Auto-balancing TRVs

There are tables or options in the app for 10, 15 and 20 degree C (Kelvin) temperature differences (flow and return temperatures)

I have the Danfross equivalent and watched a few Youtube videos and downloaded their installation/setting app to gain an understanding before buying. As with the Drayton version the lockshield is left fully open and the valves must be fitted to all radiators in the system. You leave the TRV head off the bypass radiators and screw on the cap to leave the pin in the open position.

You may get extra info by watching a video on the Danfross equivalent

Hmm, not seen those before - quite a good idea if they are reliable,

Not sure I follow the logic? The temperature drop or "delta"(Td) across the rad is not directly related to the flow temp. Normally a system is balanced to achieve a similar drop across each of the rads. With traditional (high flow temp) boilers, that was normally about 11 deg C. This prevented the primary water's return temp being dropped too far, since that could allow condensation of water out of the flue gases to occur, and that would cause rapid corrosion of the boiler.

With condensing boilers you don't have to guard against allowing condensation of the flue gases in the boiler (in fact you want quite the opposite since you get more boiler efficiency with larger return temperatures). Hence condensing boiler installs tend to be tuned for larger a larger Td. That usually means a lower flow rate through each rad. In turn that means lower output from the rad. One of the reasons that larger rads are preferred for condensing boiler systems.

It seems to make sense once you realise the he "Q dot" column is nominal the power output of the rad. This is one of the specs that the manufacturer of the rad will tell you. (note they may quote more than one value for different flow temp and Td values)[1].

So decide what Td you are going to use for your wattage radiator, then lookup the valve setting in the table.

So say you have a rad with a 1kW output at a Td of 15 deg, and you plan to run the drop at that 15 deg, then you need a valve setting of 6 according to the table.

Both Drayton and Danfross have associated apps where you can enter the size and type of radiator to give the valve settings and show the radiator output for your chosen feed and return temperatures. The type of radiator is selected by diagrams showing panels and fins as well as being identified by type (type 11, type 21 etc.). In general, if you input the same sensible feed and return temperatures for all radiators and you enter the correct type and size the resulting valve settings should give you a balanced system.

Not necessarily essential, but for sanity checking* it helps to know the heat loss of each room so that when the app indicates what the radiator outputs you can see if it matches the heat loss of the room for the worst case winter days when the outside temperature is close to 0C.

• and for some understanding what heating you will get if a system designed, and the radiators sized, for a 75C flow and a return of 64C is now run at flow of 60C, or with a ASHP with a flow of 40 to 50C. The app will show that your 1kW radiator is now perhaps only a 0.3kW radiator with a much reduced flow temperature.

PeterC snipped-for-privacy@homecall.co.uk> wrote in news:ek544ukxj7m.17ypav7um38ze$. snipped-for-privacy@40tude.net:

Weirdly there's nothing in the Drayton documentation that describes these valves as automatically balancing. The balancing process described in their recommended TRV Commissioning guide (D34-11 TRV comissioning.pdf) sounds exactly like a manual balancing procedure except that it carried out on the RT414 TRV valve end itself rather than at the lockshield end. The extra complication is that the TRV head has to be removed in order to adjust the balance which it does not need on a conventional balance. They claim that the balance is not lost during maintenance but it would be my practice in any case to record the number of turns open on the lockshield before doing anything else. In addition I'd challenge anyone not to lose the special balance adjustment tool before the next time it is needed. IMV an unnecessary complication for a relatively straightforward job.

The main idea of these valves is to save the installer time as the system can be balanced based on the paper design and without having to put hot water through it first.

The lockshield valve on all radiators is left fully open.

The only difficult to control variable is if you have weather compensation and so are not running consistent flow temps. But since that has most effect in the autumn and spring it probably matters less anyway.

Not only that, it should maintain balance when some rooms are up to temp and their TRVs are shutting down - changing the flow resistance through that part of the circuit.

John Rumm snipped-for-privacy@nowhere.null wrote in news:vfoors$14qdc$ snipped-for-privacy@dont-email.me:

How is their operation different from any other kind of manual balance? I can't see anything in the data that suggests there is anything more automatic in these valves than in any other TRV controlled and properly balanced radiator.

It seems that they have two throttling mechanisms, a primary dynamic flow regulation that maintains a constant flow rate across the rad, and a secondary TRV style temperature regulation. The required flow rate is calculated to provide enough power to match the output of the rad, hence it is preset based on the rad size and desired Td. So unlike a fixed position lockshield setting, the flow rate regulation can open or close in response to dynamic pressure changes - at least up until the point where the thermostatic action takes over and starts to reduce the flow rate to below the set point, so as to reduce the output of the rad.

The difficulty with manual balancing is that changes made at one rad influence the flow rate at others, because each will see a pressure change based on the parallel path resistance of other rads. Hence why it is quite time consuming to get a good balance manually as the lockshield settings play off against each other.

John Rumm snipped-for-privacy@nowhere.null wrote in news:vfpdc3$18ej6$ snipped-for-privacy@dont-email.me:

Yes I get it but am not sure how effective it will be. It is, after all, a very small valve body to have anything really clever in it. Will welcome feedback from users once a few systems have been installed with them and they get some tangible results.

That said, there are others at it too, Danfoss with the more unwieldly looking RAS-B2 TRV and Gamper - FloControl with their awkwardly named Vario-DP Pressure Independent Radiator Valve System.

The other factor is whether this is an entirely desirable situation:

1. Dynamic balance TRVs maintain the most efficient flow for the rad type & drop but at the lower end of demand the reduced system flow causes the automatic bypass to operate resulting in a return temp rise and boiler cycling.

-or-

1. Manual balance rads with TRVs starting to reach demand temperature. Reduced flow in areas of satisfied demand force more flow to other areas perhaps reducing temp drop efficiency but resulting in a quicker temperature rise in the remaining areas and earlier overall demand temp satisfaction. Poss resulting in less boiler cycling.

-or-

1. Would a modulating pump serve the same purpose.

I feel few would have the nouse to understand which would be more beneficial.

ps: Drayton are doing the TRV4 with auto-balance too:

I expect it is basically just an adjustable pressure reduction valve. You set a value, and it then "trims" whatever pressure is on its input to the preset limit.

Indeed - while is is a nice idea, I am not sure what the payback time would be at >40 quid per valve.

The flow should not be any less than with a manually balanced system I would have thought? (unless the TRV part is already throttling as the rooms are near to set temp)

The the flow regulation would reduce the "boost" effect seen on rads that are not up to temp. That could be good or bad depending on a number of factors.

Partly perhaps, it will respond the many TRVs shutting for thermal reasons, and prevent the bypass opening, but would do nothing to address unequal flow through an unbalanced system.

(weather compensation probably does as much or more than a modulating pump)

Well that is true of most heating systems (and many heating system installers!)

Yup saw that on SF or TS...