EVAPORATIVE “PLASTIC” REFRIGERATION
Are all Plastics Equal?
The evaporative cooling in recent times has been based on cellulose (cardboard). Which means, it uses cardboard panels to hold the water, when evaporated, will cause a drop in temperature in the air that flows through them. This is therefore the constructive form used by most manufacturers today.
However, in recent times companies that offered different products have appeared in the market, differentiated mainly because they tried to solve the drawbacks of cardboard, which go down to its short duration and practical impossibility of cleaning; consequently its high maintenance costs; and its constant loss of efficiency according to its deterioration and lime clogging.
These different products, have replaced the cardboard with a plastic material. There are two differentiated plastics, High Density Polyethylene (HDPE) and Polypropylene (PP).
Polyethylene (HDPE) is used by the manufacturer Control and Ventilation, S.L., which we highlight as it not only manufactures a pad or panel, but also supplies a complete and compact evaporative unit that sells under the brand name “HUMIBAT”. The pad is marketed under the brand name “Panal C & V”.
For the case of Polypropylene (PP) we have found the pad or panel, incorporated as a component of their products by other manufacturers or installation companies, or directly with the panel sold loose to be a replacement of those facilities that were originally designed for cardboard, this being replaced by these panels of Polypropylene (PP). In this case, there is no clear differentiating mark.
We have started this article with the question of whether all plastics are the same, and we already have two different groups, by the type of plastic, polyethylene or polypropylene, and also clearly by their appearance. The Polyethylene pad (HDPE) is flexible, while that of Polypropylene (PP) is rigid.
The main question now is that, given that the plastic in the Evaporative Refrigeration arises to solve the drawbacks of the cardboard, do they do it? Do the two do it? How much does each one do?
For our study we have based on the information provided by the company Control y Ventilación, S.L. whose reliability is contrasted to be certified information and endorsed by an independent third part, the Miguel Hernandez University of Elche; and for the information that appears in the magazine Poultry Selections (May 2013), in its pages 7 to 12 that can be seen on the web http://seleccionesavicolas.com/avicultura/2013/05/el-plastico-menos-efectivo-que-el-papel-en-los-paneles-de-refrigeracion article based on the one made by Michael Czarick (Extension Engineer) and Brian Fairchild (Extension Poultry Scientist), and published by The University of Georgia, which we have also analyzed and we can see on the web https://www.poultryventilation.com/tips/vol24/n8-0.
Control and Ventilation website, S.L., http://www.controlyventilacion.com
Duration, Cleaning and Maintenance Costs
The duration of the Cardboard is always reduced. Although it depends on the quality of the water, we all know what happens with the paper or cardboard when we wet them continuously, they deteriorate. We know that in many cases and as I reiterate, depending on the quality of the water and its percentage of lime, it could only last one season (one year). As for cleaning, we can also make a call to logic and say that it is quite impossible to clean lime and impurities from cardboard to return it to a similar state to new. The cost of maintenance is equivalent initially to the cost of periodically replacing the panels.
As for the plastic, the one based on Polyethylene (HDPE) manufactured by Control y Ventilación, SL, has a duration that in this case will depend not only on the quality of the water, but also on the cleaning that is done, because in this case, it can be cleaned to almost take it to its original state. Polyethylene, it not only flexible, so that with mere pressures lime and impurities can already fall, but its consistency (heat-sealed grid cloth) allows it to be jet washed without breaking it, and even for being Polyethylene High Density, it can be submerged or washed with a water and acid solution that would clean it perfectly. That is, with a periodic (annual) cleaning, it can last for decades, which means that the maintenance cost is minimal. In the beginning the water needed to wash them.
Regarding the plastic based on Polypropylene (PP), its rigidity, contrary to the commented quality in Polyethylene, means that it can not be cleaned by a mechanical action of compression and relaxation that causes the lime to fall, that is, if we squeeze it, we break it. Not being made with grid mesh with large cavities, as in the case of polyethylene, but by glued sheets, difficults it to be cleaned by pressurized water, since this not only could break the plastic, but does not get to establish contact with the lime and dirt accumulated inside their ducts. In addition, the glued sheets are in danger of becoming detached, both by said water and by the acid solution. It is for all commented that the maintenance cost in this case will depend a lot on the quality of the water, if it has low lime content and there is little dirt that affects the panel, it will have to be washed with a lower periodicity, but When it is necessary to do so, many panels must be replaced, thus establishing this cost at least as the replacement cost of the panels (higher than cardboard panels).
Loss of performance
Let’s talk about the performance of each pad, one of the most important factors, in our last point. Now lets see what happens with that performance as the honeycomb gets dirty and clogging with lime.
It is clear that the cardboard for everything discussed above will have a declining performance curve from the first day.
At the other end we have the High Density Polyethylene (HDPE), since the non-deterioration is added to its large cavities and grids, which allows a lot of lime clogging without harming the equipment performance at all to continue passing the same amount of water and have the same water-air surface exchange.
The Polypropylene pad, would be between one and another since its not diminishing performance is due to not deterioration with the action of water as it happens to the cardboard, but nevertheless, having smaller cavities make lime clogging and impurities reduce its water-air surface contact very much before what happens to polyethylene.
Finally and as a very important factor we are going to talk about the performance of the different pads based on the studies of the articles referenced at the beginning.
According to the study, and to some conditions of humidity, when the outside temperature was of 35º, the cardboard pad managed to reduce it between 8 and 9º, leaving it then in about 26 to 27º. However, the Polypropylene (PP) panel reduced said temperature between about 5.5 to 6.5 degrees, leaving it at about 28.5 to 29.5 degrees. This is because this plastic (Polypropylene PP) and the cardboard use the same dimensions of panel and the same amount of water in circulation, with the plastic staying without the soaking properties and therefore need a bigger exchange water-air surface, therefore the drop in temperature is lower.
However, the polyethylene pad (HDPE) corrects this problem, giving the solution that is nothing but a greater amplitude of the pads (double), and a much larger quantity of water in circulation, instead of a drip (cardboard or Polypropylene), a total soak. To this speed of airflow is added , thanks to the large cavities already discussed, which in this case will be about 2 m / s, while in the case of cardboard or polypropylene is between 1 and 1.5 m / s. This is why not only does it match the performance conditions of the cardboard, but having a higher speed of airflow it increases the performance of each pad unit, which reduces the amount of units needed in the installation.
Everything analyzed leads us to the conclusion that although each installation will have many different variables to take in mind, cleaning and maintenance costs are a problem to be corrected by the cardboard that will be corrected by the plastic materials, although not by all. It is the High Density Polyethylene (HDPE), manufactured by Control and Ventilation, S.L. the only one that achieves a true and outstanding solution to the problem.
On the other hand, regarding efficiency, it is also clear that it is High Density Polyethylene (HDPE) that is victorious. Not only because it practically does not reduce with the passage of time, but because it starts with values similar to those of cardboard, but also needs fewer panels to allow a much higher airflow speed.