Constructing High Tunnels and 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
Orientation East-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 2937# 4032# 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 mil 6 mil 8 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 speeds propagation & 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