Better than polycarbonate?

Aside

Years ago I gardened in a greenhouse that was covered with a space age film called “Tedlar.” It never really took off, but it did have some impressive characteristics. Now there is a next generation of greenhouse film that may dethrone the ubiquitous polycarbonate. It is called ETFE film. One common brand name of this film is “F-Clean®.” Special thanks to Shawn Speidel (with Soil Fertility Service, LLC www.SoilFertilityService.com), who brought me up to date on this material.

ETFE (ethylene tetrafluoroethylene), fluorine based plastic. While it is new to us in the US, it has long been used in Japan, Europe and China in commercial houses. It is also what was used on the Eden Project in Great Britain and the .

Eden Project uses ETFE film

 Advantages of ETFE glazings or “F-CLEAN®”

  • More light- ETFE films are 94 % light transparent. This beats out clear glass and most polycarbonate glazings. In shady areas of the world 1% more light may result in 1% more ‘gain’ in terms of yield.
  • Dirt Resistance- The low surface tension of the film means that all it takes to clean the greenhouse is a shower of rain or snow. Snow slides off easier helps maintain optimum light.
  • Fire resistance- Like polycarbonate, ETFE films are self extinguishing material. ETFE, the base material from which F-CLEAN is made, is rated UL 94-0 by the Underwriters Laboratories Inc.
  • Improved crop quality- Unlike glass or polycarbonate glazings, F-CLEAN® allows the penetration of ultraviolet light, which has a positive effect on the quality of fruit and plants. Fruits ripen more quickly and develop a better color. Flowers gain more intense color. UV light also makes plants less susceptible to disease. If you want, you can add a UV-block option to the process of making ETFE glazings.
  • Anti Drip Characteristics- ETFE does not allow condensation to form which could drip onto the plants, fruit and flowers. Drops of condensation also reflect the sunlight, reducing incoming light.
  • Diffused light- F-CLEAN® is available in both clear and diffused versions. Diffused light tends to grow plants better by eliminating shadows.
  • Heat retention- if you use the optional double layered F-CLEAN® It will save more energy over single layer options. However, like any glazing, when you double or triple the layers, the amount of light entering the greenhouse is also reduced.
  • Durability-ETFE has an approx. life of 15 years but F-Clean® is guaranteed for 10 years like polycarbonate (also 10 years). However, there are many greenhouses that have been covered with ETFE films that are over 27 years old and still show no sign of deterioration. It just depends what the manufacture wants to guarantee. Some expect it to last as long as 50-60 years.
  • Strong enough to bear 400 times its own weight
  • 25 to 50 times lighter than the other alternatives materials
  • It can be stretched to three times its length without loss of elasticity
  • a working temperature range of -300 °F to 300 °F
  • It Is recyclable

Downside to ETFE

  • Not readily available for home greenhouse growers (yet).
  • It is prone to punctures by sharp edges or a sharp impact (knife), but can be patched
  • Must be tensioned in order to function properly which requires specific types of mounting hardware.
  • Transmits more sound than glass.
  • It is usually applied in several layers that must be inflated and require steady air pressure thus working with ETFE is difficult for small building projects.

    Beijing National Aquatics Center uses ETFE film

Links:

Night greenhouse insulation

We lose heat from the greenhouse through your glazing (glass or plastic) at night. When you have two or more layers of glazing you gain insulation from having dead air space between the layers. Some glazing has as many as five layers thick as in the case of this polycarbonate pictured to the right. th_043Sometimes you can forgo night insulation because you have a glazing with multiple layers. By the way, the more layers of glazing you have, the cooler your summer daytime temperatures will be. But, there is a trade off in light transmission. I wouldn’t go with more than a three layer polycarbonate if you live in an area that doesn’t have many sunny days. I live in a sunny location and do fine with a five layer polycarbonate.

A cheap way to add another layer of glazing is to add a bubblewrap material to your glazing.

bubblewrap & weatherstrip
You can also add insulation by using a insulation barrier. Commercial growers have long used aluminized curtains for both holding in the heat and to provide some shading when needed. Styrofoam beads have been blown in between glazing layers to provide night insulation but have suffered from static electricity problems, making the beads adhere to the glazing. This was first experimented with at Kansas State University by Architecture professor Gary Coats back in the 1980s.

More recently a number of people have been experimenting with the use of soap bubbles to insulate between greenhouse glazings (see video below).

Bubble insulated greenhouse

Bubble insulated greenhouse

New solar heated kit greenhouse available

This site (the Suncatcher Greenhouse) just came to my attention. While they are doing

nothing new when it comes to basic solar heating as we have been advocating for over 36 years, it appears to me that they are doing everything right. It is good to see kit manufacturers embrace this at long last. Similar to this kit is Charley’s Phoenix greenhouse and the Growing Spaces dome greenhouse.

The only thing I don’t see on the Suncatcher Greenhouse site is a price which tells me that they probably are pretty pricey. Still I’m pleased to see another kit greenhouse push the 100% solar goal!

Solar Greenhouses, Chinese Style

– from Energy Farms web site

Chinese-style solar greenhouse.“Another alternative is a greenhouse design developed in northern China in the mid-1980s that relies primarily or entirely on solar energy for heat. By 2000 these greenhouses already covered about 260 thousand hectares (650 thousand acres) in northern China, and by 2004 they were supplying residents of northern China with 90% of their fresh produce in winter… Continue reading

High Tunnels

– from Hightunnels web site

“High tunnels, or hoophouses, are unheated greenhouses that can help market gardeners extend their growing season so that they can improve the profitability of their farms.
This website is part of a USDA-sponsored project that is testing and promoting high tunnel systems in the Central Great Plains…” To learn more, visit www.hightunnels.org.