Greenhouses come in many sizes – and shapes. The size or type of greenhouse that best fits a grower’s needs may be determined by the budget, by the amount of labor available for working the greenhouse or even by future plans for expansion. Keep in mind that there are ways of automating some of the jobs, and some plants are more labor intensive than others. All of these things influence the decision on the type and size of greenhouse structure. Freestanding greenhouses are usually less costly to purchase and easier to construct than a gutter connected greenhouse. However, when the greenhouse structure is 3 bays or larger the per square foot cost may become cheaper with a gutter connect than a freestanding structure because some of the equipment such as the environmental controller, electrical panel and even the side walls are shared in a gutter connect unit Determining the best location to erect the greenhouse is an important decision. A suitable greenhouse location will include a spot where the sun hits the greenhouse all day long and no shadows are cast on the greenhouse. Shadows reduce plant growth. Look for a site that is fairly level to save on grading costs and a site that will allow the greenhouse length to run North and South so that the sun can go up and over the greenhouse allowing for even lighting down the rows of plants. Most likely at least some grading will be needed to level the greenhouse from side to side, and create a 1-2% slope either North or South. A natural flow for drainage is needed to facilitate the drainage of gutters on the greenhouse and also for the growing systems inside the greenhouse. Another factor in the location of the greenhouse is the accessibility to electricity, water and fuel sources. During installation keep in mind any plans for future expansion especially if you are planning on building a commercial greenhouse. Water quality is an especially important element for hydroponic growing. Most water can be used, and possible shortcomings in water composition can often be managed, however, if the water is going to need treatment of some type to be useable, that is important to know and consider up front. Zoning regulations can vary widely from area to area. It is best to check with your local zoning authorities early in your planning stage.
Nuts and Bolts
The most obvious part of the greenhouse is the structure. It is the necessary packaging that provides light penetration at the same time that it provides isolation from the outside elements. Environmental controls and feeding systems are what make the atmosphere right to keep the plants growing even in our absence. Heaters, fans, evaporative coolers, feed systems and environmental controllers are all system components that are important. Together, they cost more than the commercial greenhouse structure itself. Some greenhouse purchasers have the unfortunate experience of purchasing the structure, then discovering that they need far more in order to make the greenhouse work. Make certain the equipment you need, like environmental control hardware, is included in your greenhouse purchase. Pay attention to the actual components of your structure, from bottom to top. Even the structure itself needs some attention in the planning stages. The quality of the structural components will determine how well and how long the greenhouse will stand. Structural steel will perform better and last longer. It may cost a little bit more than some of the alternatives, but it will outlast them and be more cost-effective in the long run. Greenhouse coverings run the gamut from glass to polycarbonate to greenhouse polyethylene (heavy plastic sheeting). Glass and tempered glass greenhouses are the most expensive structures. Except for possible breakage, the cover will probably never need to be replaced. Double walled polycarbonate has a 12 to 15 year life. A double walled polyethylene greenhouse with an air space between the two poly layers is a relatively inexpensive cover with a four year life. The plastic will last longer than 4 years, but the light transmission is diminished with age. Heat, Cold and Ventilation The covering of a greenhouse is designed to allow transfer of light into the greenhouse and are not insulated like most standard structures. Even when days are warm enough for people to enjoy the greenhouse environment, the nights may be cool enough that the plants would require some heating, based on the local climate. Good air exchange is important for the proper growth of the plants. Air movement is also used to provide cooling of the greenhouse environment. TThe rate of air movement through the commercial greenhouse is more directly controlled by the operation of the fan(s). A variety of fans are used in the greenhouse environment from vertical and horizontal air flow fans, to exhaust and gable fans. One of the most consistent ways to cool a greenhouse is with exhaust fans and louvers on one end of the greenhouse and evaporative cooler on the opposite end. An evaporative cooling wall will provide air into the greenhouse that is cooler than outside air, and are most effective where the average relative humidity is lower than in areas of high relative humidity. In most areas of the world, some form of cooling is necessary if the greenhouse is to be operated year round. An evaporative cooling system will provide the most economical cooling in most applications. A more effective, but more expensive mist system is available but likely to be reserved for a commercial greenhouse in naturally ventilated greenhouses.