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Author Topic: Tempering valves  (Read 3597 times)

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Offline ptopnz

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Tempering valves
« on: September 26, 2013, 04:53:31 PM »
What is everyone's understanding about having to installing a tempering valve if you replace an old cylinder low or mains in the same position. We always do but we are losing jobs to some plumber who don't.

Linkback: https://www.plumbers.nz/ask-plumbers-trade/43/tempering-valves/1552/

Offline robbo

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Re: Tempering valves
« Reply #1 on: September 26, 2013, 05:28:51 PM »
hi guys/ptopnz, this attachment is how i understand it, others may comment if regs have been changed,cheers

Offline integrated

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Re: Tempering valves
« Reply #2 on: September 26, 2013, 09:19:23 PM »
So going by that robbo so long as it is like for like direct replacement then no go on the temper?

where did that doc come from?

we always used to just make an on site judgement call but always try to make it work - some of those old ones where the pipework is behind the hwc can make it a real PITA

Offline Plumber

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Re: Tempering valves
« Reply #3 on: September 26, 2013, 09:45:54 PM »
Correct me if i'm wrong but my understanding is, the last person working on an installation is also required to ensure that the installation complies with current reg's and is safe. If I replace a HWC and don't install a tempering valve and someone scolds themselves who is to blame? So the question remains, is it a choice of good practice or is it a legal requirement?
Please note that the advice I am giving is only my opinion and not necessarily a fact.  Please refer to our terms and conditions.

Offline integrated

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Re: Tempering valves
« Reply #4 on: September 26, 2013, 10:56:29 PM »
I'm not sure that the legal requirement in the strictest sense exists plumber - when a job is permitted and inspections take place then there are obviously the mechanisms, procedures and paper trail created to ensure and enforce things - but I am yet to see any regulation or legislation that says it is a mandatory requirement to bring it all up to reg's spec

I do agree that I would not call it best trade practice & my way of thinking is that you could be prosecuted under H&SE Act for not taking all practicable steps to ensure the safety of others...

Offline Plumber

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Re: Tempering valves
« Reply #5 on: September 27, 2013, 08:26:17 AM »
I do agree that I would not call it best trade practice & my way of thinking is that you could be prosecuted under H&SE Act for not taking all practicable steps to ensure the safety of others...

Wouldn't that make it a legal requirement?  ::)

Offline Watchdog

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Re: Tempering valves
« Reply #6 on: September 27, 2013, 11:26:23 AM »
I believe a lot of issues like this is another way of moving responsibility.  Parents are responsible for their children so should teach them not to touch things that are hot such as hot water. Do we have any regulations on people getting burnt on heaters, ovens, hobs, and what of the exhaust of your car.

I think we get lumbered with too much regulation that takes away responsibility from others. 

Offline ptopnz

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Re: Tempering valves
« Reply #7 on: September 27, 2013, 12:43:50 PM »
Thank you Robbo for that, I read that yesterday. If I remove a 135LTR low pressure with a 1.5KW element and a thermostat that went down to 45c and replaced it with another 135LTR low pressure cylinder with a 2KW element and a thermostat that does not go below 60c is that a direct replacement?

Offline Grant Bourke

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Re: Tempering valves
« Reply #8 on: September 30, 2013, 07:22:26 PM »
If you are installing a replacement cylinder like-for-like then you need to install a tempering valve and your competitor down the road is not complying with the building act. Here is the short(ish) version why:

>Building act requires you comply with the building regulations

>Building regulations require you comply with the relevant parts of schedule 1 (the building code)

> There are two relevant parts of the building code (for the purposes of this discussion) Ė

G12.3.6: If hot water is provided to sanitary fixtures used for personal hygiene it must be delivered at a temperature that avoids the likelihood of scalding.

G12.3.9: A hot water system must be capable of being controlled to prevent the growth of legionella.

So if you are doing the ďbuilding workĒ of providing hot water to sanitary fixtures used for personal hygiene, which sticking in a water heater clearly does, then you must in practice turn the cylinder above 60 to comply with G12.3.9. Then to meet G12.3.6 you must fit a tempering valve.

Same goes if you are extending existing pipework to say an ensuite.

If you are changing a tap washer you are not doing the work of supplying hot water as you arenít sticking anything in that makes hot water so you arenít compelled to up the water temp and fit a tempering valve if you notice it isnít building code compliant. (you may wish to suggest one to the customer and note it on the invoice when they donít want to spend the money so when natural selection kicks in at their place they donít try to blame it on you).

So the earlier attachment is nearly correct in my view but not quite when it comes to the replacement cylinder.

If you donít get any joy with the PGDB (and you might in this case if you have enough evidence) then you can try the local council as they are responsible for making sure everyone complies with the building act.

Offline robbo

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Re: Tempering valves
« Reply #9 on: September 30, 2013, 08:52:07 PM »
hi guys, everything you need to know about `legionella`, make of it what you will, but as Grant says we must observe the building act,cheers

Offline Badger

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Re: Tempering valves
« Reply #10 on: October 01, 2013, 06:36:54 AM »
I have been trying to tell the Board, for many years, about a central heating system that is run off a califont, via a ring main that the hot water outlets AND rads come off.......fitted by my ex-boss, the same one that they won't look at for the explosion.

When the TRV's open the stagnant water from the rads, stored at room temp for the summer, comes out of the shower, atomising the water all ready to breath in and infect the occupier.

I tried to tell the owner but he wasn't interested and it is one of the reasons I left.

When I told this idiot of a boss I wanted to see the specification that said this was ok....he said you don't need a specification, just use poker face and make out you know what your doing! I told him I did know....and left.

I have told all this to the Board, but apparently the regs and act only apply to some.
You can't choose who you are.....but you are the sum of your choices.......

Offline robbo

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Re: Tempering valves
« Reply #11 on: October 01, 2013, 09:15:35 AM »
Hi guys, from what Iíve read, it seems that it would be very unlikely that the growth of legionella would occur in a standard domestic hot water system that was in daily use, I deduce from the info that I have read that this would most likely occur when water becomes stagnant, also that the temperature above 50deg would prevent the growth, so a setting of 55deg would solve all problems, cheers   

Offline Plumber

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Re: Tempering valves
« Reply #12 on: October 01, 2013, 04:37:20 PM »
That's great information Grant, thanks for that.

Offline Grant Bourke

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Re: Tempering valves
« Reply #13 on: October 01, 2013, 06:25:47 PM »
Robbo's last post raises an interesting point.

What I described previously is following the route prescribed by the compliance document for building code clause G12.

The building act section 22 says that if you follow the compliance document you must be treated as having complied with the building code. So you can give a two fingered salute to the council if they don't like it provided you have followed the compliance document (and note that both AS/NZS 3500 and G12/AS1 are in the compliance document so you can use either).

The building act section 23 says that you can come up with ways of complying with the building code other than the compliance document. I have attached the department of building and housing guide to coming up with alternative solutions.

So if you want to use the World Health Organisation guide to legionella as a basis for an alternative solution you are allowed to so long as you can establish it meets the performance requirements of the building code in my previous post. You would be proposing an alternative solution to the legionella requirement but probably using the compliance document for the no-scalding part ie: keeping temperature under 55 (as arguing for a temperature hotter than this will fly like a lead balloon at the council - at least we are better off than the Aussi's - its 50 max. over there).

There are a few practical issues with doing this:

1. Electric cylinder thermostats often bottom out at 60 these days.

2. If the thermostat craps out then the safety cut-out is often at 88.

3. Don't forget about stratification in the cylinder - just because the thermostat at the bottom of the cylinder (on the outside of the pressure vessel) has cut out at 55 there is absolutely no guarantee the water delivered from the very top of the cylinder wont at times be quite a bit more than 55.

To get around this you may have to spend quite a bit of time tuning the cylinder to make sure the outlet water temperature doesn't go above 55. And it will be slightly different for different heat up cycles and also different for cylinders of different height to diameter ratios.

4. If you are doing a consented job you will need to work an alternative solution through the council. Some will allow you to make an application for a "standard" alternative solution if you intend to use it over and over.

5. Remember if you are doing work which doesn't require a consent you still need to comply with the building code and if you use an alternative solution you would be really really really well advised to document the solution you applied and file this so that if anyone ever comes knocking you can trot out the folder with the information and not be in a position of having to justify your solution after the event which will put you in a seriously bad place. Even if you can come up with a reason why what you did is safe the fact you are doing it after the event will likely see you nailed for poor practice, perhaps with some justification.

If you still want to use an alternative solution based on Robbo's attached WHO guideline the guts of it are on pages 49 and 50. There are a couple of things to note about the graph:
1. The y-axis scale is a logarithmic scale - so each division is ten times the previous.
2. The time shown is that to kill 90% of the legionella. So you would usually double this time to kill 99%, triple it to kill 99.9% etc.

Combining these two means from this graph to kill 99.9 % at 60 takes about 6 minutes while at 50 it takes 300 minutes.

Having bored you all with all of that and no doubt having outstayed my welcome, my gut feeling is that for the vast majority of systems if you set the thermostat to 50 then everything would be just fine in a society with some degree of personal responsibility (provided you don't really need the small amount of extra stored energy). If a proper cost benefit analysis was done I have never thought the government would be able to justify the 60 degree heated water cut to 55 deal. Same goes with cold water expansion valves in areas where the water supply isn't scaling enough to stuff the TPR if it operates on every cycle. It is pretty easy for the valve manufacturers to scare the authorities though with stories and pictures of exploding cylinders and scalded kids....

(At the risk of getting barred - none of this is the PGDB's doing)

Offline Plumber

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Re: Tempering valves
« Reply #14 on: October 01, 2013, 07:39:58 PM »
Quick side topic .... We used to struggle with tempering valves when installing Ring mains. If your running the ring main at high temperature you will need a tempering valve at each feed. This Requires access, increases maintenance and is costly to install. The alternative that has been offered to overcome this problem is a UV filter, allowing you to run a ring main at 55 deg. To me this is also in the same department as the tempering valve scenario it requires access, maintenance etc..  An easy way to overcome this problem and to comply is to Install a HWC with two elements and run the second element on a timer. Will save your customer money and make you competitive straight away :)


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