Air Cooled or Water Cooled? An Owner-Driven Choice. Part 2.
We left off this discussion with two questions: Why wouldn’t every owner choose water cooled if it is more efficient, even if it is more expensive from a first cost standpoint? And when we say that one system is more efficient than another, how does that translate in a practical sense to an owner’s electric utility bill?
Understand that your electrical company (SCE, DWP or which ever utility serves your area) typically bills commercial customers in two ways: based on the total energy consumed over time (measured in kiloWatt hours, or KWH); and also based on the peak amount of power used at any point during each month, measured in kiloWatts (KW) and generally referred to as the “demand charge” . In general, a water cooled system offers a significantly lower demand charge. As it gets cooler outside and the air conditioning load drops, the difference between water and air cooled power consumption diminishes, and below some outside temperature (often somewhere between 65 F and 75 F ambient), air cooled actually can be more efficient…but by that time, the amount of cooling tons required has typically diminished to the point that the air cooled energy usage cannot catch up to the overall efficiency of a water cooled system. None the less, air cooled systems have made significant improvements over the past 25 years (driven to a great extent by state energy codes).
The second thing to understand is that, in addition to a construction first cost premium when the overall tons are small, there is also a maintenance requirement for any water cooled system that goes beyond air cooled. And the maintenance is not optional, and it cannot be deferred. A water treatment regimen MUST be followed to prevent the build-up of mineral scale and corrosion as the system evaporates water, and to a lesser extent there is also a maintenance requirement to prevent biological growth in the cooling tower. The maintenance does not need to high tech, but it absolutely has to occur on a regular schedule. There are many circumstances, particularly in the case of smaller systems, where a water cooled system would otherwise be desirable, but the owner is unable or unwilling to make a realistic commitment to maintenance. In that sort of situation, water cooled is a poor choice…because without the required maintenance, the life of the cooling tower and other equipment can be drastically shortened.
The next blog in this series will provide an overview of the maintenance that a water cooled system needs. Again, it isn’t rocket science. But it requires constant, predictable service. It is not a “set it and forget it” process.