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