Direct Drain Back Solar Water Heating

[johnnyloveboat]

Hi, I was wondering if anybody could tell me if I can install a Drainback solar water heating system using my direct tank (and overflow tank) without needing to get an indirect tank and finding a separate drainback vessel.

Cheers

John

 

[muggles]

Drainback systems are nasty and should be avoided at all costs. Having said that, if you really must have one, then yes you do need to have a drainback vessel, that's the main safety feature of these systems. Without the drainback vessel, when the stat detects that the water is up to temperature and shuts the pump off, you will end up with water being retained in the solar panel. This will continue to heat up until it eventually becomes steam, at which point all hell will break loose.

Drainback systems use a direct cylinder which pumps water to the heat exchanger in the drainback vessel, so your present cylinder may be suitable.

 

[Agile]

Funny drainback systems being described above!

The conventional drainback system is just like the pressurised system and the solar water is a seperate primary system. So an indirect cylinder is always needed.

The only difference is the drainback water is not pressurised and there is not enouth water to remain in the panel when the pump is off so it does not have to have expensive antifreeze or an expansion vessel.

They are much simpler, considerably cheaper and they should be the preferred type of installation.

Tony

 

[muggles]

Maybe you've come across a different system setup then Tony - the one I've seen, and I admit it is only one so maybe I'm making too much of a generalisation here, runs as I've described. We fit the glycol-filled ones every time so I'm just commenting on a drainback I came across recently when I had to go and change a pump. I'd assumed they were all the same, maybe they aren't.

 

[Agile]

There is one marketed which uses plastic pipe in the panel and just circulates the DHW through the panel. Not very efficient and expensive for what they are.

But didn't you study both types on your acredited solar course?

And I think the solar antifreeze is not called Glycol but some other fancy name because its a different chemical to resist decomposition when it gets flashed when the panels stagnate

Tony

 

[ajstoneservices]

Hi, I was wondering if anybody could tell me if I can install a Drainback solar water heating system using my direct tank (and overflow tank) without needing to get an indirect tank and finding a separate drainback vessel.

You can use your direct cylinder on a drain back system no need for an indirect cylinder scaling of the collector can be a problem so best use a water softener. Is a drain back system better, safer, cheaper than a sealed system? in my experience, no.

Drain backs are just as easy/difficult to install as a sealed system sealed systems need expensive antifreeze? (£20) not always my system has had none in four years the controller/insulation give frost protection, every system we install has antifreeze added.

tony

 

[billy bob]

There is one marketed which uses plastic pipe in the panel and just circulates the DHW through the panel. Not very efficient and expensive for what they are.

But didn't you study both types on your acredited solar course?

And I think the solar antifreeze is not called Glycol but some other fancy name because its a different chemical to resist decomposition when it gets flashed when the panels stagnate

Tony

It is called Glycol Tony, you can get either Tyfocor Glycol or Ethylene Glycol,
The problem with drainback systems is they are not pressurised, this means they will flash to steam at lower temperatures, the systems I use are pressurised to 4bar this increasing the boiling point of the heat transfer fluid thus allowing the system to operate efficiently at higher temperatures