Greenhouse Structures: More than a high tunnel Steven E. Ph.D., A.A.F. Extension Greenhouse Crops Specialist and Professor of Floriculture Horticulture and Landscape Architecture Colorado State University
Locating a Greenhouse Land-use prediction Urbanization Taxation Zoning Fire codes Set backs Microclimates No fog Topographic shadows No high winds
Locating a Greenhouse
Microclimates Avoid sites prone to fog Frost pockets Atmospheric pollutants Topographic shadows Avoid areas prone to high winds Locate where prevailing winds are consistent Avoid areas that are prone to wind acceleration Consider the occurrence of hail
Location Labor supply / economic stability Accessibility Receiving / shipping Utilities Market (retail customer traffic) Water Quality and quantity Up to 30,000 gal/day/acre for irrigation and evaporative cooling
Utilities Three phase power Water Fuel Supply
Orienting a Greenhouse Maximize light and uniformity of light Percent light entering a greenhouse depends on angle of incidence Angle that a light ray striking a surface makes with a line perpendicular to the surface An angle of incidence=0 allows the most light to enter the surface Reflective loss increases as AOI increases (up to 90 )
Orienting a Greenhouse Above 40 latitude: Run ridges of single-span houses E-W to maximize light intensity Run ridges of multi-span houses N-S for light distribution Must accept lower winter light transmission to avoid shadow pockets N-S ridge and gutter shadows move but E-W shadows do not
Angle of Incidence
Orienting a Greenhouse Below 40 latitude: Run ridges of all houses N-S Better light distribution (moving shadows) is more important than light transmission optimization Remember: WINTER light is the factor
Angle of Incidence
Reflection
Calculation of Angle of Incidence For 49 N at the Canadian Border
Calculation of Angle of Incidence For 49 N at the Canadian Border
Calculation of Angle of Incidence For 49 N at the Canadian Border
Calculation of Angle of Incidence For 49 N at the Canadian Border
Calculation of Angle of Incidence
Orientation
Rigid Glazing Greenhouses Lean-to Placed against an existing wall Typically facing south Common for institutional or hobby greenhouses
Rigid Glazing Greenhouses Even-span Two slopes of equal pitch and width Most common configuration
Rigid Glazing Greenhouses Uneven-span Roofs of unequal width and pitch Adaptable to slopes Good for high latitude sites
Quonset Hut In 1941, the Navy went to the George A. Fuller construction company in New York. The British had developed a light prefab structure called a Nissen hut during WW-I. The Navy wanted an improved version that was cheap, lightweight, and portable that could be put up by untrained people. Peter Dejongh and Otto Brandenberger went to work and within a month they'd set up a production facility near Quonset, Rhode Island. This how the famous Quonset hut came into being. Some thought the old Nissen hut had been modeled on Iroquois council lodges. Now the Quonset hut version had the same shape and an Iroquois-sounding name. The Indian connection was probably fortuitous. https://en.wikipedia.org/wiki/quonset_hut
Quonset Greenhouse
Glass and Other Greenhouses Ridge and Furrow Multiple A-frame spans connected along the eaves Gutters placed at junction of eaves Also termed gutter connect
Barrel Vault Gutter Connect
Glass Greenhouses Glass was the only choice until the 1950s Advantages Greater light intensity over plastic panels and film plastic More air exchanges with glass Lower relative humidity Less disease Greater evapotranspiration
Glass Greenhouses Disadvantages More leaks greater heat input Higher initial cost compared to plastic Initial cost vs. long-term Maintenance Plastics require recovering
Film Plastic Greenhouses Polyethylene 6-mil exterior 4-mil interior Double layer for insulation UV inhibitors to increase life span 3-5 year life Anti-fog materials to prevent condensation IR blockers = less heat loss
Film Plastic Greenhouses IR blockers to prevent heat loss Short wave energy into greenhouse Surfaces radiate IR radiation Films block re-radiation
Film Plastic Greenhouses Double-layer Covering Plastic expands and contracts with temperature changes Leave 2-3 inches or more when warm Pull plastic tight when cold Air space (inflated) 4-inches Not too much Not too little
Inflation Fan
High Tunnels
Rigid-Plastic Greenhouses Fiberglass Reinforced Plastic (FRP) Surface easily abraded Results in a pitted surface Frayed fibers bloom Gather dirt and debris Transmits 88% PAR Light less structure Less popular in the past Flexible and can be bent over a Quonset frame More resistant to glass to breakage More light diffusion than glass
Rigid-Plastic Greenhouses Fiberglass Reinforced Plastic (FRP)
Rigid-Plastic Greenhouses Fiberglass Reinforced Plastic (FRP) Bows / trusses / rafters placed 8 to 10 feet apart Distance between purlins is dependent on: Weight of FRP used Live load FRP is very flammable
Rigid-Plastic Greenhouses Polycarbonate 10-year life span guarantee Widely used to glaze end walls and gables of Quonset houses Easily retrofitted to glass houses High impact resistance UV protectant added to most products
Rigid-Plastic Greenhouses Polycarbonate Available as: Corrugated Double wall Triple wall PAR light transmission about 79% Not considered flammable
Rigid-Plastic Greenhouses Extruded aluminum locks and seals
Rigid-Plastic Greenhouses
Rigid-Plastic Greenhouses Acrylic Good PAR transmission 83% Very flammable Guaranteed for 10 years More resistant to breakage than glass, but less than polycarbonate Attachment similar to polycarbonate
Greenhouse Heating Heating Systems Capacity Meet the needs of heat loss per hour Type of systems Unit (forced air) heaters Central heat (boiler and pipes) Radiant heat
Greenhouse Heating Unit Heater Systems Unit heaters Supply 1 in2 of venting from outside for combustion for every 2,500 Btu output for oxygen Some have forced air combustion vents (good) Use sufficient exhaust stack to assure good draw of fumes (80% efficiency = gasses) Ethylene injurious to plants; other hydrocarbons Sulfur may be a fuel contaminate
Greenhouse Heating Horizontal Air Flow (HAF) Small horizontal fans above crops circulate air Offers better temperature uniformity than tube systems Min and max velocities = 50 and 100 fpm Average 1 fan/50 ft of greenhouse length Use fans 1/30 to 1/15 hp Use a 16 to 18 blade diameter
Horizontal Air Flow Fans
Greenhouse Heating Central Heating Systems Boilers Fire tube boiler Gasses run through tubes surrounded by water Large volume of water Slow to heat, yet slow to cool Burn wood, coal, oil, or natural gas
Greenhouse Heating Boilers Water tube boilers: Water runs through tubes or thin plates (fins) / gasses surround tubes (chamber is the flue) Quick to heat up, yet quick to cool down Burns natural gas or propane (no soot) Less expensive and smaller than fire tube
Pipe Placement
Tube Heating Systems
Alternative Heating Systems
Greenhouse Cooling Why is cooling needed? Solar radiation is the heat input for the earth Radiate as much as 277 Btu/ft2/hr onto the surface of the earth on summer day Coastal and industrial areas, may only be 200 Btu/ft2/hr Up to 85% of this radiation may enter the greenhouse Most of the IR heat becomes trapped inside Greatly increases the greenhouse temperature
Greenhouse Cooling Active Fan-and-Pad System Rate of Air Exchange Pad Types and Specifications Fan Placement The Airstream Active Fog Cooling System
Greenhouse Cooling Active Fan-and-Pad System Rate of Air Exchange Pad Types and Specifications Fan Placement The Airstream Active Fog Cooling System
Passive Cooling Systems
Fog Cooling Systems
Greenhouse Cropping Systems Nutrient Film Technique (NFT)
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture Bucket culture
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture Bucket culture Deep water or raft culture
Greenhouse Cropping Systems Nutrient Film Technique (NFT) Slab culture Bucket culture Deep water or raft culture Stacked pots
Pros and Cons of Growing in a Greenhouse Pros (build it) More than season extension Market precision Four season production Greater diversity of Crops Permanent Easier zoning and permitting Cons (stay with high tunnels) Expensive Not moveable High up front costs Requires utilities
Resources Greenhouse Gardener's Companion, Revised: Growing Food & Flowers in Your Greenhouse or Sunspace Shane Smith Cheyenne Botanical Garden Greenhouse Operation and Management Paul Nelson The Commercial Greenhouse James Boodley and Steven Newman
Steven E. Newman, Ph.D., A.A.F. Horticulture and Landscape Architecture Colorado State University Fort Collins, CO 80523-1173 970-491-7118 Steven.Newman@Colostate.edu Twitter: Facebook: Skype: LinkedIn: @newman1778 senewman snewman7118 snewman7118