Frost Protection Solutions Australia
Exfrost
Selective Inverted Sink System
Frost Prevention Fans
Frost Protection Quotes
Frost Prevention Partners
Contact Exfrost
 
What Is Sis™
 

Frost is more than an inconvenience - it is a drain on your resources and potentially a destroyer of your business.
In our changing environmental and regulatory climate, mitigating against frost damage is becoming increasingly problematic. You need a solution that can cope with frosts without polluting the environment or excessively impinging on your neighbour's peace and quiet. At the same time you need a solution that does not cost more than it saves.

Our aim is to provide frost protection solutions that are effective and cost efficient. At the same time our solutions are designed for minimum impact on the environment and your neighbours. The SISTM system has been designed with just these things in mind.
The Selective Inverted Sink (SISTM) system uses a horizontal fan unit to extract cold stratified air from close to the ground*, expelling it upward away from the protected area.      

The SISTM unit is located where cold air accumulates - in naturally occurring or artificially created cold air basin.
The SISTM unit draws the cold air in through the lower guard and expels it upwards in a spiral motion where it gradually mixes with the surrounding air.

*Cold stratified air occurs in radiant frost conditions.

http://www.frostprotection.com.au/sis_from_above.gif
How It Works


Stratified atmosphere
During a frost night (clear sky, without wind or fog) the soil surface gets colder by radiation. Under these conditions, the atmosphere stratifies into air layers of different temperature and density.

The coldest air, being densest, sits in the lower layers, causing the frost damage observed in the crops.



SISTM draining cold air
In undulating terrain the cold air flows, due to gravity, towards the lowest areas of the property. Cold air accumulates in various areas due to the presence of the different obstacles such as diverse embankments, barriers created by trees or other flora, slope variations, or simply because of the micro-topography. Ultimately, the majority of the cold air collects in the valleys.
 
How it works in undulating topography
Process of cold air accumulation
In undulated terrains the cold air flows, due to gravity, towards the lowest zones of the orchards. Cold air accumulates in various areas due to the presence of different obstacles such as diverse embankments vegetal barriers, slope variations, or simply because of the micro-topography. Ultimately, the majority of the cold air collects in the valleys.
In this way, cold air lakes are generated. This explains the most severe frost damage suffered by crops located at lowest areas, in comparison with the minor or no damage observed at higher areas.
Selective extraction process
The SIS units selectively drain the cold air coming from the hillsides, avoiding its accumulation and preventing the frost damage observed in the lowest areas.
The quantity and precise location of the units in a property are the result of a detailed technical study of the property. Cold air fluxes generated by the higher ground are calculated to find the optimum number of units to provide the best efficiency possible. Specific passive frost protection measures are also designed.
Process demo
 
How it works in flat topography
Process description
Under frost conditions a stable atmospheric stratification develops. On flat topography, all the property is submerged by a uniform cold layer, and the frost damage is homogeneous throughout the whole property.

Perimetric selective drainage

In this case the SIS devices make a perimetric drainage of the cold air. By placing the devices on the perimeter of the zone to be protected, the SIS devices selectively drain the cold air from inside the protected zone while preventing the entrance of cold air from outside.
A very important aspect with regards to the SIS System performance on flat topography is the possibility of reducing investment and operating costs when the area to be protected increases. The quantity of devices needed to protect a given area depends mainly on the perimeter.

An alternative, and probably more common approach is to isolate the area to be protected from the surrounding areas by the use of barriers (either artificial such as plastic sheeting or a solid fence, or natural such as as dense flora). The area to be protected is then "seeded" with SISTM units that draw the cold air out from within the protected zone.

Process demo