G3 and UVHWH

[iiplumbing]

Hi guys

I'm not sure if this should be in another section as I am asking for replies from experienced and qualified ppls.

The regs show that the water from the PRV/TRV valve off an UVHWH would normally expected to be terminated at ground level with suitable protection.

I have my thoughts about this but has anyone got definitive information as to;

1/ Why it has been done this way
2/ If the regs are not proscriptive then any other no less effective method (ownus on installer to prove that it is no less effective) could be employed, if so what could be done
3/ Given that the temp normally stored in a vessel is at no more than 50-60deg C and it is only in dire emergency (all other fail safes have failed) that temperatures approaching 95deg C would be allowed to pass and that as water at this temp cools down really quickly why can it be discharged somewhere else?

Your thought would be appreciated

Cheers

Russ

 

[Howsie]

The regs are the regs, our is not to reason why.

 

[townfanjon]

Russ, As far as I know certain 'things' have been altered on G3. I wont put anything else on here, but just get hold of a copy and have a 'ganders'

 

[SimonG]

Its what the regs state. Greater minds have thought about this and given rules to follow.

Yes the water when expelled in the majority of cases would only be about 60, but there is a possibility of 95 water at several bar pressure being expelled. Wouldnt want to be in court trying to explain that most of the time its ok.

 

[townfanjon]

Chaps ignore my post 3. I thought I was on the public forum der !!!! (I am new lol )

 

[Mike Jackson]

Hi guys

I'm not sure if this should be in another section as I am asking for replies from experienced and qualified ppls.

The regs show that the water from the PRV/TRV valve off an UVHWH would normally expected to be terminated at ground level with suitable protection.

I have my thoughts about this but has anyone got definitive information as to;

1/ Why it has been done this way
2/ If the regs are not proscriptive then any other no less effective method (ownus on installer to prove that it is no less effective) could be employed, if so what could be done
3/ Given that the temp normally stored in a vessel is at no more than 50-60deg C and it is only in dire emergency (all other fail safes have failed) that temperatures approaching 95deg C would be allowed to pass and that as water at this temp cools down really quickly why can it be discharged somewhere else?

Your thought would be appreciated

Cheers

Russ

Have you read the regulations recently? That is not the only way listed and I've used different proscribed methods for about 50% of the installs that I've done.

 

[Chalked]

Under certain circumstances, there is a possibility that steam could be emitted. I know what your saying though.
PA Combi prv can be terminated with a mushroom, but the item the boiler heats has to be discharged at ground level.
Around here even if you bring it out of the wall 6 inches above ground and then run to ground, we still have to cover the copper. (32mm waste)

 

[chris watkins]

One of the main reasons for the tight control of discharge from the temperature relief is the fact that it would continual to discharge high temperature water under fault conditions & at a considerable rate, until somebody turned the thing off.
It is the only way (under fault conditions) that the temperature can be stopped rising to >100 deg C, the water has to carry away the heat energy. Have you ever noted the T&P's have a kW rating (as well as a temp & pressure).
Un-like (closed) heating systems which only have a finite amount of water to discharge.

How do you want to run the discharge Russ ?? Have you a particular problem install to overcome?
You can now discharge to soil stacks through HepVo traps & push fit waste pipe.

 

[Dotty]

Section 3.61 states (Lifted directly)

3.61
The discharge pipe (D2) from the tundish should terminate in a safe place where there is no risk to persons in the vicinity of the discharge .

So in my view that would either be a mushroom or the termination turned back to the wall. Or into a tundish or gulley.

The regs also state that the responsibility lie with the user to turn the unit off in the event of a safety mechanism operating.

 

[bennygas]

I think the last two posters have hit the nail on the head really. With a large volume of water under pressure and conceivably near/at/above boiling point, should the pressure be dropped suddenly as a result of fracture or arguably if the tprv was late opening (obviously, how likely that is, is another question), there's scope for considerable flash steaming, which is a scenario that is harder to imagine arising from say the prv on a Combi. I think this is perhaps the reason why there is such disparency between how we run prv pipe work and d1/d2 pipe work.

 

[bennygas]

Sorry croppie - you must've squeezed one in as I was typing.

 

[bennygas]

That sounded wrong - I'll stop there

 

[SimonG]

Sorry croppie - you must've squeezed one in as I was typing.

Could have been worse

 

[chris watkins]

Sorry croppie - you must've squeezed one in as I was typing.

That sounded wrong - I'll stop there

Yes, cos he normally squeezes em out !!

Re turning the discharge pipes back to the wall or using mushrooms, we were told that this is un-likely to be allowed by BC as there is now the option to discharge to stacks.
If you are thinking of terminating like this I would strongly suggest that you check with your local one first before installing.

 

[iiplumbing]

Hi Guys

Thanks for al the reply's and Benny's comment gave me a right giggle!! Love this forum.

Anyways, to my mind the argument about a "safe place of discharge" and the potential emission of steam at pressure is a bit of a moot point when you consider that the tundish is an open device fitted within the locality of the cylinder AND is normally in an OBVIOUS places and it follows a customer would be able to get their hands in the flow!!!!

Now call me stupid (stupid) but what in hells name is the point of taking the discharge to ground floor (after it has cooled along the way) and make a really nice pipe cover over pipe sleeve to terminate 2 inches from the ground sorry 50mm, when, at the hottest point near the cylinder, you are able to touch the fooching thing?

Some clever bod really didn't think that one through did they, or am I being stupid?

Oh and how many of you have fitted a Hepvo and run to stack?

Cheers

Russ

 

[Howsie]

The point is taking hot water away and disposing of it safely. The D2 is sized to allow the flow to run from the tundish.

A continuous flow of hot water won't cool that much.

The tundish is there for several reasons, to demonstrate that there is an issue and to allow the partial release of pressure in relative safety.

Not ideal but as good as it gets in the real world.

 

[IDCHAPPY]

Just recently done my unvented cylinders again, you do have a point about the tundish but themz the rules I guess.
I'd always prefer to run the discharge pipe to outside if possible.

 

[Ermintrude]

ACV hold water at 90c ish

 

[chris watkins]

The point is taking hot water away and disposing of it safely. The D2 is sized to allow the flow to run from the tundish.

A continuous flow of hot water won't cool that much.

The tundish is there for several reasons, to demonstrate that there is an issue and to allow the partial release of pressure in relative safety.

Not ideal but as good as it gets in the real world.

Howsie is right the water (not steam, as it is below 100deg C) will always be very hot all along the pipe run.
I would say the main reason for the tun dish is from the water regs side i.e. air gap. What good is a tun dish if the cylinder is installed in the loft or some where else not often visited by the house holder. In this case you would need to see the point of termination as a warning that something is not right.
If you connect to a stack then the tun-dish must be visible to provide this, I suppose this is why they give the option if you can't do both ?

 

[bennygas]

Good point about the customer and tundish thing, didn't think of it like that. A slight aside, but kind of related, other than the demo vids during training, has anyone actually seen/heard of one of these unvented tanks blowing up as they keep saying there's a risk of? I was under the impression that the production of steam was the mechanism for these types of explosions, and that the safety controls stipulated in part G were the means to mitigate the risk of conditions where steam production could prevail. The production of steam in a compliant install would then only occur if there was a series of coincident faults, which you'd like to think wouldn't be likely, but should such conditions prevail, maybe that's why they're so particular about the d1/d2, and maybe as howsie said, this is as good as it gets in the real world. Maybe not having the tundish would pose a higher risk in general.

 

[bennygas]

Just rereading that, I think the point I'm trying to make is that if water is being sent down the discharge pipe work, who's to say that it's not because a fault that's driven the temperature of the tank above boiling point ? In which case steam production is a risk as the tank is still gonna be at some pressure, and it's then being discharged to atmosphere and in doing so producing loads of steam?

 

[Howsie]

They only blow when they are over 100c and above atmospheric pressure which is then released via a tap or other means. Very unlikley but possible.

 

[Ermintrude]

Raising steam used to be everyone's goal now no one wants 200kg of superheated steam at 120bar

 

[sheff paul]

Just recently done my unvented cylinders again, you do have a point about the tundish but themz the rules I guess.
I'd always prefer to run the discharge pipe to outside if possible.

I retook my unvented assessment last week some of the questions on bpec were trick questions,thought they were trying to catch you out a bit

 

[AlexGas]

... the tundish is an open device fitted within the locality of the cylinder AND is normally in an OBVIOUS places and it follows a customer would be able to get their hands in the flow!!!!

D2 can get blocked. And, Hey! There’s the tundish to save the day. I guess it’s a toss between a sore finger and a new roof.

 

[iiplumbing]

Hi Alex

I'm sure if I saw water coming out of the tundish emitting steam I wouldn't be daft enough to touch it to see if it was wet!! or to see if it was hot.

However, it strike me that some if the regs are designed to help ppl from hurting themselves by stupidity but then have to be tempered with the fact that the humble householder will do naff all in terms of servicing unless they have to or they see running water i.e. a warning pipe discharging in a place that is likely to be noticed (like on yer head)

Humble householders need expert water service engineers to tell them that the running water in that location means that there is something wrong which need to be looked at.

Russ