Heat Ranger

Frost-tender crops such as grapes and berries can be devastated by frosts, so vineyards and orchards will usually need some form of protection to prevent plant cells freezing. The most common methods are sprinkler irrigation, fans, and helicopters. Sprinklers rely on the release of heat as water freezes to keep plant temperatures above freezing point. The amount of water needed is about 12 times the amount needed for irrigation, so there can problems of inadequate supply and saturation of already wet soils.

Frost protection using fans and helicopters relies on the formation of an inversion layer – a region of slightly warmer air 5 – 15m above ground level, which is formed by the re-radiation from soils and foliage of heat absorbed during the day. The warmer air is blown down from the inversion layer and distributed around the vineyard to keep plant temperatures above freezing point. These methods are not 100% effective and not effective at all if there is no inversion layer, as sometimes happens. Helicopters are expensive – around $1000 per ha per frosty night and have limited effect when temperatures fall below -2ºC.

Frost pots burning diesel are sometimes used to try to heat the air at ground level but around 80 per ha are needed and they burn 6 litres of diesel each per night, and generally the heat goes straight up so they are expensive, polluting and not particularly effective.

Bruce Koller, a former MAF adviser, has worked in and around horticulture for many decades including seven years as Chairman of New Zealand Horticultural Export Authority.

In 2006 Bruce became involved with blackcurrant production in Canterbury. Frost wasn’t expected to be a problem on the property but severe damage from -3ºC frosts occurred in three consecutive seasons. Helicopters were used but around 50% of each crop was lost and the property was eventually sold.

“The cost of spray irrigation of the blackcurrants would have been too high even if we had enough water so there was no point in putting a quarter of the property into a storage pond. The only option was to use warm air but in a better way than simple frost pots,” says Bruce.

“The farm manager suggested a fan driven by the PTO (Power Take Off) on a tractor, which would push the air upwards and create convection. We worked on a simple machine that concentrated and directed the warm air from six diesel burners over 3ha of crop. This lifted the temperature by 3º and effectively replaced 240 diesel burners.”

The original machine (the Frostbuster) was basically an elbow that rotated 360 degrees with burners underneath and air blown through but its performance was sufficiently encouraging for Bruce to test the concept further.

In November 2012 several Frostbusters were deployed, each covering 4ha. After a -3ºC frost event there was zero crop loss on the areas protected by Frostbusters, a 15% loss where helicopters were used and 65% loss where nothing was done.

Agricultural engineer Fred Phillips was involved with some of the original design and instrumentation, and after the success of the Frostbusters undertook a redesign to improve aerodynamics and locate the heat source after the fan rather than before it. The revised design was renamed the Heat Ranger.

“We trialled different temperatures, designed a machine that was as aerodynamically as efficient as possible, and designed our own burner because you can’t buy a gas burner that operates in a circle. We chose LPG because that allowed us to use a round burner, it is cheaper than diesel and you can run combustion engines on it as well,” says Fred.

“We started with a PTO version but it became clear that people could need multiple stand-alone units with their own engines. We now use Subaru 2 L flat four engines converted to LPG. They are light and compact and fitted with automatic start and stop.”

The Heat Ranger stand-alone units are set up for remote monitoring and control. A solar panel on the top supplies power to the computer system, and this requires a commutator because the turret rotates while the base remains static. Use of LPG also posed a challenge in that the gas freezes just below 0º C so the gas bottles needed to be insulated and exhaust gases from the tractor or the engine used to provide heating for them.

Bruce says initial tests showed that the Heat Ranger machines protected an area with a radius of at least 200m, which equates to 12.5 ha.

“Current trials indicate protection beyond 250m and covering up to 20ha but progress with tests has been limited by frosts – or rather a lack of them. In some winters we get only three frosts so when you are trying to test, modify and fine tune that isn’t a lot of windows available per year,” he says.

“As a consequence it has taken us about four years to get to where we are now.”

The development process hasn’t been cheap – about $2 million spent so far. The company has partnered with WYMA Engineering (NZ) Ltd in Christchurch, which manufactures machinery for the fruit and vegetable industry and has a worldwide market network. Regional support teams have been set up to provide timely backup support as required and to carry out routine annual maintenance checks before the frost season begins.

The current Heat Ranger is designed specifically for big expanses of crops that are no higher than 2m, so it is suitable for vineyards, blueberries, blackcurrants etc. It is not appropriate for kiwifruit or other orchards because if they have multiple hedgerows, taller trees or shelterbelts that prevent pushing out a blanket of warm air over the top.

Air exits the machine at 100 km/h and 35° C, with the turret pointed 1.5 degrees down and taking two to three minutes for a complete rotation. The air goes straight out of it for a start and then coils out and lays down a warm blanket of warm air over the top of the crop. This reduces the moisture available for freezing, warms the plants, prevents the freezing of cells and so protects the crop. The blanket is relatively stable – a small breeze will go over the top of it rather than move it – and this is shown by temperature recordings from a number of mast-mounted sensors at strategic locations.

The machines are is very competitive with other forms of frost protection, says Bruce.

“The Heat Ranger package is $180,000 for the PTO driven machine and $200,000 for the motor powered model. These figures include eight 200L LPG tanks and fittings, and the temperature monitoring gear on poles. This is less than half the capital cost of a water system and a similar cost to wind machines but you also get warm air,” he says.

“Since they are on wheels no concrete pad is required, and noise is not an issue. Operating costs on 20 ha will be $50‐ $100 per hectare per night, depending on the time run. Again this is similar to wind machines but a fraction of the cost of helicopters, and no inversion layer needed.”

“Investment in a Heat Ranger could avoid crop damage of perhaps $100,000 per year, and we anticipate that the machines should last at least 10 years.”

Ideally, says Bruce, they would work with vineyard designers to look at layout, where the prevailing winds come from, the temperature profile of the block to determine the coldest parts and hence the best locations for machines and temperature measurement masts. Automated or remote control could be an integral part of the package.

For existing vineyards an automated machine can be sited anywhere because it is self-contained and it can link up with weather station networks if the vineyard already has them. Each machine is on its own cellular control and can operate independently or be controlled remotely.

“We have made huge advances in the operational efficiency of the machine and the fact that we can push air out and lift temperatures so far out is very significant. It is a World first,” says Bruce.

“The real issue for growers is protection of the plants, so we are monitoring temperatures closely during frosts and checking that there is no plant damage. The data are showing that the machine is doing what it is designed to do.”

Ross Trowsdale

Fiddlers Green Wines was established at Waipara, North Canterbury, about 20 years ago, and Ross’s family has owned it for the past two years. The vineyard comprises 13.5ha of Sauvignon Blanc, Pinot Noir, Chardonnay, Riesling and Gewürztraminer grapes.

The area is prone to frosts in spring, and there have been at least 15 in the last 2 years, some as low as -3 deg C. Ross says that any frost impacts production and without protection there will be a reduction in both quality and quantity, depending on the severity of frosting.

“We originally had a tractor with a PTO driven fan that worked quite well down to about -2°C but it had to be moved continuously around the vineyard and needed two people to ensure that it was driven effectively and safely,” says Ross.

“I was talking to Bruce one day and he mentioned that he was constructing a prototype machine and so we decided to help. We started testing last year and it worked very well once we had learnt when to turn it on and found the best position for it in the vineyard. We had a -3ºC frost that lasted seven hours but lost no crop at all while others in the district struggled. We had more wine to make and sell, which is huge for our business.”

“This year it has also worked very well so far and will be interesting to see the results for the additional area they are trying to cover.”

Ross sees a distinct advantage in that the machine creates a heated environment that doesn’t require an inversion layer to be effective. This has been an issue occasionally in Waipara. Other benefits are that it is mobile and can cover a large area.

“Our machine is PTO driven and from our point of view it is economic in terms of frost fighting options over the whole vineyard. The other machine is fully automated with its own converted car engine running on LPG. It can be turned on in the field by someone in another location or automatically based on the temperature differential. It is being used in an area where they are still getting frosts under the conventional frost protection systems so it will be interesting to see how effective it is in that situation,” he says.

“From an industry point of view I think the new system will have a major impact, particularly if it is taken into account in the planning and budgeting process.”

Ross is impressed with the thought and technical engineering perspective that has gone into developing the machines and the thoroughness of testing.

“The temperature recordings on the property are resulting in a lot of analysis aimed at proof of concept, and that is very good,” he says.

“The availability of ongoing support is excellent too – they have taken a very professional approach.”