Vaillant 438 with 3 zones, frequent S53

[D_Hailsham]

I'm not disputing that although the LLH does have an advantage over the CST (think about it).

The only advantages, that I can think of, of a LLH is that you can fit an air vent at the top and a drain tap at the bottom.

Oh, yes, there is another a secondary flow can be some distance from its return, so several flows can be at one end and their returns at the other.

Not at all , using the 'parallel' P/S circuit (crossover) ensures ALL 'secondary' loads recieve the same water temperature (not to be confused with the series P/S circuit)

Not sure what you mean by 'series' and 'parallel' in this context.

I think the boiler/llh/buffer manufactures would take a dim view of this type of set-up

That doesn't answer my question: what is wrong with it?

 

[D_Hailsham]

for instance the existing 15-60 may be rated up 6 metres of head but it would still be no good to use as a primary pump due to its quoted flowrate at 4m of head.

I agree. The point I was making is that the 15/60 head decreases as the flow rate increases, but the 25/55 head stays virtually constant over a wide flow range and then drops like a brick.

the pump manu would want a bypass fitted and the expansion connection isn't shown but D_H has just simplified the drawing that's all

A variable speed secondary pump would eliminate the need for a bypass. The pump would have to be connected to the zone valves.

I think we have done the Op's head in ...as it is still perfectly workable as it is with a correctly sized pump.

But the correct pump is going to cost the OP over £400. Converting to a CST will not cost anything like that.

 

[Steelmasons]

on another note steel you keep on going on about p/s systems being only used across the pond, in which case either you
a) only ever work in domestic systems
b) are winding us up

Matt

The P/S set up has been used over here for donkeys years just not coupled with CST arrangement (ring header/secondary circuits zoned) , only the last few years or so have LLH manufactures been using the CST arrangement with regard to header applications , worked in a good few plant rooms over the years with the CST arrangement being non existant.

What did we do before the LLH? (not to be confused with a ring header).

 

[matt1e]

The only advantages, that I can think of, of a LLH is that you can fit an air vent at the top and a drain tap at the bottom.

Oh, yes, there is another a secondary flow can be some distance from its return, so several flows can be at one end and their returns at the other.

you also get handy pockets for temp sensors
but to be fair to steel a LLH is a better choice is you have got the dosh

Not at all , using the 'parallel' P/S circuit (crossover) ensures ALL 'secondary' loads recieve the same water temperature (not to be confused with the series P/S circuit)

Not sure what you mean by 'series' and 'parallel' in this context.

He's confusing the issue, absolutely no baring on the Ops system whatsoever, he will be getting onto underslung,overslung and tertiary loops next

I think the boiler/llh/buffer manufactures would take a dim view of this type of set-up

That doesn't answer my question: what is wrong with it?

Nothing mate apart from a bypass will be req for the secondary pumps if it isn't interlinked with the valves but I'm sure you know that
and may be req anyway to regulate flow when valves close

I reckon Steel is on a wind up mission

Matt

 

[Steelmasons]

The only advantages, that I can think of, of a LLH is that you can fit an air vent at the top and a drain tap at the bottom.

Mmm , close but not close enough.

Oh, yes, there is another a secondary flow can be some distance from its return, so several flows can be at one end and their returns at the other.

So a parallel circuit of sorts.

Not sure what you mean by 'series' and 'parallel' in this context.

Just because your diagram of CST's (series) doesn't show a parallel circuit doesn't mean it doesn't exist , think about a 1 pipe versus a two pipe.

 

[matt1e]

The P/S set up has been used over here for donkeys years just not coupled with CST arrangement (ring header/secondary circuits zoned) , only the last few years or so have LLH manufactures been using the CST arrangement with regard to header applications ,worked in a good few plant rooms over the years with the CST arrangement being non existant.

What did we do before the LLH? (not to be confused with a ring header).

b) are winding us up

I knew it you little tinker you

funny enough was going to mention the fact that we have plenty p/s systems over here that don't use a cst or llh arrangement, was at one yesterday, will go through my pics and post a couple when I get back in if any are good enough

Matt

 

[Steelmasons]

To be honest Matt I have not come across the CST arrangement in any boiler/plant set up , what I have fitted is a LLH whereby each secondary pair of f/r are spaced together tightly (8 sets)

D-hailsham , the parallel set up is simply each pair of secondary CST's are conected across the primary F/R (all zones recieve the same temperature) , the 'diagram' i was refering too was the one you posted from the internet regarding the CST and not the diagram you posted regarding the OP's set up.

 

[D_Hailsham]

the parallel set up is simply each pair of secondary CST's are connected across the primary F/R (all zones receive the same temperature) , the 'diagram' I was referring too was the one you posted from the internet

I assume you are referring to this diagram:

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• D_Hailsham
• 16 Jun 2013
• 1

If so, the zones do not all receive the same temperature as this diagram makes clear. What each zone receives will depend on the relative proportion of the flow and temperature drop in the earlier zones.

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• D_Hailsham
• 16 Jun 2013
• 1

 

[Steelmasons]

I assume you are referring to this diagram:

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• D_Hailsham
• 16 Jun 2013
• 1

Yes , which is a series set-up

If so, the zones do not all receive the same temperature as this diagram makes clear. What each zone receives will depend on the relative proportion of the flow and temperature drop in the earlier zones.

Yes I know , the parallel set up WILL allow a constant temperature across the zones , you have posted a SERIES configuration much like a 1 pipe set-up.

If we were to connect EACH pair of CST's ACROSS the primary F/R then all zones would recieve the same temperature (ladder system using CST's).

 

[Steelmasons]

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• D_Hailsham
• 16 Jun 2013
• 1

Would you like the EXACT temperature drop figures for that circuit? (based on info forthcoming.)

Google may be your friend but it isn't your best friend.

 

[D_Hailsham]

If we were to connect EACH pair of CST's ACROSS the primary F/R then all zones would receive the same temperature (ladder system using CST's).

I see what you mean. But what happens when only one zone is open? The excess flow has nowhere to go.

Would you like the EXACT temperature drop figures for that circuit? (based on info forthcoming.)

Thanks for the offer, but I can work it out for myself.

 

[Steelmasons]

thanks for the offer, but I can work it out for myself.

Go for it , 20 kw load per zone @ 20dt temp drop.

 

[Steelmasons]

I see what you mean. But what happens when only one zone is open? The excess flow has nowhere to go.

Of course it does (back to boiler).

First zone is far right of that drawing , your temp drop suggests otherwise.

 

[D_Hailsham]

Go for it , 20 kw load per zone @ 20dt temp drop.

If that's a 20C dT per zone you get:

Zone 1: Flow = 75; Return = 55
Zone 2: Flow = 70; Return = 50
Zone 3: Flow = 65; Return = 45
Zone 4: Flow = 60; Return = 40

If it's a 20C deltaT at the boiler then it's a different game. I'm still working on that one.

Of course it does (back to boiler).

First zone is far right of that drawing , your temp drop suggests otherwise.

I hadn't noticed the pump and automatically thought the flow was clockwise.

 

[D_Hailsham]

Go for it , 20 kw load per zone @ 20dt temp drop.

If that's a 20C dT per zone you get:

Zone 1: Flow = 75; Return = 55
Zone 2: Flow = 70; Return = 50
Zone 3: Flow = 65; Return = 45
Zone 4: Flow = 60; Return = 40

If it's a 20C deltaT at the boiler then it's a different game. I'm still working on that one.

I've just realized there's no difference! Although the return water from zone 4 is 40C, the return to the boiler will be at 55C. giving a 20C delta T at the boiler.

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• D_Hailsham
• 18 Jun 2013
• 1