The lifetime of any industrial equipment , be it an evaporative condenser or a cooling tower, also depends on the proper maintenance of its components.
This article shows the ordinary maintenance activities to carry out on a Decsa's CFR-C closed circuit evaporative condensers, made of Z-725 galvanised steel sheet, equipped with centrifugal fans and ideal for industrial refrigeration applications.
We would like to remind you that the indications given here are also valid for the closed circuit cooling tower model REF-C, which is a closed industrial cooling tower also built with centrifugal fans and designed for water cooling in industrial and HVAC applications.
The two equipment, in fact, differ only in the type of fluid circulating inside the coils. While only water (H2O) is circulated in the REF-C series cooling tower, in the evaporative condenser the fluid flowing is a refrigerant gas (e.g., ammonia).
Both models consist of an upper exchange section and a lower ventilating section with a water collection basin. Let us start from the latter to present the various activities to be carried out.
Routine maintenance activities on a cooling tower or evaporative condenser are generally performed when it is scheduled to shut down equipment, a period in turn determined by the needs of those operating the plant.
In the case, for example, of a system that goes to serve the air conditioning of a commercial complex, the cooling unit remains operational for about seven to eight months of the year: the remaining period, therefore, can be exploited to carry out all the necessary checks and any extraordinary maintenance work.
If the unit is part of an industrial plant that operates all twelve months of the year, it is advisable to set aside consecutive days for maintenance activities and, in addition, to define a few more hours outside this period to allow for those periodic maintenance activities that require more than a single annual intervention.
Before carrying out any maintenance work, it should be ensured that the motor of the evaporative condenser (or cooling tower) is switched off and that the area concerned is secured in accordance with the procedures of the applicable regulations.
That said, the first maintenance activity we suggest is to check the drive belts on the fans, an operation that should be carried out at least twice a year using a tool designed for this purpose: the tensiometer.
To perform the check, it is first necessary to remove the protective grids by unscrewing the bolts that attach them to the structure. Next, you need to calculate the free stretch (t), as shown in the image below, to know the force to be applied with the tensiometer.
The free stretch (t) defines the distance between the center of the two pulleys, i.e., the motor pulley and the pulley connected to the drive shaft. The force to be applied through the use of the tensiometer is the one by which the minimum and maximum values referring to type A belts and type B belts are noted.
Once the free stretch (t) has been calculated, it is necessary to calculate the center and flex the belt using the tensiometer for a measurement defined by the length of the free stretch.
Let us consider that the force to be applied is that required to flex the strap by 1.6 mm per 100 mm of the length of the free end (t). If, for example, the free end (t) is 1 metre long, the strap will have to be flexed in relation to the one alongside by 1.6 cm. If the free length is two metres, the strap shall be flexed by 3,2 cm.
It is very important to check the tension of the belts periodically: incorrect tension shortens the life of the belt and bearing, especially if the belt is over-tensioned. Once the belt is flexed, the value triggered by the tensiometer should be between the minimum and maximum values, as shown in the table below.
A second operation to be carried out during maintenance of the evaporative condenser is the lubrication of the belts; in this case it is necessary to make use of a silicone lubricating spray product suitable for the purpose. We recommend making a spray of the product on each individual belt of the equipment and then spinning the transmission manually so as to distribute the product evenly.
In case the cooling unit is idle for several months, it is a good idea to remove the belts and keep them in storage, so as to preserve their integrity. Later, when restarting, it will be necessary to remount them and carry out lubrication.
Bearing greasing is an operation that should be carried out every four months or 3,000 hours of operation of equipment. To carry out this maintenance activity, it is necessary to have a pump containing a cartridge of lithium grease suitable for the bearings.
Above each bearing there is a grease nipple to which the pump tube itself should be connected; then an amount of product corresponding to about three pump strokes should be introduced. Again, once the bearings have been lubricated, it is important to run the transmission manually to distribute the grease evenly within the bearing.
Recall that an ungreased, or undergreased, bearing will dry out and thus become damaged; similarly, putting in too much grease can also cause bearing damage. In fact, excess grease may leak out of the oil seals and introduce dirt into the bearing itself, inevitably damaging it.
Another important maintenance activity is to check the inside of the evaporative condenser water basin. To perform this task, it is first necessary to manually remove the inspection hatch and then the protective filter, and then proceed to clean it.
At this stage, it is possible to assess whether it is necessary to clean the inside of the basin and check for sediment or scaling. Recall in this regard that, in addition to proper maintenance, the integrity of any unit also depends on proper water treatment, which must be carried out by a specialized company. For any clarification on this matter, we refer to the water treatment company of your reference and to the appropriate table provided in our manual.
During the inspection of the inside of the basin, the fall of water, coming from the nozzles, to the bottom of the basin should also be checked for obstructions in the heat exchange coil: if the rain from the bottom of the heat exchange coil flows evenly from the entire surface, it is possible to rule out the presence of specific problems due to the obstruction of the heat exchange coil.
The inspection of the electric water recirculation pump is a visual check aimed at verifying that there is no wear and tear and no signs of scaling or oxidation inside the terminal box (after removing its cover).
Next, with the pump in operation, it is also a good idea to check that the data resulting from the electrical panel to which the pump is connected matches the data on the nameplate attached to the pump.
To carry out inspection and maintenance of the exchange section, it is necessary to reach the height of drift eliminators, i.e., the top of the unit. If the evaporative condenser does not have a walking platform installed on the unit, a lifting platform or a vehicle with a basket must be used.
In this regard, since this is work at height, we remind you that it is essential to have the PPE required for this type of activity (safety belts, hard hat, ...).
First, it is a good idea to remove the drift eliminators, so as to check their integrity (dirt, clogging) and check the water distribution system. In particular, it should be checked that the water sprayed from the nozzles evenly covers the entire surface of the exchange coil; if this is not the case, it is necessary to manually remove the secondary manifolds (i.e., the pipes to which the nozzles are connected), bring them to the ground, clean them, and replace them if necessary,
After all checks in the exchange section are completed, you can reposition drift eliminators and restart the unit.
Recall that if in the case of maintenance activities related to the fan section (checking belts, greasing bearings, ... ) it is as much as ever necessary to stop the motor, in the case of the exchange section it is possible to keep the unit running, at least if control maintenance activities are being carried out.
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