Additional pump on a combi system

[dcawkwell]

Installation of thermostatic valves will probably sort the problem out.
As rooms warm up and the thermostatic valves close it will send the water to other parts of the house.
Set thermostatic valves to 2 or 3.

It should be possible to balance up a system with 12-15 radiators.

 

[mysteryman]

No. If you do that with a combi, the external pump will run in DHW mode as well, which you don't want. You need the power source for the relay or pump to be from the central heating call from the room thermostat.

Are you sure that the extension work is laid out, filled, vented and balanced correctly? This needs addressing before you start adding more pumps etc.

 

[davewyorks]

low loss header would cure problem with a pump for each floor, still means splitting the flow i.e one for up one for down.

 

[SimonH2]

I still take the view that correcting the problem is the solution.

True, but sometimes the "right" answer isn't practical for a variety of factors.

Back to the OP's question.
If you fit a pump in the system that boosts the flow to part of the circuit, then it will divert flow from parts just before it. For simplicity, consider two long pipes with (say) 10 radiators between them at intervals. As you go down the pipes, the differential pressure will get lower and lower due to friction in the pipes. By the time you get to the end, there's very little pressure and so it's hard to balance the system - rads near the pump need an almost closed lockshield and may be noisy.

So suppose you add a pump between rads 7 and 8 to boost the flow to the last 3 ? Depending on flow rates etc, you may find that you've reverse the pressure differential (and hence the flow) across rad 7 and possibly 6, even 5. In effect your've created a system where there's flow round the small loop of rads 8, 9, and 10 and rad 7 (and possibly 6).
So now the flow for rads 8 - 10 is a mix of hot from the boiler and cold from rad 7. The backwards feed for rad 7 is the cold return from rads 8 - 10.

I saw this sort of thing happen where I used to work. Unfortunately they didn't want to spend amy money employing someone who had a clue, and the plumbers (they tried several outfits) just kept bodging on more and more "fixes". it wasn't helped by the original system designer (it started as a small system with 5 heat/cool fan coil units) specifying 4 port valves so there was a bypass at each point when the valve was off.

The minimal fix it to bring at least one of flow or return for the smaller end loop back to the main boiler. Ideally you bring a separate flow AND return back. But if you are doing that, you probably don't need the second pump anyway.
Or, in the case of a simple string like that, you take the return from the far end of the string so the pressure losses in the two pipes balance and all rads see a similar differential pressure - but you're back to running more pipes again.

 

[gaswizzard]

All that is required is to fit the additional pump on the flow/return of boiler dependant on EV connection , flow rate should remain the same although head will more than likely double (series) , the additional pump (circulator) will be switched via the room stat , any issues with dead heading then fit an ABV/bypass , simples.

 

[Dan Robinson]

Or fit a different boiler where the pump only does the heating, then replace the internal one for a bigger unit?


Ahem, Atmos, ahem

 

[DP]

Or a Ferrolli with two pumps says I while sitting in a bunker

 

[Dan Robinson]

Or a Ferrolli with two pumps says I while sitting in a bunker

How did that get past the swear filter?

 

[Onetap]

I dont understand the anamosity???
All i wanted was to chat with other engineers,
To pick peoples brains, as to speak!

There is no animosity.

DeltaT suggested that you were out of your depth with this. Maybe you are or maybe you aren't.

It is a technical problem and either you have earned the technical ability to fix it or you haven't. If you do not have that particular technical competence, then it's not a problem that can be answered on an internet forum and those that are proposing solutions are doing you a disservice.

I'd suggest that you start by estimating the differential pressure required at the pump to achieve the design flow rate through the index run. When you have those numbers, you will be able to decide whether the problem can be solved by balancing alone, installing a different pump and balancing, or by reducing the differential pressure by increasing the pipe sizes of the index run. If you can do that, then you're not out of your depth. You cannot do that over the internet.

Installing a second pump is, IMHO, a measure of last resort and would never be installed in series with the existing pump. I have installed second pumps on systems, but I had the use of commissioning sets and flow meters to make them work.

If your gas safe, get yourself into the combustion Chamber.

A good idea, if you also need to find out something about gas.

 

[simond]

We are shortly going to be trialling this product on one of our installations - it may be suitable for your application;

Www.oxyvent.com

 

[Dan Robinson]

Its just a fancy header????

 

[Dan Robinson]

and stupid money considering how vague that website is.

 

[Terry lambert]

The idea of him getting into the combustion chamber, is that there is a hell of a lot of information and help not just relating to gas but also to central heating and other aspects to being an engineer.

There is a lot of good engineers in there that do not post or look in here, that would offer him good sound advice

 

[SimonH2]

Its just a fancy header????

Or a buffer tank depending on how you want to look at it.
The idea is sound, but how much

While I can see valid uses for it (or something like it), the website has clearly been designed by someone more used to selling snake oil than plumbing components.

 

[Onetap]

The idea of him getting into the combustion chamber, is that there is a hell of a lot of information and help not just relating to gas but also to central heating and other aspects to being an engineer.

There is a lot of good engineers in there that do not post or look in here, that would offer him good sound advice

As with any other internet forum, there will be those who sincerely believe they are good engineers and others who enjoy passing themselves off as something they're not and these will confuse him. How would someone like the OP, who cannot distinguish the sound advice from the misinformed nonsense, tell the difference?

The requirement for access to the CC is a gas qualification. The recommended method for determining the pressure losses in gas pipes (similar to determining the pressure losses for pump sizing) for the ACS qualification are abridged and simplified; dumbed down. I'm sure there are some in the CC who have more experience of fluid flow in pipes and ducts, but the chances of getting sound advice there are no different to any other plumbing forum.