H&CS 521 Greenhouse Crop Production Lecture 1 Greenhouse Structure Overview PowerPoint Lecture Developed In Part by Jennifer Leopold and Lindsay Paul
Greenhouse Structures: Styles, Construction, and Materials
Greenhouse Styles American (high profile) Dutch (low profile) Different ridge to eave distances Heating differences Light interception differences
Greenhouse Styles Single-ridged Multi-ridged American or high profile Dutch or low profile
Greenhouse Styles Multi-ridged or gutter-connected Fewer exterior walls - save energy and materials, less construction More room to maneuver inside (more suitable for automation) Can have different temperature zones Snow loads in the gutters can be a problem
Greenhouse Styles Quonset 2 layers of polyethylene with air in the middle Cheap to build Expensive to maintain “Temporary” structures Also used for overwintering of landscape materials
Double-layer polyethylene greenhouse Fans are needed to keep the two layers of plastic inflated. These are often referred to as “squirrel cage” fans.
Greenhouse Styles Retractable roof greenhouses Shade structure Flexible plastic roof and walls To cool, just retract roof
Greenhouse Styles Unusual greenhouse designs U. S. Botanic Garden in Washington D.C.
Greenhouse Styles Shade Structures Generally used in southern U.S. for foliage and bedding plant production Inexpensive Provide protection from solar radiation Provide some frost protection
Shade Structures Heaters in Shade House in Florida Mesh roof-covering holds in heat.
Shade Structures Greatest risk is with hurricanes and severe weather produced by storms. In 1992 Hurricane Andrew destroyed much of south Florida's floral production. Devastating hurricanes in 2004 and 2005 have also had a large impact on southern floral production.
Where to locate a greenhouse? Water Supply Quality**** Quantity Climate Light availability Temperature Labor Available and low-cost Transportation Interstate highways Airport Accessible location for retail customers Room for expansion Room for support structures 4:1 ft2 greenhouse to support structures Headhouse, storage, etc. Zoning Topography
Greenhouse Design Loads = Forces on the greenhouse Dead Load Live Load National Greenhouse Manufacturer Association (NGMA) standards Dead Load Weight of permanent structure (frame, glazing materials, heaters, lights, etc.) Live Load Weight of temporary structures (repairmen, hanging baskets) > 30 days, no more than 15 lbs/ft2
Greenhouse Design Snow Load Wind Load Ps=Ce Ctg Cs I Pg Ps = snow pressure Ce = exposure factor Ctg = thermal factor Cs = slope factor (roof) I = importance factor Pg = ground snow load Wind Load 70-80 mph = 16-20 lbs/ft2 Lateral and lifting forces
Greenhouse Design Wind Speeds
Greenhouse Design Unusual Loads For more information: Hurricane Load Seismic or Earthquake Load For more information: National Greenhouse Manufacturers Association http://www.ngma.com American Society of Agricultural Engineers http://www.asae.org
Greenhouse Design Foundation Concrete foundation below frost line No shifting with freezing and thawing Permanent foundation Columbus = 4 ft, Fargo, ND = 6-9 ft Resist wind loads especially Special soil testing for appropriate soil pressure Depend on type of structure (polyhouse vs glass or rigid plastic structure)
Ridge and Eave Greenhouse Design
Quonset Greenhouse Design
Superstructure Materials Qualities Wood Strength Weight Durability Cheap but not durable Standard in the past Steel Durable & cheap Heavy & rusts **Aluminum** Light & strong More $ than steel Reflective Qualities Strength Weight Durability Maintenance Costs (initial & long term)
Glazing Materials--Qualities Cost initial & replacement Life expectancy Photoxidation Oxidation Surface erosion Thermal degradation Light transmission Thermal Proportion Strength Mechanical shocks & shattering (hail) Tensile strength Weight of Material Ease of installation and maintenance Insurance - some materials are flammable