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Thursday, 27 June 2013 15:51

Drain-back vs. Pressurized Glycol Systems

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Drain-back versus Pressurized Glycol Systems. Again, another comparison. Which one is better? It Depends! In a nutshell, the solar loop (includes panels tanks and connecting piping) within drain-back systems is only partially filled with heat transfer fluid. This design allows the fluid to reside in a dedicated tank inside, if the solar pump is not running. This design ultimately protects the heat transfer fluid and the solar tank from over-temperature conditions. More on this later! The solar loop within pressurized glycol systems (which includes the collectors) is completely filled and pressurized with heat transfer fluid. This provides less protection from overheating the heat transfer fluid, which can accelerate the breakdown of the antifreeze. This type of system can benefit from a larger than average solar tank, which would help avoid over-temperature conditions. In addition, a heat dump of some type, can be designed into the system, allowing excess or unneeded heat to be rejected to the outdoors, into a radiant slab, into a pool, etc. Overheating typically can occur when occupants go away on vacation. If no hot water is used in the house, solar tank temperatures will continue to rise and rise, so a heat dump is one possible solution. Some solar controllers have a vacation setting, which operates the pumps at night, to cool the solar tank(s) to reduce/eliminate the potential for overheating. Basically, the design of your home and the location of the panels and tanks, as well as the piping path (drain-back systems need all piping pitched downhill, toward the drain back tank) may determine which type system you install. Also, if you desire a PV-pumped system, you will most likely need to go with pressurized glycol system (PV pumps are not capable of lifting the weight of the fluid as required within drain back systems. Piping Drain Back systems are typically more piping intensive than pressurized glycol systems. But, if you are planning on installing a heat dump on your pressurized systems, the amount of piping can be closer to equal or could exceed that of drain back systems. Myself and other professionals give drain-back systems the nod for performance. Disadvantages are that the panels and piping must be tilted slightly(to assist in fluid draining. It is could potentially be noticeable from the ground, if you stare long enough. Advantages to installing pressurized glycol systems include system simplicity, smaller pumps, pumping power, PV driven pumping becomes an option, and a potential to use smaller piping to panels. Contact APEX Thermal Services to help you decide which system is best for your needs

Read 85885 times Last modified on Friday, 28 June 2013 14:32
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