Black Shade Cloth Versus Reflective Screens

Black shade cloth (left) and FLS reflective shade on Quonset greenhouses in evaluations at North Carolina State University.

Few factors can affect plant development as much as temperature fluctuation, particularly in the heat of summer. Monitoring and controlling both air and leaf temperature can drastically affect a plant’s productivity and quality.

Leaf and air temperature can differ greatly, by as much as 10°F to 30°F. Proper greenhouse shading, however, can help keep leaf temperatures in the most productive range.

As greenhouses transmit sunlight, they also trap heat, raising the internal temperature of the structure. Both plants and workers become stressed, and reducing the heat load becomes imperative. But what is the best material to accomplish that goal?

Recent studies conducted by Dr. Daniel H. Willits at North Carolina State University (NCSU) help shed light on the impact greenhouse shading selection has on plants.

These studies found that common black, knitted shade cloth provided little to no thermal improvement in the greenhouse. Installing reflective materials for external shading, in this case the Svensson FLS, resulted in lower greenhouse temperatures and net radiation.

The studies reported a 30 percent decrease in greenhouse heat gain for reflective materials compared to black shade cloth at the 60 percent shading level. This translated to significant reductions in both leaf temperature and greenhouse temperature, which increases a greenhouse’s productivity potential overall.

Early Research

As early as 1983, researchers speculated that shade cloths should reduce temperature in direct proportion to shade value.

Studies by Willits and Matthew M. Peet, an assistant professor of aerospace engineering at the Illinois Institute of Technology, in 2000 and Willits in 2001 found that shade cloths reduced energy gains less than the shade factor would suggest. Field tests indicate little or no temperature reduction can be expected from 30 percent black shade. The best estimates suggest black shade cloths are about 40 to 50 percent effective at reducing energy gain inside a greenhouse.

Full-Scale Testing

To compare the cooling characteristics of the two different types of shading, Willits and his team conducted computer model testing, physical model testing and full-scale testing on a single span polyethylene film covered greenhouse.

Computer modeling included radiation properties of the under and upper sides of the shade/poly layer and also transmissivity testing.

During the physical modeling, researchers mounted different shade cloths on wooden frames, then monitored and collected data on each configuration for four to six days. For these tests, researchers oriented the greenhouse shade frames south, and then tilted them to minimize the incidence angle at solar noon. Each was equipped with direct current fans at the upper end of the frames, and thermocouples were added to the air intake and exhaust to measure energy rise across the simulated fan-cooled house.

For the full-scale testing, researchers covered two 22 by 40 foot double-polyethylene covered Quonset-style greenhouses in the various cloths.

They tested two cloths from Ludvig Svensson, both rated at 60 percent shade. OLS 60 featured aluminum facing upward with white facing down. The second, FLS 60, featured white facing upward with black facing down.

Each four to six day testing cycle compared one of the Svensson cloths on one greenhouse with typical 60 percent black shade cloth on the other greenhouse. The researchers then switched the cloths to the other frame to eliminate any differences between the two frames. Each test greenhouse contained 208 tomato plants.

Researchers measured dry and wet bulb temperatures in two locations at both the entrance and exhaust end of each greenhouse, as well as dry bulb temperature and relative humidity at 12 locations along the length of the house, solar radiation at the top of the house and leaf temperature on the underside of each canopy. An external weather station recorded outside weather conditions.

They calculated the percentage difference in temperature rise from inlet to exit, energy rise and leaf canopy temperature for each reflective shade, using the 60 percent black shade cloth as the standard.

Black vs. White Results

Researchers found that 60 percent shades, both the FLS and OLS, reduced temperature rise by approximately 24 percent, energy gain by approximately 36 percent and leaf temperature by nearly 1°C.

They concluded that the cooling efficiency of external shade cloth is related to its temperature. In addition, reducing cloth temperature, either by water evaporation or other means, increases cooling efficiency.

Cooling efficiency is a term that could be used to express the amount of heat that accompanies light useful for growth (PAR light). This means that by replacing an absorbing (black or dark colored) shade with a reflective shade, you could:

• select the same shade and realize less heat gain,

• select a lower level of shading and benefit from higher PAR light transmission

Takeaways

Where heat stress is a challenge, choose a more efficient shade cloth to improve cooling. Where heavy shade has been necessary, choose a more efficient shade cloth with higher light transmission.

While black shades block light, they allow heat to radiate onto plants. External screens like Svensson’s FLS are made with highly reflective aluminum foil laminates or white films to reflect heat and light. They protect plants from stressing under too much sun, yet allow some light to penetrate by shading in a more efficient way.

Reflective external shades are not made to retain heat during the night. Instead, the screens provide daytime shade to cool greenhouse temperatures.

Leave a Reply

More From Equipment...

May 22, 2015

Nexus Greenhouses Is Optimistic For Expansion Into New Markets

Cheryl Longtin and Mike Porter, who own Nexus Corporation, say they were excited to attend the grand opening of Gotham Greens’ new structure atop the new Whole Foods grocery store in the Gowanus neighborhood in Brooklyn, N.Y., when it opened in December 2013. The project is just one example of some of the new and expanding markets that Nexus Corporation has expanded into over the past few years. Jeff Warschauer, vice president of sales for Nexus, says the company has enjoyed getting to know and working with the founders of Gotham Greens, Viraj Puri and Eric Haley, and Jennifer Nelkin Frymark, the chief agriculture officer, on their innovative approach to business. “They are very excited and work hard internally – just great people,” he says. “From our perspective, it’s great to see that excitement and vision. The employees there are happy and there’s no turnover; they’re only adding new people […]

Read More
Farwest2015

May 20, 2015

2015 Farwest Show Announces Second Annual Equipment Innovation Day

The second annual Equipment Innovation Day will be Tuesday, Aug. 25, prior to the 2015 Farwest show, which will be August 27-29 in Portland, Ore. Equipment Innovation Day, which was enthusiastically received in 2014, offers a real-time opportunity to see new heavy and automated nursery equipment in action. The demonstrations take place in manufacturing and nursery settings, adding value to the showcase. Attendees will be able to talk with participating manufacturers and learn first-hand from innovative growers who use the equipment in daily operations. The day-long event will be held at the main manufacturing plant of GK Machines, Inc., Donald, Ore. Further demonstrations of field equipment will take place at the nearby nursery of A&R Spada Farms, LLC. Bus travel to and from the event is planned, starting at and returning to the Oregon Convention Center. Attendees are welcome to provide their own travel to and from the site. Preregistration is required. The cost […]

Read More
Bee On Flower

May 20, 2015

White House Task Force Releases Pollinator Health Strategy

An interagency Pollinator Health Task Force commissioned by President Obama released its “Strategy to Promote the Health of Honey Bees and Other Pollinators” on May 19. The strategy, released in accordance with the Presidential Memorandum issued last June, is accompanied by a Pollinator Research Action Plan, which outlines needs and priority actions to better understand pollinator losses and improve pollinator health. The recommended actions will be supported by a coordination of existing federal research efforts and accompanied by a request to Congress for additional resources to respond to losses in pollinator populations. Pages 47 through 52 specifically address pesticides and pollinators. The report calls out plant production, native plants, mosquito control and all urban uses in its Pollinator Action Plan. RISE (Responsible Industry for a Sound Environment) says it supports the goals of improving pollinator health and habitat contained in the White House Pollinator Task Force’s release of its National […]

Read More
Latest Stories
Growers are looking for low-cost options for temperature control, like circulating fans and exhaust fans.

April 10, 2015

New Ways To Give Growers Control Of The Greenhouse Envi…

From heating systems to circulation fans, manufacturing companies are finding new ways to help growers control the greenhouse environment, save on energy costs and streamline production.

Read More
Polyarch Berns

March 12, 2015

The Energy Efficient Greenhouse

New coverings technology means today’s films, plastics, shade cloths and climate screens slash heating and cooling costs while improving crop productivity year round. We checked with manufacturers to see what’s new and uncovered some best practices for buttoning up your greenhouse. Here’s what you need to know about the latest trends.

Read More
FormFlex_MTZ Hanging Basket

March 11, 2015

4 New Ways To Automate Your Operation

These new automation products can help streamline labor-intensive tasks, saving time and labor and increasing productivity.

Read More
Outfitting Your Greenhouse

February 24, 2015

Save Energy With The Right Greenhouse Glazing

The glazing you choose can make a big difference in your energy bill and the uniformity of your crops.

Read More
Michigan State University Extension

February 24, 2015

Ethylene From Defective Greenhouse Heaters Damages Crop…

Malfunctioning greenhouse heaters can lead to crop damage from ethylene and carbon monoxide induced illness for workers. Michigan State University's Extension educators Tom Dudek and Randy Beaudry teach you how to recognize the symptoms and check greenhouse heaters to avoid the concern.

Read More
Havest Automation Robot

February 18, 2015

Robots Grab Hold Of Growers’ Material Handling Needs

Harvest Automation’s HV-100 robots automate one of the hardest, most labor-intensive jobs at growing operations – plant spacing. With more technology coming, investing in robots could become even more realistic for growers of all sizes.

Read More

February 1, 2015

4 Lighting Products For Your Operation

These new lighting products have been developed for maximum energy efficiency in greenhouse production. Check out the slideshow to see which products are right for your operation.

Read More
LumiGrow

January 30, 2015

LumiGrow Expands Customer Base In 2014

LumiGrow, Inc. is adding more than 125 new commercial, governmental and research customers to its roster of customers, and beyond the new accounts added this year, many existing customers significantly increased the number of LumiGrow products they use and research customers made LumiGrow a part of their efforts to add to the body of knowledge about spectral science.

Read More
harvest automation featured image

January 13, 2015

Harvest Automation Extends Robot Rental Program

Harvest Automation's robot rental program proved to be such a success for the company that it is being extended through the spring. The program was unveiled last year as a way for customers to get started with HV-100 robots.

Read More

January 9, 2015

Innovations In Irrigation

Need help improving your irrigation? Check out these new products.

Read More

December 2, 2014

Hanna Instruments, Inc. Introduces pH Electrode With Bl…

Hanna Instruments recently released HALO, a professional pH probe with Bluetooth Smart (Bluetooth 4.0) technology that transmits measurement data directly to an Apple iPad running the Hanna Lab App.

Read More

November 24, 2014

Biomass Six Years Later: Would Pleasant View Do It Agai…

Pleasant View gardens installed its first biomass boiler six years ago and has added a second one since. Now it’s reaping the benefits of lower heating costs and dollars saved.

Read More

November 18, 2014

7 New Media And Light Products For Greenhouse Productio…

New media and light products cover a broad sweep of growing conditions.

Read More

October 21, 2014

GreenClocks New Generation City Farm Fitted With Philip…

Osaka Prefectural University’s new city farm, which has been fitted out with Philips LEDs, opened September 19.

Read More

October 1, 2014

Harvest Automation Introduces Robot Rental Program

Harvest Automation has unveiled a new introductory robot rental program as a way for customers to get started with HV-100 robots.

Read More

September 15, 2014

Precision Horticulture: What Piece Of Equipment Or Syst…

Let us know what product you can't live without.

Read More

September 15, 2014

New Products For Precision Growing

Increase efficiency with these new offerings in equipment, automation, structures and software.

Read More

August 12, 2014

LEDs Comparable To High Pressure Sodium Lamps For Cutti…

In his Cultivate'14 presentation on lighting the future of young plants with LEDs, Christopher Currey, Iowa State University, shared recent research on how LED lights stack up against high pressure sodium lamps for liner and plug production.

Read More