Different Types of Green Houses
Greenhouses can be classified in a number of ways; by shape, structure or even by materials. Greenhouses are designed based on regional weather patterns as well as the type of plants to be grown.
To start from the basics there are three types of greenhouses. Gutter connected (ridge and furrow), contiguous and free standing (even span). Free standing is pretty self-explanatory, they are not attached to another structure and the design is up to your imagination as long as you can find a manufacturer willing to make it. Gutter connected greenhouses are a series of houses connected at the gutter that do not have partitions separating houses and contiguous houses have the same design but with partitions. The illustration below clarifies the structural differences.
Within gutter connected and contiguous greenhouses there are many types of designs such as; arch gothic, open roof, A-frame, atrium, sawtooth, and Venlo. Below is an illustration with common greenhouse designs.
Greenhouses can also be identified by the materials they are made out of. The primary materials used in the construction of greenhouses today are glass, poly and polycarbonate but fiberglass and acrylic are also available. Advances in polycarbonate has significantly improved the life as well as efficiency of greenhouses by offering excellent UV protection with an excellent R value. When deciding on which material to choose for construction you should consider lighting, insulating value, condensation, longevity and cost.
Some materials such as glass provide direct light which can be too much for some plants (many glass houses are sprayed with a coating to diffuse the light), while other materials like poly carbonate diffuse light.
Insulating value is another important consideration because heating costs are some of the biggest expenses growers face after labour and plant material costs. Having a well-insulated greenhouse will hold in the heat during colder seasons lowering energy costs. An example of an improvement to insulating value is the idea of double poly. Some greenhouse is simply a frame with poly sheeting stretched over it. With the addition of another layer of poly, builders install a blower between layers so that an air pocket provides insulation improving efficiency.
Issues with longevity include UV degradation, material ripping (poly sheeting), rust and rot. Greenhouses are incredibly damp and humid because of plant transpiration and evaporation; this environment may be great for plants but is very hard on building materials over an extended period.
Another way to classify greenhouses could be by the systems used to control the growing environment. There are two main heating systems; unit heater and boiler systems. Boiler systems have a variety of delivery options from fin tube under bench to bench top systems. There are also steam, infrared, and electrical resistance systems available but are not as common.
There are a variety of cooling systems such vent systems(ridge, pad, sidewall), pad and fan (evaporative cooling), swamp coolers(evaporative cooling), fan systems, AC units, and custom evaporative fan units.
Pros & Cons
A freestanding greenhouse is just what the name implies: a structure that’s not attached to another structure. It may be a simple arch shape with no sidewall, have sidewalls just a few feet high, or have sidewalls 8-10’(2.4-3.0m) high. This is in contrast to the other common greenhouse design---the gutter-connected house—in which numerous houses, or “bays”, are connected together to create one large greenhouse.
The freestanding poly greenhouses could be built, covered, and put to use in a matter of days, compared to weeks or months for a glass-covered greenhouse. The basic uses for these greenhouses were similar, but there seemed to be a greater emphasis on using the structures for starring material from seed, such as starter plants for vegetable field crops, as well as for overwintering woody and perennial nursery crops.
The plastic greenhouses were considerably tighter than glass houses, which had laps between the panes that leaked air. The solar gain was equal to or greater than glass (even with approximately 15% less light transmission), and they held temperature much longer. These environment changes were now creating distinctly different reasons to use greenhouses for a variety of cultural applications. A whole new growing environment was available for various plant material and to traditional growers as well as the new breed of poly-greenhouse growers.
Pros and Cons
Several major issues arise when considering whether to build freestanding greenhouses versus gutter connected structures, including land value and tax implications, production planning, the crop type, the labour involved, utility costs, and time to build.
Freestanding greenhouses still offer the lowest investment dollars per square foot of facility space. However, heating and ventilation costs can be higher, as each house needs its own heating and ventilation equipment.
Labour and mechanization costs are usually higher in individual houses compared with gutter-connected buildings once your business approaches 1/2 acre (0.2 ha) in covered production area, as it's difficult (although not impossible) to use automation such as monorails, conveyors, or movable tables to move product.
Freestanding houses take up more space than gutter-connected houses, as you need to leave space between each house. If useable building space on your site is at a premium, by the time the plan is properly laid out with all the required outbuildings, along with all the bells and whistles you might want inside the greenhouses, the initial benefits of low-cost individual house may diminish compared with a gutter-connected house.
Pros and Cons
If you need a sophisticated level of environment control and auto motion within your greenhouse for the crop you plan to grow, for the crops you plan to grow, for example with bedding plant plugs, you may want to consider a gutter-connected structure.
With freestanding houses, if you have an insect or disease problem in one house, you can easily keep the problem isolated.
Freestanding houses can be relocated on your property more easily than a gutter-connected house if your land-use plans change.
Many growers have been very successful using low-cost freestanding houses for the bulk of their production. Several of the nation's largest growers, such as Harts Nursery of Jefferson, Oregon, utilize hundreds of freestanding houses to produce bedding plants. These buildings offer speed, flexibility, and few complications.