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Greenhouses. Planning A Home Greenhouse

The fan in a forced air heating system can sometimes

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Unformatted text preview: urn these fans off during the summer when the greenhouse will need to be ventilated. The fan in a forced-air heating system can sometimes be used to provide continuous air circulation. The fan must be wired to an on/off switch so it can run continuously, separate from the thermostatically controlled burner. Summer sun Winter sun Figure 1. Select location carefully. Note where the shade line occurs in both the winter and summer. rapidly. The lean-to should face the best direction for adequate sun exposure. Finally, consider the location of windows and doors on the supporting structure and that snow, ice, or heavy rain might slide off the roof of the house onto the structure. Even-span. An even-span is a full-size structure that has one gable end attached to another building (Figure 2). It is usually the largest and most costly option, but it provides more usable space and can be lengthened. The even-span has a better shape than a lean-to for air circulation to maintain uniform temperatures during the winter heating season. An even-span can accommodate two to three benches for growing crops. Window-mounted. A window-mounted greenhouse can be attached on the south or east side of a house. This glass enclosure gives space for conveniently growing a few plants at relatively low cost (Figure 2). The special window extends outward from the house a foot or so and can contain two or three shelves. rounding ground so rainwater and irrigation water will drain away. Other site considerations include the light requirements of the plants to be grown; locations of sources of heat, water, and electricity; and shelter from winter wind. Access to the greenhouse should be convenient for both people and utilities. A workplace for potting plants and a storage area for supplies should be nearby. Types of Greenhouses A home greenhouse can be attached to a house or garage, or it can be a freestanding structure. The chosen site and personal preference can dictate the choices to be considered. An attached greenhouse can be a half greenhouse, a full-size structure, or an extended window structure. There are advantages and disadvantages to each type. Attached Greenhouses Lean-to. A lean-to greenhouse is a half greenhouse, split along the peak of the roof, or ridge line (Figure 2). Lean-to’s are useful where space is limited to a width of approximately 7 to 12 feet, and they are the least expensive structures. The ridge of the lean-to is attached to a building using one side and an existing doorway, if available. Lean-to’s are close to available electricity, water, and heat. The disadvantages include some limitations on space, sunlight, ventilation, and temperature control. The height of the supporting wall limits the potential size of the lean-to. The wider the lean-to, the higher the supporting wall must be. Temperature control is more difficult because the wall that the greenhouse is built on may collect the sun’s heat while the translucent cover of the greenhouse may lose heat Freestanding Structures Freestanding greenhouses are separate structures; they can be set apart from other buildings to get more sun and can be made as large or small as desired (Figure 2). A separate heating system is needed, and electricity and water must be installed. The lowest cost per square foot of growing space is generally available in a freestanding or even-span greenhouse that is 17 to 18 feet wide. It can house a central bench, two side benches, and two walkways. The ratio of cost to the usable growing space is good. When deciding on the type of structure, be sure to plan for adequate bench space, storage space, and room for future expansion. Large greenhouses are easier to 2 Ventilation Ventilation is the exchange of inside air for outside air to control temperature, remove moisture, or replenish carbon dioxide (CO2). Several ventilation systems can be used. Be careful when mixing parts of two systems. Natural ventilation uses roof vents on the ridge line with side inlet vents (louvers). Warm air rises on convective currents to escape through the top, drawing cool air in through the sides. Mechanical ventilation uses an exhaust fan to move air out one end of the greenhouse while outside air enters the other end through motorized inlet louvers. Exhaust fans should be sized to exchange the total volume of air in the greenhouse each minute. The total volume of air in a medium to large greenhouse can be estimated by multiplying the floor area times 8.0 (the average height of a greenhouse). A small greenhouse (less than 5,000 ft3 in air volume) should have an exhaust-fan capacity estimated by multiplying the floor area by 12. The capacity of the exhaust fan should be selected at one-eighth of an inch static water pressure.The static pressure rating accounts for air resistance through the louvers, fans, and greenhouse and is usually shown in the fan selection chart. Ventilation requirements vary with the weather and season. One must decide how much the green...
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