Vaillant 438 with 3 zones, frequent S53

[Steelmasons]

Matt
Ps what you have overlooked is hinted at in my post before this one

Sorry Mattle you'll have to explain.

FWIW Mattle i have a great deal of respect for you , this is from someone in a previous guise.

 

[matt1e]

I also know that if your secondary circuit is split into more than one load then they are, Period
Has the penny has dropped yet?

Matt

Suggest the penny hasn't dropped on your side mattle , the WHOLE point of the CST arrangement is multiple zones off the primary circuit , whther 1 zone or 10 secondary zones off primary circuit it doesn't matter , the spacing of the 'TEES' at each zone will not influence any pumped flow through redundant circuits , this is the whole point of using the CST arrangement , works in exactly the same way as a LLH (as long as LLH does not excees .3 m/s flow rate) , anyway gonna pop over to the CC and make a nuisance of myself.

I despair
anyway have fun Steel
now where were we? Oh yes
Op ya pumps are nee good Mate

 

[Steelmasons]

I also know that if your secondary circuit is split into more than one load then they are, Period
Has the penny has dropped yet

, yes the penny has just dropped (edit)

Then it begs the question why use the CST arrangement when using two zones off of one pair of SECONDARY flow/returns.

 

[matt1e]

Matt
Ps what you have overlooked is hinted at in my post before this one

Sorry Mattle you'll have to explain.

FWIW Mattle i have a great deal of respect for you , this is from someone in a previous guise.

Well since you asked nicely I will explain
Let us say that the op decides to go for hydraulic separation between the boiler and the system and installs a LLH
He finds that by pure chance the spacing between the flow and return is such that all he has to do is cut out 2 sections of pipe and slot the LLH straight in, happy days!
so he gets himself a suitable pump to fit on the Primary and fits It
He then learns that because of the fact it now doesn't have to pump through the boiler its now suitable as the secondary Pump even more happy days
Now
That's all he has to do mate!
he has got a perfectly working S-Plan system (think of the LLH as a heat because, thats what it is)
no need in his case for two secondary pumps,nor check valves etc
He may need to tweek the auto bypass but thats already installed and it would need tweaking anyway but the boiler or boiler pump dont need it
OP pleased and the Boiler as happy as larry

all a Low loss header is,is a packaged set of "closely spaced tees" with some nice extras thrown in the working principle is the same

That took me bloody ages!
Matt

 

[Steelmasons]

Took ages

Then again if the OP had the header made with 6 secondary tapping paired up at at a max of 4 pipe diameters apart then he wouldn't require zone valves.

EDIT.....maybe a slight alteration of pipework to boot.

 

[matt1e]

, yes the penny has just dropped (edit)

Then it begs the question why use the CST arrangement when using two zones off of one pair of SECONDARY flow/returns.

I knew you would get it before I finished writing

that ones easier to to answer
because it is always more desirable the boiler on a primary
and hydraulic separation between circuits,means you have more control, on large systems its the only way anyway
its the same with chiller systems
Reet now can I watch some Telly DT?

Matt

 

[Dan Robinson]

13 pages to end up back where we all started off

 

[matt1e]

13 pages to end up back where we all started off

I know, we do go on

 

[D_Hailsham]

I seem to have stirred up a hornets nest suggesting CSTs.

What hasn't been mentioned is the temperature drop between one pair of tees and the next. That's fine if you have a rad circuit and an U/F circuit. You put the pair of Tees for the rads first and the pair for the U/F next.

But what if all circuits need the same flow temp, as in the OP's case?

The solution would be Matt's suggestion of one pair of secondary tees, one secondary pump and an S plus arrangement.

The OP already has the three zone valves and the existing 15/60 will do fine for the secondary pump. The only query is whether you will need NRVs on the zone returns to prevent reverse circulation. You don't have them on a normal S plus, so why would you need them here?

That just leaves the question of the primary pump. The existing 26/55 appears to be adequate if the boiler is set to 26kW but would struggle of it is upped to 38kW. You would need a Magna 25/80, which wouldn't be a bad idea as it is a variable speed pump.

 

[matt1e]

That just leaves the question of the primary pump. The existing 26/55 appears to be adequate if the boiler is set to 26kW but would struggle of it is upped to 38kW. You would need a Magna 25/80, which wouldn't be a bad idea as it is a variable speed pump.

The primary pump only needs to be sized for the primary loop dave
So it would be sized for req flowrate against a head loss of 4.05 m + the primary loop resistance ( the system losses are only relevant to the secondary pump) so the magma 25-80 would likely be overkill
By the way I did find an equivalent pump for the 26-50 (another manufacturer) that seems to suggest that the head is 5.5 m
Will see if I can find it again when I get home

Matt

 

[Steelmasons]

The OP already has the three zone valves and the existing 15/60 will do fine for the secondary pump. The only query is whether you will need NRVs on the zone returns to prevent reverse circulation. You don't have them on a normal S plus, so why would you need them here?

.

You won't , NRV's are not required if Mv's are fitted neither is the CST arrangement (don't confuse a LLH with a CST) , the CST arrangement which is used over the pond use a pair of CST's for EACH zone which is the reason they use the circulators with the 'inbuilt' NRV at suction side of circulator , the whole point of the CST arrangement is to eliminate any flow through 'off' circuits when using multiple circulators.

What would be the point of using a zone valve to each distribution circuit when boiler pump/distribution pumps only assist in moving water through their 'own' respective circuits?

A Vaillant LLH uses 4 tappings , two for primary (boiler) and 2 for distribution (secondary) , due to the spacing of the distribution tappings (wide) circulation from primary pumps would be apparent in distribution circuit , if the distribution tappings were placed within 4 pipe diameters appart then primary circulation through header would have no influence on flow through distribution side , another factor being velocity which is another subject.

It wasn't me who suggested the use of CST's , i'm just saying it would be pointless in the OP's case as it would require an extensive re-pipe.

Lets not forget , a LLH is a de-coupler and NOT a closely spaced tee , a slight difference.

 

[D_Hailsham]

The primary pump only needs to be sized for the primary loop dave
So it would be sized for req flowrate against a head loss of 4.05 m + the primary loop resistance ( the system losses are only relevant to the secondary pump) so the magma 25-80 would likely be overkill

I realized that. My only thought was that the existing 26/55r might not be OK if the boiler is turned up to 38kW.

I did find an equivalent pump for the 26-50 (another manufacturer) that seems to suggest that the head is 5.5 m

The problem is that the quoted head is not a good guide; it all depends on the shape of the performance curve. Compare the Selectric 15/50 with the UPS 25/55.

 

[D_Hailsham]

You won't , NRV's are not required if Mv's are fitted neither is the CST arrangement (don't confuse a LLH with a CST)

A CST and a LLH both serve the same purpose: to separate the boiler (primary) from the radiators (secondary).

the CST arrangement which is used over the pond use a pair of CST's for EACH zone which is the reason they use the circulators with the 'inbuilt' NRV at suction side of circulator , the whole point of the CST arrangement is to eliminate any flow through 'off' circuits when using multiple circulators.

But that's just one way of doing it.

What would be the point of using a zone valve to each distribution circuit when boiler pump/distribution pumps only assist in moving water through their 'own' respective circuits?

No point at all, but that only works if the required flow temperature for each zone reduces as you go from the first CST to the second.

What's wrong with this?

3 Zone CST

• D_Hailsham
• 14 Jun 2013
• 1

 

[Steelmasons]

A CST and a LLH both serve the same purpose: to separate the boiler (primary) from the radiators (secondary).

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

No point at all, but that only works if the required flow temperature for each zone reduces as you go from the first CST to the second.

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)

What's wrong with this?

3 Zone CST

• D_Hailsham
• 14 Jun 2013
• 1

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

 

[matt1e]

I did find an equivalent pump for the 26-50 (another manufacturer) that seems to suggest that the head is 5.5 m

The problem is that the quoted head is not a good guide; it all depends on the shape of the performance curve. Compare the Selectric 15/50 with the UPS 25/55.

absolutely
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.

What would be the point of using a zone valve to each distribution circuit when boiler pump/distribution pumps only assist in moving water through their 'own' respective circuits?

look at DH's diagram, the point is to stop flow in circuits you don't want on

What's wrong with this?

3 Zone CST

• D_Hailsham
• 14 Jun 2013
• 1

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

Rubbish,
discounting the LLH/and buffer manufacturers for obvious reasons the boiler manufacturers would prefer that over a standard primary flow and return system every time
(well 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)

Anyway I think we have done the Op's head in with all this talk of p/s systems which he doesn't technically need as it is still perfectly workable as it is with a correctly sized pump

Matt

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