern. That’s why it’s important for suppliers to be honest and work within a grower’s budget, Kurt explained. And for large growers, who are under pressure to deliver in tight windows, reliability is very important. Reliability of delivery and installation, but also reliability over time.
“As growers become larger and more sophisticated through working in large, demanding retail channels, their appetite for risk diminishes,” said Kurt. “Growers invest in facilities to make sure that they can deliver through the seasons and over the years. This means that it is important to get good advice from suppliers that understand how components fit into the larger picture.”
Saving some money
An obvious one, and something manufacturers continue to focus on when developing new products and working with growers. Most use energy curtains to provide some shading, which holds in the heat as an added perk, said Zachery. A curtain that’s versatile tends to be the most popular.
“Energy costs for heating are typically a grower’s second largest expense behind labor,” said Kurt. “Crop management—or labor associated with watering, spraying, and pruning, etc.—is more intensive when climate conditions are less than ideal. All things being equal amongst skilled greenhouse growers with the capability to deliver in a competitive marketplace, the low cost producer is going to win. Low costs arrive out of investing in efficiencies, like the insulating benefits of curtains.”
Meeting the need
You also have to look at what you’ll be growing and where you live. Maybe you just need some new shade cloth because you’re still growing the same crops … but what if you decide to dabble in something new, like vegetables? You’ll need an energy curtain that offers more diffused lighting, said Hans.
In the future
Light diffusion
Kurt said there has been an increase in popularity of curtains that diffuse more light. We’ve known for a while that diffused light offers a lot of benefits, but now it’s actually being quantified by looking at how the plants are performing. The hot spots aren’t as hot and damaging, the bottom leaves are receiving more light, and shadows from the greenhouse and equipment is lessened.
“Light diffusion comes at the expense of a loss in light transmission. Therefore, if diffuse light is realized permanently through the glazing, then light is reduced during dull periods when a decrease in light transmission is undesirable,” explained Kurt. “Think about production early in the year—light diffusion is most valuable when solar radiation is too intense, not when conditions naturally create diffuse light from cloud cover. So creating diffuse light on demand, only when radiation conditions are too intense, is functionally a natural fit for a retractable curtain.”
How to use your energy curtains
It’s not just about what the curtain does, but when you should be using it. Kurt says Svensson gets that question from growers all the time—especially when you’re trying to get optimum growing conditions while saving a few dollars. It depends on light needs, set-point temperature, the change in U-value of the cover (when it’s extended), the value of the plants, the cost of heating and light-use efficiency to convert sunlight. More and more growers are using computerized climate control systems to help them reach this, which takes the guesswork out of figuring out when you need to cover and uncover. Manual systems will be a thing of the past.
Saving even more on energy
Victor Encinias of Growers Supply said he’s seen a lot more growers asking them to retrofit existing structures with energy curtains to help them save on installation costs. Really, the main desire is keeping energy costs down, so even if you can’t afford to improve or build a new greenhouse, you can still invest in a curtain system.
More growers are also asking suppliers to tell them the actual percentage they can save … and to prove it, said Zachery.
“Manufacturers are focusing on proving their product worth by running trials and collecting case studies,” Zachery said. “One example of such advances is the use of white or reflective shade material as opposed to traditional black knitted shade material. Although black shades, it also re-radiates heat that it has absorbed back into the greenhouse. A white 40% shade may cool the greenhouse, as well as a 60% black shade. The white shade also lets in 20% more light that is used for plant production.”
Saving on water
When you think about energy curtains, do you think about irrigation? You should, said Kurt, who talked about a term called “evapotranspiration,” which is the loss of water from the Earth’s surface through a combination of evaporation (from soil and plant surfaces) and plant transpiration (internal evaporation). He said that net radiation is a major factor in evapotranspiration rates and is influenced by shade curtains.
“Some early work in areas where water is scarce and valuable indicate that water-use efficiencies can be doubled [produce plant products with half of the water] with the use of reflective-shading curtains,” said Kurt. “In the greenhouse and nursery industries, we can save a tremendous amount of water—some of which is expensively amended—through a combination of appropriate material properties, appropriately timed use and know-how.”
GT