Overview - WaterForce were employed to design, supply and install this water frost protection system for protecting intensive apple plantings from spring frosts.
Design considerations - the pump system had to handle a well that was flowing during the winter (positive artesian) but dropped off during the summer. The client was having problems with keeping the old surface pump primed during the summer months. The new pump had to be flexible to handle both smaller irrigation flows through to large frost protection flows.
Water supply and pumping - water is supplied from a 250mm flowing artesian welll. When water is not being pumped the well has a positive pressure however once pumping comences the water level in the well can drop by 5-6 metres.
A Caprari vertrical turbine pump was selected for pumping the 80 litres per second required. The pump motor was fitted with a variable speed drive (VSD) to enable the same pump to be used for much smaller flows. The vertical turbine style pump offered the following advantages:
1) The motor is standard off-the-self and is mounted above ground and can be easily serviced.
2) The pump flow can be adjusted from 15 to 80 litres per second using the Variable Speed Drive without motor cooling problems. This would not be possible with a submersible style pump motor combination.
3) The pumping impellers are installed down inside the well below the low water level so the pump does not require priming.
Fixed sprinkler system - Nelson R2000 sprinklers were installed on fixed uPVC risers. The sprinklers were able to match in with the existing post and row spacing reducing the amount of structural changes required in the orchard. The system applies adequate water to protect against a 3-4 degree frost.
Automation - the system is connected to a controller that monitors the outside temperature and automatically switches the system on when the temperature approaches freezing.