LLH required?

[matt1e]

Had my boiler chap come round tonight and he's suggested a LLH and the flow and returns coming from this. The idea is that it provides a quicker heat up time and less issues with balancing. He's worked on commercial systems before and seemed very sure that was the best idea and that 3 long flow and returns with zones off them would be a nightmare.


2) he's suggested one larger pump for the primary also being able to provide adequate flow for the secondaries to each rad....each LLH system I've just been googling has a separate pump for each circuit from the LLH

He might have worked on some commercial installs but he hasn't grasped how they work, a low loss header provides hydraulic separation between the circuits, what he is suggesting wont work, and you are correct in thinking that you would req a pump for each secondary.
If you go that route you have to size all the pumps only for the requirements the circuit they serve
increasing the primary pump size will only affect the primary circuit

As for multiple zoning off a standard flow and return, commercially you would tend to fit a three port and bypass arrangement rather than a 2 port

Matt

 

[Agile]

He could always have a LLH and just one pump and then lots of motor valves.

Although, apart from enabling a 400 series boiler to operate happily, I dont see what great advantage a LLH would have.

Of course with a LLH a pump could be used on each circuit without a motor valve. Big and bulky but one way to do it.

 

[virgilns]

He could always have a LLH and just one pump and then lots of motor valves.

Although, apart from enabling a 400 series boiler to operate happily, I dont see what great advantage a LLH would have.

Of course with a LLH a pump could be used on each circuit without a motor valve. Big and bulky but one way to do it.

So your saying no need for a 2port AND a pump per circuit from the LLH as there'd be no flow if the pump was not working...which totally contradicts what my guy said about just needing the 'primary' pump...or would the primary pump just be sized consdderably smaller so as not to actually create any flow in the secondaries...kind of makes sense, but as you say, not sure the wife would be that impressed if I turned her (albeit very large) airing cupboard totally into a plant room


Thinking about it...a 15-50 into the LLH and a 25-60 into a manifold with circuit to each rad with motor valves would negate the need for one pump per circuit????

 

[virgilns]

10mm? and all the manifolds I;ve seen are for plastic push fit...I'd rather go copper all the way if possible...are there copper manifilds out there?

Is it a new house or complete strip out? Would UFH be practical, if you're going to the expense of a multi-zone system? You'd also gain the floor insulation. Copper's nice, but it's getting eye-wateringly expensive.

Old house but renewing all the heating and DHW side. Only thing is I'm doing it room by room as to minimise disruption in house as were living in it with a very inquisitive 2yr old!

UF heating is great, but not with a leaky old solid brick wall house and carpets....

 

[Dan Robinson]

Why insist on making life hard on yourself?

I can appreciate not wanting wireless, but having dozens of two port valves and sticking with copper under the floor is barking if you want to zone down to room level.

 

[SimonH2]

There's nothing fundamentally wrong with a load of 2-port zone valves and stats. I don't believe that they'll give as comfortable temperature control as TRVs because they are on-off devices. If heat loss is low relative to rad capacity then the valve will open, the rad will heat up rapidly, eventually the stat will turn off and close the valve, then the rad will still be fully hot and the room temp will overshoot. Sensitive electronics stats with low differentials might help - at the expense of more frequent switching.
It does mean that you can have any combination of zoning and times that you want. Fit timer/stats and you can have individual programmes for each room.

The valves also tend to be a tad noisy in operation, so will need to be sited carefully.

You can get thermo-hydraulic actuators for some rad valves, and these might be better. Upsides is that you keep a standard system, but the downside is that they are slower to operate - can be a minute or two to start opening, and after a long open spell can take even longer to close. if the rad capacity and heat demand are well matched (weather comp on the boiler ?) then they'll tend to work fairly quickly as they'll never get completely cold or saturated hot.

A little while ago, by chance, we happened to be giving a lift to someone that lives 2 doors up from where we used to live. The guy that had it built did exactly that - a stat and zone valve for each room. It had since been ripped out - probably accompanied with a "sucking through teeth" and a "you need that lot out, it'll never work" from someone who couldn't troubleshoot it (I imagine it must get through valve heads from time to time).

 

[Dan Robinson]

I don't think as a system design it won't work; but if you want room level zoning AND you are re-piping a house; AND especially in phases doing it as a separate run for each rad to a central manifold seems are much simpler method.

It's what I have done at home, and several customers and are very happy with the comfort and silence of the operation.


Although I have gone uber wireless with full Evohome with OT bridge and HCC80, CS92a and DT92e's... but that is OTT. .

I don't understand people's irrational fear of plastic. Especially at the <15mm end - copper is no more durable and more likely to kink - not counting joints under the floor.

Granted plastic looks utter pants when you can see it.

 

[Agile]

On a LLH the primary pump is small and just sized to provide the small flow through the boiler to keep it happy.

The secondary pumps "suck" the flow out of the LLH.

It means that the boiler flow is relatively isolated from the flow to the loads.

Typically fitting a spring loaded non return valve after a secondary pump will prevent any unwanted gravity or spurious circulation round that look when the pump is off.

In a typical LLH it can be thought of an "H" arrangement where the vertical part is quite wide so the pressure loss across it is minimal.

The flows are created by the primary and secondary pumps. In a totally balanced flow situation there will be no flow through the vertical part.

Tony

 

[gaswizzard]

copper is no more durable and more likely to kink -
.

, c'mon Dan.

(you know I love ya )

 

[Onetap]

On a LLH the primary pump is small and just sized to provide the small flow through the boiler to keep it happy.

The primary flow has to be greater than the total secondary flow rates, otherwise you will get reversed flow and mixing in the LLH. The primary circuit typically has a high flow but a very small pressure difference.

Some boiler manufacturers (Viessmann, ISTR) aren't keen on LLHs, since it isn't usually practical to install a system in which the primary flow is always exactly equal to the variable secondary flows. The excess is mixed with the return and can reduce the efficiency of the boiler.

The LLH or not issue seems to have eclipsed every other consideration for this system.

• Will the OP really operate the 3 zones at different times?
  How about weather compensation ( which would allow the circulating pumps to operate near the design flow rate for most of the time, and reduce the role of the TRVs to minor trimming control; less noise)?
  How is the HWS to be generated?
  Is HW priority acceptable (no heating when there's a HW demand), allowing a modulating burner to vary the heating flow temperatures?
  Do the heating zones require secondary mixing?

 

[Agile]

Yes, I phrased that badly in my effort to try to make it simple.

LLHs are widely used in large industrial installations and can often have variable speed pumps to prevent the problem of the return to the boiler reaching too high a temperature.

Some think a LLH is the answer to everything. This is true from an installer's point of view as the boiler works fine irrespective of the load flow.

But this is at the disadvantage of a potentially serious reduction in condensing as a result of an increased return temperature. It is sensible of Viessmann to discourage them and so should every manufacturer.

Tony

 

[Dan Robinson]

copper is no more durable and more likely to kink -
.

, c'mon Dan.

(you know I love ya )

On the small stuff dude :d