CONTROLLER CONCEPTS III

We’ve talked in this column about the critical nature of feed-system sizing so a pool controller can actually control, and the importance of a representative and responsive sample for that controller. Now we should decide what’s worth tying to today’s smart electronic automation devices and what’s probably not.
      If one must summarize the answer to that opening query in a single sentence, he’d have to say “control everything that moves quickly; skip everything that doesn’t.”
      We wouldn’t focus so much on pH if it didn’t migrate up or down so fast, would we? If our sanitizer didn’t move so rapidly towards zero, we’d probably not bother hanging its feeder on a few thousand dollars’ worth of electronics. Not only do we control these two standard variables because of their rate of movement, we do so because they are critical. So maybe we should add “critical in nature” to our requirement list for automation. Let’s list all the things we might automate in the pool, then look at each one. In the list we can take a stab at typical units of time within which one might expect to measure significant changes, then show the minimum-value change (one that we might want to correct) that applies to each:

ORP, chlorine/bromine	minutes or hours	10 mV
[PPM, chlorine/bromine	minutes or hours	.5 ppm
pH	hours	.1 pH unit, up or down
Calcium Hardnesse	weeks or months	50 ppm
Total Alkalinity	weeks	20 ppm
Total Dissolved Solids	months	indefinite; many thousands of ppm
Temperature	hours	1 to 2 deg. F.
Flow	days	gpm, 10% of total
Filter backwash	days of weeks	psi, specific differential
Pool water level	hours	one-quarter inch, threshold set
Air temp and humidity	hours	3 deg. F, 5%
Superchlorination	as needed, or cyclic	n/a
Acid flush of electrodes	as needed, or cyclic	n/a

It’s clear from this list, whether your pool conforms to these common ranges and rates or not, that the only variables screaming for control are ORP, pH, temperature, pool-water level and air handling. And only the classic first two relate to water chemistry!
      Examining the five fast movers in reverse order, we find that air handling is performed by stand-alone air systems, simple to complex ? yet never so far built into the “pool controller”. In high-end, newer indoor-pool-enclosure systems, a building-wide or campus/complex-wide central station ? run by facilities maintenance, not the pool operator ? usually manages natatorium air. The likelihood of pool systems being tied into these central systems is far greater than the opposite ? the case where “air” might be included in the pool-water controller. For outdoor pools... well, you know who has control over air handling there!
      Water level is controlled in every way imaginable, from float valves, solenoids controlled by probes or infra-red beams, Clayton valves... right on down to diligent operators with garden hoses. In every case, however, there seems no need to attempt electronic control of water level from the water-chemistry control center, no matter how sophisticated it may be. Levels are never recorded; and additions are triggered simply to replenish physical losses back to the desired elevation. Even summations of water use over long periods are done the old-fashioned way, by a totalizing water meter. You won’t ever find make up water on your pool controller.
      Pool water temperature is virtually always controlled by a thermostat ? integral to any installed heater, old or new. Temperature data may be gathered and archived by a central system at the maintenance office, but control is left with the heater system provided by the respective manufacturer. It doesn’t make much sense to locate a thermostatic control anywhere else, duplicating the integral one. We do find multi-channel, data managing pool controllers asked to keep records of temperature readings, system-on times, even energy consumption if there is no “facility central”. Remote control of temperature, on the other hand, may be infringing on the heater manufacturer’s design. Since he would have no control over the quality of that temperature management, partial voiding of the warrantee is likely!

       Now we’re getting to the important stuff.

      ORP, that qualitative oxidation/reduction potential developed by residuals of chlorine or bromine, is so fleeting it is a must for automation. In smaller, high-load bodies of water ? like public spas, therapy pools and wading pools ? sanitizer residuals can dive to zero in minutes. This is of such concern that health departments across the country are beginning to add ORP minimums and, in a few states already, ORP controllers are required, set to their guidelines and/or codes for all public aquatic vessels. ORP, as discussed thoroughly in PrP Issues 5 and 6, is the variable managed by every major pool-water control system made in the world today. ORP, (sometimes called HRR, high-resolution REDOX,) should be found on the face panel of your controller, now and in the future.
      Chlorine or Bromine PPM control is performed in a back-door fashion on some controllers in an attempt to simplify the display for un-initiated observers (some health inspectors, maybe?) as well as to enhance competitive featureship. Very, very few controllers truly read quantitative residuals (ppm); most actually read ORP. Some controller companies simply over-print meter faces with PPM numbers, almost never accurate or consistent. Others make calculated approximations for the readout, equally unreliable. A few high-end controllers offer PPM control as an option to HRR/ORP, using sophisticated PPM probes. Don’t use it as your control choice; PPM control, indeed digital PPM readout, invites criticism of the machine as too many variables bear on the readout to allow constant accuracy.
       pH control is actually more important than chlorine/ORP control. What? Read it carefully... “control” is the key word. The presence of chlorine is all-important; however the actual chlorine value, to be precisely controlled, is not as critical as pH. As you know, it's pH that determines both how effective the chlorine will be and if your pool is going to be intact next year as well! So careful, moment-by-moment management of pH could be considered the most important variable of all. In better controllers you’ll find that extremes are tied to alarms and to the sanitizer feed system itself ? an important feature. Too high or too low? Not only does the pH alarm activate but the sanitizer ? usually the cause for the un-corrected pH shift ? is locked out as well!
      Now on to the whistles-and-bells variables many of which, we will show, aren’t worth the pretense of automation:
"Automated superchlorination” is, frankly, a joke ? a result of consumer demand. If you can’t electronically read the values and the ratio of ammonia compounds to active halide (and you ? the controller, that is ? can not. Our machines read results, not the literal chemical content of water. It can’t, therefore, can’t calculate a dosage or residual required to reach breakpoint. Manual override with full-output sanitizer feed for a specified number of hours is not automation. These overfeed periods usually are of little value ? ineffective, unnecessary and wasteful. Maybe we could make a machine responsive to kids' complaints, or to levels of chloramine odor...!
      Total Dissolved Solids, that mystified and maligned variable blamed for so much that's otherwise unexplainable, is ridiculous to “automate”. First of all, even if it were important, TDS can’t be read accurately. Meters use conductivity as a crude approximation ? good enough for a pool-guy's purposes but by no means precise. Second, TDS is so “total” in nature that one cannot easily determine what miniscule portion of it’s content may qualify water to require dumping or dilution. Almost always, TDS is harmless and does not need reduction (see “What’s All This Fuss Over TDS:, PrP #1 or the updated version on the PPOA’s Internet home page: www.ppoa.org). The classic concern is over the "salty taste" complaints, and if you can’t handle that one with a little psychology then you deserve to waste all that water! Finally, TDS moves too slowly to bother spending money on its control. This is a classic case of un-necessary technology following inaccurate science.
      Electrode acid flush, if needed, is so simple we might as well do it with a time clock within the controller. In this case, we could call such switching "automation".
       Calcium Hardness moves quite slowly so doesn't need automation. That's handy, because CH can't be read with a sensor anyway. Monthly hand corrections are simple and usually quite adequate. It's the presence of plenty of calcium hardness that is important, not the precise value.
Automation of Total Alkalinity, tried by a controller company in the 70s, is almost impossible and simply not necessary. No variable easily read by instrumentation, like conductivity for example, is adequately proportional to TA. Hand tests are important, on a timely basis determined by the rate of change, followed by manual adjustment. Better than being a slave to frequent hand-dosing of bicarb or acid, however, one can spend some time evaluating the sanitizer influences choices and influences, thus greatly reducing the TA drift.
      That's about it for our expanded view of automation potential. After all this conversation, it pretty well boils down to the need for a machine that controls the ol' standard two and does it really well. Rather than "automating" dubious, spec-motivated variables, top machines should focus on offering: 1. Computerized remote access and control by phone or remote station. 2. Voice, beeper or fax call-out alarms for everything from un-expected extremes, excess feed duration, flow failure, even to out-of-code-compliance conditions. 3. Excellent and detailed records management, archiving and display, with complete event data as well as value data. 4. Capability for serious analysis ? of water chemistry, equipment set-up, system function, and system operation ? allowing the reported data to become a valuable management tool.
      There is one, final variable we haven't talked about, and it might be the most important of all ? quality Operator Training! As technology improves and becomes more available we learn more about a pool's maintenance needs. Equipment and systems are becoming more sophisticated as well. Pool owners then demand more of operations staff...A problem pool almost always has a problem operator; he may be well intended, but not well enough trained to deal with today's controllers, today's stiff requirements and today's risks. Current trends with the state health departments show us moving towards certification requirements for one or sometimes all operators assigned to any public pool. Someday, we may see periodic currency evaluations or even licensing. In the bigger picture, a pool guy is part of the "automation system". There's no buttons to push to fix an operator who needs experience and knowledge; she or he's got to go out and get trained. So stay current, renew your certification, and seek out advanced courses when available. It's your pool and your job we're talking about!
      Finally, a controller's "start-up training" is about as critical as the operator's certification, and he often is shortchanged. A controller in a box with a book is pretty worthless, yet many are sold that way. When shopping for a controller, an important part of the system's evaluation must be a review of what the owner receives in equipment training. Don't overlook it.
          ~ kw

w