The characteristics of an irrigation system

The charm of a garden results from several factors including its design, composition (plants, flowers and lawn surfaces), state of maintenance and positioning of plant species which, combined with the chromatic contrasts, give depth to open spaces. However, it is crucial to consider all these factors together with the state of health of the plant species present in the garden.

We should consider that green areas are able to provide “ecosystem services” improving aesthetic of the sites, contributing to mitigate pollution, improving the microclimate and maintaining biodiversity; nevertheless, to maintain the best the health conditions of plants, it is essential to provide the correct amount of resources, first of all the water. A rational use of the water resource is achieved through proper irrigation, respecting the actual and different needs of individual plant elements.

In the light of recent studies on climate change which foresee a tropicalization of weather events, characterized by very intense rains followed by long periods of drought and consequent increase of water needs for plants, the sustainable use of resources and, therefore, “smart” irrigation, became even more important.

The sustainable use of water in green areas, through irrigation systems designed to limit water waste, may be the only rational and ethical response to environmental problems and those relating to growing competition for resources due to the increase in population (the world population is expected to reach 9 billion in 2050).

An automated irrigation system consists of a controller, or control unit, capable of commanding the opening and closing of the valves that bring water to the irrigation sectors. The water is distributed from a main source (tap fed by the aqueduct, storage tank with relaunch pump, water from a well raised by a submerged electric pump, etc.) along a series of plastic pipes (generally polyethylene) on which a series of dispensers are connected (sprinklers, dripping wings, porous pipes, drippers, etc.) capable of supplying water to the various cultivated plants.

CONTROLLERS

The controller is the “memory” of the irrigation system; the controller is able to perform irrigation cycles (therefore the program) managing departure times (when), duration of the intervention (how much) and frequency (how often). The controller is wired with the solenoids of the valves; the execution of the irrigation program comes from the emission by the controller of electrical signals capable of “commanding” the opening and closing of the solenoids and, therefore, the passage of the water inside the pipes.

Controllers can be powered by 220 V alternating current or from batteries (direct current). Controllers powered by alternating current (220 V) are usually equipped with a transformer, either external or internal, capable of allowing the output of a 24 V signal suitable for the control of 24 VAC solenoids.

Controllers with external transformer can only be installed in places protected from rain (technical rooms, tool stores, etc.).

On the contrary, controllers equipped with an internal transformer can be installed outdoors (however in a position not totally exposed to raindrops).

The battery-powered controllers can supply 9V bi-stable solenoids in direct current (DC). This type of controller is as well suitable for installation in sheltered or in covered places. Some battery-powered controllers can be placed directly inside the irrigation wells. In this case the controllers must be equipped with a total dust protection system and be waterproof (IP 68).

A more detailed overview on types of controllers will be reported in following posts.

VALVES

The valves (solenoid valves) are electro-hydraulic devices, of a number equal to the number of sectors of the irrigation system; these open or close the passage of water to the irrigation lines following a command from the controller. Inside they are housed a membrane that separates the body in an upper and a lower chamber, held in the closed position by a spring.

The body is closed at the top by a waterproof cover and the solenoid housing is obtained above the cover. The solenoid can be operated by alternating current (AC) or it can be bi-stable operated by direct current (DC). The 24 V solenoids are open only in the presence of an electrical signal sent by the programmer which lasts for the entire watering time.

When the signal is interrupted, a spring calls the solenoid piston to the closed position; this causes an increase of pressure in the upper chamber. Under the action of the spring, the membrane lowers and closes the valve. The DC solenoids are used with battery-operated controllers; the programmer activates the solenoid with a first impulse that determines its opening; a second impulse at the end of the cycle causes the solenoid, and therefore the valve, to close.

A more detailed overview on types of solenoid valves will be reported in following posts.

RAIN IRRIGATION

Sprinklers are mechanical devices capable of providing water in the form of artificial rain. These devices are connected to a network of pressurized pipes and normally water a circular shape area.

The most popular irrigation sprinklers in parks and gardens are the retractable or pop-up ones. Pop-ups are made up of a body, a boat and a head or inlet. In rest conditions, the head completely re-enters the body throughout the functioning of a return spring; then this head comes out due to the operating pressure. Sprinklers, whether pop-ups or above ground, can be classified as static or dynamic.

A more detailed overview on types of sprinklers will be reported in following posts.

DRIP IRRIGATION

Drip irrigation (or micro-irrigation) is a localized micro-delivery irrigation system that become popular in Israel and California in the 1960s.

The water in drip irrigation is distributed by means of some low flow dispensers. In irrigating green areas, the most important are the drippers, the dripping wings and the porous tube.

AUTOMATION AND WATER SAVING

The reduction of water waste is possible with some automation of the irrigation system. In recent years, numerous steps forward were made from on efficient management of irrigation systems and related sensors.

The simplest rule of saving water is to wet when needed and consequently not to wet when it rains. To avoid watering when it rains, it is needed to connect a rain sensor to the controller; this will stop irrigation if a rain event occurs.