Comparison of different heating systems for spring frost

The heating is a suitable late antifouling measure, especially for crops where other frost stabilization measures are not possible

or recommended, eg. B. because the culture is not suitable irrigation (stone fruit) or another Frost defense method.

Several systems are available for heating: Anti Frost candles and frost ovens with different fuels. All systems have in common a

relatively high demand for manpower in preparation, implementation and follow-up as well as an additional logistical effort

(storage, transport). Depending on the system and materials used, high fuel costs may also be expected. Depending on the fuels,

there are relevant effects on air quality, odor pollution and soot and smoke development. The fuels used are either fossil fuels

(paraffin, soft wax, petrolatum, peat) or come from renewable sources (wood).

It is desirable to use fuel materials which have a correspondingly good antifreeze effect with high efficiency and, on the other

hand, are both inexpensive and environmentally friendly. In addition, the burden on the population due to smoke or odor

development must be taken into account. The company OPST developed a self-made frost oven in 2017, which represents an

alternative to antifrost candles.

Test description

In order to compare the efficiency of different fuels in the OPST frost furnace with antifreeze candles, two series of measurements

were carried out (June 2018, November 2018). The series of measurements were carried out on both dates in orchards, whereby

identical measuring fields were each equipped with one of the antifreeze systems. Between the trial areas a distance was kept,

so that a mutual influence was excluded. The measuring fields were equipped with several calibrated temperature sensors at

different heights and distance from the heat sources and a reference sensor was mounted outside the surface.

The conditions of the two experimental dates differed from the temperature level (reference temperatures in June: between 13

and 18 ° C, in November: between -2 and 1 ° C), with regard to wind and humidity the measuring nights were comparable (<1m /

s, 96% resp 97% RH).

The following heating systems were compared with the same installation density (equivalent to 300 pieces / ha):

June / November: Against Frost candles "STOPGEL" (6 l soft wax)

June / November: OPST freezer, heated with peat briquettes (20 kg peat briquettes, 1 kg wood chips)

November: OPST freezer, heated with wood briquettes (20 kg wood briquettes)

The heat sources were placed offset in every second lane, with a distance of 5 m. The row spacing of the orchard was 3.25 m.

With the measured values, the temperature profiles and the achieved temperature difference to the ambient temperature

could be displayed at different positions. In addition, a mass / energy balance was created for each heating system.