Temperature of the feed water is the most noticeable environmental condition effecting the performance of RO systems. The general rule of thumb is to estimate productivity change at 3% per degree Celsius (°C) for each deviation from the standard of 25°C. If water temperature is 10°C during winter, you would estimate element productivity to be approximately 55% of the rated capacity. If summer produced water temperature of 30°C, then the estimate would be 115% of stated capacity. The range can be very large and it should be part of the factors used to size systems for the amount of water needed for the application. There are equations to provide a more exact estimate of productivity (see MS Excel program WEBGPD, available for downloading).
Extremes of temperature need to be avoided because of the potential for permanent severe effects on element and system performance. The expansion of ice will damage RO membranes just as it brakes water pipes in winter. High temperatures will accelerate compaction, the loss of porosity due to compression under pressure. Fortunately, elevated temperatures are not that common in most residential and small commercial systems.
The MS-Excel program can be used interactively or downloaded from our web site. The purpose of the program is to use mathematical descriptions of the temperature response of RO membranes as well as approximations for pressure effects on productivity to estimate performance for local conditions. Pressure is approximated by direct proportionality to productivity. Temperature correction is an exponential function related to the membrane material.
Temperature Correction Factor for Osmotik® Elements
TCOR = Q25 / QT = eX
X = 2600 ( 1/ T+273 - 1/ 298 )
TCOR= Temperature correction factor
Q25 = Permeate flow at 25°C
QT = Permeate flow at temperature
T = Temperature in degrees Celsius