One item that is grossly misunderstood by people considering reverse osmosis systems is the "gallons per day" (or GPD) rating for their system. Reverse osmosis systems are, as far as I can tell, unique as appliances in the fact that the harder and more they work, they better they work and longer they last - I can't think of another appliance that works along those guidelines. One thing that all reverse osmosis systems have in common is they have a membrane of some sort.
Some systems use the older cellulose triacetate (CTA) membranes and most new systems use what's called a "thin film composite" (TFC) membrane. These membranes, regardless of construction will have a rating for daily water production; that is how much treated water they can produce over a 24 hour period. These ratings are done at laboratories under ideal conditions (these are RARELY, if ever, realistic conditions for a residential home, but they are used as a guideline.) Typical membranes are rated at 12, 24, 36 and 50 gallons per day production and it is getting more and more common to see manufacturers installing 50 gallon per day membranes in their systems.
Sounds good right? More production is better, isn't it? The best answer to that is MAYBE. It all depends upon your needs. The higher the GPD rating on a membrane, the larger the molecules that are allowed to slip through the system are, therefore increasing flow rate and production. Under ideal conditions, a 24 gallon per day rated system will produce superior water to a 50 GPD system. If you are treating city water that is presumed to be microbiologically safe and simply improving the taste, "safety" may not be a big issue.
That being said, under ideal conditions, a 50GPD system will make about 2 gallons per hour (50 Gallons Per Day divided by 24 hours in the day,) whereas a 24 gallon per day system will yield about 1 gallon per hour. What does this mean to you? Well, depending upon the size of the storage tank you have, this will tell you how long your system will require to refill the tank if you should empty it. Most systems ship with a 3 gallon tank, storing about 11 Litres of water. If you're making a pot of coffee or tea, this is much more than is required for most residential use.
I like to see our clients using their RO water for everything that touches their food and drink - water to cook rice, boil/steam vegetables and making pasta, for example. To make enough pasta for a family of 4 for dinner, usually 1-2 gallons of water is needed. If you're steaming veggies and pouring 4 glasses of water to drink with the meal, we're now getting closer to the 3 gallon capacity of the tank - if all this water was drawn out simultaneously. As long as the tank holds enough water to meet your immediate demands, everything works as planned, you get the water you need and as soon as you stop pouring water, production begins and the tank starts refilling.
Here again we need to look at the amount of time that is required to re-fill that tank. A 24 GPD system will need 2-3 hours to refill that tank completely, where a 50 GPD system will take just a little over an hour. This is usually not a problem as it is relatively rare that a household will need that much water, that quickly, and keep in mind water will be available during the production time, its not a case of having to "wait" for the tank to refill before you can draw any more water from the system. (To put it in perspective, needing that much water would be roughly equivalent to draining a "big blue" 5 gallon water jug of bottled water. If one of those wouldn't last you more than an hour or so, you may need to consider a faster-producing system, or a larger storage tank.)
Where the smaller, lower-capacity systems really shine is in the maintenance. Because people rarely completely drain a tank, consideration needs to be given for how long the RO system will run to refill the tank. If you only pour off a glass of water at a time, perhaps 16 ounces of water, then the 50 GPD system will barely run at all to refill the tank before it stops production. The 24 GPD system will run twice as long. Why is this a good thing? The life of the membrane is directly related to how clean it is kept. The only time and the only way a membrane is cleaned is when it is producing water.
One problem oversized systems face is early membrane failure due to the fact the system never seems to run long enough to get a good, thorough cleaning. Although any membrane from 12 GPD all the way to 300 GPD can be installed in our reverse osmosis systems, for residential use we normally supply a 24 GPD rated membrane. For residential purposes, this rating typically yields the best balance of production capacity when you factor in maintenance and cleaning of the membrane. When combined with a good whole-home water conditioning system like the Hague WaterMax, you can expect 5 to 7 years from your membrane, assuming it is properly sized for your home. Since membranes are the most-expensive part of your reverse osmosis system, it makes sense to choose the most-appropriate membrane for your family. Bigger isn't always better! (My apologies to Tim the Tool Man Taylor; you'll need to stifle your infamous "MORE POWER" mantra when it comes to drinking water systems!)
Posts
No comments:
Post a Comment