And another question for the assembled experts ...
I'm building a 3 zone heating system and plan to fit gate valves to allow a rough balance between the zones. I'd intended to fit them after the zone valves but someone has just said that they should be on the return side - does it make any difference whether they're on flow or return?
I would balance the radiators individually with all zones open. I would not balance the zones as a whole.
Christian.
Normal (commercial) practice is to fit a double regulating valve on the return, with an isolating valve on the flow. The only reason for the regulating valves on the return is that they're subject to lower temperatures, so it doesn't make any difference. The DRVs usually incorporate a flow measuring device.
Gate valves aren't much good for regulating, most of the flow regulation occurs in the last turn & they can generate noise. You'd do better to get some proper DRVs. They show up on E-bay occasionally and rarely attract any bids. A manifold with built in valves & flow indicators would probably be best of all, but the flow indicators become illegible after a year or two.
Thanks, I hadn't heard of these.
Double Regulating Valves look like this;
Agreed, with the assumption that all zones are to be operated together, at least some of the time.
There is no benefit in attempting to balance the zones the way you suggest, Dave, as the objective is to get the correct flow through each radiator and that means restricting the individual radiator flows. Once that is done you have finished!! There is no point in restricting any flow any further, indeed that would simply starve that zone.
As to whether LSV's go in flow or return, it does not matter either. Any restricting device will work equally well in the flow as the return - there is really no difference, its just a continuous circuit. The only 'difference' between flow and return is that the water is a bit cooler by the time it reaches the return to the boiler.
Phil The uk.d-i-y FAQ is at
By the way, Dave, you have read the Balancing FAQ haven't you?
That's interesting. I've often thought there should be an absolute way of setting the correct flow rates. Those DRV's, though ugly, are presumably much quicker to set up than the iterative temperature drop method.
Phil The uk.d-i-y FAQ is at
This could be noiser than using the valves on each radiator. I do install a valve on the return from each circuit (with the zone valve on the send) but only so I can drain each one individually if needed.
LSV (or rather, flow restriction) in the return is quieter for the week or so after the system has been filled when there are still air bubbles working their way out. They can be quite noisey going through the flow restrictor into a radiator, but of course they don't leave the radiator in the return pipework, having separated out.
BTW, I noticed my Dryton TRV's all also have the flow restrictor balancing adjustment in them. You need a special tool which I don't have and the instructions are rather vague. It says something like you can only turn the restrictor one way to adjust it, and it's not very clear if having closed it down, you can actually decide to open it any afterwards. Maybe if you carry on turning it flips back to fully open if you go all the way round? Has anyone used this feature of the Dryton TRVs?
I have, but I'll read it again.
I've got 3 CH zones (z1=5+2 rads on different runs, z2=7 rads, z3=4 rads), one zone for DHW, the zones have very different pipe runs and the DHW cylinder is next to the boiler. It should be fairly easy to balance rads within a zone but, if I balanced just with the lockshields, I thought that the different zone impedances would mess-up an overall balance and the zones with the lowest impedance would dominate until their TRVs shut down. By equalizing the zones I should be able to get a better balance.
Where is my thinking screwed-up?
... snipped
That's a point, but I don't think a couple of weeks of hissing valves out vote the advantage of having control (or TRV) valves on the most convenient end for the householder. There are often situation where a radiator is mostly behind some piece of furniture, and one end is much easier/convenient for the end user to reach than the other.
Phil The uk.d-i-y FAQ is at
Dunno! But try envisaging the same radiators without the desire to zone them. In that case balancing works just fine as normal, and all that adding ZVs does is to shut off some rads when they are not needed. There is nothing magic about a zone - it is just a group of rads that you want to be able turn off with one valve (instead of running round shutting off each rad's control valve).
Phil The uk.d-i-y FAQ is at
There is a morsel of logic in there somewhere.
Commercial system balancing is done by measuring the flow rates and proportionally balancing the system.
If you call the furthest heater/rad No.1 & the second furthest No. 2, then you'd measure flow rates on No.1 and No.2. Then you'd reduce No.2 flow rate until 1 & 2 are the same percentage of the design. At the start No.1 might be 45% & No. 2 might be 70% of the design flow rate. You'd reduce No.2 flow rate & this would cause No.1 to increase. When you're done they might both be 55%.
Then you do the same with No. 3 & No. 2. This time, as you reduce No.3 flow, Nos.1 & 2 flows will increase in the same proportion. Then No.4 & No. 3, etc., etc., ad nauseam.
You'd then balance all the zones using the zone valves (DRVs) and finally set the system flow rate using a DRV on the pump outlet.
You could apply this logic using return temperatures.
Any restriction will generate some noise. The noise is less likely to be intrusive if some of the restriction is done at zone valves, rather than all at the rad valves.
You mean in Dave's post?
"Furthest" being in the hydrodynamic sense, presumably, since a small, close radiator, fed by a narrow bore may well be 'further' away in terms of resistance than a beefy rad which is physically further away, fed by a large bore pipe?
Surely this example is true only if No.1 and No.2 are the same loading?
Basically you are trying to adjust each radiator circuit's resistance until they all take their design percentage of the total system load (for that zone), yes?. This is the same aim as the temperature drop method, and the iterative procedure seems to be nearly as 'ad nauseous', as you note. I see a couple of advantages though; 1) you don't have to wait for temperatures to stabilise, and indeed you don't even need to fire up the boiler. 2) Reading off a pressure gauge should be quicker and more repeatable than trying to get an accurate temperature reading.
Well, yes - it is the exact same concept. We DIYers only use temperature drop because we don't have the luxury of flow measurement. I have thought long about a simple non-intrusive method of measuring flow rates inside central heating pipes, but with singular lack of success.
True, but I reckon most domestic c/h need all the flow they can get, what with tubing and pumps sized to minimise cost. Should you find the flow is excessive, the domestic answer is to turn the pump down.
Thanks for the interesting insight into large scale techniques.
Phil The uk.d-i-y FAQ is at
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