Combi or heat only?

The flow will last along time if you size the accumulators correctly to the system they are feeding, a 500L one will give you about 250 L's of water.

 

I can't see what you're not understanding Mr Devs, the 16ltrs is going into a system that's packing it in tight, if the taps were open, then it wont accumilate and you'll only get at the taps whats going in (16 ltr), but the taps are not running 24/7 so the accumilator in the unvevted cylinder will build up the volume and pressure of water, bear in mind the water can't go back, the systems got check valves so the water builds up till a tap opens, the taps restricts the flow so it can't come any faster than the tap can let it out, there'll be a pressure reducer also on the system as a safeguard and a couple of blowoff valves too,
any clearer?

 

tell you what, I'm thinking of doing a series of talks about stuff from my favorite place in the world, the greenhouse, maybe i'll do a talk about unvented cylinders,

 

LOL!!

 

Er, I mean NNNOOOOOOOOOOOOO .

I get what yer saying, Mr Plum.

The one I don't get is how a pure unvented system, sans accumulator, can provide 26lpm when the mains supply is only, say, 16lpm.

 

ok, that's my first project tomorrow from the greenhouse,

 

(How do I delete this thread... )

Looking forward, Mr Plum

 

No, you're asking some good questions Dev (I'm learning too).

I get this air charge in the accumulator bit which directly fills with mains water until the air is so compressed in the accumulator that it will equal the force of the incoming main supply and an equilibrium will be reached between the two.

Then when a tap is opened (altering the equilibrium) the water will flow at a higher pressure gradually reducing all the time and if left running the accumulator would eventually return to the same pressure as the incoming main.
You would have a really full/overflowing bath by then!!

These are just my thoughts (hope I can delete) on what an accumulator is (at this moment).

I don't know if tom is confusing the pressure vessel on unvented with an accumulator!

Keep it simple.

Tappy,

 

Yeah, yeah, yeah - I get all that stuff about accumulators (tho' curious whether it's compressed air in contact with the water in the same tank or are they isolated from each other by a rubber membrane?)

But the non-accumulator type (assuming there's such a thing) - surely the outlet flow is limited to being the mains inlet flow?

 

so ok lets keep it simple,

 

Ah!

So all unvented systems have an 'accumulator' in them to store that extra capacity?

There wuz me thinking that it was just a sealed hot tank which was fed by the mains so could output only what the mains fed in...


Cheers, Mr plum.

 

that's right Mr Devs, when you think about it, the hot water needs somewhere to expand, some cylinders have a built in one and others need one attaching ,

always glad to help

 

D'oh! Of course...

A sealed hot tank with no room for expansion would not be something you'd want in your house...

Ta muchly.

 

The OP seems to have vanished after posting his question.

Could it be because the "experts" have spent all their time arguing over which solution is the "best"?

 

Don't worry, Sam - I'm sure the OP took my advice before he left...

 

you'd have to travel a looong way to get a more in depth debate on the subject, expert advice from hands on plumbers,diyers and self proclaimed solar system design engineers and a camio appearance from the newly formed green house enviroment protection society , no short change given on this advice forum,

 

Very well explained Mr Plum.

 

Don't worry too much Dev -
If the expansion membrane does fail there are still 3 more safety devices fitted on all unvented cylinders.

A pressure reducing valve (normally 2 bar) will also be fitted on the mains just upstream of the unvented cylinder to prevent excess mains pressure (which the system is not designed for) entering the unvented system/cylinder.
Tappy,