Greenhouse Structures and Design
Shade Houses
Shade houses provide outdoor shade and protect container-grown plants from excessive sunlight by suspending shade fabric over the plants (Figure 1.14). Reducing sunlight also serves to create a cooler, more comfortable climate. Provided the outdoor conditions are conducive to growing, shade houses offer not only a low-cost alternative for expanding the growing area but also provide an excellent environment for hardening off the plants prior to sale. Growers in some sunbelt locations, such as Florida and Texas, are able to grow in outdoor shade houses year-round. Regardless of the location, shade houses offer a unique way of expanding the growing operation.
Fabric
While the vast majority of shade fabrics employed in fixed-roof shade houses are black knitted or woven materials, there are other options that can improve the quality of crops and customer comfort. Traditional black fabrics absorb heat and can even transmit heat to the crop below. Increasing the height between the crop and the shade fabrics can help reduce this heat transfer. Aluminum-backed shade fabrics are available and designed to re-radiate heat back into the atmosphere instead of absorbing the heat.
Structural Designs
In general, there are three recognized designs for shade houses: cable-frame, rigid-frame, and retractable roof systems. Typically, shade houses 8 to 10 feet (2.4–3m) above grade. However, over the past few years, growers have increased this height to 14 to 16 feet (4.3–4.9m), which offers multiple advantages, including increased airflow and putting more space between the crop and the shade fabric (which can absorb and transfer heat).
Ridge-Frame Systems
These systems incorporate rigid framing members between the columns instead of cables. Due to the spanning limitations of steel or wood, upright columns must be spaced much closer together. Most rigid-frame structures employ knee braces mounting to the vertical upright column and angling up to the bottom of the horizontal cross member.
Cable-Frame Systems
These systems generally employ upright columns spaced evenly along the length and width of the structure. For obvious reasons, the closer the columns, the stronger the system becomes. Virtually any rigid material can be used as an upright column, including wood, galvanized steel tubing, or preformed steel profiles. It is generally accepted that steel columns with a galvanized finish will provide the highest return on investment.
Retractable Systems
Retractable flat-roof structures incorporate the traditional concept of a fixed shade house, with upright columns and dead-man bracing, though with a very distinctive difference. These structures employ a drive system that opens and closes the fabric on demand. Typically, the drive mechanism consists of a motor, a drive shaft, and a series of drive cables plus pulleys that allow the fabric to travel from one set of columns to another.
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