Get the most for your automation buck

What does it take to automate a greenhouse? Not as much as you might think.

By Amy Rigazio

automation (ot e ma shen) n. A technique by which mechanical processes are subject to some degree of automatic control, without human intervention. (The New Lexicon Webster’s Dictionary of the English Language, Encyclopedic Edition, 1989)

Automation within a greenhouse takes on a variety of forms ranging from simple thermostats for ventilation control to complete computer systems. The reasons for automation are far less varied: rising labor costs and the demand for high-quality, consistent products. Regardless of whether a grower has a single, 3,000-square-foot quonset house or a 10-acre production facility, automation can be economically incorporated into daily growing practices.

Temperature control
Basic automation starts with temperature control, which, in greenhouses used year-round, is vital. Most growers who have electricity on site already rely on thermostats to run their heaters during winter and their fans during summer. These units have been used for so long that they are no longer seen as an automation technique, but as a necessity. Ranging from $40 to $100 each, thermostats are an inexpensive yet successful way to avoid stressing a crop because of an improper growing environment.

Irrigation
The first step toward real automation is irrigation. A great deal of time and money is spent watering crops, and as growers know, if not done properly, a great deal of money can be lost. Instead of depending on workers who may not understand that irrigation involves more than simply wetting the growing medium, automatic irrigation systems can be installed to ensure proper watering. This example assesses the economic advantage of installing such a system.

If it takes, on average, one minute per 10 square feet to sufficiently water bench crops, a single bay of a 30-foot-by-96-foot greenhouse with 2,500 square feet of usable growing space will require just over four hours to hand-water. Assuming that the person doing the watering is paid $5.75 per hour, it costs $23 each time the house is watered.
A simple bench-top drip system for this greenhouse would cost approximately $800. This irrigation system consists of low-density polyethylene pipe running down the benches and four-way splitters with 36-inch spaghetti tubing and pressure compensating drip stakes for every pot. All of the hardware required for installation, manual shut-offs for each line, a basic disk filter and an automatic timer are included in the price. Installation of the system does not require professional help, so the setup cost would include about three hours. At $23 per watering, the cost of installing an automated drip system would be recouped in less than 35 waterings. After this, the grower saves $23 every time a crop is irrigated.

For hanging baskets, a drip system can be installed in the greenhouse rafters. If the plants are handled regularly, which might make drip stakes inconvenient for workers, a sprinkler system can be installed for a slightly larger investment. An overhead micro-sprinkler system has a payback of about 60 waterings. Automatic fertigation can be included in any of the mentioned systems for about $300. Besides the obvious financial savings that automated irrigation and fertigation provide because of reduced labor expenses, the amount of water and fertilizer used will be reduced.

Advanced irrigation
Larger greenhouse facilities may want to consider more sophisticated automated irrigation systems such as ebb-and-flow and nutrient-film technique. These systems are completely contained so that the irrigation solution is collected after use, treated for contaminants and recirculated for future use. Not only do these systems provide control over the amount of water available to the crop at any given time, but they also control the quantity of fertilizers used. By allowing for zero runoff, there is no waste of fertilizers from draining containers and no fertilizer contamination of the local water table. A fully contained system will have a longer payback time then simple systems.
The same 30-foot-by-96-foot greenhouse can be equipped with ebb-and-flow bench system for approximately $6 per square foot. Ebb-and-flow floors are priced per site by the installing contractor, so prices will vary.

Streamlining automation
Once growers have automated the basic controls for the environment and irrigation, they can begin to streamline these controls to maximize profits through increased plant quality. Most thermostatically controlled environments rely on a minimum of four individual thermostats -- two two-stage units to control ventilation fans and inlet shutters, and two single stage thermostats, one per heating unit. With an average price of $60 for each thermostat, the minimum investment to control the greenhouse environment is $240.

Although this four-thermostat system will work, it is imprecise and doesn’t provide an economically managed growing space. Simple thermostats have a large differential within their preset calibrations, which can result in equipment cycling and imprecise temperature maintenance. Often, the initial temperature calibration is several degrees off of the set-point temperature, which can lead to regulation problems when several thermostats are used together. If a crop requires a daytime temperature of 75@F and a nighttime temperature of 65@F to initiate flower buds, but the heating thermostat is calibrated four degrees lower, a lower temperature could delay bud set and reduce the crop’s value. No one wants Easter lilies the week after Easter.

Precise control, reasonably priced
Reasonably priced control units for a multiple number of environmental parameters are available eliminating the need for individual thermostats. Prices vary depending on the number of components that are to be automated. A simple unit with four stages of temperature control starts at approximately $270. Although this is a higher price than individual thermostats, the reduction in cycling will increase the overall life of the components being controlled and the resulting precise temperature control will help maximize plant quality. Other automation units control not only ventilation and heating equipment, but also horizontal airflow fans, shade curtains, roof and wall vents and irrigation/fertigation equipment. The cost of a non-PC system, which has the capacity to control all of the above equipment, starts around $2,500.

A more complex control system would be custom designed to meet a grower’s specific needs and is a practical investment for facilities as small as 1/4 acre. Operations of this size have at least six temperature manipulation units along with an air circulation system[can be HAF or inflation tubes], making thermostats problematic.

Weather-monitoring station
The addition of a weather-monitoring station is highly recommended, since it allows for an additional level of control. Growers won’t be required to use subjective methods, such as intuition, to determine adjustments in growing practices to compensate for weather. The control unit, with the aid of the weather-monitoring station and parameters provided by the growers, will automatically adjust all of the normal settings. When it begins to rain, roof vents will close. When it is overcast, the crops will receive less water. When it is clear and hot, shade curtains will close. A computer can be used with the above system to track and log weather trends. These logs can be used to determine the cause of a disease outbreak within a structure so that preventive measures can be taken.
All open-roof greenhouse structures, regardless of size, should use a weather-monitoring station. These units can detect an increase in wind speed or direction that, if ignored, could cause damage to or total loss of the roof assembly.

A simple weather station, which is independent of the type of control system described above, will cost approximately $800. Since this unit will only safeguard against adverse weather conditions, environmental controls will need to be automated separately.