UVC safety question

[Jeremy Harris]

@PeterStarck, it would be worth contacting Genvex themselves, I think, in Denmark.  They have a pretty good technical department and were able to quickly answer my question about adding an external hygrometer switch to activate the boost function, and included the additional information that there was some spare 24V DC power available from the connector block in the unit to power ancillary devices.

 

IIRC, I just emailed the contact on this page, in English, and got a pretty prompt reply: http://www.genvex.dk/en/contact/

[Gone West]

2 minutes ago, JSHarris said:

@PeterStarck, it would be worth contacting Genvex themselves, I think, in Denmark.  They have a pretty good technical department and were able to quickly answer my question about adding an external hygrometer switch to activate the boost function, and included the additional information that there was some spare 24V DC power available from the connector block in the unit to power ancillary devices.

 

IIRC, I just emailed the contact on this page, in English, and got a pretty prompt reply: http://www.genvex.dk/en/contact/

That's strange because I have used that contact page twice and not had a reply on either occasion. That's annoying.

[Nickfromwales]

22 minutes ago, PeterStarck said:

Very interesting discussion between yourself and Jeremy.

"10 paces then turn!"

With assumption being a non-starter you can simplify this by buying a <£100 worth of controls / peripherals and its put to bed with any decent G3 fitter more than happy to put his / her name to it. . 

T'will be compliant with ( normally stipulated ) G3 by design, safe by over-engineering, robust and reliable. If we as a collective are left stumped for the right solution here, any G3 fitter would just walk away with anything less than the regular boxes ticked. May be unnecessary, may be overkill, but for such little effort and so little cost why arse around any longer?

 

Maybe this should be fired across to your BCO first and the info relayed back here ? It's only a phone call after all. 

[Jeremy Harris]

15 minutes ago, PeterStarck said:

That's strange because I have used that contact page twice and not had a reply on either occasion. That's annoying.

 

That is annoying, as around three years ago they were very helpful!

 

One thing has occurred to me.  As the electric heating element is, effectively, optional, and as it is only the electric heating element that can cause an over-pressure event if there are multiple control system failures, I wonder if the standard control group diagram is intended to be only for the version without the electric element?

 

Off the top of my head I don't think the tank pressure would increase much at all from cold to 55 deg C, and it couldn't get hotter than this with just the EAHP, as that's pretty much the limit of the system, physically.  It may well be that no EV is shown  because one just isn't needed when the hot water is only heated from the EAHP, as there is no possible fault condition that could cause the temperature to increase above the EAHP maximum.

 

The EV is fitted to a conventional UVC as a means of preventing very hot water from being discharged via the PRV, because of the scalding risk, primarily.  If the temperature is physically limited to 55 deg C, there is no scalding risk from a PRV discharge, as well as the pressure rise possibly being too low to cause the PRV to discharge.  Such a system would comply with the regulations here, but is not specifically referred to in the Approved Documents, I think.  I remember having this discussion with my BCO over the 58 deg C maximum discharge temperature of the Sunamp PV PRV, and being asked to just put maximum temperature labels on pipes as a reminder to anyone later that this was not a high temperature discharge, so did not carry the scalding risks associated with a high temperature UVC or combi boiler PRV discharge

Edited October 18, 2017 by JSHarris

[Nickfromwales]

2 minutes ago, JSHarris said:

 

That is annoying, as around three years ago they were very helpful!

 

One thing has occurred to me.  As the electric heating element is, effectively, optional, and as it is only the electric heating element that can cause an over-pressure event if there are multiple control system failures, I wonder if the standard control group diagram is intended to be only for the version without the electric element?

 

Off the top of my head I don't think the tank pressure would increase much at all from cold to 55 deg C, and it couldn't get hotter than this with just the EAHP, as that's pretty much the limit of the system, physically.  It may well be that no EV is shown  because one just isn't needed when the hot water is only heated from the EAHP, as there is no possible fault condition that could cause the temperature to increase above the EAHP maximum.

 

The EV is fitted to a conventional UVC as a means of preventing very hot water from being discharged via the PRV, because of the scalding risk, primarily.  If the temperature is physically limited to 55 deg C, there is no scalding risk from a PRV discharge, as well as the pressure rise possibly being too low to cause the PRV to discharge.  Such a system would comply with the regulations here, but is not specifically referred to in the Approved Documents, I think.  I remember having this discussion with my BCO over the 58 deg C maximum discharge temperature of the Sunamp PV PRV, and being asked to just put maximum temperature labels on pipes as a reminder to anyone later that this was not a high temperature discharge, so did not carry the scalding risks associated with a high temperature UVC or combi boiler PRV discharge

Which fortifies the advice to get the BCO involved. . 

If time were money here we'd have already gone into the red. . 

[Jeremy Harris]

5 minutes ago, Nickfromwales said:

"10 paces then turn!"

With assumption being a non-starter you can simplify this by buying a <£100 worth of controls / peripherals and its put to bed with any decent G3 fitter more than happy to put his / her name to it. . 

T'will be compliant with ( normally stipulated ) G3 by design, safe by over-engineering, robust and reliable. If we as a collective are left stumped for the right solution here, any G3 fitter would just walk away with anything less than the regular boxes ticked. May be unnecessary, may be overkill, but for such little effort and so little cost why arse around any longer?

 

Maybe this should be fired across to your BCO first and the info relayed back here ? It's only a phone call after all. 

 

Bear in mind that I'm running a non-Part G3 signed off sealed system, and have been through the hoops on this.  If the temperature in the sealed system cannot reach that where there is a scalding risk, because of either design (in my case the same as @PeterStarck, a heat pump that cannot deliver more than 55 deg C even under fault conditions) or built in safety systems, then BCOs can, if shown the regulations (not the Approved Documents) agree that the system doesn't need certification.

Edited October 18, 2017 by JSHarris

[Gone West]

4 minutes ago, Nickfromwales said:

"10 paces then turn!"

With assumption being a non-starter you can simplify this by buying a <£100 worth of controls / peripherals and its put to bed with any decent G3 fitter more than happy to put his / her name to it. . 

T'will be compliant with ( normally stipulated ) G3 by design, safe by over-engineering, robust and reliable. If we as a collective are left stumped for the right solution here, any G3 fitter would just walk away with anything less than the regular boxes ticked. May be unnecessary, may be overkill, but for such little effort and so little cost why arse around any longer?

 

Maybe this should be fired across to your BCO first and the info relayed back here ? It's only a phone call after all. 

I had already fitted a PRV and EV for the Genvex Combi before it was delivered, but anything can be changed if necessary.

 

 

If a pipe was attached to the HW circulation outlet and run vertically up the back of the unit and bent to the side and a PRV attached wouldn't there be enough height for the tundish etc? Not being awkward I'm just trying to understand.

 

[PeterW]

Playing devils advocate here....

 

If Genvex sell a unit into the UK market then their MIs should provide for a safe and compliant install as the unit has to be CE marked. To meet that standard it is required to be installed in a manner to meet the regulations of that country.

 

So whilst I take on board what @Nickfromwalessays, I do wonder if this is not actually a standalone UVC, but is actually a complete unit with systems that when installed using the MIs, is compliant with the regulations....

 

I think an email to the manufacturer asking for the correct installation instructions to meet the UK regulations would be the quickest - and safest - method. 

 

And @PeterStarck - nice tidy pipework ..! Are they Speedfit manifolds..??

[Gone West]

Just now, PeterW said:

 

And @PeterStarck - nice tidy pipework ..! Are they Speedfit manifolds..??

Yes they are. Speedfit is not everyones favourite but I think for amateur plumbers like me they are safer as when the connection is made and a collet clip is inserted you know its connected properly.

[Jeremy Harris]

5 minutes ago, PeterW said:

So whilst I take on board what @Nickfromwalessays, I do wonder if this is not actually a standalone UVC, but is actually a complete unit with systems that when installed using the MIs, is compliant with the regulations....

 

That's my thinking, too.  Knowing a fair bit, from experience, as to how Genvex systems are engineered, I'm near-certain that this integrated unit is designed to be safe and compliant with UK regs as it stands, as long as it is installed as per the MIs.

 

If it were a stand-alone UVC, with none of the built in safety systems that the Combi 185 has, then I'd agree 100% with @Nickfromwales, and I think the stand alone UVC where we have to add stuff in the right place order to make it comply with the regs is what we are used to.

Edited October 18, 2017 by JSHarris

[Gone West]

As @Nickfromwales has suggested I'll ask the BCO what his take is on it.

[dpmiller]

Never mind the G3 side of things what about looking at is purely as a pressure vessel? Domestic is different to industrial but still...

[Nickfromwales]

1 hour ago, JSHarris said:

 

Bear in mind that I'm running a non-Part G3 signed off sealed system, and have been through the hoops on this.  If the temperature in the sealed system cannot reach that where there is a scalding risk, because of either design (in my case the same as @PeterStarck, a heat pump that cannot deliver more than 55 deg C even under fault conditions) or built in safety systems, then BCOs can, if shown the regulations (not the Approved Documents) agree that the system doesn't need certification.

My point exactly, it's been signed off . 

Thays what I've been reiterating throughout. 

58 minutes ago, PeterStarck said:

As @Nickfromwales has suggested I'll ask the BCO what his take is on it.

The way forward I think. 

 

 

[Jeremy Harris]

1 hour ago, Nickfromwales said:

My point exactly, it's been signed off . 

Thays what I've been reiterating throughout. 

The way forward I think. 

 

 

 

 

Strictly speaking it was not signed off, we both reached an agreement that no certification or signing off under Part G3 was required, after having read the intent of the law within the Building Act 1984, as amended to that date.  In other words, Part G3 did not apply in this particular case, because it fell outwith the reasoning in law for having the installation signed off, with a commissioning certificate, by a competent person. 

 

BCOs have some authority to determine whether, in their view, a non-standard arrangement falls under a particular certification requirement or whether it does not.  In my case the intent of the law was clear, the limitations and safety provisions within the system were deemed adequate, and so the system was declared to fall outwith the guidance provided within Approved Document Part G3.

 

The key was whether or not the "pressurised vessel" could ever reach a temperature that could cause a scalding risk if the PRV operated.  The conclusion was that it could not, as there was no way for the temperature to exceed 55 deg C under any possible fault condition.

 

I think it's worth noting exactly what the guidance in Part G3 has to say, remembering that it is only guidance, not law or a regulation with the power of law.  I've highlighted the wording that makes it clear that alternative approaches are acceptable, if they are deemed to be safe, and that proprietary packages may satisfy the requirements:

 

Quote

Unvented hot water storage systems – all systems

 

3.17 To minimize the danger from excessive pressure, unvented hot water storage systems should incorporate a minimum of two independent safety devices. These shall be in addition to any thermostat provided to control the desired temperature of the stored water. The selection of safety devices should take account of the physical location of the devices, and the design, configuration, location of components and performance characteristics of the system to which they are attached.

 

3.18 An acceptable approach might consist of:

 

a. a non self-resetting energy cut-out to disconnect the supply of heat to the storage vessel in the event of the storage system over-heating; and

 

b. a temperature relief valve or a combined temperature and pressure relief valve to safely discharge the water in the event of serious over-heating.

 

Alternative approaches to this are acceptable provided that they provide an equivalent degree of safety.

 

Note: See 3.35 for suitability of devices for primary thermal stores

 

3.19 Water heaters with a capacity of 15 litres or less that have appropriate safety devices for temperature and pressure will generally satisfy the requirement set out in G3(3).

 

Unvented hot water storage systems – systems up to 500 litres capacity and 45kW power input

 

3.20 Paragraphs 3.21 to 3.24 are in addition to the provisions of 3.17 above.

 

3.21 If an indirect supply of heat to an unvented hot water storage system incorporates a boiler, the energy cut-out may be on the boiler.

 

3.22 Any unvented hot water storage system up to 500 litres and less than 45kW should be in the form of a proprietary hot water storage system unit or package. The package and components should be appropriate to the circumstances in which they are used and should satisfy an appropriate standard that will ensure the requirements of regulation G3(2) and G3(3) will be met

 

(e.g. BS EN 12897:2006 Water Supply. Specification for indirectly heated unvented (closed) hot water storage systems or BS 6700:2006 + A1:2009 Design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages).

 

Note that there is nothing in Part G3, or the underpinning law, the Building Act 1984, as amended, that requires an expansion vessel.  That requirement arises solely from Manufacturer's Instructions, not any regulation.  The fact that we're used to seeing EVs fitted as a matter of course comes down to a lot of UK manufacturers including them in their MIs.

[Onoff]

3 hours ago, Nickfromwales said:

If time were money here we'd have already gone into the red. . 

 

There's another thread on here for that...

[Nickfromwales]

11 hours ago, JSHarris said:

Note that there is nothing in Part G3, or the underpinning law, the Building Act 1984, as amended, that requires an expansion vessel.  That requirement arises solely from Manufacturer's Instructions, not any regulation.  The fact that we're used to seeing EVs fitted as a matter of course comes down to a lot of UK manufacturers including them in their MIs.

I know that, but my argument regarding the discharge of a 'teacupful' of water vs no discharge / wasted water at all would be more to do with the regs surrounding conservation of potable water, like the ones that make you put restrictors into your taps and showers to reduce max consumption accordingly. Surely that needs to be negated by design though, especially when there is an easy solution such as adding an EV? My reference to the EV is to prevent the possibility of any water ever routinely being dumped to waste. The decider in this particular case is the spec of the cylinder in the HP which has a higher ( nearly double ) pressure tolerance than its regular counterparts. 

Yes, I agree that if the MIs state it has a working tolerance that will absorb the max expansion that is common in day to day use WITHOUT releasing any potable water to drain then I'd say don't bother with the EV as the PRV would only ever go under fault condition, but other than that id recommend an EV be fitted of suitable size. 

I think quoting any existing and clearly dissimilar case study here is pointless TBH as each system needs to be installed and commissioned on its own merit. 

I say we wait and see what the BCO has to say as I think it would be quite interesting to hear what their take is.  

[Jeremy Harris]

Not sure that my 55 deg C max cylinder is significantly different to the conditions and safety systems that the Combi 185 has, though.  I think the key here is that Genvex have added enough safety devices to ensure that the integral tank doesn't exceed 65 deg C, plus have added an arrangement of check valves, PRedV and a PRV to cover the case if there were multiple failures.

 

I'm not even sure that the PRV would release any water at all under normal operating conditions, with no inlet side EV.  We're guessing that it may do, but in my case that guess is based on experience with two very different systems, the boiler on our boiling water tap, that has no EV by design, as it is intended to maintain a high internal pressure, and my experience fixing a friends electric water heater in France, that also had no EV, but just a PRV.

 

I accept that water waste is undesirable, but I'd guess that even if the PRV does dribble a bit the waste would be less than the evaporative loss from a vented header tank.

Edited October 18, 2017 by JSHarris

[Gone West]

On 18/10/2017 at 09:02, PeterStarck said:

As @Nickfromwales has suggested I'll ask the BCO what his take is on it.

Sorry I forgot to update this. The BCO accepted that the Genvex Combi was a self contained unit with built in safety controls and didn't require G3 certification.

[Jeremy Harris]

1 hour ago, PeterStarck said:

Sorry I forgot to update this. The BCO accepted that the Genvex Combi was a self contained unit with built in safety controls and didn't require G3 certification.

 

 

That's very useful to know, had I known that I think I might have looked at the Combi rather than the Premium 1L, as it does seem to be a very neat package.