Delta 30 or 60 degrees for radiators?

[solarCH]

Please don't forget that your system still has to be compliant with Part L of the Building Reg's ? (an auto one is a requirement, if a by-pass is required) Leaving a rad without a TRV fitted is only allowed for the room with the room thermostat installed (it is providing the "boiler interlock") & this is to stop conflict between them not so it can maintain a min flow rate in the system.

There is 180m2 of space but all on one level and 2 of the 3 bedrooms have daytime use- the 'true' bedroom has only 1 rad with the TRV set at 16deg. Its hard to justify the cost/ time for an additional circuit for one radiator (8% of total requirement)

Yes, control rad will be near thermo and we there will be an external sensor too.

So, back solutions to run at 50/30 (or 60/40 or 70/50). So I could add an ABV and restrict less the flow across the control rad and the 3 towel holders. Anything else to reduce cowtailing/ cycling?

 

[DirksPlumbing]

Are you talking about the new Stelrad Radical radiators? They look very interesting, but can you see the average installer bothering to adjust the TRV to meet the specific conditions?

These are not a new invention. But they now come preset already and have some additional features like preference to the front plate to cut radiation losses.
Being preset means even if the installer does not bother he automatically has it set nearby the right rate.
Which is smart as the Stelrad knows the output of his radiator and can preselect a flow rate already unlike the manufacturer of external valves.
Kermi, Korado and the lots make those type of radiators since decades. So it was just a matter of time for Stelrad to make them as well. The good thing is that they have looked into it and made it a bit more "fool proof".

 

[DirksPlumbing]

So, back solutions to run at 50/30 (or 60/40 or 70/50). So I could add an ABV and restrict less the flow across the control rad and the 3 towel holders. Anything else to reduce cowtailing/ cycling?

To be fair if you plan to use an A rated pump the ABV should not be fitted but legislation askes for one. So finally you could fit one and just set it to ist highest pressure to fulfil legislation and let the pump and your bypass rad do the work.

 

[DirksPlumbing]

There is 180m2 of space but all on one level and 2 of the 3 bedrooms have daytime use- the 'true' bedroom has only 1 rad with the TRV set at 16deg. Its hard to justify the cost/ time for an additional circuit for one radiator (8% of total requirement)

The (assumed master) bed room you could "zone" with a programmable TRV.

 

[doitmyself]

I agree that the flow rate should be lower, less than 0,5m/s if you want to avoid noise and unnecessary pipe friction losses. At 16mm you can get achieve flow rates of 0,04 to 0,15m/s, well below the recommended 0,3m/s

But a low flow rate can be as bad as high ones as it can allow sludge to settle in the pipes. I don't know where you got 0.3m/s as the recommended velocity, but according to Small Bore heating Systems that's the minimum. The recommended velocity is between 0.3m/s and 1.5m/s. In my earlier post I sized the pipe based on a 1m/s velocity.

I agree that friction losses have to be taken into account. so you may have to go to a larger size pipe for longer runs. However, the point I was making is that most installers do not bother calculating the index circuit of an installation or the flow rates/velocity down each pipe; they just bung in 15mm to each rad and 22/28/35 mm pipe for the main runs and boiler connections.

 

[DirksPlumbing]

The real zone (piped) I had meant for the bathrooms as they might get usage outside the heating period.
There might even be a smaller percentage but you normally would run 100% of the pipework just for 2-3 towels rails /rads. And some radiators might not be shut as well so you are having a lot more losses being cut by this zoning.

 

[DirksPlumbing]

I agree that fiction losses have to be taken into account. so you may have to go to a larger size pipe for longer runs. However, the point I was making is that most installers do not bother calculating the index circuit of an installation or the flow rates/velocity down each pipe; they just bung in 15mm to each rad and 22/28/35 mm pipe for the main runs and boiler connections.

Guilty, that is why valves have been invented decades ago to regulate the throughput in different zones independent of your TRVs which should be used in bigger houses too as too many variables there can upset the flow in a way to have times when certain parts of the house will be cut off no matter how good you calculated or even balanced your system.

 

[doitmyself]

There is 180m2 of space but all on one level and 2 of the 3 bedrooms have daytime use- the 'true' bedroom has only 1 rad with the TRV set at 16deg. Its hard to justify the cost/ time for an additional circuit for one radiator (8% of total requirement)

It seems the DCLG agree with you. See http://www.ukplumbersforums.co.uk/c...nes-new-replacement-systems-4.html#post335423

Zoning is only required if it is cost effective.

 

[DirksPlumbing]

Zoning is only required if it is cost effective.

At the moment I am let to believe that even the use of programmable TRVs is accepted as zoning. Someone knows that for a fact or know that this would not suffice?

 

[solarCH]

But a low flow rate can be as bad as high ones as it can allow sludge to settle in the pipes. I don't know where you got 0.3m/s as the recommended velocity

Uponor Plumbing Tech Install Guide MLCP Jan 2012:
Radiator connection pipe: ≤ 0.3 m/s
Radiator distribution pipe: ≤ 0.5 m/s
Heating main pipes: ≤ 1.0 m/s

Of course, MLCP pipes only go down to 12mm.

 

[solarCH]

I was thinking about the min flow calculation and think we can estimate this using the specific heat capacity of water.

A 35kW combi with a 6,8kW min burn for a 20 degrees jump (say 70/50) gives 6800/(20*1,163) = 292 L/h. The pressure/ motor speed graphs in the manual stop around 200 L/h, suggesting this number is ball-park.