Constructing High Tunnelsand
upgrades on farms around New England
John W. Bartok, Jr.Agricultural Engineer -Emeritus
University of Connecticut
High Tunnel - Greenhouse
Placement of the tunnel
• Zoning• Location• Orientation• Shading• Drainage
Zoning/Building code regulations
• Local regulations– Zoning– Wetlands– Building code
• Setbacks
Location
• Consider– Light– Temperature– Water– Electricity– Access
Poor choice
OrientationEast-West ridge• More winter sun• Greater heat
collection
North-South ridge• More uniform light• More early
morning light
Shading
Drainage
Design
• Hoop vs gothic• Movable• Vertical sides• Truss/collar ties• Bracing• Wind loads• Snowloads
Hoop vs gothic
Movable tunnels
Wheels/rollers
Snow loads
• Light and fluffy – 12” snow = 1” rain• Heavy and wet – 3” snow = 1” rain• 1” rain = 5.2 pounds/sq ft• January 2011 after snow storms –I had 39 psf snow load on the ground at my house in Ashford CT
Snow damage
Snow loads
2” x 4” Bracing
Effect of a 90 mph wind on 18’ x 48’ tunnel
4032#
2937#
3384#
Wind loads
Bow failure Racking
Construction
Attachment to the ground
• Anchor posts 2’ into the ground
• Screw anchors• Duckbill anchor• Deadmen
Truss/collar tie
Bracing/connectors
Endwalls
Many choices in plastic
• Thickness• Sheet size• Life• Additives• Light transmission• Color• Single/double layer
Thickness
3 mil 4 mil6 mil8 mil
Sheet size• Widths to 52’ wide• Tubes – 20’ – 24’• Folds – for ease of
installation• Lengths to 500’
– Standard lengths• 100’• 110• 150’
Anti-condensate Control
• Condensation– Reduces A.M. light– Greater disease potential– Burning of leaves – droplet acts as lens
Infrared Inhibitor - winter
• Traps infrared part of the short wave radiation (heat)
• Reduces heat needed by 10 – 20-%
• Best on clear nights• Always placed as inner
layer
Infrared inhibitor
• Penn State Research on high tunnels– Mixed results– Increased night temperature – 2 - 3ºF– Did not increase daytime overheating– Yield of colored bell peppers was higher with
standard poly– No difference in sunflowers
Infrared reflecting - summer
• Reflected near IR radiation
• Controlled diffusion• Reduces daytime
temperature inside• Reduced watering• Reduced Botrytis
Light Transmission
• UV stabilized – 88 - 91%• IR-AC film 82 - 87%• IR_AC with diffusion 77 – 88%• White 55 or 70%
• Rule of thumb – one percent increase in light = one percent increase in plant growth
Single or Double Layer?
• Single layer– Spring, Fall– One time use poly
• Double layer– Higher night
temperature– Heated tunnel– Winter operation– Windy locations– Requires electricity
Secure poly
Wear
Shading
Black polyproplyene Pink plastic
Ventilation
• Large endwall doors• Roll-up sidewalls• Solar vents• Fans
Rollup vent closure
Roof vent
Solar powered vent
• Top or side• 60º - 75ºF• Wax or oil motor• No power needed• $50 - $75
Root zone heat speedspropagation & growth
• Floor heat• Provides 25 – 100% of heat needs• Lower air temperature• Saves energy• More uniform temperature• Easy to install
Domestic Hot Water Heater
In-line propane water heater
Piping installation
Pipe installation• Pipe spacing – 9” to 12” on center• Tomatoes – one line under each row• Depth – 4” to 6”• 12” or more if rototilled• Single pipe – 10 Btu/linear foot• Bed – 15 to 25 Btu/sq ft• Insulate below pipe if water table < 6’• Unheated tunnel – antifreeze or blow out
Reverse Return Headers
Circulating pumps• Low pressure• Flow – 2.5
feet/minute (5 -10ºF difference)
• Place on return line• Need expansion
tank
Temperature sensor• Thermostat or
controller• Remote bulb sensor• Place in flat or bed• Small differential
Modine Effinity heater
Wood heat
• Renewable resource• Readily available• Low cost• Large selection of
equipment
Bubble wrap wall insulation
Air Circulation
• Eliminates cold/hot spots
• Reduce disease• More uniform
carbon dioxide
Use small circulating fans
• 1/15 hp• Create horizontal air
pattern• Space 40’-50’ apart• Operate
continuously
Summary
• Select a good site• Decide the season of
use• Is heat needed?• Type of ventilation• Automate where
possible
Greenhouse engineering info sheets
• http://www.ipm.uconn.edu/pa_greenhouse