RO Water Output versus Temperature, Pressure & TDS (Total Dissolved Solids)
Reverse Osmosis Membranes (also know as TFC, Thin Film Composite, membranes) work by pushing water through layers of membranes. This is a fairly slow process. A 50GPD Membrane will produce 50 gallons of water in a 24 hour period; or approximately 2 gallons of water per hour (translating to 2-½ hours to fill up a 5-gallon bucket). There are 3 factors that affect how quickly water can be pushed through the membrane:
- Water Pressure
- TDS (total dissolved solids)
Factor 1 - Temperature
Water temperature changes how viscous (thick) the water is. The lower the water temperature, the thicker the water; making it more difficult to push through a membrane. Most RO membrane outputs are rated at 77-degrees. A 100GPD system that produces 100GPD at 77-degrees will only produce 52GPD at 50-degrees. This reason is why filling up an RO reservoir takes so much longer in the wintertime than in the summertime.
Factor 2 - Water Pressure
How high the supply / tap water pressure is also impacts how quickly water can be pushed through the RO membrane. The stronger the pressure, the more quickly the water can be pushed through and product water is produced more quickly. The weaker the pressure, the slower the output. An RO membrane is most-efficient at 80PSI: not only providing a fast output, but also yielding the best rejection rate. If you do not have a pressure gauge on your system, it is super easy to add on with our Pressure Gauge Kit. RO Membrane outputs are rated at a 65PSI. At 50PSI, your water production will slow down by 33%; translating to a drop from 100GPD to just 77GPD. The efficiency also drops as the water pressure drops; wasting more water. We typically recommend adding a booster pump if the water pressure is below 45PSI.
Factor 3 - TDS (total dissolved solids)
The last factor is TDS. Similarly to temperature, the more solids dissolved in the water the thicker the water; making it more difficult to push through the membrane. Fortunately, for most residential applications the impact is not too drastic. Tap water TDS typically ranges from 50ppm to about 700ppm. Every 100TDS increase translates to about 1.5% reduction in output. Where TDS will impact the RO system significantly is the usable life of the RO membrane. The higher the TDS, the more quickly the RO membrane will become clogged. While a RO membrane will last 2 years or more with low TDS, that same membrane may last only 6-8 months with very high TDS. Additionally, performance of the membrane (both rejection rate and output rate) declines as the membrane becomes clogged. Using a flush kit and flushing the membrane regularly and/or softening the water with a whole-house water softener are especially helpful when the TDS is high.
Each of these 3 factors will reduce system performance. Often, multiple factors have to be dealt with; which compounds the problem. Fortunately, we have all the tools and all the knowledge to help resolve any water quality issues. Call us at 407-599-2123 or email us at [email protected] today!
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