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The Physics of Humidification

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Watering with Fog ?

It sounds a little bit like a crazy idea to water plants with fog.

One of the most important attributes of a fogging system is the creation of a freely hovering fog of microscopic droplets. If we think of mature plants which need quite some water for their health the objection is correct
The ideal area of application for fogging systems is plant propagation - irrelevant whether it is vegetative or generative propagation. An exception may be meristemal propagation where care for the "seedlings" plants with fogging is needed when the plantlets are extracted from the glasses and planted in substrate.
As we have mentioned in other documents one of the criteria of successful plantlet-raising is the quality of the substrate. We do not want to go too deep into the various recipes of substrates, we want just to mention that the substrate should be moist and aerated to provide for fast and healthy root growth.

On the other hand for most seedling cultures the rule applies that the plantlets should be rather dry during the night when their growth is inactive to avoid fungal attacks and other ailments which can be caused by too much moisture.

If regular watering is interrupted during nighttimes the substrate tend to dry off - even if no substrate heating is present
If the humidification system would now simply restart fogging in the morning - for example controlled by a humidity feeler - within some days a water deficit would appear in the root are of the substrate, which can be alleviated only by additional hand-watering.

Installation of a good humidification system is no minor investment, so the customer can expect to get an automatic system which will need him only for control tasks and parameter setting
The automated tasks of the system should counteract especially the drying-off effects in the early morning and prepare the substrate with its ideal moisture for the coming day.

Plantfog has recognized this necessary "watering option" since 1986 and developed this function according to the valuable recommendations of the senior nurseryman Mr. Haas from the Municipal Gardens of Vienna.

The function works once more according to the principles of water physics. Cool air can take up less water than warm air until saturation. This means that the dew point will be reached earlier. As the temperature inside an (unheated) propagation house is still quite low the air will reach saturation rather fast (refer also to Evaporation Cooling) by means of the cooling fog and the surplus water will condensate.

If the humidity feeler is disabled during this period and the "watering time" is regulated by a control device the duration and therefore the amount of condensing water can be precisely set.

A rule of thumb states that approximately a quarter of the water a nurseryman would add manually during the day is enough for this morning dew. The amount needed during the day will be provided by the periodic fogging function. By this setting can be guaranteed that the substrate provides the right moisture while it remains aerated for the growing roots. The correct setting will be achieved very fast by the observing nurseryman who knows his cultures best. The success of this rather simple switching option was astonishing right from the start.

If the propagation houses are heated several short watering periods can be activated during the day if this promises success. From our numerous reference-installations we know that with some plant families - for instance Croton, Ficus, Schefflera, etc - a short activation of the watering function can be beneficial also during nighttimes at the end of the production cycle.

Plantfog then installed an additional refinement to this function; with an activated watering option the system starts at dawn (setting by means of an electric timer) with a preprogramed watering cycle with disabled moisture feeler to insert fog exceeding the dew point. If the watering cycle is completed the normal automatic cycling start for a "normal fogging day".

The practical consequences are that propagation can run a fully automated cycle where the nurseryman can withdraw to controlling.

Our control system „plantfog“ designed originally for research and development provides all these functions; with the somewhat simpler and therefore more affordable system  „profi-plus“ the "watering option" can be provided by a simple upgrading if the need arises.

(also refer to Technical Description of „profi-plus“)



The Physics of Humidification

back to Overview


last modified JAN 2020
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