Open Vented Primary Solar Circuit

[Axel]

Can anyone comment on the pros and cons of using an open vented primary solar circuit instead of a pressurised system (used where freezing presents no risk)?

Thanks in advance..

 

[PullerGas]

Can anyone comment on the pros and cons of using an open vented primary solar circuit instead of a pressurised system (used where freezing presents no risk)?

Thanks in advance..

What, you want to install a Drain-Back system??

 

[Axel]

No, just using a header tank instead of an expansion vessel. System will work at lower pressure when hot. Means it will 'stagnate' earlier but also safer and lower spec components. No special filling process etc.
Drain back is a closed system. I'm proposing an open vented one.

 

[PullerGas]

No, just using a header tank instead of an expansion vessel. System will work at lower pressure when hot. Means it will 'stagnate' earlier but also safer and lower spec components. No special filling process etc.
Drain back is a closed system. I'm proposing an open vented one.

Drain Back doesn't need to be a closed system & rarely is. Most early thermal solar systems were Drain Back. Just ensure your system can accommodate the circulation pump head & monitor the water's glycol content closely.

You've been educated by the beard stroking, tree hugging, tramps on the Navitron forum by the sounds of it??!!!

 

[PullerGas]

Read what it says here regarding the drain back tank for example, it's not a sealed system;
http://www.solarconsultants.com/library/DrainbackRheemGL-30Man.pdf

 

[Axel]

Thanks Dick, looks good. Most of the info seems to be outside of UK.

Just one thing I fail to understand: In a drainback system, when the pump is off (so there is no fluid in the collector), how does the temperature sensor at the collector measure that the collector temperature is high enough above the tank temperature if the collector is empty of fluid? Surely it could only measure the temperature of an empty pipe / collector housing and not the water that would be heated by it?

 

[bernardgreen]

Looking at http://www.solarconsultants.com/library/DrainbackRheemGL-30Man.pdf

It seems strange to put the hot water from the panel into the drain back tank before it gets to heat the water in the storage cylinder.

This method of putting the solar heated fluid directly to heat the cylinder and then into the drain back tank would seem more efficient.

Or is the drain back tank more than just a tank.

 

[PullerGas]

Thanks Dick, looks good. Most of the info seems to be outside of UK.

Just one thing I fail to understand: In a drainback system, when the pump is off (so there is no fluid in the collector), how does the temperature sensor at the collector measure that the collector temperature is high enough above the tank temperature if the collector is empty of fluid? Surely it could only measure the temperature of an empty pipe / collector housing and not the water that would be heated by it?

A fairly simple differential controller can be calibrated by adjusting the Pots to suit.

 

[Axel]

But how can the collector sensor sense the panel temperature if it is dry? It would only be sensing the temperature of the empty pipe / fitting connected to the pipe coming out of the panel?

 

[PullerGas]

But how can the collector sensor sense the panel temperature if it is dry? It would only be sensing the temperature of the empty pipe / fitting connected to the pipe coming out of the panel?

Maybe just a thermistor sensing ambient at the panel, it can't be that complex. I'm sure if you route around you'll find a controls schematic on-line for a Drain-Back system.

 

[bernardgreen]

But how can the collector sensor sense the panel temperature if it is dry?

It does not matter if it is wet or dry. If the metal work of the panel is hotter than the water in the store tank then pumping fluid through the panel will result in that fluid becoming hot enough to increase the temperature of the water in the store tank.