Fixing church heating systems

[SimonH2]

Sorry this is turning out to be a bit long ...

We have a problem with the heating system at church which I believe was caused by modifications, and then the system bodged to hide it.
The original system would have been coal/coke fired, and consists of the once common large pipes (2off 3") down each side wall with returns (2") down the sides of the aisles. These days it's a pumped system with a 60kW oil fired boiler. In addition, at the front (I suspect as a later addition) the flow goes through a large segmented radiator.
A few years ago, some fan-coil units were added and are plumbed in series with everything else - greatly adding to the heat output and de-stratifying the air, but at the expense of noise which means they get switched off during services/events. It's thought that at the same time the fan-coils were fitted, the pump was replaced with a larger one.
A while ago I noticed a check valve installed in the feed pipe from the F&E tank to the boiler - but until recently the penny didn't drop ... Then one day I happened to be outside when the system was heating up and noticed that one of the radiator vent pipes was dribbling and the penny dropped regarding that check valve. This is a diagram of the current system - I've separated out the radiators & fan coils for clarity, both sides of the system are identical. The dashed sections represent long sections that have been shortened to save space.

Obviously, with the check valve in place, the expansion can't go up into the F&E tank - so it has to go up one of the vent pipes and dribbles out. When the system cools down, the system fills up again with fresh water. Generally no-one had noticed as the system normally heats up and cools down when no-one is about.

So I thought about why that check valve was there, and my guess was that since the fan-coils and larger pump were fitted, there's too much resistance in parts of the system and the check valve is there to stop the water just being pumped up the feed pipe till the F&E tank overflows. So I tried removing the check valve - and sure enough, that's exactly how the system behaved

So clearly the people (apparently professional plumbers) responsible couldn't be ar**d to think about the problem and just bodged it and scarpered

So, having established that the pump pressure is just too high, I set about estimating the numbers. While heating up, the boiler manages about 10˚C delta-T, and so I estimated that the flow rate will be around 1.5l/s (5.4m³/hr) if the boiler is running at 60kW.
60kW / ( 4.2 kJ/(kg K) * 10 K )
I know it may well be less than that, but it seems that won't make all that much difference. Next I tried finding specs for the pump (Wilo SE150-N) but couldn't find any. Wilo's site has a "recommended replacement" function which suggested their Yonos MAXO 40/0.5-4 and the curves for that pump are :

So that would put the system somewhere around the red line I've added. With over 4 bar available, no wonder it's pumping back up the feed pipe Even turning the pump down to speed 1 leaves it pumping up - just not as fast.

First off, this is an area I'm not too familiar with - am I correct in taking that family of curves (like the red line I've added) represent different system flow resistances ? So where that curve intersects the pump performance curve (for a given pump speed setting) then that's the flow rate through the system.

So I've been thinking about ways to fix this. One obvious way is to raise up the F&E tank and the radiator vent pipes until there's sufficient head available to cancel the effect from the pump. That's probably not practical - I think the best we could achieve would be around 4-5 feet

So I'm thinking of adding a bypass and local circulation pump as shown here :

With this in place, the flow resistance round the main loop is considerably reduced - moving to the right on the pump performance curves and reducing the pressure differential in the system. Ignoring the locally pumped loop - it's just back to the old large bore cast pipes.
The local pump takes care of pushing the water round the fan-coil and radiator - and also some additional radiators we're thinking of adding.

Does the plan make sense ?
Anything I've missed ?
Any other suggestions ?

 

[John D v2.0]

the problem is the vent and feed are miles away from each other by the looks of it so there's bound to be a big pressure difference with the pump running.

 

[Dan Robinson]

So clearly the people (apparently professional plumbers) responsible couldn't be ar**d to think about the problem and just bodged it and scarpered

Where was God in all this?

 

[SimonH2]

the problem is the vent and feed are miles away from each other by the looks of it so there's bound to be a big pressure difference with the pump running.

Yes, opposite ends of the building. But bear in mind that between the boiler and the other end was mostly 2off 3" pipes (and some 2") untoll they added the fan coils. That's why I'm thinking that adding the bypass so the main loops are only the twin 3" out and 2" back - need a lot kess pumping.
But now I've just had another thought ....
If the plumbing we're altered so the water went through the old roads first, then there'd be little pressure differential between boiler and vents - the pump would be running
at a negative head at it's inlet. But it's a fair bit of work (it takes a day to drain down and half a day to refill !) to try with no guarantees

 

[Gasguru]

These are low head high flow pumps...in fact the maximum head is well under a normal domestic pump.

You're confusing meters head on the Y axis with bar pressure...deadheading the pump will only result in a 4 meter head or 0.4 bar.

The exisiting pump spec is here...Russian but I guess it can be relied on.

https://www.google.com/url?sa=t&rct...es/wilo2.pdf&usg=AOvVaw3DJ2xxP9cY9AD6OhJgri5B

As an urgent priority you need to disconnect the additional rad and fan coil units and loose the check valve...you currently have a potential bomb in the Church.
See what the boiler manual recommends regarding the position of feed and vent pipework...the existing single feed pipe is suspect too.
With the constant loss of water there's a good chance the system will be heavily corroded and uninhibited.
Check out high level electric infra-red heating as a simpler solution to the fan coil/rad bodge.

 

[SimonH2]

These are low head high flow pumps...in fact the maximum head is well under a normal domestic pump.
You're confusing meters head on the Y axis with bar pressure...deadheading the pump will only result in a 4 meter head or 0.4 bar.

Oops, I had "m" in mind, no idea why my fingers typed "bar"

The exisiting pump spec is here...Russian but I guess it can be relied on.

Ah yes, the graphs are there which is all that matters really. Not a lot of difference, still around 3m head and without serious surgery we don't have scope for raising the F&E tank plus the vents to cope with that.

As an urgent priority you need to disconnect the additional rad and fan coil units and loose the check valve...you currently have a potential bomb in the Church.

It would have to block both rad vents for that to happen, and in any case I'm sure one of the old joints (or possibly, one of the new ones !) would fail before anything "explodes". It's survived like that through many very cold spells - says me while reaching to find some wood to touch
I would prefer to see a vent from the boiler as well, I'm looking into where stuff runs (for sorting the electrics) and might be able to fit the pipework in with that - I'd like to "retire" the last of the old galv mains water piping at some point.

It then goes through my mind ... With a vent off the boiler, ditch the open vents at the rads. Problem with that is why the vents would have been (retro)fitted in the first place - it's a PITA bleeding them every time they start gurgling (and especially on an initial fill) and AAVs tend to be "a bit unreliable". There is a reason you see so many of these old "high volume" systems with pipes going up through the windows and the like.
Ideally it would also require moving the pump to the boiler flow side so that the rads didn't go to negative head and have the AAVs (or just bleed nipples) draw air in when trying to clear the air out - and that would be serious surgery to "quite old" threaded steel/iron tube & fittings.
That would be a more reliable system though, minimal risk of pumping over as the feed and vent would both be to a boiler with a large water volume and negligible flow resistance. That needs more consideration, when the engineer comes to look at the burner problem I'll try and be there and see what he thinks about moving the pump (and whether he even has the tools to work with 2" threaded stuff )

See what the boiler manual recommends

Manual ? There isn't even any legible identification on the boiler (other than the burner unit). As I mentioned, it was second hand (we think) about 46 years ago All I can say is that inside the outer case and lagging, it's a cast iron job that's ribbed like it could be a segmented job like the rads - I only got a brief look while it was being worked on.

With the constant loss of water there's a good chance the system will be heavily corroded and uninhibited.

Indeed, given (rule of thumb) 4 - 5% expansion each time it heats up and cools down, it's heading on for a complete water change every 20 cycles. It didn't take much persuading for the PCC to agree it needs dealing with before much more expensive problems manifest.
We did ask the guy who repaired and recommissioned the boiler to add antifreeze and inhibitor - he put 5l in. I read the label and saw that it requires minimum 20% to have any inhibitor function, and set to estimating the water volume. I sort of calculated and guestimated to get to around 400 to 500l total.

I'm also thinking that it's not going to be very easy/practical to try flushing the system either - I bet there's some sludge in the whole system

Check out high level electric infra-red heating as a simpler solution to the fan coil/rad bodge.

Good god no Been in places with that and it's just horrible, really horrible. Sat there with cold feet and a grilled head We still have cold feet with our system, but at least our heads don't get grilled.

 

[Gasguru]

Boiler safety systems aren't a choice...it's law.
You don't have the experience and you're prepared to take the risk without sufficient knowledge.
If you won't listen then I'm out.

 

[John D v2.0]

sounds very complicated, I still don't understand why the vent pipes have to be so far away, why not put one on the main circuit near the boiler before the pump instead? If the old ones are for filling the system then that's what AAVs are for nowadays. As gasguru presumably means, don't go removing the vents without adding a suitable new one though.

 

[fixitflav]

I still don't understand why the vent pipes have to be so far away, why not put one on the main circuit near the boiler before the pump instead?

Neither do I. If the actual layout is anything like the OP's sketch, I would put the open vent on the pump inlet pipe (with inverted U outlet above the tank), and while at it, change the cold feed to 150mm after the vent (both before the pump).

I read the label and saw that it requires minimum 20% to have any inhibitor function

I can understand that for the antifreeze, but the inhibitors I'm familiar with say 1%.

 

[SimonH2]

sounds very complicated, I still don't understand why the vent pipes have to be so far away, why not put one on the main circuit near the boiler before the pump instead?

It's because these old systems hold a lot of water and are right ******s to vent. A lot of old system like this have vent pipes on the top of radiators or a high point of the stacked pipes. These allow the system to "just work" when the people runming them don't have a clue - many would not have a clue how to bleed a rad.
As you say, these days an AAV can deal with that, but not as reliably.
In our case, it's the addition of the fan coils without considering the hydraulic resistance that's caused the problem, and fitting AAVs as we stand now wouldn't work as these let air in when the reds have negative head pressure in them.

As suggested, feed & vent to the boiler, and AAVs on the rads would make more sense after moving the pump.

 

[fixitflav]

As suggested, feed & vent to the boiler, and AAVs on the rads would make more sense after moving the pump.

Perhaps I missed it, but I didn't see anything about moving the pump. But if you do, pipe it boiler - open vent - cold feed - pump. Cold feed up-and-under. The open vent and cold feed must be close together, and if possible, the connection points should be directly below the tank, for convenience, but can be remote from the boiler and pump.

 

[SimonH2]

Perhaps I missed it, but I didn't see anything about moving the pump. But if you do, pipe it boiler - open vent - cold feed - pump. Cold feed up-and-under. The open vent and cold feed must be close together, and if possible, the connection points should be directly below the tank, for convenience, but can be remote from the boiler and pump.

It was in the post I've (part) quoted below ...
We're rather constrained in that only a short bit of pipework is accessible in the boiler room - the rest is inaccessible and would be unsuitable to be putting something like a pump in. So I'd be looking to leave the feed as it is and add the vent from the top of the boiler.

Boiler safety systems aren't a choice...it's law.
You don't have the experience and you're prepared to take the risk without sufficient knowledge.

I hope you just misunderstood what I wrote - not that it's hard with my ramblings I wouldn't dream of not having a reliable open vent - and at the moment we have two. The system as it is now is as it was left by "professional" plumbers/heating engineers, and it's been pronounced safe just last year - a different engineer repaired and re-commissioned the boiler. I would absolutely not consider removing either of the current open vents before having another one in place.

I would prefer to see a vent from the boiler as well ...
It then goes through my mind ... With a vent off the boiler, ditch the open vents at the rads. ...
Ideally it would also require moving the pump to the boiler flow side so that the rads didn't go to negative head ...

I can understand that for the antifreeze, but the inhibitors I'm familiar with say 1%.

This was antifreeze/corrosion inhibitor - so mostly ethylene glycol. The inhibitor is only a small part of the mix so that it's at the right strength when the additive is up to 20% or more. As long as we can get the boiler firing reliably (so the frost stat can do it's work), I think we can dispense with the antifreeze and just put inhibitor in.

 

[SimonH2]

OK, taking the various comments into consideration, along with knowledge of what might be practical, I arrive that this option.

I think it would be "difficult" at least to get the pump running that way and connect F&E pipes to the pipe between boiler and pump. The feed is already into the bottom of the boiler, and I see there's a plugged hole in the top of it. Where the pipes go into the dashed area, they go through a wall in the boiler room and on the other side (I believe, it's one of the things I'm looking into) a duct topped with fixed slabs (in the base fo the tower), then through another wall into the nave of the church (under the floor, and for good measure, under the organ), then tee out and then "pop up" through the floor.
The wall where the pipes go through has been made up, so one of the things to investigate is how hard it will be to open up to add pipes - ie how well they filled in the hole after putting the pipes in. The vent pipe should (ideally) go this route - the F&E tank is actually above that slab topped duct in the tower.

As it happened, I bumped into one of the churchwardens in town this afternoon. He told me he's rung the engineer who is going to try and get out this week to look at the oil burner lockout problem - and he's told him that I'll be wanting to talk to him about this issue as well. I'll see what he says - not least, whether he thinks we stand a chance of undoing pipe fittings or if he has the gear to thread a pipe stub in-situ if we cut the pipes.

 

[SimonH2]

Heating engineer came this morning to look at the burner and we discussed the options.
He's suggesting a combined F&E pipe just before the pump, and replacing the rad vents with either bleed nipples or AAVs. We'll leave it till warmer weather, and it's not going to be trivial to do - 2" screwed connections that have almost certainly been as they were over 40 years ago.
Not much room, the entire accessible pipework for this is between the blue tape and the gate valve above the pump. Otherwise there's a lot more pipe to disturb.

Oh yes, there is a pressure relief valve in the flow pipe - I'd forgotten about that.

 

[SimonH2]

And we'd end up with this