Double pass on a cylinder

[roamer808]

Howdy,

I have a triplecoil cylinder that has a gravity circuit and a pumped circuit from a solid fuel stove, both of which are working nicely and well thanks to advice in a previoius post.

The third coil at the bottom is for solar, which is sitting doing nothing as solar panel = money, which I have little of.

Would it be possible/advisable to reroute the DHW circuit to go into the cylinder, back out and then into the solar coil and back out.

While the stove is getting the cylinder upto nearly 80degrees, I doubt it is heating much more than 65% (guess) of the cylinder volume (copy of cylinder spec is hard to read for coil ratings).

Would I be able to heat the water quicker?
Images show my cylinder and heating layout.

triple cylinder

• roamer808
• 27 Mar 2011
• 2

Heating Plans

• roamer808
• 30 Jun 2011
• 1

 

[gasafengineer]

Running primary flow & return in parallel would be a better option.

 

[mysteryman]

Yes if the single coil performance is less than the boiler output. I would put them in series from top to bottom.

 

[Onetap]

Yes if the single coil performance is less than the boiler output. I would put them in series from top to bottom.

Yes, but be aware that that the wood-burner stove is gravity circulation and adding the additional coil will add to the hydraulic resistance of the circuit and slow down the water flow rate. It probably won't be a problem, if you're prepared to try it and see, but some high-efficiency cylinders are not suitable for gravity circulation.

 

[mysteryman]

He said it was pumped, although the pump or power can fail. OK I suppose if it can still circulate by gravity.

 

[Agile]

He did not just say that it was pumped!

Actually this is what he said:-

Howdy,

I have a triplecoil cylinder that has a gravity circuit and a pumped circuit from a solid fuel stove, both of which are working nicely and well thanks to advice in a previoius post.

Of course what he means may well be something different!

Tony

 

[Onetap]

He said it was pumped,,,,,,,,,,,

He did, but the diagram he posted shows gravity circulation from the stove to the cylinder and a pumped circuit to the heating headers.

 

[Agile]

The diagram he posted is only a heating plan for a two coil cylinder and not representative of what the OP actually has as far as we know.

It also gives uncontrolled hot water temps too which could be dangerous if its gets to boiling point.

If he wants clear advice he needs to give us clear informatioin on his system.

Tony

 

[roamer808]

Diagram shows 3 coils (not 2 - agile)

excluding the heat leak rad and solar setup - it's exactly as shown..

so anyway - are we agreed on replumbing it in paralell?

 

[Agile]

Yes, sorry it does have three coils.

One connected to the stove as a gravity circuit.

The other upper one on a pumped circuit from a boiler.

I dont know who you are "all agreed" with.

But MM has suggested a series connection and I would agree with that for the pumped circuit.

If its the gravity circuit you are talking about then I would probably just reconnect that to the lower coil PROVIDING the lower coil is 28 mm which it most likely is NOT if it is designed for the solar connection. In that case the gravity can only be connected in parallel.

These situations are very critical and any advice needs to be very clear as to whats being suggested.

Tony

 

[Agile]

Yes, sorry it does have three coils.

One connected to the stove as a gravity circuit.

The other upper one on a pumped circuit from another boiler ??? Or what is the item in the top left corner?

I dont know who you are "all agreed" with.

But MM has suggested a series connection and I would agree with that for the pumped circuit.

If its the gravity circuit you are talking about then I would probably just reconnect that to the lower coil only PROVIDING the lower coil is 28 mm which it most likely is NOT if it is designed for the solar connection. In that case the gravity can only be connected to it in parallel.

These situations are very critical and any advice needs to be very clear as to whats being suggested.

Tony

 

[Onetap]

I'd pipe it in series, as MM's first post, but be prepared to disconnect it if there are problems.

The manufacturers will have data for the cylinder giving the diameter and length of the internal coils, and the resistance (Pa pressure loss at one flow rate); this should cause concern only if the solar coil's resistance if much larger than that of the gravity coil.

 

[Busby28]

but be prepared to disconnect it if there are problems

Why would there be any problems?
The gravity circuit won't be compromised as it remains unaffected.

The extra coil is added to the pumped circuit from the systemlink.

 

[Onetap]

Why would there be any problems?
The gravity circuit won't be compromised as it remains unaffected.

He's asking about connecting the unused solar coil in series with the coil heated by the gravity circulation from the wood burner. I think.

Whatever, it's the same problem. He will add resistance and will reduce the flow rate for a given dP, whether that dP is provided by gravity or a pump. You could calculate the revised design flow rate, but it is probably quicker for him to do it on a suck-it-and-see basis.

No valves in the gravity circuit, BTW. None, not of any type, not ever.

 

[roamer808]

Thanks guys.

If we do it in paralell:
-> existing DHW coil will offer the same resistance as it does now.
-> solar coil is slightly smaller in coil length but will only take what circulation in that it's design will allow and not impeed the DHW coil above it?

If we do it in series:
will the flow rate will be reduced after the circulation leaves the DHW coil and enters the solar coil?

My cylinder is number 5 on the chart - 250 litres