Non standard boiler installation

I have been asked to price a “non standard” boiler installation

It will have

3 x 30kW heat only boilers

4 x circulation pumps

1 x automatic filling loop

1 x single channel programmer

It will not have a thermostat

The boilers are going to be Ideal Logic + and they require a supply and demand signal....

Ive just talked to Ideal and all that they will say (loading wise) is that each boiler will have to be treated as a separate installation

The programmer has a 3A switching capacity

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I don’t know if I’m overthinking this (i have a tendency to!) or not, but I’m starting to think that the programmer will have to switch the boiler demand signal through a contractor (or two), which will also need to switch the pumps ..... the auto fill will need a permanent supply

So.... I’m now thinking that I’ll need a panel making up with a DP switch for each boiler, pump and the auto fill.... then fused and a neon each (to show supply)..... and obviously a main switch and fuse for the programmer

Does this sound right?????????? Or am I indeed over complicating matters

So how is all this going to be plumbed are the boilers operating in parallel with multiple zones and how is it supposed / expected to function, how is demand controlled if you have no thermostats. Are you sure you need a supply to the auto fill loop

Its in a church... they don't want a thermostat apparently

The plumbing isn't in my remit, but apparently its all going through a "Low loss header"..... there's only the 1 zone and they're using 3 x 30kW boilers to replace an ageing  single 90kW boiler

As for the automatic filling loop,,, I've been told that it needs a supply as it gives an alarm after it auto fills "x" number of times

Re the "auto fill"  Is that an admission that the system leaks?

Not an electrical issue but I would plumb it with a header tank not a sealed system, and the isolator feeding the header shut down so if the leak becomes catastrophic then the refil rate would be very slow to limit damage.

The "call for heat" input to the boilers are usually very low power so I don't see why one time clock could not just feed all 3 boilers directly?

I haven't a clue TBH Dave.... as I say the plumbing side is not my remit.... I don't think that they think that it will leak, it's more a matter of just in case

I've phoned Ideal and they said that each boiler needs to be wired as a separate entity.... so I think that the only way will be to use a contactor for the demand signal

I hope they know what they are doing. My semi-retirement job was maintenance in a care home, where three boilers had been connected together and it gave all sorts of problems.

For instance when one boiler shut off it acted as a bypass to the other two, effectively becoming a radiator, but reducing flow in the heating zones.  

Also multiple pumps, which fed three 'stat controlled zones from the common header suffered from backflow. It was clear from numerous obvious modifications, redundant motorised valves, extra pumps, etc that it had never worked well. During my time the three boilers were reduced to two, but the basic problems I mention persisted. 

Geoff1946 said:

I hope they know what they are doing. My semi-retirement job was maintenance in a care home, where three boilers had been connected together and it gave all sorts of problems.

For instance when one boiler shut off it acted as a bypass to the other two, effectively becoming a radiator, but reducing flow in the heating zones.  

Also multiple pumps, which fed three 'stat controlled zones from the common header suffered from backflow. It was clear from numerous obvious modifications, redundant motorised valves, extra pumps, etc that it had never worked well. During my time the three boilers were reduced to two, but the basic problems I mention persisted. 

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I agree.  Having separate Heating Zones is simpler than trying to make 3 boilers share the load and work economically 

I installed a dual fuel system for my house, a gas boiler, two 3/6kW electric boilers and an immersion heater. The NWEB gave me a lot of help with bits and pieces to put it together. Back feeds are the main problem so the house became non-return valve central.

When the system starts up stager the boilers. 18kW in is a hell of a jolt on the supply.

Bruspark said:

I agree.  Having separate Heating Zones is simpler than trying to make 3 boilers share the load and work economically 

Click to expand...

In that set up I was trying to run economy didn't come in to it.

Just trying to keep the place warm was the best I could do.

I settled for running the two boilers continuously in winter, relying on TRVs for local control, then isolating one boiler to prevent reverse (bypass circulation) operation in summer. 

My main contribution to the system design was fitting TRVs throughout the building.

The lesson I learned was to get someone who knows what they are doing to design or modify heating systems, AND not to just connect boilers in parallel assuming they will work.

General thoughts are,

The pump associated with each boiler should be run from the pump overrun terminals on that particular boiler. The main circulation pump should be run whenever there is a call for heat as otherwise when the boiler is in cool-down it'll only be able to dump heat into the pipework in the plant room, so either main pump running whenever any of the boiler pump overruns are running, or have its on its own overrun (probably easier) set to run just a bit longer than the normal overrun on the boilers.

Pressuration unit needs a supply, and you probably want to do something with the fault signal, very least light an indicator lamp, prossibility inhibit the system.

I can't imagine the system would be very efficent without termperature sensing and sequencing. It sounds like the system is being chucked in without any proper design of the mechnical side, and while, yes, you'll be able to wire it to make it work, its not clear if it'll work well

Ok guys.... thanks for the comments, but I am only doing the wiring, the plumbing layout is none of my concern

however the 3 boilers will each have their own pump and fees into a low loss header, the main system will have its own pump and there will also be an automatic filling loop..... of the system works or not I don’t care so long as the electrical side works

one of the main problems that I have found is that programmers only have a switching capacity of 3A, but the boiler manufacturer cannot give me any idea as to how much current the boiler draws other than the fact that they’ll each Individually need to have a 3A fuse ..... so I’ll have to power them through a contactor...

I just need to work out my parts list and cost now 

NozSpark said:

one of the main problems that I have found is that programmers only have a switching capacity of 3A, but the boiler manufacturer cannot give me any idea as to how much current the boiler draws other than the fact that they’ll each Individually need to have a 3A fuse ..... so I’ll have to power them through a contactor...

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How about an immersion heater type programable controller rated for a 13A load?

https://www.heatingcontrolsonline.co.uk/immersion-heater-controls-c-27.html/immersion-heater-timers.html/optimum-digital-general-timer.html

Doc H.

This is my block diagram, I’ve omitted neutrals and earths to keep it simple and TBH I can’t see any other way to do it and keep each boiler fused individually (as I was advised to by the manufacturers)
 

Check to see if those boilers have pump overrun output terminals, rather than looping the supply off the call for heat (which would prevent it cooling down in the way its meant to). I'd also put a run on on the main circulation pump. Something like this https://www.automation24.co.uk/analogue-multifunction-timer-relays-selec-600xu-a-1-cu  pulling in a two pole contactor, I know it says it can switch a reasonable amount but it doesn't sit right to drive it directly somehow.

I like the idea of all the neons, so its clear what's happening at any time.

I would see this constructed as a row of switched fused spurs, with indicator, plus a box with a contactor in, which makes it look simpler than the diagram suggests.

Are you sure your boiler demand signal is just mains live?   Some use a low voltage derived from the boiler control panel. It could get expensive if you put mains on one of those, - or three even.

Phoenix said:

Check to see if those boilers have pump overrun output terminals, rather than looping the supply off the call for heat (which would prevent it cooling down in the way its meant to). I'd also put a run on on the main circulation pump. Something like this https://www.automation24.co.uk/analogue-multifunction-timer-relays-selec-600xu-a-1-cu  pulling in a two pole contactor, I know it says it can switch a reasonable amount but it doesn't sit right to drive it directly somehow.

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Ive already checked that.... they don’t have pump over run

planning on using a 4 pole contactor btw

Geoff1946 said:

I like the idea of all the neons, so its clear what's happening at any time.

I would see this constructed as a row of switched fused spurs, with indicator, plus a box with a contactor in, which makes it look simpler than the diagram suggests.

Are you sure your boiler demand signal is just mains live?   Some use a low voltage derived from the boiler control panel. It could get expensive if you put mains on one of those, - or three even.

Click to expand...

Yeh, was thinking of using an 18 mod switch plate.... boilers on right hand side and the rest on the left... with an enclosure for the contactor and all the boiler/pump connections in din rail terminals

so long as they keep to the boiler that they’ve said, it only has a demand terminal

I have down one of these set ups a few years back now but I seem to remember a control module box being supplied at the time? I’ll see if I can find any details.