Constructing High Tunnels

Transcription

1 Constructing High Tunnels and upgrades on farms around New England John W. Bartok, Jr. Agricultural Engineer -Emeritus University of Connecticut

2 High Tunnel - Greenhouse

3 Placement of the tunnel Zoning Location Orientation Shading Drainage

4 Zoning/Building code regulations Local regulations Zoning Wetlands Building code Setbacks

5 Location Consider Light Temperature Water Electricity Access

6 Poor choice

7 Orientation East-West ridge More winter sun Greater heat collection North-South ridge More uniform light More early morning light

8 Shading

9 Drainage

10 Design Hoop vs gothic Movable Vertical sides Truss/collar ties Bracing Wind loads Snowloads

11 Hoop vs gothic

12 Movable tunnels

13 Wheels/rollers

14 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

15 Snow damage

16 Snow loads

17 2 x 4 Bracing

18 Effect of a 90 mph wind on 18 x 48 tunnel 2937# 4032# 3384#

19 Wind loads Bow failure Racking

20 Construction

21 Attachment to the ground Anchor posts 2 into the ground Screw anchors Duckbill anchor Deadmen

22 Truss/collar tie

23 Bracing/connectors

24 Endwalls

25 Many choices in plastic Thickness Sheet size Life Additives Light transmission Color Single/double layer

26 Thickness 3 mil 4 mil 6 mil 8 mil

27 Sheet size Widths to 52 wide Tubes Folds for ease of installation Lengths to 500 Standard lengths

28 Anti-condensate Control Condensation Reduces A.M. light Greater disease potential Burning of leaves droplet acts as lens

29 Infrared Inhibitor - winter Traps infrared part of the short wave radiation (heat) Reduces heat needed by % Best on clear nights Always placed as inner layer

30 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

31 Infrared reflecting - summer Reflected near IR radiation Controlled diffusion Reduces daytime temperature inside Reduced watering Reduced Botrytis

32 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

33 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

34 Secure poly

35 Wear

36 Shading Black polyproplyene Pink plastic

37 Ventilation Large endwall doors Roll-up sidewalls Solar vents Fans

38 Rollup vent closure

39 Roof vent

40 Solar powered vent Top or side 60º - 75ºF Wax or oil motor No power needed $50 - $75

41 Root zone heat speeds propagation & growth Floor heat Provides % of heat needs Lower air temperature Saves energy More uniform temperature Easy to install

42 Domestic Hot Water Heater

43 In-line propane water heater

44 Piping installation

45 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

46 Reverse Return Headers

47 Circulating pumps Low pressure Flow 2.5 feet/minute (5-10ºF difference) Place on return line Need expansion tank

48 Temperature sensor Thermostat or controller Remote bulb sensor Place in flat or bed Small differential

49 Modine Effinity heater

50 Wood heat Renewable resource Readily available Low cost Large selection of equipment

51 Bubble wrap wall insulation

52 Air Circulation Eliminates cold/hot spots Reduce disease More uniform carbon dioxide

53 Use small circulating fans 1/15 hp Create horizontal air pattern Space apart Operate continuously

54 Summary Select a good site Decide the season of use Is heat needed? Type of ventilation Automate where possible

55 Greenhouse engineering info sheets