unvented and secondary return circulation

[heatman]

have a job to fit albion 300L unvented(indirect) and secondary return circulation+ bronze pump on return, im using 22mm pipe to feed
1 bathroom
2 ensuites
util sink
basin in toilet
kitchen

Question1, is the pump to be on 24/7 or timered (conserned about legionella)

Question2, when looking at unvented manual it says
"On large secondary circulation systems it may be necessary to incorporate an extra expansion vessel into the circuit to accommodate the increased system water volume"

Pipe capacities (copper)
15mm o/d = 0.13 litres per metre run (10 litres = 77m)
22mm o/d = 0.38 litres per metre run (10 litres = 26m)
28mm o/d = 0.55 litres per metre run (10 litres = 18m)

job req about 30meters of 22mm

does any body have info on what size extra vessel is required?

Question 3 what size insulation would you recomended on secondry return pipes?

thanks for any advice (btw yes i have unvented ticket)

 

[Deleted member 2053]

1) It is normal for these circulation pumps to be timed. Many have a built in timer. Legionella tkes up to 10 days to incubate so it is unlike to be a problem.
2) You must allow 4% for expansion so at 30m you are looking at about 12litres of pipework hence minimum expansion of 0.48 litres.
3) I seem to remember that 19mm and 25mm pipe insulation meet regs. Best to call local building control (who strictly speaking should be notified of this before the work begins) and ask them.

 

[Bernie2]

Yeh! They are strict on unvented.

 

[heatman]

hi thanks for help, i have been looking an grundfos 15/50 bronze an i cant see a built in timer, so can i use a normal timer ?

and so "local building control" need to be told before i start , is this done via phone or letter?

 

[Deleted member 2053]

Single channel external timer will be fine. Building control will be so surprised that you are telling them in advance that a phone call will suffice. This IS the correct protocol but as I understand things hardly anyone ever does it. Don't forget that your real purpose for calling is to enquire about pipe insulation!

BTW These pumped DHW systems often incorporate towel warmers in the bathrooms. Unless you are absolutely sure that this is not a requirement it may be worth you sizing your expansion vessel to allow for these.

 

[heatman]

BTW These pumped DHW systems often incorporate towel warmers in the bathrooms. Unless you are absolutely sure that this is not a requirement it may be worth you sizing your expansion vessel to allow for these.

do you mean plumb the hot water to taps via towel rail

from cylinder > through towel rail > to taps ?
if yes are there any problems with towel rails rusting

or Tee off (bolier flow and return) to cylinder to towlrails?

i have always just had towl rails fitted on heating system.

thanks

 

[migoplumber]

in the olden days bathroom rads or towel rails were connected to dhw. i have come across several.


just think about it under todays regs?!? legionella for a start, oh the towel rail is too hot (close valves) bugs appear. 3 weeks later, open valves. deep joy. some things just arnt rocket science.

shaun

 

[Deleted member 2053]

do you mean plumb the hot water to taps via towel rail

from cylinder > through towel rail > to taps ?
if yes are there any problems with towel rails rusting

or Tee off (bolier flow and return) to cylinder to towlrails?

i have always just had towl rails fitted on heating system.

thanks

You run the towel warmers in the loop from which the taps are spurred. Obviously you have them after the taps as otherwise the tap water would be cooled. There are special non-ferrous towel rails available just as there are special non-ferrous pumps. I have the T-shirt.

Legionella is less of a problem with pressurised hot water than it is with an open system. In an open system the CWS tank water can become tepid and often the incorrect positioning of the fill and flow tend towards stagnancy. The water in unvented is, by definition, not open to the atmosphere and legionella is picked up by inhalation. And if you are thinking "Aha you could catch it in the shower" it dies instantly at 60 degrees C and takes about ten days to incubate in water.

Sadly there seem to be as much misunderstanding about legionella as there is about asbestos.

in the olden days bathroom rads or towel rails were connected to dhw. i have come across several.


just think about it under todays regs?!? legionella for a start, oh the towel rail is too hot (close valves) bugs appear. 3 weeks later, open valves. deep joy. some things just arnt rocket science.

shaun

1. There won't be any bugs in the water because it has come straight from purified mains and has never been open to the air.
2. If there were any bugs it is extremely unlikely that the towel rail would be warm enough for them to incubate.
3. The warmers are plumbed in such a way that the water is reheated before it ever reaches the taps. Legionella dies instantly at 60 degrees.

We don't need rocket science. Just good science.

 

[migoplumber]

graham your point taken humbly. guess we will just agree to disagree!!

shaun

 

[alph250]

In accordance with L8 as long as you have system turnover every 24 hours and water is stored above 55^C and delivered to your outlets above 50^C in 2 minutes then your pretty safe, if you suspect that your not getting cylinder turnover within a 24 hour period then consider installing a smaller cylinder sized to match your peak load, usually morning!

Expansion vessels are sized to the density change of the water as it is heated, for example;

(This is the formula I frequently use when sizing) E = C x (P1 - P2) / P2

E = expansion in m3
C = capacity or volume of water in the complete system
P1 = Density of water before heating (kg/m3)
P2 = Density of water after heating

So a system contains a cylinder holding 300 litres with around 100 litres within the pipework (ridiculous I know but keep it simple!), temperature of cold water main 10^C temperature set point of calorifier 65^C, is as follows;

0.4m3 x (999.7 - 980.4) / 980.4 = 0.008m3 or 8 litres of expansion.

Insulation wise, well it depends how green you want to be! I will usually specify a maximum thermal conductivity of 0.045W/mK, however if I were you just the normal snap on foam stuff would suffice however everything leading up to a draw off point I would aim for a decent grade insulatuion armourflex etc to ensure your getting a reasonable temperature at the tap.

Hope that helps!

 

[migoplumber]

sorry cant help it, but to carry on being negative, what is wrong with just connecting the towel rail to the heating circuit? surely that way it eliminates all the problems?

shaun

 

[Deleted member 2053]

In accordance with L8 as long as you have system turnover every 24 hours and water is stored above 55^C and delivered to your outlets above 50^C in 2 minutes then your pretty safe, if you suspect that your not getting cylinder turnover within a 24 hour period then consider installing a smaller cylinder sized to match your peak load, usually morning!

I struggle to see where you think that the water is going to get contaminated. There is no legionella is mains tap water so unless the bacterium has some magical way of spiriting itself through the wall of copper pipe it is not going to penetrate an unvented system

 

[alph250]

I struggle to see where you think that the water is going to get contaminated. There is no legionella is mains tap water so unless the bacterium has some magical way of spiriting itself through the wall of copper pipe it is not going to penetrate an unvented system

FYI legionella is a naturally occuring bacteria, it lays dormant in water and can be found naturally in water sources such as rivers, lakes and reservoirs. the only way to fully remove the bacteria is by pasturation which occurs at 60^C, so by some feat of 'magic' do you think that the waterboard heat all the water supply for the entire country prior to feeding it through our mains water supply?

Legionella will multiply and breed most efficiently in stagnant water at 37^C, this is why you maintain a system turnover every 24 hours and keep hot water above 50^C minimum and cold water delivered at no more than 20^C

There are lots of myths and misunderstanding about legionella and your comments are a classic example. Read the ACOP L8 it tells you all about it!

 

[Deleted member 2053]

sorry cant help it, but to carry on being negative, what is wrong with just connecting the towel rail to the heating circuit? surely that way it eliminates all the problems?

shaun

The thing is Shaun that in a large house with underfloor heating from a thermal store, trying to provide a feed for towel rails can be a *** needing extra pipework, controls and probably a pump so some opt for running towel rails off a hot water loop. Nu-heat do this kind of thing all the time.

Nothing to stop you doing it the more conventional way.

G

 

[migoplumber]

now i see where your coming from graham. thanks for clearing it up 4 me.
just seems we all have a different point of view on the legionella word.
will re read l8 and find meself a decent answer to my own doubts.
whatever the answer is, i still wont be doing that type of system in my own house!!

shaun

and thanks to aplh.

 

[Deleted member 2053]

FYI legionella is a naturally occuring bacteria, it lays dormant in water and can be found naturally in water sources such as rivers, lakes and reservoirs. the only way to fully remove the bacteria is by pasturation which occurs at 60^C, so by some feat of 'magic' do you think that the waterboard heat all the water supply for the entire country prior to feeding it through our mains water supply?

Legionella will multiply and breed most efficiently in stagnant water at 37^C, this is why you maintain a system turnover every 24 hours and keep hot water above 50^C minimum and cold water delivered at no more than 20^C

There are lots of myths and misunderstanding about legionella and your comments are a classic example. Read the ACOP L8 it tells you all about it!

No I obviously don't think that tap water is pasturised but perhaps I was foolish enough to think that the treatments the water board had were capable of keeping us alive. I'm amazed the human race has survived this far.

H&SE are experts at making knee-jerk reactions based on partial info. When I have a bit of time it will be interesting to read some of the papers on Legionella studies and see just how competent they have been this time. If you have a few hours to spare read 'Scared to Death' by Booker and North.

 

[unguided1]

Hi all
I was always under the impression that you had more chance of finding legionella in a shower head, where the temperature of the water is lower and is dispenced through a spray. I also have been lead to believe (I still am not sure if its true)that very soon there are to be new regs stating that water from an outlet should be no hotter than 45 degrees, what happens then?
mind you knowing me, Ive got it wrong and look forward to being put right.
regards
Mike

 

[migoplumber]

no mike your totally right, and yes the regs are changing again.
was on the phone to hvac yesterday because this whole post bugs me a bit, just cause i cant get my head round throwing hot water through your towel rail.
alph has it right. if you read l8 you can interprete a lot of things as you like.
there will be a clear statement in next ammendment about this type of installation
my head got filled with gobbledygook, just talking to the man!

shaun

 

[alph250]

Hi all
I was always under the impression that you had more chance of finding legionella in a shower head, where the temperature of the water is lower and is dispenced through a spray.

No your completely right legionellosis can only be harmful to us in an aerosol form and thats exactly what showers produce, However the biggest risk and which is usually overlooked is AHU with heater or cooler batterys in them, only if the condensate is not drained away and maintenance isnt kept up, the condensate will be at a temperature which legionella will multiply (lets face it plant rooms are usually around 35^C!) and then get circulated through the normal ventilation route, google Gillian Beckinsdale, it was a court case a few years ago.

The other high risk in the domestic area is jacuzzi's, think about it bubbles creating aerosol and what temperature is the water at? Theres been alot of people in the past becoming ill from these, even within showrooms!

 

[A H & P]

I've just come across this forum whilst looking for clarification on the legionella question. My angle is I have installed solar panels on my roof, an unvented cylinder and system boiler. In the mixed summer days we get in this country I can get between 65 deg and 43 deg at the bottom of my 250ltr cylinder, obviously it is going to be hotter at the top of the cylinder but I don't have a stat in there.
So I've turned my boiler off, as anything over 40 is hot enough for a shower or bath, but is legionella an issue ?
I don't want to have to use gas to lift the temp to 60 only to then mix it back down to 40. I was told by a cylinder rep that legionella isn't an issue with unvented and i have read the same on an ariston unvented pdf, but I am looking for a "official" answer if poss.

 

[migoplumber]

lots of the larger cylinders i work with, have anti "stratisfication" pumps on them.
basically a pipe from top of cylinder, joined to the bottom of the cylinder with a bronze pump.
helps keep the cylinder tempereature equal from top to bottom, and wont confuse your stat to thinking everything is ok when its sat on top of cylinder reading 65 degrees, whilst at the bottom you have a lovely 40.

i imagine the same principle works for smaller cylinders.

shaun

 

[heinz57]

I did the legionaire course, got shouted at by all these funny french blokes in poofy hats chasing me across the desert. By the way, frogs legs taste like chicken but ya can keep the fuc#ing snails.

But seriously, is it worth doing the legionella course, its about £90 if im not mistaken but the basics are covered in the water regs! All for health and safety but £90!!!

Will surely read the above recommended leaflet - peace out.

 

[Plouasne]

The CIPHE design guide has a page on Legionella, and it cost only £40 to non members and I think £25 for members, half the price of going on a course

But if you like and when I can find it, I could post the actual French legislation on hot water cylinder and the risk of Legionella, and the methods of prevention

 

[radswilldo]

The CIPHE design guide has a page on Legionella, and it cost only £40 to non members and I think £25 for members, half the price of going on a course

But if you like and when I can find it, I could post the actual French legislation on hot water cylinder and the risk of Legionella, and the methods of prevention

Oh yes please, could you also post the legislation from Botswana and Peru, cheers