Conflicting Opinions - a Low Loss Header or not?

[ajrobb]

I don't see a huge difference between the complexity of a low loss header and a plate heat exchanger. Both require a boiler pump and a separate CH pump. With a 4-pipe boiler like the Veissmann (with internal diverter valve), would the DHW circuit typically be on the boiler side of the CH plate heat exchanger?

I quite like the idea of having the boiler, hot water cylinder and plate heat exchanger on a sealed circuit and the mix of old pipes and radiators on an existing open-vented circuit.

 

[holty]

I don't see a huge difference between the complexity of a low loss header and a plate heat exchanger.

price maybe?. on a small domestic circuit maybe not. but a LLH is ideal for cascading boilers etc and multiple zones in bigger instances .e.g commercial.

 

[ironman1]

I take it most guys posting on this thread are domestic guys with limited knowledge regards non domestic installations?

 

[transam]

Why do you think that ??

 

[ironman1]

Maybe not the case for the OP but.........................................i've seen many light commercial systems (40/50kw) utilising the low loss header , the problem in some cases was the absence of shunt pump coupled with close coupled tees , problem here is the primary circuit (header) acts similar to a one pipe system due to return water from zone 1 mixing with flowed water to zone two , this becomes a problem with multiple zones especially when HW zone is last pair of tees into LLH , hence the reason for shunt pump to equal all zone pumps plus boiler & LLH losses.

While some may disagree i normally use the 'header loop' type system which eliminates the 'one pipe' header deal....................i only mention this as i had an issue a few years back with two Keston 55s using the LLH , HW was fine in the summer months but come heating season HW recovery time became an issue , had the HW zone been taken off the the first pair of tees then maybe it would'nt of been an issue. .

 

[ajrobb]

had the HW zone been taken off the the first pair of tees then maybe it wouldn't of been an issue.

Doesn't sound like it would be an issue with a 4-pipe boiler with internal diverter valve using W-plan.

 

[Chris43]

Your answer comes close to what I was looking for - i.e. guidance, not a detailed technical discussion of plan / plate / KKH options etc.

It would seem that a LLH is NOT required. The proposed replacement would have a filter system in in anyway, something like Magnaclean.

I think I understand the arguments about water temperature wrt the LLH, and with quite hard water here, I would be worried about a plate exchanger geting furred up and decreasing the actual flow ability.

Fianlly, I have seen on a boiler parts website Remeha / Broag LLH for theri comercial boilers at £247 including pump. Installing would be what? a max of a 1/ day? And what controls the sump pump?

Thanks again, but keep the replies as easy to understand as you can, please.

 

[D_Hailsham]

The heating system itself is old, with a mixture of old iron pipes and newer copper ones, 20 radiators in all.

Old iron pipes would suggest that part of the installation is single pipe - current systems use twin pipes. Has this been checked?

You need to use the Boiler Size Calculator to find out what size boiler you need. There is no sense in using the original boiler size or guessing.

 

[silverback18]

I would think it was more to do with pressure loss through the system, with system boilers quite a lot of the pump output is lost within the boiler heat exchanger, which only leaves a smaller amount for the system, with an old unknown system, it would be difficult to determine the index circuit and with old iron pipes, they are likely to have a restricted bore due to corrosion, for example when you use an Atag Q51S to Q60S they insist on a LLH due to the pump not having sufficient power after the heat exchanger, from their manual it states.

"If the installation resistance is higher than the stated value the pump will rotate at maximum pump capacity and the load will be adjusted until an acceptable temperature difference between flow and return water has been obtained. If, after this, the temperature difference remains to much then the boiler will switch itself off and wait until an acceptable temperature has arisen.
If an unacceptable temperature is detected, then the control will repeatedly try to achieve water flow, and if this does not work then the boiler will switch off. If the capacity of the boiler pump is insufficient, an extra external pump can be installed in combination with a low velocity header in series with the boiler".

 

[Chris43]

Thanks for the link for the heating assessment tool. I went and measured all the rooms, and had to divide the house into 4 areas, which I could then treat as semi-detached. The calculations added up to 29.92 kwh, so 30kwh looks to be spot on!

The system has a pumped heating circuit, and a pumped hot water circuit.

 

[Chris43]

I think that you are talking about multiple commercial boilers here, and I don't think that is what I am dealing with here. Sorry, if I have missed the point, but the relevance escapes me. Feel free to correct me though, if I have got your intent wrong.

 

[transam]

Plate exc's ?? a method of heating a system indirectly eg seperating the boiler from the heating system so as there is no direct connection between the two ! e.g there was a thread on here a good while back concerning an open system that was converted to a sealed combi system the system was an old servowarm install the increased pressure caused several rads to burst , the use of a plate would have been the answer !

Done several systems with plates for various reasons , old iron 1 pipe systems with cast iron school rads , u would never flush em out correctly in a month of sundays , use a plate negates any manu's carp in the system warranty excuses & allows the boiler to be sealed up ! plates IMO are under used in domestic installs ! small systems use a combi plate exc eg vaillant as they have a threaded connection as opposed to the o ring sealing method , larger systems go to a purpose made plate as posted previously by holty ! some plates one should stay away from as IMHO & from expeirence they are poorly designed & give poor heat transfer a particular Italian make from a well known mail order company!
Always protect the plate , always provide isolation so as plate can be removed for maintenance/cleaning

LLH installs done several generally were 2 or more boilers are installed in tandem for a given out put IMO , several linked boilers are better than 1 large boiler ( obviously this is not always possible ) most if not all manus ? would recommend a LLH system for multiple boiler installs IMO each boiler should have its own pump!

 

[Agile]

Transam ( wish I knew your real name ), if the perceived problem is from dirt in the system and you want to protect the boiler from it.

Then if using a secondary heat exchanger how do you protect that from the dirt?

Tony

 

[silverback18]

You don't Tony, but far easier and cheaper to clean or replace a heat exchanger rather than the boiler, a plate heat exchanger ensures that the boiler side remains clean.

 

[Agile]

Well, actually you can use filters etc. on the secondary return to the heat exchanger.

The main point is that a heat exchanger will both keep dirt out of the boiler where the dirt can block the boiler heat exchanger and also enable the flow rate through the boiler to be adequate regardless of the dynamics of the varying heating load.

Tony