Low Loss Header - plumbed wrong!?

[tom107]

Hi, had a boiler installed with low loss header but I think it is plumbed incorrectly. When either zone is on radiators are hot however, when both zones are on, zone 2 radiators are much colder. Here is plumbing diagram

Shouldn't the flow pipes be at the top and return pipes at the bottom?

 

[Dan Robinson]

Proper photos and a proper system description are needed for this. There are far too many variables.

 

[fezster]

Which low loss header do you have? Who designed the system? As Dan says, LLH systems are extremely complex and have a lot of different variables to them. IME, only commercial heating engineers have the required knowledge to do the calculations and size the LLH, pumps and pipes correctly.

From my own experience of having one installed, I used a Worcester Greenstar LLH with a Vaillant boiler. The LLH is designed to handle input heat loads of up to 70KW. All of the boiler flows are located *below* the heating flows (unlike yours - was this done for any specific purpose?).

For my own setup, I have 3 zones (2 heating and 1 HW) - however, I have only one secondary flow and one secondary return, from the LLH. The secondary circuit is then driven by a single variable speed pump (sufficient for my needs and sized accordingly), and each zone is balanced by way of a gate valve on the return.

 

[tom107]

Hi, system specs are:

Ideal Harrier boiler
set to 100kw
70c

2 zones

1st zone 20 radiators
1 1/2" pipe

2nd zone 24 radiators
2" pipe

boiler 2 1/2" pipe

 

[fezster]

That's a very large system. I'm afraid I can't offer any more advice beyond what I've already said (i.e. my gut feeling is that the top secondary flow will steal all of the heat, leaving little for Zone 2). You definitely need a commercial installer (or one with commercial experience) with that kind of setup.

 

[Gasguru]

How old is the header? Do you know who fabricated it? Some LLHs have internal baffles but on face value it looks as though Zone 2 pump could be pulling water from Zone 1s return.

 

[Dan Robinson]

Can't see any check valves either.

 

[snb]

i would say first that check that rads are balanced down to 11 degree differentials individually for both zones. If they are allready then it is possible that the boiler output is not enough to cope with both zones.

 

[bellairaphon]

Is this in a residential or commercial building?

 

[Gary_Funwick]

I suspect that when both your zones are operating the total flow on the secondary side exceeds the flow on the primary side causing (I assume unwanted given the question) reverse flow through the header. This might be made worse by the fact that your Zone 2 flow is adjacent to the Zone 1 return but the real issue is the relative flow rates on the primary and secondary sides.

Assuming that the pumps on the radiator zones are correctly set (adequately quick, even heat up time, desired delta-t through the radiators), can you increase the pump speed on the primary side? (Note this will reduce delta-t through the boiler when the heating load is low probably taking the primary return temperature >55 degree and out of condensing, equally ATM you might be stressing the boiler's heat exchanger with too big a delta-t.)

What little I know of headers is from having one, I'm not a heating engineer (someone more expert that I should chime in if the above is not appropriate), however, I found this article useful:

http://portfolio.cpl.co.uk/CIBSE/201402/best-practice-low-loss-headers/

 

[Gasguru]

I think you'll find the boiler is non condensing.

 

[Dan Robinson]

That line strainer is probably full of cack too.