Radiator balancing - flow meter?

[Set Square]

Had to re-balance my system yesterday after adding an extra radiator, and it's a pain - even with an IR non-contact thermometer - because you have to re-establish steady state conditions after each tweek.

It occurred to me that it would be a hell of a lot easier if there were some way of measuring the flow going through each rad. You could then adjust each lockshield to give a flow rate commensurate with each rad's heat output, and voila! Get the flow rate right, and the temperature drop will look after itself.

In the electrical world, there are ammeters which simply clamp round a cable and measure current without any direct electrical connection. Does anyone know of anything which can do a similar job for liquid flowing through a pipe - and at consumer rather than industrial prices, of course!?

[Dave Plowman (News)]

Yes.

But the problem is that the resistance in the circuit alters the flow rate from the pump. I well remember starting out with my new installation - over three floors. With all the lockshields fully open, I needed maximum on the pump to get the top floor rads to work. By the time they were all balanced, minimum. Left on maximum, it was pumping over.

There's certainly a difference in noise with flow rate, and this could be measured. But quite honestly, the half day or so required to set up the average system properly wouldn't justify the cost.

Dunno about these modern vari-speed pumps. Perhaps an expert will comment?

[Set Square]

Yes, I'm not suggesting that you could adjust each radiator independently without affecting each other - but simply that if you could see the effect on *flow* caused by each adjustment, it would be very much quicker than waiting for a steady state to be re-established before measuring temperature drop.

[Tom]

I seem to remember in the dim and distant past we used calibrated valves which had a known flow rate/pressure drop characteristics. they were installed with two pressure sampling points on mounted on either side of the valve. To check flow rate all you had to do was to insert two probe needles through the rubber seals of the pressure sampling points, the probe needles were connected to either side of a manometer, you read the flow rate from a graph. All this came at a price of course. Regards Tom

[Aidan]

They're balancing valves, double regulating valves, DRVs, commissioning sets, etc. Look at the D931 valve at

They're probably impractical for balancing individual domestic radiators. The manufacturers recommend a flow rate to give a minimum pressure drop of 1kPa. The valves needed for fan coil units LTHW heating coils usually required an ultra-low flow valve. The accuracy was +/- 5% for a fixed orifice meter & DRV or +/-10% for a variable orifice DRV. They might be useful to set the flow rate to a zone manifold serving say radiators on one floor of a house. You need a differential pressure meter to be able to get a flow reading from the valve. Drowned mercury manometers were used but mercury & water systems are non-PC, so electronic dP meters are generally used. I've got a few on my heating (HWS primary return and 2 LTHW MT heating zone returns) but I've never bothered to set them with a dP meter. Their main advantage is the lockable maximum setting on the DRV. Near enough is OK for most domestic stuff.

You can also/get ultrasonic flow meters which strap to the outside of a pipe. They work by doppler effects, but I don't know the details. I doubt that you'd get an accurate reading at typical domestic flow rates.

You don't need this level of balancing accuracy for domestic systems. The valves would cost more than the radiatiors. TRVs will also alter the flow rates and make nonsense of the balancing. If you need some flow measurement, I'd look at the flow meters used on underfloor heating manifolds. The transparent tube usually gets obscured after a year or two, so they're only useful for initial set-up. I think the Yanks have balancing valves with a flow meter scale attached (Watts?).

[Tom]

Yes, they'r the ones, the D901 looks useful, but at a price no doubt.

Regards Tom

[Phil Addison]

The TRVs should be wide open, or better still take the head off, when balancing. They do not make nonsense of the balancing, and it is important to do it to get an even heat-up of rooms. TRVs do not like high pressure, so in the extreme if you opened all the LSVs and relied on the TRVs for balance, not only would you have uneven warm up, but the first TRV to close would be hit by almost the full pump pressure. It may work some of the time for some of the people, but you are likely to get complaints of early TRV failure and water-hammer.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[Aidan]

systems.

relied

Oh dear.

The OP's query was about flow measuring devices; Tom had mentioned orifice meter regulating valves. My post had added some detail about flow measuring devices.

You seem to have interpreted my post as recommending relying solely on the modulating TRVs and leaving the LSVs fully open. I did not suggest that. I had said that you do not need to use these flow measuring devices to adequately balance a domestic system. I do not see any point in using expensive flow measuring devices to adjust all the flow rates to an accuracy of + or - 5% of the design value, when you will be putting on TRV control heads which are intended to modulate the flow rates. One TRV partially closing will alter the flow rates throughout the entire system. This would make nonsense of all the painstakingly measured and adjusted flow rates.

"....but the first TRV to close would be hit by almost the full pump pressure."

I do not think so. One of us has an inadequate understanding of this subject.

"Tom" wrote:

The D901 is a bare orifice meter, with tappings to measure the pressures upstream and downstream of an orifice, as you'd said. They're usually used with a double regulating valve screwed onto the outlet so that the flow rate can be altered to the required value. The D931 has the orifice meter and DRV in one component.

[Set Square]

Indeed! What I was hoping for was some cheepo non-contact device - along the same lines as as IR thermometer - which would give an *instant* indication of how much you had changed the flow by adjusting the lockshield - rather than having a wait a long time for the modified flow rate to produce a new steady-state tempeerature differential.

Presumably, no such device exists?

[Aidan]

I don't know of any.

SFAIK, the ultrasonic flow meter is the only device that doesn't require fittings in the pipes. The last time I saw one, 10+ years ago, it certainly didn't meet the cheepo requirement.

[Phil Addison]

Yes, and I thought the flow measuring aspect had been thoroughly answered so did not address that.

It is the implication in your post that there is no point in balancing a TRV controlled system, that could give a wrong impression, and I thought needed a "balancing" response, although this point has been debated several times previously.

However well the system is balanced, TRVs simply serve to cut the heat when it is not required. That has nothing to do with balancing, and is just an automatic version equivalent to the user turning down a hand valve on a warm day.

You are quite right that the bit I added that "the first TRV to close would be hit by almost the full pump pressure", and "complaints of early TRV failure and water-hammer" is utter bollox. I withdraw that entirely, as of course, with all valves open, the pump is short-circuited and so the pressure on the first TRV (in fact, all of them) will be LESS not more. I do apologise for that.

On the issue of balancing accuracy, the OP "Set Square", was not suggesting the use of flow measurement as a means of improving accuracy, but as a means of speeding up the process. I agree that it is impractical in the domestic situation for the reasons others have given.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me