Gravity hot water to fully pumped / sealed

[eagleeye]

One of our installers currently fitted a new heat only boiler to replace an old floor standing with gravity hot water. At the time he never fitted any valves or cylinder stat etc so I have been called back there to basically start again. Been there today to do it and found that he had the pump on the return. Anyway I drained system and made the necessary alterations to the pipework by the boiler and fitted a mid position valve and a wireless cylinder stat (as the run is impossible to get a cable between the two). So currently the feed from the F + E tank goes into the return of the cylinder and the vent on the flow. The boiler is in a tight cupboard low to the ground in an extension of the side of the house and the cylinder is on the 1st floor in the middle of the main part of the house so you can imagine how the pipework runs

 

[Stu-B]

Crikey that looks snug! The filter is gonna be a devil of a job to open up!

 

[eagleeye]

Crikey that looks snug! The filter is gonna be a devil of a job to open up!

Yeah very tight. The filter is tight but can be open now. I've attached a pic of what it looked like before. Our surveyor has really mucked up here to be honest. He should of quoted for a system boiler for a start.

 

[SJB060685]

So this is an open vented system and not sealed? Pump can go on return on a vented but the cold feed should be piped to down into return shortly after the pump outlet, the system would be under negative pressure though. To be honest that looked a mess beforehand

 

[eagleeye]

So this is an open vented system and not sealed? Pump can go on return on a vented but the cold feed should be piped to down into return shortly after the pump outlet, the system would be under negative pressure though. To be honest that looked a mess beforehand

yes, open vented at the moment. Problem is that I cant make any alterations to the feed & vent on the cylinder as its as tight as a .......... and there is no way i can get feed or vent down to pump / boiler position. Bloody nightmare of a job.

Do you think my idea will work ok ?

 

[Chuck]

Er, careful, this is a public forum... Might want to take it to the Plumbers' Arms?

 

[ShaunCorbs]

agree pump should be on the return as they tend to last longer due to lower temp

check valve on the feed from the f and e
and a 2 bar safety valve on the vent
expansion vessel

thats along as you have an okish head eg 3m+

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[eagleeye]

agree pump should be on the return as they tend to last longer due to lower temp

check valve on the feed from the f and e
and a 2 bar safety valve on the vent
expansion vessel

thats along as you have an okish head eg 3m+

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So are you saying still use the F + E tank to fill the system and fit a check valve to the feed, 2 bar PRV on the vent as well as an expansion vessel or am i doing away with the f + e and filling via mains water ?

Also gonna have to leave the pump on the flow now as ive already changed it all now. Will that matter ?

Only place I can get vessel in is either above the boiler on the ground floor or in the place of the f + e tank.

 

[SJB060685]

If you leave the vent as is then whenever HW is called for it will pump over, in time it will sludge up the system. Im assuming Shaun is suggesting seal the system and do away with f and e tank, which is what I would suggest. Preferably the expansion vessel will go on return where it’s not exposed to high temperatures, if the pump is on return the vessel should be close to suction inlet of pump to maintain a positive pressure through boiler and around the system, thus eliminating any air ingress.

 

[ShaunCorbs]

So are you saying still use the F + E tank to fill the system and fit a check valve to the feed, 2 bar PRV on the vent as well as an expansion vessel or am i doing away with the f + e and filling via mains water ?

Also gonna have to leave the pump on the flow now as ive already changed it all now. Will that matter ?

Only place I can get vessel in is either above the boiler on the ground floor or in the place of the f + e tank.

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

 

[SJB060685]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

But the vent is on flow of HW, not only will this pump over when calling for HW but the vent is not open if valve is shut?

 

[eagleeye]

If you leave the vent as is then whenever HW is called for it will pump over, in time it will sludge up the system. Im assuming Shaun is suggesting seal the system and do away with f and e tank, which is what I would suggest. Preferably the expansion vessel will go on return where it’s not exposed to high temperatures, if the pump is on return the vessel should be close to suction inlet of pump to maintain a positive pressure through boiler and around the system, thus eliminating any air ingress.

Thats what I thought. Think I will fit the vessel above the boiler on the return, remove the f + e tank and fit AAV's on what used to be the feed and vent. At least this way the coil can release trapped air
[automerge]1578097374[/automerge]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

[automerge]1578097473[/automerge]

leave the f and e tank in so it will stay the same pressure

sealing could cause issues with leaking on joints etc if in a concrete floor

Would love to but cant see how im goona get over the airlock issue. This way I can fit AAV's on the old feed and vent pipe once i remove the tank

 

[ShaunCorbs]

But the vent is on flow of HW, not only will this pump over when calling for HW but the vent is not open if valve is shut?

will have a 2 bar blow off on the end of it so no pumping over
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Air lock issue ??

 

[SJB060685]

Yes I see what you're suggesting Shaun. How many systems have you known to be configured like this, personally I wouldn't feel comfortable

 

[ShaunCorbs]

I’ve done one to date couldn’t seal due to pipework and not enough pressure

worked ok and no complaints so far been in 2 years

 

[John.g]

In case of any worries re pressurising the system (old pipework etc) it might be no harm adding that the E.vessel should have its pre pressure reduced to whatever the static head is and be as large as comfortably possible , that way the final pressure will still be very very low, probably < 1 bar with hot system.

 

[SJB060685]

I agree with John to a degree. The expansion vessel pre charge should be set higher than the static head at that point. The system should be then be pressurised to roughly .2 bar higher. Yes a larger expansion vessel is not a problem but one you're tight for space and two theres no point spending additional money on a 50 litre if a 12 is enough. You need to calculate the vessel volume required using system volume etc. Like I said ideally you want the vessel on the return, tapped in just before pump inlet, this will give the neutral point at that tap in, negative pressure in short piece of pipe before pump and then positive pressure through boiler and rest of system back to neutral point, thus eliminating possibility of air ingress.

 

[John.g]

I wouldn't like to see the EV pre pressure < 0.4 bar in case it doesn't push the diaphragm up against the opposite end, and because you will always have "auto filling" via the F&E tank then there is no need for a EV water reserve so Pre & filling pressure in these systems can be the same IMO, assuming system volume of 100 litres and a mean boiler temperature of 75C and assuming a static head of 4M with a 12 litre EV then the maximum system pressure will still only be 0.76 bar when hot. If one "forgot" to reduce the pre pressure then 1.0 pre pressure will result in a final pressure of 1.52 bar and 1.5 pre pressure will result in a final pressure of 2.15 bar.
Bord Gais approved RGIs here have installed literally "tens" of these systems near me on converting from oil to gas with no problems whatsoever, they use(d) swing check NR valves (which have to be installed in the horizonal) rather than the poppet type.

 

[SJB060685]

John where are you getting this info to calculate the vessel charge and system pressure when hot? It seems to be more in depth than what I have in front of me, can you supply a link?

 

[John.g]

I just work(ed) it out from first principles many years ago when I was involved in industrial pressure vessels, boilers etc, you (or anyone) can input your own numbers here.

 

[SJB060685]

How do I change the numbers John to calculate?

 

[ShaunCorbs]

How do I change the numbers John to calculate?

in excel I’m guessing well that’s where I would think it’s made

 

[SJB060685]

Yes I've worked it out thanks Shaun. Still getting used to my new phone

 

[ShaunCorbs]

Yes I've worked it out thanks Shaun. Still getting used to my new phone

same got no home button now

 

[John.g]

That's it, it was in lotus 123 originally before excel was even heard of!!
I have just added another "box" to give a taste of a fairly typical (fully sealed) installation, its quite handy.

 

[SJB060685]

Thanks John mate. Question. Theres no mention of static head or system volume in these boxes. Why is that?

 

[John.g]

Re Static Head, I didn't include this is because I don't know where the EV will be located, if its located just above the boiler on the ground floor then you would add ~ 0.1 bar to the final pressure to get the maximum (and ) boiler system pressure, more significantly, but a bit unusual, if the EV was located in the attic then you would add ~ 0.4/0.5 bar to the final (EV) pressure to arrive at the maximum (and ) boiler system pressure, if in the hot press then add - 0.25 bar, and so on, with EV mounted above boiler (ground floor) then the pre pressure should not be less than 0.4/0.5 bar to ensure that you will get circulation through the upstairs rads on boiler start up.

Re System Volume, again I didn't include it directly in the calcs BUT I give a table with the % expansion for water temps from 50C to 110C, so for example if you estimate that your system contents are 100 litres and that the flow/return temps are say 75C/60C, mean of 67.5C...from the table this equals ~ 2% expansion so total expansion is 100*2% or 2 litres which you insert in the yellow box adjacent to "expansion"
You can see the calculations in the excel S.Sheet if you highlight each cell.

 

[SJB060685]

Thanks John. I was overlooking thermal expansion coefficient on the left of boxes
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How would an expansion vessel under charged at ground floor level affect circulation in upstairs rads on start up @John.g?

 

[ShaunCorbs]

Re Static Head, I didn't include this is because I don't know where the EV will be located, if its located just above the boiler on the ground floor then you would add ~ 0.1 bar to the final pressure to get the maximum (and ) boiler system pressure, more significantly, but a bit unusual, if the EV was located in the attic then you would add ~ 0.4/0.5 bar to the final (EV) pressure to arrive at the maximum (and ) boiler system pressure, if in the hot press then add - 0.25 bar, and so on, with EV mounted above boiler (ground floor) then the pre pressure should not be less than 0.4/0.5 bar to ensure that you will get circulation through the upstairs rads on boiler start up.

Re System Volume, again I didn't include it directly in the calcs BUT I give a table with the % expansion for water temps from 50C to 110C, so for example if you estimate that your system contents are 100 litres and that the flow/return temps are say 75C/60C, mean of 67.5C...from the table this equals ~ 2% expansion so total expansion is 100*2% or 2 litres which you insert in the yellow box adjacent to "expansion"
You can see the calculations in the excel S.Sheet if you highlight each cell.

Thanks John. I was overlooking thermal expansion coefficient on the left of boxes
[automerge]1578166817[/automerge]
How would an expansion vessel under charged at ground floor level affect circulation in upstairs rads on start up @John.g?

might be best to start a new thread as im sure theres more people who would like to learn this information

 

[SJB060685]

Would you mind starting it mate? I wouldn't know how to word it lol

 

[John.g]

might be best to start a new thread as im sure theres more people who would like to learn this information

Thanks John. I was overlooking thermal expansion coefficient on the left of boxes
[automerge]1578166817[/automerge]
How would an expansion vessel under charged at ground floor level affect circulation in upstairs rads on start up @John.g?

I'll just answer this and maybe some one can/would transfer these posts to a appropriate thread.

If, for any reason, the pre pressure and fill pressure (due to leakage or improper charging or whatever) fall below the static head then the water level will start falling in the upstairs rads (first) and because the circulating pump is just that, a circulating pump, eventually there will be no circulation upstairs, after start up , and depending on the water temperature, the EV pressure will start to rise and may provide enough pressure (head) to allow circulation through these rads again. IMO poor or failed upstairs rad circulation is a indication of EV/water leakage problems.
Or to put it another way, if you pre charged to say 0.3 bar and initial filled to 0.3 bar then IMO there will be no upstairs circulation.

 

[eagleeye]

One of our installers currently fitted a new heat only boiler to replace an old floor standing with gravity hot water. At the time he never fitted any valves or cylinder stat etc so I have been called back there to basically start again. Been there today to do it and found that he had the pump on the return. Anyway I drained system and made the necessary alterations to the pipework by the boiler and fitted a mid position valve and a wireless cylinder stat (as the run is impossible to get a cable between the two). So currently the feed from the F + E tank goes into the return of the cylinder and the vent on the flow. The boiler is in a tight cupboard low to the ground in an extension of the side of the house and the cylinder is on the 1st floor in the middle of the main part of the house so you can imagine how the pipework runs

Hi all just thought id update you with todays result. So i did what i thought was best and fitted and 18 ltr vessel above the boiler, took out the f + e tank and fitted AAV's on the feed and vent pipes from the cylinder coil. works an absolute treat.

 

[SJB060685]

Yes I understand how low water pressure can result in no circulation of upstairs rads, especially when you say it's a circulator and not a lifter which some people misconceive. I had however overlooked low EV pressure and it possibility acting as an accumulator

 

[John.g]

Hi all just thought id update you with todays result. So i did what i thought was best and fitted and 18 ltr vessel above the boiler, took out the f + e tank and fitted AAV's on the feed and vent pipes from the cylinder coil. works an absolute treat.

So now, a fully sealed system.

 

[eagleeye]

So now, a fully sealed system.

yes and the best way. do like your info on the other way though but why mess about with that when its just as easy to seal it isn't it ?