Air Cooled or Water Cooled? An Owner-Driven Choice. Part 3.
We left off at the end of part two with the issue of maintenance. Maintenance is not optional with water cooled systems; it is mandatory, and if maintenance slips then much of the equipment can be damaged in a matter of months. So what do professionals do about this?
The first thing to understand is that a cooling tower evaporates water in order to reject heat from your building. The water that has evaporated in the cooling tower needs to be replaced, which is easy to do automatically. But as the water is evaporated, it leaves behind the minerals that were in the water, and that is what needs to be managed. Without care, the minerals will form scale on all the interior surfaces of the tower. This leads to both inefficient operation and corrosion that will quickly damage the metal portions of the tower. The most basic chemical water treatment system involves a digital controller with some sensors that monitor the build-up of the minerals in the tower. Periodically, some of the water is automatically drained to keep the mineral level below a critical point. Scale inhibiting chemicals are added to help prevent scale from forming. Biocides are added to keep things from growing in the tower. And today, most systems also incorporate a way to measure water use, to help make sure that excessive chemicals are not used. Our industry has been doing this for 60 years or more and knows how to do it well, but this kind of system has to be regularly checked, adjusted and the chemical levels maintained. The most common frequency for this activity is monthly.
The other thing to recognize about cooling towers is that they are great air washers. Vast amounts of air are blown through a tower, where it is exposed to water sprays in order to evaporate the water. These sprays also do a great job of washing all the dust out of the air…and the dust ends up in the sump at the bottom of the tower. In the Los Angeles basin, depending upon how dusty it is near the tower, we typically have to clean out the mud accumulation 1 – 4 times per year to avoid damaging rust under the layer of mud, where the chemical treatment cannot reach.
Maintenance for a water cooled system is therefore a regular activity, and it involves both automated systems and manual removal of dirt and mud. But the energy savings can make all of this worthwhile…more about that in the next blog in this series.