• What is SIS Technology?

SIS Technology (TSIS) aims to control a set of phenomena (radiation frosts, odours and dust propagation and radiation fogs) which occur in calm (windless) and clear (cloudless) nights and which effect on the activity or human life is often very negative.


TSIS arises from the application of advanced concepts in mechanics of fluids and heat conduction to the lower layers of the atmosphere and to the ground in contact with them. This application aims to act on the mentioned phenomena to protect crops, in the case of frost; the welfare and health of the people in the case of odours and dust, and to safeguard the lives of those who travel on highways or use airport runways, in the case of  radiation fogs.


TSIS has made ​​possible the development of two types of mechanical devices, the Selective Inverted Sinks (SIS) and the Jet-SIS. These devices are patented internationally and the application of them is exclusive of Frost Protection Corporation (more details on this website) and their authorized representatives. 


  • How does TSIS control frosts? 

TSIS performs the selective extraction of the cold air generated over cropped areas which is responsible of the observed frost damage. The referred selective extraction is made in those areas where cold air is accumulated (low lying areas, cold air flow obstructions, etc.) and where cold air flowing downhill reaches crop height thus affecting the crop. SIS devices also mix the extracted cold air with higher warmer layers of the stratified atmosphere, thus avoiding the effect of cold air over crop’s sensible tissues.  

  • Which type of frost can be protected using TSIS?

TSIS controls radiation frost events, in other words those events which are produced during calm and clear nights when soil losses radiation heat and consequently cools the air existing in the lower atmosphere layers (tenths of meters above soil). This type of frost events usually affects to a greater degree the low lying areas in comparison with higher cropped areas. As the other traditional frost protection methods, TSIS is not adequate for protecting advective frost events which are characterized by the invasion of significant freezing air masses over the cropped area. These extremely cold air masses usually affect to a greater degree the higher areas (highly exposed to cold wind) in comparison with low lying areas

  • What is a stratified atmosphere?

Under radiation frost conditions (clear sky, wind and fog absence) the soil loses radiation heat through the atmosphere. The soil, which is colder than the adjacent air cools the air, being this cooling process more significant in the lower atmosphere layers (first tenths of meters) and reducing its effect with height. 

When the above described process occurs, in the lowest part of the atmosphere (closer to the ground) the well known “thermal inversion” is produced as on the contrary to what happens during daytime when temperature decreases with height, under radiation frost conditions temperature increases with height in the atmosphere lowest layers.

Due to the fact that air density decreases with temperature, a stable organization of the atmosphere is developed (which does not change spontaneously with time) as the lower layers are the coldest ones and therefore the densest ones. Under these conditions the atmosphere can be ideally represented as a vertical succession of horizontal air “layers” or “strata” with increasing density towards ground. The referred process is called “atmosphere stratification”. 

  • What is the selective extraction?

Selective extraction is a property of stratified fluids (as the case of the atmosphere’s first tenths of meters above soil during a radiation frost event) that occurs when by some mean (i.e. installation of a sink inside the fluid) a continuous extraction of the fluid is made. This property coming from the general laws of fluids motion under gravity effect, establishes that the fluid will travel horizontally towards the sink and that the denser strata which is under sink reach will be firstly captured by it in comparison with the less dense ones. In the case of the stratified atmosphere, if the sink is located near the ground, it will firstly capture the coldest air strata (which is denser and thus closer to the ground) in relation with the warmer strata.

  • Where does the cold air extracted by SIS go?

Cold air captured by SIS is impelled by the device in the form of a vertical jet. This jet captures in its way the warmer air existing in the strata that the jet runs through. Warmer air captured by the jet mixes with the air initially captured by the SIS, thus increasing the final temperature of the mixture.


When the kinetic energy given by the SIS device to the jet transforms into potential energy due to jet ascent, fluid particles which are already warmer as a consequence of the mixture with particles existing in those layers ran through by the jet, will not descend towards the crop. The reason for this is that the descent will not be allowed due to the existence of intermediate temperature layers that lay over the crop. At the height reached by the jet, which TSIS design predicts to be several tenths of meters above the soil (more than fifty meters), the originally cold particles that were warmed after mixing with warmer strata will disperse horizontally in the layer whose temperature matches particle’s final temperature. 


  • Does TSIS use any heater or burner for its operation?

The SIS does not use any type of heater or burner for introducing thermal energy into the air. SIS device simply extracts the cold air that generates frost damage to cropped areas  end expels it, by the action of a propeller, up to a height in which it has no effect over the crop. 

  • Does TSIS operation cause any damage to the crop? May suction speed cause branch or leaves damage?

The SIS does not cause any damage to the crop due to its operation. The suction speed, enough for draining the cold air from the plantation, is not capable of affecting any sensitive vegetal element of the crop; even those plants located some tenths of centimetres from device inlet section

  • Which is SIS effect during a frost event in a low lying area?

The SIS avoids cold air accumulation in low lying areas of the site. It is important to note that it is topography itself who avoids cold air accumulation in higher areas. Therefore, SIS effect over low areas is the same as topography effect over the higher parts of the plantation. As a consequence of the previously mentioned, during SIS operation the temperatures of the low lying areas will tend to equalize that existing in the higher areas thus significantly reducing the existing frost risk in lower areas where it is usually observed the most severe damage areas. 

  • How does TSIS act on a flat terrain?

SIS devices are strategically located within the area to be protected and the perimeter of the subject area is surrounded by a natural dense shelterbelt or an artificial barrier. The design of the number, model and location of SIS devices is driven by the net temperature increase required for each case. In the short term with the use of JETSIS (a specialized adaptation of SIS, currently being patented worldwide) will eliminate the need of using barriers covering protected area’s perimeter. 

  • Is TSIS capable of increasing the temperatures registered at higher areas of a given plantation?

TSIS may increase the temperature in higher areas in those cases where cold air accumulation processes are developed in the referred areas. 

  • How the SIS is powered?

SIS can be powered by using electric motors, gas engines or through a tractor PTO. The motorization type is selected with the client considering the orchard/vineyard energy infrastructure and each application particularities.  

  • How much power uses the SIS per ha?

In average, the SIS System uses 2 to 7 HP per hectare, depending on the orchard/vineyard topography and the desired temperature increment. Usually in large areas the required power is much lesser.    

  • What can I expect in regards a SIS System typical investment payback period?

In most cases and according to data extracted from FPC client´s database, the SIS investment is recovered in the first year of operation. 

  • What are TSIS investment and operating costs?

The investment cost of TSIS is strongly dependant on the size of the protected area. For large areas (more than 50 ha), and under undulated topography conditions, the investment cost can vary between 1500 to 2500 USD per ha. The final figure depends on the topography and the severity of the experienced frosts.  Small areas (less than 10 ha) have a typical investment cost between 2500 and 5000 USD per ha.


In regards operating costs, TSIS present very reduced costs. In large areas the average is 1 USD per ha per frost night (for a 6 hr operation time and 0.1 USD/kw/hr). In small areas the average is 4 USD per ha per frost night (for a 6 hr operation time and 0.1 USD/kw/hr). 

  • What are the advantages of applying SIS to large planted areas, with tents or hundreds of hectares?

As the protected area increases, the investment and operating costs per ha decreases in a very significant way.  The availability of large scale SIS models (as SIS M15 and SIS M25) as well as the progressive reduction of the surroundings influence over the protected area when the area increases, allows a very significant reduction of the investment and operating costs.  

  • What about the environmental impact of TSIS?

It is almost none. The SIS operation drains the coldest air (which damages the crop) by using just a fan and without using any source of heating. The utilized energy is minimal (2 to 7 HP per ha).

Even the noise pollution is minimal. This aspect is increasingly being taken into serious consideration by environmental and government agencies due to the exploding population increase near planted areas. Noise pollution generated by other frost protection methods can be very high, considering that the noise is generated during nighttime.

SIS noise pollution is very low due to three main factors:  the very low energy needed to operate, the low propeller height off the ground (usually between 1.5m and 3m) and lastly the non-variable, fixed rotating section of the propeller (which is always horizontal).  

Summarizing, the TSIS is the system with less environmental impact on the market. This was recognized by many awards, among them the Tech Award, California 2004. 

  • Is TSIS compatible with other forms of frost protection?

Yes. The SIS is fully compatible with irrigation sprinkling (overtree or undertree), heaters, Wind Machines and cryoprotectants. This is of utmost importance when an insufficient active method is already installed on an orchard/vineyard (and more frost protection is needed), or in the case of high-severity frost risk situations, especially when it is impossible to continue protecting with traditional frost protection methods (lack of water, air pollution consents, noise pollution consents). 

  • For what reason a Technical Study (which details the SIS number, type and final location in field) is needed?

The determination of the SIS number, type and final location in field is essential to assure a correct system operation. This is best understood when considering that SIS must act in a very site-specific and diverse scenario on each orchard/vineyard, draining the coldest air produced within the property borders or even neighboring properties.  In addition, the phenology and cold-hardiness of each crop and each variety demands a personalized approach. 

Therefore, each SIS application in the world is custom-designed. 

  • Where can I find testimonials and case studies from happy customers?

In the section Case studies & testimonials diverse testimonials and case studies of SIS happy customers are presented. Please check back regularly for new testimonials. 

If you would like to directly see TSIS operating in field (California, Oregon, Washington, New Zealand, Australia, South Africa, Argentina, Chile and Uruguay) please contact us so as to arrange a visit to the most convenient or interesting sites, according to your preference. 


  • How can I get a TSIS quote for my property?

Please, complete the following form.