When do G3 regulations apply? Buffer tanks?

[OldSpot]

I understand the requirement for G3 on an UVC but what about with buffer tanks?

For example, if you were to fit an indirect buffer tank where a sealed system boiler (gas/oil) heats tank via coil and then the tank water is used to supply rads or UFH?

Would G3 certification then be required? If so (or not) why?

Accepting that an expansion vessel would need to be fitted to the top of tank.

[PeterW]

System boiler already has the controls for over pressure built in to it so you are always best having the buffer direct connected. Any reason for using the coils as most also are open volumes unless they are on ASHP and you’re trying to reduce the antifreeze volume. 

[OldSpot]

Agreed but would G3 come into play in the scenario described?

[PeterW]

Depends on where the controls for the heat source are located (such as thermostats).
 

But my question is why would you design such a scenario as it is doesn’t have any benefit..? 

[SteamyTea]

Interesting question.

I would assume yes, as it can be pressurised.

Isn't it more a case if an invented does NOT need G3.

Is it possible to download the regulations from somewhere?

[Triassic]

11 minutes ago, SteamyTea said:

Interesting question.

I would assume yes, as it can be pressurised.

Isn't it more a case if an invented does NOT need G3.

Is it possible to download the regulations from somewhere?

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/504207/BR_PDF_AD_G_2015_with_2016_amendments.pdf

[SteamyTea]

Is there a plumbing equivalent of the 18th edition electrical regulations, or is it that Part G.

[OldSpot]

I had a look through prior to posting here.

Reading the definitions, on page 6, it cites

"Hot water storage system means a vessel for storing:

a. heated wholesome hot water or softened wholesome hot water for subsequent use

b. water that is used to heat other water

together with any ancillary safety devices described in paragraphs 3.10 and 3.11 of this Approved Document and all other applicable operating devices."

Which is slightly confusing. If you use a coil to heat the buffer tank and then draw the water directly from the tank, the coil passing through the tank is the vessel used to heat the water...but the coil isn't a hot water storage vessel.

Edited March 9, 2021 by OldSpot

[dpmiller]

I'd have to say no, not G3 *but* still requires a safety valve as it's still a stored-volume pressure vessel even if the supply temperature is controlled externally and failsafe.

 

/just like a radiator on a sealed system.  The pressure/volume  may make it a "pressure vessel" but the rest of the system has redundant controls for temperature and the safety valve is the failsafe for the expansion vessel's pressure control.

[OldSpot]

I'm inclined to agree @dpmiller.

At what pressure does a vessel become a pressure vessel...............?

[dpmiller]

250 bar litres, IIRC.

[JamesPa]

I'm resurrecting this thread to clarify a possibly interesting scenario.  

 

The ashp I'm about to have installed does it's legionella cycle natively (ie using the ashp not an immersion).  Clearly it can't itself boil the water in the tank.  The cylinder currently proposed has an immersion solely for 'backup'.  The reheat mechanism is an external PHE not a coil in the cylinder

 

If either (a) the immersion were removed altogether or (b) replaced by a Willis heater or similar in the pipes feeding the PHE (and suitable safety devices incorporated so the willis can't send steam through the pipes), does the cylinder itself need the full G3 works (and in particular the visible, continuous fall vent/tundish)?

 

As it happens it will have the full G3 works but the question interests me because of the problems with routing the G3 vent pipe which are forcing me to put the cylinder in the loft (I don't particularly mind this, but am curious nevertheless).

 

The regulations (as opposed to the guidance on what the secretary of state thinks) say only:

 

'(3) A hot water system that has a hot water storage vessel shall incorporate precautions to: (a) prevent the temperature of the water stored in the vessel at any time exceeding 100˚C; and (b) ensure that any discharge from safety devices is safely conveyed to where it is visible but will not cause a danger to persons in or about the building.'

 

Thoughts?

 

Edited August 17, 2023 by JamesPa

[JohnMo]

I would say if you have an immersion either directly or indirect you need G3.

 

The safety cut out on the immersion alone, isn't compliant as you need a minimum of 2 layers of safety. So you will also need the discharge safety devises also.

 

In an indirect immersion situation, it would also be a pressurised system, so boiling temperature the would be above 100 degs and it has antifreeze even higher again.

[Jenki]

For me, I did my G3, so I can self install, cheaper than some quotes to sign off.(so no expert) but

I would say if the buffer is pressurised, and has an external heat source and or immersion heater, and over I think 15 litres it needs G3. 

 

[JamesPa]

4 hours ago, JohnMo said:

I would say if you have an immersion either directly or indirect you need G3.

 

The safety cut out on the immersion alone, isn't compliant as you need a minimum of 2 layers of safety. So you will also need the discharge safety devises also.

 

In an indirect immersion situation, it would also be a pressurised system, so boiling temperature the would be above 100 degs and it has antifreeze even higher again.

 

3 hours ago, Jenki said:

For me, I did my G3, so I can self install, cheaper than some quotes to sign off.(so no expert) but

I would say if the buffer is pressurised, and has an external heat source and or immersion heater, and over I think 15 litres it needs G3. 

 

Perhaps I should have been a bit clearer where my thoughts were taking me.  Im trying to think 'out of the tank' both metaphorically and literally.  The principal practical pain with G3 is routing the vent pipe.  So my thought process was - can this be avoided. 

 

The requirement is:

 

(3) A hot water system that has a hot water storage vessel shall incorporate precautions to:

(a) prevent the temperature of the water stored in the vessel at any time exceeding 100˚C; and 

b) ensure that any discharge from safety devices is safely conveyed to where it is visible but will not cause a danger to persons in or about the building.'

 

So if we have indirect heating from the HP, we know that cant boil the water.  If we also have indirect heating from the backup immersion, then I grant that it can.  So it has a safety cut out as usual, plus some other mechanism, not involving the tank, to ensure it cant boil the water in the tank. 

 

A simple overtemperature tank bypass (similar to a car thermostat) would do the job.  Result, tank cant be boiled and all the safety features can be located somewhere convenient, not tied to where the the cylinder is.

 

How would that not satisfy the requirement?

[Jenki]

@JamesPa, like I said no expert. But the discharge. You need to follow the rules resizing if D1&D2, and distances etc. But if the tun dish is visible then the discharge can go into a stack and not be visible from my very pointed questions during doing my G3.

 

Wouldn't like to comment on your idea. The regs are old and pretty black and white, doesn't seem room for new inventions. 

[JamesPa]

2 hours ago, Jenki said:

@JamesPa, like I said no expert. But the discharge. You need to follow the rules resizing if D1&D2, and distances etc. But if the tun dish is visible then the discharge can go into a stack and not be visible from my very pointed questions during doing my G3.

 

Wouldn't like to comment on your idea. The regs are old and pretty black and white, doesn't seem room for new inventions. 

Well the D1 D2 stuff isn't actually in the requirements, it's in the guidelines.  But my key idea here is to remove all of that from the cylinder so you can put it somewhere more convenient or do something more convenient.

 

The rules of physics are older than the hills, but still people keep inventing things.

 

 

Edited August 18, 2023 by JamesPa