Sizing a Salt Chlorinator

Sizing a salt chlorinator based on pool gallonage may result in inadequate sanitation — but a few calculations can ensure a correct fit.

While electrolytic chlorine generators (ECGs) for residential pools have traditionally been sized by pool volume, ECGs for commercial pools take bather load into account. Commercial pools are highly regulated, and in order to maintain appropriate chlorine levels, it has proven necessary to know what kind of usage the pool receives. Is it a health club, where exercisers and children swim all day long, or is it a senior center, where members swim only occasionally?

Anticipating usage — and planning for the “worst case scenario” — has made it relatively common to size commercial units based on expected chlorine demand along with volume. Residential units, on the other hand, can be more difficult to judge.

Sometimes new pool owners aren’t sure what their usage will be. Traditionally, it has been easier for homeowners and builders to assume average usage and size ECGs based on volume alone. Gallons are relatively straightforward; usage often isn’t.

But pools with oversized usage and undersized ECGs eventually exhibit problems related to improper sanitation, including hazy water, odors, algae, and even bather illness. An undersized ECG can also lead to shortened cell life, since ECG life expectancy can be decreased when units are overworked trying to maintain proper chlorine levels.

For example, a unit may have a lifespan of seven years based upon a run time of 12 hours per day during the season. If that unit must run 24 hours per day to keep up with chlorine demand, it will last between three and four years rather than the full seven.

It’s difficult to understand the extent of this problem because we don’t know how many salt water pool sanitation issues are correctly attributed to an improperly sized ECG. If a pool owner has repeated issues with maintaining enough chlorine to properly sanitize his pool, do pool professionals ask about ECG size related to pool volume and usage? They may. But they may also attribute the problem to other causes and recommend supplemental chlorine shocks to solve the problem.

So, how can pool builders and retailers size ECGs with chlorine demand as part of the equation?

Calculation factors
Start by having a simple conversation with the pool owner. How many swimmers will use the pool on a daily/weekly basis? Will small children or frequent exercisers be using the pool? (Compared to average swimmers, both tend to add more organics to the water, increasing chlorine demand.) Will pets have an occasional swim? (While not recommended for a variety of reasons, many homeowners still let pets enjoy their pools.) This will start the process of determining whether a pool has a light, medium or heavy chlorine demand.

Then, review other factors that tend to drive up chlorine demand. Are there flowering trees, plants or other vegetation surrounding the pool? Are fertilizers or pesticides used near the pool regularly? Does the climate include unusually warm weather or regular heavy rains? How many hours does the pump run each day? Does the source water contain organic material or added chloramines for sanitation? As one can see, many factors can influence any given pool’s chlorine demand.

These types of questions can help you determine whether a pool will have light, medium or heavy demand during the season. Generally speaking, pools with light demand can stick close to an ECG size based upon gallons (i.e., a 20,000-gallon ECG for a 20,000-gallon pool). Pools with medium demand will need 1.5 times the size (a 30,000-gallon ECG for a 20,000-gallon pool). And pools with heavy demand will
require double the size (a 40,000-gallon ECG for a 20,000-gallon pool).

It’s important to note that these sizing recommendations assume that the pump is running for at least eight hours per day — the minimum recommended run time. Pump run time is an important consideration for sizing ECG units. If the pump will run for shorter periods, an ECG with higher chlorine output should be used.
When in doubt, don’t be afraid to oversize the ECG. While it may cost more for the pool owner initially, that cost will be more than offset by the benefits in water quality and the extended lifespan of the ECG.

If the ECG is sized correctly, it will produce and maintain at least one part per million of free chlorine. (One to four parts per million is the recommended range for salt water pools.) The amount of free chlorine available can be easily tested and measured to ensure equipment is sized appropriately.

Sizing ECGs based on gallons is a fairly straightforward task. Taking usage-related chlorine demand and pump run time into account adds a level of complexity to the equation. However, customers will have better results in the long run if we take the time to factor in pool usage and other chlorine demand factors, which leads to loyal customers, word-of-mouth referrals, and a positive presence in the marketplace.

Source: Bob Harper- Pool and Spa News | 6.10.2011

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