Unvented Ticket

T

toasty

Chaps,

I know you need an unvented ticket/qualification to install unvented/mains pressure hotwater cylinders (megaflow, santon etc...)

I also know that you DON'T need an unvented ticket to install a sealed central heating system (i.e no expansion tank, just a expansion vessel)

What about a sealed heat/thermal store system, do you need a ticket for that? (i.e one with a vessel and not an expansion tank)

Thanks in advance.
-Dan
 
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B

BigBurner

Chaps,

I know you need an unvented ticket/qualification to install unvented/mains pressure hotwater cylinders (megaflow, santon etc...)

I also know that you DON'T need an unvented ticket to install a sealed central heating system (i.e no expansion tank, just a expansion vessel)

What about a sealed heat/thermal store system, do you need a ticket for that? (i.e one with a vessel and not an expansion tank)

Thanks in advance.
-Dan

No, it can be DIYed, not covered under G3. They come with a pressure relief valve on the cylinder and there will be one on the boiler if heating directly. They work very well.
  • You will need to fit an extra expansion vessel to supplement the one in the boiler.
  • Fit a high temperature cut-out stat on the heat bank cylinder, set to 95C.
  • The heat bank cylinder is just a large pipe in a sealed CH system.
  • Always put a magnaclean on the CH return to the cylinder.
  • Always insert full bore isolation valves on the plate heat exchanger (between plate, pump and flow switch, so all can be isolated) and also the CH loop.
  • Always put in enough inhibitor for the whole system, although as a sealed system it will not be subject to corrosion as much as an open vented system.
  • Best use stainless steel, although Copperform
    http://www.copperform.co.uk/mains_pressure/thermaflow/index.htm
    use copper pressurised thermal stores and a small combi-boost version.
  • Ideally have full CH & DHW electric back up by having two immersion bosses.
  • Fit two cylinder stats to prevent boiler cycling.
  • Set to 1 bar as per a normal sealed system.
  • Leave a stub of 22mm pipe with a compression cap to aid filling with inhibitor.
Many makers will make them to suit with internal DHW take-off coil or external plate heat exchangers, stat probes, etc.

Look at this thread "Heat Banks" on how an integrated heat bank is put together. An amateur DIYer figured it out and bought one to order. He put to shame the so-called professionals on this forum, even doing some tests on how it performed, noting low return temperatures that promoted extensive condensing efficiencies, which was impressive (Not to be disparaging, however it could be improved even further that is how efficient they can be, however a great result and efficient system):
//www.diynot.com/forums/viewtopic.php?t=137289
They can also be purchased off-the-shelf.
 
T

toasty

Thanks BB.

I've read the thread you mention a few times now, very informative.

So presumably the reason an unvented cylinder needs a ticket is becuase the pressure releif valve isn't integral to the cylinder? ..but on thermal stores it is?

Which does beg the question why unvented cylinder manufacturers don't just make them part of the cylinder, doesn't it?

Ok, one more question if I may, is there any regulation/rule/law prohibiting me from building my own store from scratch (i.e from sheet steel) I would of course use normal commercially available PRVs and expansion vessels. And needless to say, I would pressure test it to well in excess of 1.5bar before using it, I don't really fancy 200litres of 80C water throughout the house!

Cheers
-Dan
 
T

toasty

Oh, forgot to mention that I think I have a novel way of connecting said store to an (my) exisiting system which means that it can be connected using only a couple of tappings and also so that it can be isolated (using a two port motorised valve) should it become depleted (and then reheated when there is no demand elsewhere.

From what I've seen of other designs, this is one failing of the thermal store idea, that being that once depleted it puts further demand on the boiler at a time when it's trying to service the system elsewhere.

I *think* my system will mean that in a situation like this is can be isolated to prevent such an occurance.

Cheers
-Dan
 
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B

BigBurner

Thanks BB.

I've read the thread you mention a few times now, very informative.

So presumably the reason an unvented cylinder needs a ticket is becuase the pressure releif valve isn't integral to the cylinder? ..but on thermal stores it is?

Which does beg the question why unvented cylinder manufacturers don't just make them part of the cylinder, doesn't it?

A sealed thermal store store does not operate to the pressures an unvented cylinder does (only 1 bar cold and rises when heated to around 1.5 - 1.75 bar). There is no cold water, at pressure, replenishing any super hot water in the cylinder if it blows off.

Ok, one more question if I may, is there any regulation/rule/law prohibiting me from building my own store from scratch (i.e from sheet steel) I would of course use normal commercially available PRVs and expansion vessels. And needless to say, I would pressure test it to well in excess of 1.5bar before using it, I don't really fancy 200litres of 80C water throughout the house!

Nothing stopping you doing that for yourself. If tested to 1.5 bar only have it vented. Test to min of 4 bar if pressurised, with relief valves of 3 bar. Best check this. Check the web what the makers pressure tests their steel vessels to.
 
B

BigBurner

Oh, forgot to mention that I think I have a novel way of connecting said store to an (my) exisiting system which means that it can be connected using only a couple of tappings and also so that it can be isolated (using a two port motorised valve) should it become depleted (and then reheated when there is no demand elsewhere.

From what I've seen of other designs, this is one failing of the thermal store idea, that being that once depleted it puts further demand on the boiler at a time when it's trying to service the system elsewhere.

I *think* my system will mean that in a situation like this is can be isolated to prevent such an occurance.

Cheers
-Dan

No further demand is put on the boiler. It heats the cylinder top down and the top section is for DHW. The store of water acts as a buffer assisting the boiler. A CH pump running when reheating will not take too much heat away from DHW side.

An integrated CH & DHW thermal store is in two sections: the top is DHW and the bottom CH. Have it priority. This can be done by switching out the CH pump when the boiler is reheating the cylinder (pump interlock, which is simple to do). This gives quick DHW recovery as all the boilers heat is dumped into the cylinder, and quick cylinder recovery too. Have two anti-cycle stats with probes.

If it is a 20 minute cylinder reheat from cold that is the most you will be without CH. In reality it will be much less, as the boiler kicks in the CH cuts out and if DHW is being draw off the boiler is replenishing simultaneously and only kicks in when 60C 2/3 from the top of the cylinder, so not kicking in from stone cold.
 
T

toasty

Thanks for your advice BB.

It's just as well that I am allowed to make this thing, because I've already started it :D


...strange looking eh?!
I reckon, although I'm happy to be proved wrong that the 'thing' I'm building pictured above will allow me to get boiling hot radiators as soon as I swtich on the heating, prevent boiler cycling and provide a quick reheat on my unvented cylinder.

Which I admit are all things a normal thermal store can do...

However... I think I'll only need the existing pump, and the two port motorised valve pictured will allow me to isolate the store when and if it gets empty and I can then reheat it when all other demands are met.

I don't think a normal thermal store allows this, i.e you need multiple pumps and there is no way of isolating the store when it's depleated.

I'll post more info when it's finished, at present it only has two sides, so won't be storing much!!

Cheers
-Dan
 
B

BigBurner

Thanks for your advice BB.

It's just as well that I am allowed to make this thing, because I've already started it :D


...strange looking eh?!

I can't see an image.

I reckon, although I'm happy to be proved wrong that the 'thing' I'm building pictured above will allow me to get boiling hot radiators as soon as I swtich on the heating, prevent boiler cycling and provide a quick reheat on my unvented cylinder.

A heat bank is not an unvented cylinder. Are you fitting one of these as well?

However... I think I'll only need the existing pump, and the two port motorised valve pictured will allow me to isolate the store when and if it gets empty and I can then reheat it when all other demands are met.

I don't think a normal thermal store allows this, i.e you need multiple pumps and there is no way of isolating the store when it's depleated.

A normal thermal store with pump(s) on CH can be isolated (I think you mean switched out). You just switch out the pump(s) with a simple relay when the boiler is firing, as I have explained. Simple. Just put a check valve in front of the pump and this will prevent gravity circulation. Depending on CH pipe arrangements, you may need on on the return too.
 
T

toasty

Yeah I watched that one too.
Needless to say (and as you can see in the picture, I'll be using a PRV set at 3bar on the store, additionally as it is a sealed system, there is another one integral to the boiler.

So I'm fairly sure this won't happen to me! :D
 
B

BigBurner

Yeah I watched that one too.
Needless to say (and as you can see in the picture, I'll be using a PRV set at 3bar on the store, additionally as it is a sealed system, there is another one integral to the boiler.

So I'm fairly sure this won't happen to me! :D

It happens to many unvented cylinders around the world.

Put a high temperature cut-out stat (needs resetting if stripped) at the top of the store set to 95C. This cuts out the boiler if it runs wild.
 

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