S Plan wiring using a Low Loss Header and a single System Boiler running 2 pumps

[Elforleather]

I'm revising a system for a customer, it's a large property that really does need zoning but he is not keen on the idea of having all the floors up. In short, I'm going to remove an old heat only boiler and standard S Plan and have a system boiler run a primary circuit and install a low Loss header. Ultimately I aim to improve the poor flow of the heating system.

There will be a 15/60 pumping into an UV cylinder from the header and use a Grundfos Magna1 to circulate the heating system. The wiring is my challenge, it's all standard S Plan, however I need the pumps to run independently as they have their own circuits from the LLH, if I wire them both in at 10 on the wiring centre at the switched live, I will find both pumps becoming live by way of a back feed.

I pondered wiring them from the stats but didn't like the idea of the Magna1 coming on at the same time the zone valve gets it's first live rather than off the orange. So I thought maybe a time delay relay of 10 seconds, but went off the idea when I tried to source one. So now I'm thinking of using two 240v SPST or SPDT, using only NO, relays one after each of the zone valves and before terminal 10. The relays would stop a common back feed and the pumps can pick up live from the orange of the zone valves, leaving 10 as my switched live.

Has anyone else come up with anything else? I have a diagram I can post if anyone is interested.

 

[chris watkins]

Wire from the zone valve brown for the pump the zone valve will start to open slowly but the modern pump if set on the auto PP setting will slow itself reading high pressure then adjust as valve opens fully. If you like put an auto by-pass in but I have found these are not needed.
You should not need the 15/60, 50 will do all domestic cylinders.
I theory you should not need zone valves just the pumps but never had the balls to try it.

How big is system ?

 

[Elforleather]

Thanks Chris, its an 8 bedroomed property with a total of 26 radiators. Its 20 years old and today would have needed to be done very different. I have knocked up this sketch, it has none of the usual S Plan stuff on, it just deals with the pump control, it should make sense.

 

[chris watkins]

As I said personally if only one pump to one zone valve I would take it from the live out of each stat before it goes to brown wire on 2 port & just leave the end (micro) switches to signal the boiler. That way relays are not required.
The room & cylinder stats have reasonable switches but you would need to check the carrying capacity of the micro switches & the start up draw of the Magna1 25/80 pump if you were going to do it your way.
Why 15/60 may I ask for the HW primaries ?

 

[Ermintrude]

I'm with the above smart start pumps will be fine with zv. Wire them on s/l from stat then to boiler. Wiring centers are the devils spawn.

 

[Ermintrude]

LLH will also need a shunt onto the boiler. Hope ur using ideal logics or a CDI regular 40kw. Don't ever use a Worcester system!

 

[happyflyer]

As I said personally if only one pump to one zone valve I would take it from the live out of each stat before it goes to brown wire on 2 port & just leave the end (micro) switches to signal the boiler. That way relays are not required.
The room & cylinder stats have reasonable switches but you would need to check the carrying capacity of the micro switches & the start up draw of the Magna1 25/80 pump if you were going to do it your way.
Why 15/60 may I ask for the HW primaries ?

Like you say Chris always worry about the rating of the valve micro switches, like the man has drawn external relays are always nice, he wont go wrong doing it his way

 

[Elforleather]

Trouble is Chris, and I get your point because that was my first plan, is that if I don't use the relays then there will be some noise as the Magna1 effectively pushes against a closed valve, it's a big pump. I am not sure that the pumps smartness will help? I need to signal the pumps to start only once the zone valves have fully opened, hence energising the relays using orange. All the relays are doing is acting as electrical non return valves in allowing the pumps to start on the normal green light the oranges provide.

 

[Elforleather]

It's a logic plus system boiler so it won't need a shunt as such, it will pump the primary itself with it's inbuilt pump. I don't use regular boilers any more it's just added expense and hassle sealing them.

 

[Elforleather]

It's a fair point, the Magna1 max draw is 1.03 amps so the micro switches will handle it, it's more about having the two pumps running at the appropriate time for the zone valves and being able to run one or both pumps at the same time. If the relays come out then nothing will stop pump 1 energising pump 2 each time a zone valve is called for.

 

[Ermintrude]

Relays will stick open or closed after a few 1000 cycles. Your over complicating this. Use lots of logic heats and systems. I personally wouldn't worry about the noise and more about the size of boiler. 30kw seems a touch small for 28 rads and a cylinder.....
Your wiring is a touch spurious. Fit a 3port instead of a 2 port if your that worried about startup flow as then when the pump kicks in and the valve is in neutral it by default runs back to header as valve energises it swings into zone valve and just runs on zone. But 28mm 3 port £££££ or use a bypass or u could just scrap zone valves and let pumps work as valves like in days gone by? Your need for relays is " unusual" do quite a few of these jobs and always use zv micro switches to switch in boiler , pump is on the valve side. The pump has a 5 - 10 second start up, and can pump against a closed head nee bova. Honeywell 28 2 port opens in about 7 seconds

 

[Elforleather]

The boiler is fine on size, I have sized it all and I only need 26 kw. Your 3 port point is fair, I thought about that but I can't use a Y plan as I'm connecting to 250 litre unvented cylinder and it would still need the additional two port on the primary to be G3 compliant in regard to overheat, so nothing would be saved and likewise, I can't scrap the zone valves. I didn't think it was complicated, it's all S Plan with just a relay added to stop two pumps running when I don't want them too, other than that it's all standard and switched using the ZV micro switches. It's good to chew the fat though, I don't find that many engineers locally that get their heads into too deeply.

 

[chris watkins]

The boiler is fine on size, I have sized it all and I only need 26 kw. Your 3 port point is fair, I thought about that but I can't use a Y plan as I'm connecting to 250 litre unvented cylinder and it would still need the additional two port on the primary to be G3 compliant in regard to overheat, so nothing would be saved and likewise, I can't scrap the zone valves. I didn't think it was complicated, it's all S Plan with just a relay added to stop two pumps running when I don't want them too, other than that it's all standard and switched using the ZV micro switches. It's good to chew the fat though, I don't find that many engineers locally that get their heads into too deeply.

As Ermi states you will likely have trouble with the relays in the not to distant future so why risk it when you don't need to. I think he had in mind a divertor not a mid. (could be wrong, who know what goes on in that warped genius head of his)
I only used one here cos had 2 zone from 1 pump but if only 1 & 1 remove relay.
If you only have a load of 26kWs those pumps are might big to shift the water required, remember you have taken out the biggest resistance i.e. boiler, by going for the LLH a standard alpha 15/50 set low will murder a domestic cylinder on 22's

 

[Elforleather]

Chris I really appreciate what you and Ermi are saying, it's a quality thread and good discussion. I'm stuck with using two ports because of the cylinder no matter which 3 port we use. Building control are involved in the project so the unvented side needs to be text book. And your diagram is sound, similar to mine in principle. Your comment about the pumps is also good, and I had considered that. The fact is that I'm trying to resolve a circulation problem that ideally should be done using pipework, but the customer doesn't want it so I've come up with an alternative. I also want to fix it in one hit, so after some discussion with Grundfos over resistance decided on the Magna1, I guess I want to be sure I don't have to go back and upgrade pumps later? The system is over 25m long and all rads are on 8mm. I can't even find out if it's manifold or simply reduced.

 

[chris watkins]

OOoooooo. best of British to who, it sounds like you will need it !!!

P.S. Divertor would be allowed on unvented (so long as it was installed so normally closed to cylinder) & you will be very lucky to find anyone in BC who would question it anyroad.

 

[doitmyself]

The boiler is fine on size, I have sized it all and I only need 26 kw.

Good to know that you didn't rely on the exsting boiler/rads to tell you what size boiler was needed. I can also appreciate why you think a LLH is necessary - 1.9m available head is not much when there are 26 rads.

However, have you, and your client, considered HW priority. You would then need only one pump on the secondary side.

The system should be designed/balanced for a 20C differential across boiler and rads. This will halve the flow rate and quarter the head, so a Magna pump may not be necessary

 

[Ermintrude]

But as he's said the pipework is probably undersized, so he's going to be increasing water velocity, smash it's back in! Can anyone hear water pishing out of microbore? If the system is a straight through micro ***** manifold no matter what size pump you fit it's still going to be poor. In situations like this I like to separate flow and return fully. Any of the rads single port entry? Use a diverter sorry. You could design for 20 but by sounds of it goodluck getting 10 in the correct pressure range! If labc involved and making significant mods to system shouldn't it be getting zoned up any way?

 

[Elforleather]

Your not wrong, it's a best attempt to make things better. The property is only 20 years old and well over the 150m2 rule, it does need splitting up and would never be built like this today, but the level of decor and carpets etc is high, they want minimal disruption and it's got wayrock floor.

Deep down I suspect it is manifolded and the heating F&R is 28mm at the current zone valve, so I have a good feeling that I can make it work better. It was the controls side of things that became interesting but then I like these jobs, it's more fun when the wheel comes off, who wants to bolt combi boilers to the wall each day.

The pump has some smart capabilities so hopefully it will come good. Thanks for some good points excellently made though, I usually steer away from forums but his had been good.

 

[chris watkins]

Good stuff Elfor, glad we could be of some help even if it is just as a sounding board.

Come back & play some more another day soon !!

Pic's of some of these "interesting" jobs are always nice.

 

[doitmyself]

But as he's said the pipework is probably undersized, so he's going to be increasing water velocity, smash it's back in! Can anyone hear water pishing out of microbore? If the system is a straight through micro ***** manifold no matter what size pump you fit it's still going to be poor.

Sorry, but I don't see what you are getting at. A bit too obtuse for me.

Increasing water velocity: That means increasing the flow rate by reducing the differential.

smash it's back in: What's back in??

water pishing out of microbore: What's that all about?

straight though manifold: ???

Even if it is 8mm back to the main pipe, or to a manifold, that shouldn't be a problem. After all, 8mm pipe can carry 3kW at a 20C differential with a velocity of 1m/sec, which is high enough to prevent sludge settling, but not so high as to produce flow noises in the pipework.

 

[happyflyer]

You might try not using motorised valve at all, as long as you don't get gravity circulation in the minibore, like Emi says if you have a shunt on the LLH that takes care of the min flow
rate in the boiler, if you did have gravity circulation you could put a good swing none return valve in the flow after the pump, you might get noise, they used to make silent NRV to stop
gravity circulation on larger diameters pipework, not anymore, they made one that had a disk in it with a rubber seat, only fitted in the vertical then they made one with a soft spring
that could be used in the horizontal, see you got me going on a bit now I'm getting all filled up, but every job is different, you need to know your own job when you looking it and what will work.

Hydraulics are not always an exact science, I have installed 100s of minibore jobs when it first came out, bet if I went back most have been taken out, plastic push fit plumbers jeeez!

Elf let the force be with you, use your light sabre.

PS your drawing only shows one heating zone, did you want two???

 

[Worcester]

With what you're doing you could still multi-zone using either the Honeywell EVO system or the new LightwaveRF with the remote TRV's

Just adds a layer of complication to what you are doing however it is a great way to achieve multi-zone control (up to 12) in a retrofit environment.

What would others think of using flow switches after the pumps to trigger the boiler?

 

[Ermintrude]

With what you're doing you could still multi-zone using either the Honeywell EVO system or the new LightwaveRF with the remote TRV's

Just adds a layer of complication to what you are doing however it is a great way to achieve multi-zone control (up to 12) in a retrofit environment.

What would others think of using flow switches after the pumps to trigger the boiler?

Get stuck on a dirty micro system ?

 

[happyflyer]

Worcester,

What kind of flow switches were you think of using , they tend to be bulky and like Ermi says they do stick easily especially on a mucky old system, we use them
commercially but now only a last resort, there is always a risk whatever you use but flow switches, IMO is not for me. Commercially there are so many other bits of electronic
you can measure water flow or pump current with these days and they all all cheap.

You all keep these good ideas coming someone will always shoot them down:66:

I think use internal valve relays backed up by external relays will do for domestic, that's much more than most people would do, it normally gets thrown in and most engineers
would not drill down too deep like this.

Worcester I am with you on multi-zone you are getting down to the real business and I think you know how I hate TRV, its time the EU stepped in and banned them, they will if we stay
in there, the building regulations with 2 zones is feeble too, they will go much further but it will take time, domestic sustainability in the UK is pre-historic, the lord only knows how many
old terraced house still not got proper roof insulation.

 

[Elforleather]

With what you're doing you could still multi-zone using either the Honeywell EVO system or the new LightwaveRF with the remote TRV's

Just adds a layer of complication to what you are doing however it is a great way to achieve multi-zone control (up to 12) in a retrofit environment.

What would others think of using flow switches after the pumps to trigger the boiler?

Hi Worcester. Thanks for the comments, but the multi zone idea, for me, is more an end user interface? It doesn't really add anything to the heart of system other than controllability. I'm more focused on making a poor system function better. I have used flow switches and they would work here but as other have said, they can be unreliable as they age. Essentially the micro switches within the zone valves will be doing exactly the same job in signalling my relays, all I'm doing is an S Plan with two relays to give the two pumps some independence and limit the potential for noise.