Improved Ventilation for High Tunnels

I have received many inquiries about how to improve ventilation of high tunnels from growers with tunnels that have only roll-up sides. The issues they are facing tend to be either high temp, high humidity or both, leading to plant stress or disease. These situations tend to be in less than ideal sites for ventilation and/or temperature control. For example, crowded lots with trees or other significant wind breaks close to the tunnel, high southern exposure (which can be good of course), and/or simply calm sites that provide little ventilation.

Keenan Meier Shutters with flanged seal highlighted.

Roll-up sides alone tend to work for tunnels on sites with generally good air flow. Diffusion between inside and outside does happen, of course, but is slow and unlikely to achieve good ventilation along the center of the tunnel, especially with dense vegetation later in plant maturity. But, I think of a tunnel in this instance a bit like a wood stove. Without a chimney-effect natural draft, you’re really only getting ventilation from the sides and only then if there is a decent breeze. Warmer air and, therefore, humidity will tend to collect in the canopy and peak.

Passive wax cylinder louver actuator. [Photo Credit: http://www.littlegreenhouse.com/accessory/vent2.shtml]
This probably is OK in many sites for most crops. But not always. In many cases gable vents will improve ventilation by acting as outlets for warm humid air in warmer seasons and by allowing for low volume ventilation in colder weather. I recommend a simple 24″x24″ gable vent (for a 30’x96′ tunnel) on each end wall, with a thermostatic wax cylinder actuator like the ones made by J. Orbesen Teknik APS available from LittleGreenhouse.com., FarmTek, and Agricultural Solutions among others  The actuators require no electricity, are relatively inexpensive and are passively controlled by the wax cylinder based on temperature.

At the very least, when building end-walls consider framing in a rough opening to accept a 24″x24″ in the end wall so that a future install is easier. If you want to skip the expense of a louvered, wax cylinder system, you can use a manually-controlled sheet of plywood to open and close the vent. If you go with a louvered vent, seek one that has a flanged seal it closes against. Keenan Meier, and Munters-Euroemme has such flanged, louvered dampers.

Munters Euroemme fan with flanged seal being pointed out.

These have zero daylight when closed which results in a solid seal. Most others on the market that I have seen have no such closure seal.

Fans

Fans in greenhouses and high tunnels generally perform two tasks: (1) circulation / mixing / stirring and (2) ventilation.

  1. Circulation / Mixing / Stirring – Sometimes referred to as horizontal air flow or “HAF” fans, these fans are generally hung from the inside horizontal structural tubing.  They only mix the air.  The benefit of this is consistent, well distributed growing conditions.  It also ensures that your control sensors are seeing the “average” conditions of the space. Remember that HAF fans work to mix the space (circulate the air) but don’t significantly improve ventilation. HAF combined with roll up sides can do the trick, but the site is the key. There needs to be a steady cross breeze for any significant air exchange to occur.
  2. Ventilation – Ventilation, or “exhaust” fans provide air exchange between the inside and outside. This is really important in controlling temperature (cooling) or humidity (drying).  The only way to remove heat or humidity from a standard high tunnel or greenhouse is by actively removing air from the space and bringing in outside air.  Ventilation (cooling) systems are covered very well by Bartok and Aldrich (p. 70).  Basic rules of thumb for ventilation are 8 CFM/ft2 (of growing space) for summer cooling and 2 CFM/ft2 for cooler months.

References:

Bartok, J., & Aldrich, R. (1994). Greenhouse Engineering, NRAES – 33. Natural Resource, Agriculture and Engineering Service (NRAES). Retrieved from http://host31.spidergraphics.com/nra/doc/Fair%20Use%20Web%20PDFs/NRAES-33_Web.pdf

Rats (and other rodents)

Download the PDF version of this page here!

When considering storage rooms, wash and pack sheds with growers there is one topic that is sure to strike a nerve: RODENTS.

This document is intended to provide summary information about measures you can take to reduce crop losses from these pests.  It is the result of a review of current literature on the topic and feedback from the Listserv of the Vermont Vegetable and Berry Grower’s Association (VVBGA). This document includes both active measures (traps, rodenticides, FSMA compliant cats and ball pythons, etc.) and passive measures (sealing, doors, packing, hardware cloth, novel construction, accepting the loss, selling everything early). But why are these creatures so challenging?  Here’s some background1:

House Mice Can

  • Enter openings larger than 1/4 inch
  • Jump as high as 18 inches
  • Travel considerable distances crawling upside-down along wire
  • Survive and reproduce at a temperature of 24°F if adequate food and nesting material are available.

Rats Can

  • Crawl through or under any opening higher or wider than 1/2 inch
  • Climb the outside or inside of vertical pipes and conduits up to 3 inches in diameter
  • Jump from a flat surface up to 36 inches vertically and as far as 48 inches horizontally
  • Drop 50 feet without being seriously injured
  • Burrow straight down into the ground for at least 36”
  • Swim as far as 1/2mi in open water, dive through water traps in plumbing, and travel in sewer lines against a substantial water current.

As one grower put it, “To deal with rats, you’ve got to think link a rat!”

Bottom Line

Cleanliness and Sanitation – Keep food sources well contained and sealed up, reduce “harborage” (places they can hide and live including weeds around the edge of a building), minimize available standing water. In short, make it unappealing and uncomfortable for them.

Rodent Deterrent Construction – Keep them out of the building. [References 1-3 provide very detailed guidance and novel, passive and relatively inexpensive construction ideas] Some examples from the references include keeping all wood products like cardboard, roots, or lumber off the ground and away from the building. Installing proper drainage with sand, stone and proper slope away from your building helps reduce moisture which can carry other pests like beetles and termites. Think about your exterior landscaping and its ability to trap moisture against the building. Keeping grass and weeds trimmed won’t leave a place for rodents to hide and travel. Think about all possible points of entry, sills, doors, windows, roofs. Mice can sneak into small holes and cracks so do your best to seal up all possible points of entry.

Population Reduction — Bait, trap, kill.

Using snap traps, sticky pads, poisonous bait are all the most effective ways of dealing with a rodent problem [References 5-7].

Responses from the VVBGA LISTSERV 

The following are responses from Vermont growers. These are some of their challenges and solutions related to rodents on their farms.

  • I have had over 20% of my sweet potatoes damage by voles.  Usually the largest sweet potatoes are the ones half eaten.  The next year I put five “yard windmills” in the sweet potato bed, 100 ft. long, along with a half stick of gum under the black plastic by each plant – cheap gum from the discount food store.  Both were done after I removed the row covers and before the vines spread. That reduced the damage to less than 5%. Very anecdotal and empirical data but worth exploring.  Supposedly the voles do not like vibration of the windmill and eating the gum gives them a bellyache, if fatal I do not know.  Bigger windmills, four inches in diameter and larger, with metal post seem to work better.  How much gum is actually needed I do not know. A SARE  grant in your future.
  • Not the cheapest retrofit, but have had the best luck with making all walls tin or concrete, and having rat traps permanently set at every overhead door jamb, since the seal is not 100%.  Ventilate with in-wall intake and exhaust fans instead of opening doors.
  • I recently tried the tin cats and was happy. Baited them by putting small amount of oats in the trap and tilting it so the grain slid to the end where the screen was. After the mice got a few seed through the screen, they were drawn into the trap to get the remainder. Two mice in the same trap on the first night. The downside is that you have to clean out all the grain each time so it doesn’t hamper the trap mechanism. Have used Contract waxy block in bait stations for at least 4 years. Switching to a different bait because I think they are starting to get a resistance.
  • I’ve been using that old root cellar all winter for 3 years now without any rodent problems. The process of having someone cement hardware cloth over every crack and crevice was time-consuming but really seems to have worked. I think I finally got rid of the rats in my toolshed through a combination of trapping and disturbing their nesting spots. I’m curious about rodent solutions that apply to the field and high tunnel. I’ve tried to keep cats but the fishers get them.
  • I have not had a single animal in the new barn that I built with the 12” concrete knee wall. I partly contribute the success to the fact that I do not set the bins on the ground. They are filled on the trailer and go directly from the trailer to the barn. This reduces the chance that a hitchhiker will take a ride into the barn.

  • We are a very small pumpkin farm and don’t have the storage needs for food, but I use lots of snap traps and dump those little, dead vermin bodies while wearing a happy smile!
  • We have only killed rats by accidentally moving a pallet onto one. Can’t bait them. They are very intelligent.
  • “We have a great barn cat and a Jack Russell terrier for our farm.”
  • Mice – kernel of corn wedged into mousetrap trigger covered in peanut butter. Rats – same as above but do not the set the trap for several nights and remove all other food sources (in chicken hutch empty all food containers) then set the trap.  Putting a milk crate over the trap prevents chickens, cats, dogs from getting caught.  Also works with chipmunks, and occasionally with red squirrels. Voles – hard to trap, run them down and stomp.

REFERENCES

  1. Baker R., Bodman G. and Timm, R. 1994. Rodent-Proof Construction and Exclusion Methods. The Handbook: Prevention and Control of Wildlife Damage. Paper 27.  http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1025&context=icwdmhandbook
  2. Hoddenbach, G., Johnson, J., Disalvo, C. 1997. Rodent Exclusion Techniques. A Training Guide for National Park Service Employees. National Park Service. http://www.ehs.ucsb.edu/files/docs/e
    h/ihrodentexclusion.pdf
  3. Simmons, S. 2005. Pest Prevention Construction Guidelines and Practices. CASBO Journal. http://www.cdpr.ca.gov/docs/pestmgt/pubs/casbo_article.pdf
  4. UMass Extension. 2008. Rodent Control on Farms. Fact Sheet – https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/RodentControl08-44.pdf
  5. University of Maryland Extension. 2014. Rodent Control on Small Poultry Farms. Fact Sheet. https://extension.umd.edu/sites/default/files/_docs/publications/FS-
  6. 985%20Rodent%20control%20on%20small%20poultry%20farms.pdf
  7. Pierce, R. 1982. Bait Stations for Controlling Rats and Mice. Fact Sheet G-9444. University of Missouri Extension. http://extension.missouri.edu/p/G9444
  8. Vantassel, S. M., Hygnstrom S. E. and Ferraro, D. M. 2012. Bait Stations for Controlling Rats and Mice. Fact Sheet G1646. https://wildlife.unl.edu/pdfs/bait-stations-controlling-rats-mice.pdf.

Pumps and Pipes

A Taco 007
A Taco 007, shaken not stirred.

“Will the 007 be enough?”  is a common question in early spring as greenhouses around the region fire up and we do our best to keep seed trays and their cargo warm on the still-cool nights.  My mind instantly goes to “which movie?” And then I crash back to earth and realize this is a question about pumps and I am not Q. Continue reading Pumps and Pipes

Thermostats for Agriculture

I am often asked by growers and processors to recommend a thermostat for a greenhouse, cooler, or postharvest process use.  There are many to choose from and their specifications can be confusing. It is important to remember just what a thermostat does. It is essentially no different from the light switch on the wall with one very significant exception.  Instead of depending on a person to switch it from ON to OFF, we use a temperature measurement.  The accuracy of both the temperature setpoint (what you set) and the actual temperature (what the actual condition is) can be critical for production quality and energy efficiency. Continue reading Thermostats for Agriculture

Vermont Farmers Food Center Heats with Biomass

Rob Steingress (VFFC), Bill Kretzer (12 Gauge Electric) and Greg Cox (VFFC) perform final inspections before the initial firing of the boiler.
Rob Steingress (VFFC), Bill Kretzer (12 Gauge Electric) and Greg Cox (VFFC) perform final inspections before the initial firing of the boiler.

UVM Extension and others supported the recent installation of a 341,200 BTU/hr (output) multi-fuel biomass boiler at the Vermont Farmers Food Center (VFFC) in Rutland, VT.  The boiler heats the Farmer’s Hall building with the capability to use several alternative fuels to displace propane. The boiler was fueled primarily on wood pellets but was also able to feed and burn grass biomass pucks. This demonstration project carried a cost premium when compared to a typical propane heater installation.  That premium is paid back over time due to recurring fuel cost savings. A simple payback period of 2.2 to 8.0 years is feasible against a cost premium of $51,255 for the boiler depending on the fuel used and the amount of use. For more details about the project and the economic performance please see the report.

Continue reading Vermont Farmers Food Center Heats with Biomass

Grass and “Ag Biomass” Competitive with Wood Chips

Chris Davis (Meach Cove Trust) prepares the boiler and combustion testing equipment for a trial run of the new fuel.
Chris Davis (Meach Cove Trust) prepares the boiler and combustion testing equipment for a trial run of the new fuel.

Recent testing at the Meach Cove Trust has demonstrated strong economic and technical feasibility of grass-based biomass combustion fuels.  The use of solid, densified, cellulosic biomass fuels has been well demonstrated with wood pellets in residential and light commercial systems and wood chips in larger, often centralized systems.  The Grass Energy Partnership of the Vermont Bioenergy Initiative has been exploring an alternative form of fuel; grasses densified in a specially developed processor to take the form of 1.5”-2.0” round cylindrical pucks.  Grass fuels may be produced on otherwise marginal agricultural land, sometimes in perennial production and even in buffer strips offering environmental benefit.  Additionally, fuel can be made by densifying agricultural residue or biomass harvested from idle pasture or fields.  We have referred to this fuel as “Ag Biomass”. The testing summarized in this report has demonstrated the technical and economic feasibility of such fuels.

Continue reading Grass and “Ag Biomass” Competitive with Wood Chips

Finish Surfaces for Produce and Food Areas

This cooler space was finished with Trusscore PVC panels resulting in a smooth, cleanable surface.

Download an updated PDF version of this information here!

Smooth and cleanable surfaces are an important aspect of areas where produce is washed, packed, stored and processed.  Many farms are investing in renovations and expansions of these areas and are seeking materials to meet this “finish surface” need regardless of specific regulation.  Meanwhile, food processing companies are often required to incorporate these materials due to regulation.  This is a summary of some of the finish surface materials that are available, their pros, cons and pricing at this time.

 

Notes:

A properly outfitted cooler results in a clean install both visually, and physically. Note the use of trim pieces to close gaps at corners.
  • These are not necessarily compliant for food contact surfaces; they are meant to be finish materials for areas where food is being washed, packed or stored.  The general guidance is “smooth and cleanable.” Check with the appropriate local and/or state enforcement agency to confirm applicability to your project.
  • The prices listed are material cost only. The products differ in with regard to installation labor.  For example, flexible sheathing like FRP will require some sort of rigid wall material to mount to where as rigid panels such as Trusscore, Extrutech and Utilite can be installed on top of furring strips.  No installation costs have been captured in the prices listed.
  • Links to manufacturer info are included.  Most manufacturers sell via distribution channels.  Check with your local building supply company for availability and current pricing. As with most materials, higher volume purchasing generally results in lower unit costs.
  • The pricing on these materials is quite variable depending on the source, when you obtain a quote, the quantity being ordered and how it is delivered. The listed price is the best information available at the time of writing.  Shop around and obtain quotes from several distributors.
    Several manufacturer’s use panel locking mechanisms such as the tongue and groove system found in Trusscore. This provides for a smooth finish and hides the fasteners.

    Common shapes of available trim options to cover and seal all edges and seams. This keeps water from seeping behind the finish surface and entering the walls which can lead to molds and mildews and structural damage.
  • Most manufacturer webpages include an easy to find, specific, installation guide for their product that will be helpful in guiding installation.
  • FRP panels use H or J channel trim between pieces and corners which are calked in place to ensure a moisture proof seam. Follow the manufactures installation procedures.

    Ribcore 3’ or 9’ rib pattern options for ceilings

 

New Crop Storage Planning Tool

DSCN1606I have been toying with an Excel-based crop storage planning tool for several years.  I finally have it at point where I want to make it available to others and start collecting feedback for improvement.  You can download the tool here, and instructions are available in the tool and at this page.  Enjoy and please be in touch with feedback.

 

Final Report – Increasing Supply and Quality of Local Storage Vegetables

We recently completed a project aimed at improving the ability of Vermont vegetable farms to store crops such as beets, carrots, parsnips, potatoes, onions, squash and sweet potatoes, all of which have unmet demand in late winter when local supplies run out.

Beets can be stored in bulk bins for months at the right conditions.
Beets can be stored in bulk bins for months at the right conditions.

The physiology of these crops allows them to be stored for many months after harvest if specific storage conditions are met. However, several distinct sets of conditions are optimal for different groups of crops, and achieving each condition requires careful control and monitoring of temperature and relative humidity in storage. Currently, Vermont’s commercial vegetable farms rarely achieve the optimal conditions due to lack of sufficiently separated storage compartments, and lack of modern environmental monitoring and control equipment.

Installing a remote monitoring system to keep track of temperature and humidity of a storage facility.
Installing a remote monitoring system to keep track of temperature and humidity of a storage facility.

This project installed environmental monitoring equipment to improve storage conditions and ultimately the quality of 1,736 tons of winter storage crops at 9 farms throughout Vermont .  The cumulative market value of these storage crops produced during the 2012-2014 growing seasons was $3.5 million.   Improved storage monitoring led to better control of storage conditions, in part through automated notification to farmers when abnormal conditions were occurring. This allowed for prompt correction of problems such as open doors and failing or inoperative cooling equipment. Losses of storage crops (cull rates) were reduced from ~15% to ~5% of stored volume. Sixty-six  energy efficiency measures were also implemented at 5 of these farms, saving a total of 40,269 kWh of electricity and $5,800 annually.  The systems deployed have increased the confidence of growers to expand their winter storage of Vermont-grown vegetables, leading to an increased supply of local produce outside of the traditional growing and marketing season.

You can download the complete report here.