Sealed system boiler primary flow and return size

[eltricky]

1st time on here so hi to everyone. I'm an electrician who on a recent contract had to design and install a bespoke control system for zoned central heating and hot water. Upon comisioning my bit of the system it became apparent that all was not well with the water side of the system. Layout is as follows:- 103 ish K BTU system boiler with own pump feeding 22mm primarys to the airing cupboard, total length (flow & return) 30M, head 2.5M. In the A/C is a 210L pressurised tank with a 22mm union boost pump feeding 4 x 2 port 22mm valves.

Valve 1 tank estimate 12 K BTU
Valve 2 upstairs rads 33 K BTU
Valve 3 Downstairs rads 15 K BTU
Valve 4 Under floor heat 8 K BTU

Total 68 K BTU

The problem is that with valves 2,3 & 4 open we are struggling for heat at all the rads (UFH set ok) and balancing is a nightmare. Call for hot water and the rads cool(restriction set for tank flow).

I suggest that 28mm primaries are needed from the boiler split through a 28mm manifold to feed the two port valves but opinion seems divided with other plumbers hence this post to see if anyone would like to comment.

If you are wondering why im involved the original plumber has been kicked of site for other reasons and I don't want to abandon the 70 year old + clients.

Thanks

 

[Andygasman2010]

Do you mean they have fitted a second pump inline with the boiler's own pump to help circulation? If so this isn't really the best way to do it unless connected via a "low loss header" You're right, sounds like it should have at least 28mm flow/returns to the boiler and preferably the plan too (zone valves)

Any chance you could post some photos?

How is the underfloor heating connected?

How many radiators are there in total?

What make/model boiler is it?

Is it a sealed system?

Is there a system bypass?

 

[Agile]

The pipe size depends on the temperaure differential of the system.

It sounds as if the system needs to be properly balanced.

I dont know why you are quoting old fashioned units. Its been normal for at least 30 years for boiler and radiator sizes to be specified in kW.

Tony

 

[eltricky]

Thanks for responding.

System boiler Worcester CDi 30 with buit in bypass sealed system
9 rads on valve 2
2 rads on valve 3
Valve 4 upnor UFH manifold kit fitted as per spec. Balanced to 43 C for screeded floor
The tank is a 210 L Tribune which is supplied with pre-formed pipework including pump and 2 port valves

 

[eltricky]

Thanks Tony, Regards BTUs. Lazyness on my part. The client provided me with the rad specs which had the outputs in BTU.

 

[petit_pablo]

I love the fact that the sparky knows more than the plumbers! Cause for concern!

 

[eltricky]

Thanks Pablo. Wouldnt quite say that though. I have a reasonable knowledge. Been at this for 20 years so picked up loads from other trades. Plus reading up on things out of interests sake.

I know, I need to get a life !!!!!

 

[Agile]

There is a potential balancing problem because there are four circuits which all have to be able to work in about ten different combinations.

There is a way to tackle this but I am reluctant to give away the secret in front of all the plumbers who read this forum.

I would offer to advise you privately but as I dont know you could I trust you not to just post it up here? I have lived long enough to know that one cannot trust people one has known for years and certainly not people who have never even been met.

Tony

 

[grahamderek]

Check cylinder input.
The latest 210L Tribunes take 23 Kw

 

[eltricky]

cheers GD. Appreciate the input. I had a similar figure quoted by Tribune but they said this is heating the tank flat out so to speak. With other circuits on the system the pre- fitted gate valve needs to be trimmed to balance the tank against the rads. They recon that 3 to 4 KW should heat up in an acceptable time.

 

[eltricky]

Appreciate what ur saying Tony. Got some elekey tricks that im selective who I share them with. Could I ask though, and I appreciate its tricky not seeing the job but do you recon the 22s from the boiler are enough. I have been researching the recomended KW capacities of various pipe sizes and 22mm seems to be around 12 KW with the usual considerations made for run length, number of bends, head of water etc. With the total load around 20 KW it thought 28mm feeders were needed.

Then someone suggested that there ratings were for open vented systems and the capacities increase for pressurised systems. Back to the drawing board. Need more paper !!!

 

[Agile]

Its not that easy to say yes or no. However, with everything on if the flow rate is too low then there will be too great a temp differential which should be a nominal 11°C.

Generally I would expect 22 mm to be adequate if its not too far to the valves.

There is always the possibility that the UFH is not set correctly as far as the boiler is concerned.

We need real measurements to be more helpful. Can you measure the flow and return temps at boiler and at each of the CH circuits when they are all on?

Tony

 

[Andygasman2010]

It's a pre-plumber cylinder with it's own pump, and the boiler has it's own integral pump also. Could this be causing problems??

If there's 30m of flow/return pipe to the boiler, before the plan, it could be too small.

 

[eltricky]

Cheers Tony. Will get some temperatures this week hopefully. Just to re-cap the valves are about 15M from the boiler so a 30M loop. Looking at the run I would estimate that there are about 6 bends in the flow and return, so 12 in total. If the rule of thumb that one bend is equat to about 1M of pipe then the effective flow and return loop is a good 40M.

Regarding the UFH. Its a 3 circuit system and the individual L/min flow rates have been set according to the pipe lengths. Then the manifold lockshield has been trimmed to give a blended temperature of 43/44 C. The Watts/SQ M calc gives 2.5 ish KW Load

Appreciate your help

 

[eltricky]

Hi Andy. The pre-plummed pump is a three speed. Had to run this on 3 to get the rads to work. There is what I would consider excessive water turbulance noise from the airing cupboard. On speed 2 less heat at the rads.

By the way, to all who are offering help. I installed an auto air bleeder just ahead of the boost pump at the system high point. Original plumber did not do that either. Quite honestly I would not let him fit a fish pond pump.