Top Bottom Same End

[sharpener]

Is this a sensible way of connecting a radiator? We have a restricted space which will just take a 1400 wide rad provided both the valves are at the same end and the other end has blanking plugs.

 

Is this reasonable or will it result in such poor water distribution that we would be better off having a 1200 with TBOE connections?

 

Rads in either case will be 600 mm high K2.

 

I am mindful that radiator performance figures are usually quoted for Top Bottom Opposite End which of course hardly anyone does in practice. So I wonder if TBSE is any worse than having both connections at the bottom which is a common practice.

[Bonner]

It might work only if the flow goes in at the top but I would go for a smaller radiator connected at opposite ends, which most likely to work effectively.

[sharpener]

 

  On 12/06/2024 at 05:47, Bonner said:

It might work only if the flow goes in at the top but I would go for a smaller radiator connected at opposite ends,

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That is my preferred option, in either case the flow will go into the top to avoid having the TRV at low level obstructed by furniture. System will have a powerful pump (in Vaillant 12kW HP) but I am still concerned about the flow reaching the far end.

 

However the installer is keen to fit the very largest possible rad.

 

Does anyone know the performance penalty for the usual BBOE connection compared with TBOE for which the charts are given? 10% springs to mind but I have no idea of the basis for it.

 

OTOH this link states BS EN442 requires rads to be tested using TBSE. It allegedly gives 2% more output compared to BBOE. Not what I thought but if true it will in fact be slightly better.

 

Maybe @JohnMo will know, as with many other things?

 

[SimonD]

The multiplication factors for rad outputs and connections are:

 

TBSE 1.00

TBOE 1.05

BOE 0.96

 

You're fine with TBSE

[JohnMo]

This video at about 12 minutes in says 5% uplift as TBOE, just the same as @SimonD - just beat me.

https://youtu.be/OzSEQ77t20I?si=RX9qyHswllF3Q9cx

Edited June 12, 2024 by JohnMo

[sharpener]

  On 12/06/2024 at 11:05, SimonD said:

TBSE 1.00

TBOE 1.05

BOE 0.96

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Here are the actual figures.

 

Installer's Heat Engineer emitter schedule has 1172W for the 600 x 1400 with MWT of 47.5C. I don't know what conditions the s/w assumes, maybe TBSE if that is in the BS/EN.

 

Under the same conditions the 600 x 1200 will  be approx 6/7 of that so 1005W. But I can plumb this one as TBOE so it wiil be 1.05 x as much, 1055W, and recouping some of the loss from the smaller length, I will put this to the installer as it will look better in the room.

 

Useful discussion as I realise another bedroom also has a TRV which will be easier to get at if TBOE and as a bonus 9.4% more output over BOE (so my 10% upthread was very nearly right!).

 

Thanks both, invaluable input once again.

 

 

[SimonD]

  On 12/06/2024 at 22:30, sharpener said:

Heat Engineer emitter schedule..I don't know what conditions the s/w assumes,

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I've used the Heat Engineer calculator once for a new installation and don't recall there being any input for connections, but that was about a year ago now. I'm not a fan of the software - I did all my calculations for the system and then after a couple of weeks it all disappeared from my account with no records available. Won't be using it again as I also didn't receive any reply from one of my support messages which was actually about why my payment wasn't going through when i was trying to set up a subscription! I prefer my own spreadsheet which not only has a rough calculation section for strawman design which is surprisingly accurate, but I have complete control of every input I want and can really play around with it as I wish.

[markocosic]

The trv might actually work too. (yhey sense air temperature, so want to be higher in the room than they are usually installed)

[John Carroll]

Here are my actual readings. The BTOE is by far the worst, even though the (flow+return)/2 was 60.5C, the actual mean temp was only 51.5C.

 

[Boab]

I was looking at your readings John but the BOE don't look right. The water in is 64 and the water out is 58 giving a difference of 6, not 11 as you state. 

And regardless of the temp readings at various points on the rad, wouldn't the one with the biggest temp difference from flow to return be the one that is emitting the most heat. So TBOE would be the winner? 

[marshian]

  On 12/02/2025 at 06:24, Boab said:

And regardless of the temp readings at various points on the rad, wouldn't the one with the biggest temp difference from flow to return be the one that is emitting the most heat. So TBOE would be the winner? 

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The radiator with the highest mean temp would be the one that emitted the most heat (that might not be the highest difference)

[SimonD]

  On 12/02/2025 at 06:24, Boab said:

So TBOE would be the winner? 

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Yes. Like the figures I posted earlier, this provides the best output. Radiator manufacturer figures are usually based on Top and Bottom Same End.

 

But remember that rad output depends on the air temperature differential too.

 

So for example with a flow temp of 70 with return of 50 you have a mean water temp (mwt) of 60. Mean water - air temp differential is then mwt - air temp so output differences between 21 degrees and 16 degrees are as follows:

 

60-21 = 39

60-16 = 44

 

To get the actual radiator output you then divide this by the manufactures delta, usually 50 so:

 

39/50=0.78

44/50=0.88

 

This means that with a room temp of 21 the radiator output is 78% of catalogue and with 16 degrees it's 88%

 

Which clearly shows that even just 5 degrees has a big impact on output.

 

You then take these results and multiply by the connector emissions factor which for TBOE is 1.05 or 0.96 for BOE

 

Plus there are other factors used for the whole calculation.

 

[John Carroll]

You should use the exponential 1.3, thats why they speak of weather compensation curves even though heat loss is linear but rad output isn't.

So its (39/50)^1.3 = 0.724

and    (44/50)^1.3 = 0.847

not hugely different to the above but does become significent at low rad mean temps.