Bather Loads

In Blog, Chemistry, Controllers by Cathy Erntson

The Importance of Really Real Numbers in Pools: The Saga of Sizing for Reality

When looking into changing the equipment we use to chlorinate our bodies of water, one of the first questions asked is “What’s your bather load?” How much thought did you put into your answer before you gave it? Very often we find that people guess. They’re educated guesses, based on what they have witnessed over time at their facilities. But they are still just guessing, and quite often we find them to be very wrong.

Knowing true bather load numbers are so vital to a healthy pool. Not only is it a regulated number (NO, you CAN’T squeeze in as many bodies as will fit in at one time) it is also one of the key parameters for correct equipment sizing. While the plethora of pictures of crazy overcrowded pools available on the internet could make a pretty interesting article, I’m focusing on bather load in relation to disinfection equipment.

Regardless of what type of disinfection system you use, it was sized to work (correctly) under certain parameters; gallonage, flow rate, and Cl Demand. Gallonage and flow rate are the pretty easy ones to get right on the nose; we all know how to figure our volume (hopefully) and we all have flow meters in the pump room (preferably working ones that are actually visible). But then there’s that last one, the chlorine demand. In other words, how many people are in the water. I’ve seen huge pools that required miniscule amounts of chlorine and tiny pools that burned thru vast amounts faster than you could add it. The differentiator was the bather load. More people in the pool means more human organics in the pool; sweat, spit, hair, dead skin cells…and that’s not even the worst of it! It also means more products in the pool as well; lotions, sunscreens, hair products, used band-aids. It goes without saying that all this additional “ick” is going to require more chlorine than usual. And here is where sizing issues become real apparent really quick. The minute you elevate a facilities bather load and they can no longer keep up with Cl demand is usually the moment they realize they are undersized. Your primary system should be large enough to handle your daily summer bather loads, for the most part. You will still have an afternoon here and there, or an especially hot day where the back-ups kick in, but the bulk of your operations should be handled with your primary system. If it can’t, why are you investing in only part of what you need?

Liquid feeders, erosion feeders, and salt generators all have a finite output. They can only get so much Chlorine into the water at any given time. Having automating controllers is awesome, being able to constantly monitor and adjust water chemistry parameters helps you keep a much tighter control on your levels. It’s actually the most ideal way to add chems, feeding small amounts as soon as a reading starts to slide out of range instead of waiting till it’s way out of whack and needing a large volume of chems. But having instant control, instant ability to start getting more sanitizer in the water isn’t going to change the hourly output capabilities of the disinfection system itself. Liquid pumps can only move so much product so fast, erosion feeders can only erode at a certain rate (and this timing can be further complicated when using the incorrect product for your feeder), and generators can only produce so much Cl in an hour.

Taking the time to accurately gauge your facilities bather load will save you from so much potential headache down the road, saving time and money by getting you into the correct equipment the first time around. Remember, sizing for your slowest day might be the cheapest upfront, but you will pay thru the nose for it later in employee time and additional chlorine, not to mention a second set of installation charges/hourly labor when more equipment has to be added later on. To borrow a phrase from woodworkers, “Measure twice, cut once!”