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

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

DIY Auto-fill Humidifier

I recently built a humidifier I think others might find useful.  This could be useful for cheese aging, meat curing, and storage of winter crops all of which require maintaining specific temperature and humidity. The details are available on the Tool Wiki at FarmHack.  Take a look, and let me know if you find ways to improve it or if you have any questions.  As part of this project I also developed this handy spreadsheet that calculates relative humidity based on dry-bulb and wet-bulb temperature and/or calculates wet-bulb temperature based on dry-bulb temperature and relative humidity.  The spreadsheet also helps you tailor the humidifier design to your needs by estimating humidification capacity in gallons of water evaporated per 24 hours.

The idea was to turn a 5 gallon bucket into a high capacity (4 gal/day), automatic fill humidifier. The bucket serves as a reservoir for the water and also as a mounting platform for the parts required to operate the humidifier. Water heated to a know temperature will transfer a predictable amount of water vapor to an air stream of a known temperature and humidity (wet bulb temperature). We use this property to develop a highly controlled humidifier using a temperature control to sense water temperature and control the heater, tank deicer for heat, and a CPU fan for air flow. We also add a toilet fill valve to the assembly to allow for automatic fill of the humidifier.

Slide1

UVM Hops Harvester, Yellow Dog Hopyard and Rock Art Brewery on Across the Fence

Across the Fence, the longest running daily farm and home television program in the country, joined us when we were harvesting last summer with the UVM Mobile Hops Harvester. In this segment, hear from Nick Aleria of Yellow Dog Hopyard in Cabot. VT and Matt Nadeau of Rock Art Brewery in Morrisville, VT about how local hops are important to their businesses and how the machine has helped this to be feasible. Across the Fence is a 15 minute program produced by University of Vermont Extension. The program airs weekdays at 12:10 pm on WCAX TV, Channel 3.

Hop Harvesting Roundup

I recently presented a summary of mechanical hop harvesters at the 2013 NEHA Hops Conference in Morrisville, NY.  As I prepared that material I was struck by how far we’ve come since 2010. In just three years since our small team embarked upon the development of the UVM Mobile Hops Harvester, several independently designed mechanical harvesters have become available and several builds of the UVM type harvester have also been developed by others. These are summarized in the presentation file linked above including videos of some of them.

Does Mechanical Harvesting Pay?

I also thought it may be helpful to show the impact of mechanical harvesting on a small hop farm. The reality is that hand picking hops is only realistic early in the development of a hop farm and only at very small scales of production. It depends on the interest of the pickers and the community atmosphere that many growers develop around their young enterprises.  However, it is unlikely that the hand picking can support larger volume production at current labor rates and the rate of harvest will also be slower than necessary for preserving maximum hop quality.

So how expensive is a mechanical harvester? And can it actually pay for itself? Let’s do the numbers.

Assume a machine cost of $20,000, assembled, installed and ready to go (actual costs for the available machines are included in the presentation file above).  Let’s say that machine is capable of harvesting 60 bines per hour (a light load for most) and that each bine is yielding 1 dry pound of hops.  Let’s also assume 1000 bines per acre, and a one acre yard. We’ll look at high volume scenarios later.  The benefit of mechanical harvesting is labor savings, so we need to assume the base case is paid hand picking at a wage of $7.25 per hour and a rate of 1 dry pound per hour (about one bine). Let’s also note that the machine might require 4 people vs. the one person we’re comparing it to, so it has a higher “per hour” labor rate. We’ll also assume that the machine has a life of 20 years, over which it’s initial cost is spread (as though it is being depreciated like other assets).

We have to make one simplification to the calculation before proceeding. We need to assume a common gross profit prior to harvest.  In other words, the cost of the yard structure, the rhizomes, water, nutrients, any pest and disease management, etc. is all the same between the two cases and allows for a gross profit of, say, $10 per dry pound. With all that laid out, we can summarize the case as shown in the following table.

Yard size 1 acre
Density 1000 bines per acre
Plant yield 1 dry pound per bine
Gross profit prior to harvest  $10.00 per dry pound
Machine cost  $20,000 initial
Machine life 20 years
Machine rate 60 bines per hour
Machine labor 4 persons
Labor cost  $7.25 per hour
Hand picking rate 1 bines per hour
Machine harvest cost  $1.48 per dry pound
Hand picking cost  $7.25 per dry pound
Mechanical advantage  $5.77 per dry pound
 $5,767 annually
Simple payback period
Ammortized 0.2 years
Non-ammortized 3.5 years

Admittedly, we can argue over the assumptions presented here.  A machine could cost more to build or buy than I have assumed.  Someone may be able to hand pick much quicker than I have presented.  The machine rate could (and probably will be) higher than assumed above. The gross profit of $10 per dry pound assumed may be more or less.  But I think it is safe to say that mechanical harvesting can pay for itself and, perhaps as important, allows a certain scale and quality of production that isn’t supported by hand picking.

2013 UVM Mobile Hops Harvester Summary

On the Road Again
On the road with the UVM Mobile Hops Harvester.

The UVM Mobile Hops Harvester visited six hop yards this year, harvesting approximately 400 dry pounds of hops, over a 4 week period plus harvesting the UVM Extension NW Crops and Soils Team’s research hop yard. This harvester, developed as a result of a Northeast Hops Alliance, UVM Extension, VT Agency of Ag Food and Markets, and MA Department of Agriculture sponsored project, aims to provide proof of concept of a mobile hops harvester in support of the re-emerging hop industry in the Northeast US.

The reintroduction of hops to the northeast requires scale-appropriate harvest and processing equipment. At the start of this project there was no feasible mechanized harvest options for a 1-2 acre hop producer. Handpicking is the most wide-spread current practice which is labor intense and time consuming leading to expense and quality impact due to delayed harvest.

As a result of this project, cooperative use of a single, mobile harvester has been demonstrated and logistics for this operation are being continually improved. The harvester has a demonstrated capacity of 60-120 bines per hour compared to 1 bine per hour per person for manual picking. This rate enables the harvest of a 1 acre yard within 8 hours resulting in optimal harvest timing and improved quality. Assuming a harvest team of 4 people in either case, this translates to a harvest labor cost savings of 97% or $3,120 per acre at $15 per hour wage (approximately $2 per lb of dried hops (10-20% of retail price)).

Kris Anderson of Addison Hop Yard and Chris Callahan of UVM Extension.
Kris Anderson of Addison Hop Farm and Chris Callahan of UVM Extension. (Addison, VT)

“The hop harvester significantly sped up harvesting.  With the size of the bines this year, some may not have been harvested at all without it’s use.  Knowing the UVM harvester is available helps me plan for hopyard expansion over time.  Without a large harvester, such a UVM’s, expansion would not be practical.”, notes Kris Anderson of Addison Hop Farm in Addison, VT.

Trevor Lewis of Mad Mountain Hop Farm in Berlin, VT concurs, “Absolutely amazing! My harvest time went from 5 days to 5 hours! Though I am unsure of expansion at this time, this machine makes it possible to expand beyond a half acre which really isn’t an option without a harvester.”

Trevor Lewis and the Mad Mountain Hop Farm crew.
Trevor Lewis and the Mad Mountain Hop Farm crew. (Berlin, VT)

This mobile, trailer-based mechanized hop-harvester was developed and documented as an open-source design for others to replicate and adapt to their needs.  The design was the result of a collaborative design effort involving growers, brewers, agronomists, fabricators and engineers. Additionally, 255 people have downloaded the plans for the machine and 5 others have built harvesters at least partially informed by this work. This harvester pulls a complete bine (central bine/vine, leaves and cones) through a section of stripping fingers that separate the cones and leaves from the bine.  The cones and leaves are conveyed to a secondary sorting section with rolling dribble belts against which the leaves lie flat while the cones roll backward down the belts. In this way the machine takes a loaded bine and produces two output streams of cones and leaves.

We’ve been reasonably pleased with capacity and efficiency of the machine.  There is still room for improvement, and we plan to install chutes and fences over the winter to better contain all matter within the machine, improve separation and, thus, net yield. We also had two bearings fail this harvest season and will likely upgrade them to heavier duty bearing housings.

The entire machine is placed on an 18 foot equipment trailer for ease of transport.  This year, the machine traveled approximately 3,400 miles visiting some yards multiple times as different varieties matured. Each year, the harvester travels further afield for an outreach demonstration.  This year we traveled to Westfield, Maine (Aroostook County) to Aroostook Hops to help with their harvest and to give them some experience with the harvester.

Kathleen, Krista, Marie and Jason Johnson of Aroostook Hops in Westfield, ME with their first bin of cones off the machine.
Kathleen, Krista, Marie and Jason Johnston of Aroostook Hops (Westfield, ME) with their first bin of cones off the machine.

“Having the UVM mobile hops harvester had a HUGE impact on our success this year.  We had a hops picking party the previous weekend (Labor Day) with many volunteers handpicking hops (we estimate about 60 people passed through that weekend) and we got about 40% of our crop harvested,” says Krista Johnston, ” We had two articles in the local press about us and lots of interest was generated, so we couldn’t have done better on “many hands”, but without the harvester here the following weekend we could not have gotten all the hops in this season by handpicking alone.”

Krista and her husband, Jason are thinking ahead to building a harvester of their own.

“We plan to fabricate a version of the mobile machine, so being able to use it ourselves and have our fabricators come out and operate it (for about 2 hours of time x two men) was absolutely invaluable to us.  We had thought that “mobile” was less important to us and that we would build stationary with electric motors, but seeing how convenient it was to move around different locations made us reconsider that.  Also, we recently expanded (last year) 3 acres so can’t even think about getting bigger any time too soon, but having the capacity to harvest at the rate that the harvester can accomplish will remove that as a limiting factor when we catch our breath and consider future operations.  We do plan to contract our harvester to other growers, and had thought we’d have bines come to us, but mobile is looking attractive.”

Others have replicated and adapted the UVM design to their needs for the 2013 harvest season.

Nick Aleria and the Yellow Dog Hop Yard crew (Cabot, VT).
Nick Aleria and the Yellow Dog Hop Yard crew (Cabot, VT).

“We wouldn’t have been able to build our harvester without the knowledge and research from the UVM machine,” says Dean Heltemes of Lunatic Fringe Farms in Wisconsin. “I’m sure this picker will create a lot of buzz around our co-op. We might have the opportunity to do some harvesting for a farm a couple hours from here. The more hours we can get on this thing, the better off we will be for next year.” Video of Lunatic Fringe Farms’ harvester can be viewed on YouTube.

And so it goes, each year more hours are accrued on the harvester, more variations are built and we all continue to learn and improve together using this open source design. Plans for the machine can be downloaded from the UVM Hops Project Wiki at http://www.uvm.edu/extension/cropsoil/wikis. Chris Callahan can be reached by email or phone at 802-773-3349.

CoolBots(TM): Inexpensive Cold Storage

Demand for on-farm cold storage of produce and other Vermont agricultural products is increasing as local markets for these goods expand. I receive many inquiries regarding CoolBotsTM, an adaptation of a window air-conditioner to make a cooler out of an insulated space. This article is intended to collect related resources in one place and to also highlight some considerations adopters of CoolBots should be aware of.

In a nutshell:

A farmer-built cooler (photo from storeitcold.com).

These systems utilize a commercially available controller ($299) to allow the AC unit to run with a lower temperature than normal. Store-It-Cold, The manufacturer’s website has excellent resources and FAQ’s. They include a list of AC units that they have had positive experiences using. They are also very clear about who should consider NOT using a CoolBot. Applications for which the CoolBot is not well suited, according to the manufacture, include;

  • rapid “pull down” of temperature (e.g. high levels of field heat or frequent exchanges of product)
  • freezers – CoolBots perform best above 36 °F.
  • sites with many door openings per day (e.g. > 6 times per hour)
  • running through the winter – not a show stopper, but you need to be more careful about which AC unit you choose

Other things to be very aware of, according to the CoolBot controller manufacturer, include

A CoolBot installation (photo from storeitcold.com)

A report commissioned by NYSERDA summarizes the cost, energy efficiency, and greenhouse gas emission benefits of a CoolBot installation when compared to a conventional walk-in cooler system at certain conditions. The cost estimate of the CoolBot system (15,000 BTU/hr) is $750 installed compared to $4,400 for a conventional system (8’x10′ cooler box cost not included).

The authors conclude that a CoolBot system can result in approximately 230 kWhr/year of energy savings ($30/year at $0.13/kWhr VT average) when cooling 100 ft2 of cooler floor area to 35 °F (assumes Albany, NY conditions). It is important to note that this analysis highlights the main energy efficiency benefit of the CoolBot system comes from the reduced operating time of evaporator fans. High efficiency fans and improved controls exist for conventional walk-in systems and they are even supported by rebates from Efficiency Vermont. When the CoolBot system was compared with a conventional cooler that also had evaporator fan controls, the savings went the other way; i.e. the conventional walk-in system resulted in 74 kWhr/year savings.