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TBOE radiators in new build incorrectly piped

Discuss TBOE radiators in new build incorrectly piped in the Plumbing Jobs | The Job-board area at PlumbersForums.net

It must be remembered that normally the mean rad temperature is conveniently taken as (flowtemp+returntemp)/2, this in turn infers that there is a gradual fall in temperature between the flow and return which can be seen quite clearly in the sketch in both the BOE & the TBOE cases but not in the BTOE case where several temperatures are only in the 40s. To put it another way, when I average the 15 readings in both the BOE & the TBOE and compare them with their mean temps based on (flow+return)/2, one gets (BOE) 60.9 vs 61 & (TBOE) 59.1 vs 59, very close in both cases.
If one compares these numbers in (BTOE) one gets 51.5 vs 60.5, a huge difference (obviously because of the non linear fall in the actual rad temps).
If one accepts this reasoning, then the BOE is the best performing rad and is a (61-20) "41 deg rad"(partly because of the low flow temp of 65C), the next best is the TBOE, a (59-20) 39 deg rad, almost identical (apart from slower warm up) than the BOE.
The BTOE rad is only a (51.5-20) 31.5 deg rad so its performance using the BOE as the bench mark is only outputting (31.5/41)^1.3, ~ 71% of the BOE output?.
 
I have just cleaned up the sketch, it seems pretty clear that convection just won't work properly in any system with the return on the top. In the BTOE there are 8 readings between 45C and 38C, the flow just seems to flow upwards to the top of the rad and then partially short circuits out the other end whereas in the other two it flows along the top of the rad and then drops down in parallel flow paths and out the return, (makes sense I suppose).
BTOE, BOE & TBOE Rad Temp.jpg
 
John.g how did you arrive at the figure of 71% output in comparison with the BOE? I understand everything but your calculation of (31.5/41)^1.3 ~71%. I’m not an installer, I work with oil fired appliances but I’m keen to fully understand this.
 
Rads are now based on a "50 degree" basis (formerly 60C), this is the mean rad temperature minus a nominal room temperature of 20C, For example if your rad had a flow temperature of 75c & a return of 65C then you would have a "50 deg rad", ((75+65)/2)-20. If you had a flow temp of 75C & a return of 45C ( to get full condensing benefit) then you would have a "40 deg rad, ((75+45/2)-20, you would then have to install a bigger rad(s) to compensate for this and all the rad manufacturers have correction tables, I don't bother looking at them because I figured out (from the trend line on a spreadsheet) sometime that they are using (generally) a correction factor of ^1.3, so the correction factor for your rad is,(50/40)^1.3, 1.34 which means that the rad would have to be 34% "bigger" or if you installed the rad based on 50 degrees then it would output only, (40/50)^1.3, 75%.
The reason I used 41 degrees as the base is because the boiler had its set point at 65C which resulted in my rad(s) being only a "41deg"one so I just compared the output of the BTOE rad based on this. I could have and maybe should have corrected both of them to the 50 deg standard, this would equate to outputs of 77% & 55% respectively to the BOE & the BTOE rads so the BTOE rad would still output (55/77), 71% of the BOE one as stated above.
 
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Based on your calculations I’m arriving at the same answers, just doing it differently lol. Like I said I’m not an installer, I service, repair and commission oil fired appliances. I’ll leave the plumbing to someone who wants it lol
 
Im keen to see Johns answer to your question Chris. Like I said I don’t install, just service oil appliances. However I always went by the formula of flow temp is say 70, return is say 50, so average rad temp is halfway between. Then minus room temperature of 21 gives the final figure. Similar to how you guys have said you do it above.
 
Yes, this is quite correct in the case of a BOE or a TBOE plumbed rad but is not (IMO)) the true mean temp in a BTOE (wrongly??) plumbed rad.
BOE Two Outputs.jpg


Re Chris's query above, I can,t really get higher than 70C flow temp as I have a oil fired boiler which has a max set point of 75C and a hysteresis of 10/12C so hard to get a steady flow temp for readings but they are quite reasonably correct.
His "39 deg rad" should emit 72.3% of a "50 deg rad" and the "38 one "will emit 69.9%
 
ImranF said:
Can anyone recommend a cheap infrared thermometer that I could use to measure the temps. I might go into another flat and compare the temps of the RADS.
Click to expand...

Plumb Center are doing a Testo 830-T2 infrared thermometer for £50 + vat currently.
I have a more expensive Testo model
 
I agree, I will focus on the fact that the flow temperature is 53 degrees where it should be much higher.
Then they can rectify the fact that they have piped it incorrectly.
They also need to get rid of the air in the system.
When engineer was on-site he showed me the heat exchange unit had temp of 80 degrees but I believe that was the incoming hot water from district plant.

Anyway I will order a thermometer to take readings of all my rads.
Will then see if neighbor will assist to provide theirs.
 
One more thing I can recollect in my mind is when the first visited the flat last year, they did mention they moved something to the highest setting. It could have been the pump or it possibly could have been the thermostat for the heating in the heat exchange. The thermither range is between 35 and 75 degrees. Maybe there could be a possibility that the thermostat setting is still stuck on the original setting or maybe it's not functioning correctly. I can't turn it as it seems to be stuck in its current position which is at the highest setting.
 
If the rad inlet temperature is 75C then you won't be able to keep your hand/finger on this for very long, if its = or < 53C then you will be able to.
 
ImranF said:
Ok I have a response.
They contacted the manufacturer stelrad and they told them they need to swap the flow and return.

I have also asked them to resolve the incorrect flow temperature as it should be much higher.
Click to expand...

Good result, do hate how these developers take the pish so badly, you really shouldn't have to fight that hard for them to provide a pre agreed upon service/result!
 
To be honest, most people wouldnt even check. As long as their rads get hot they would be not realising there is a problem.
Anyway they also have to resolve the fact that there is a lot of air in the system. Not sure how power flush is going to solve it. Assume their must be air ingress from somewhere.
 
ImranF said:
Anyway they also have to resolve the fact that there is a lot of air in the system. Not sure how power flush is going to solve it. Assume their must be air ingress from somewhere.
Click to expand...
Check the inlet side of the pump & pipe work until you get to the expansion vessel.
What is the pump set to ? (let me guess fixed speed III)
 
That's interesting.
Perhaps the developer looks after the secondary circulation as well? and has a flow meter plus the flow and return temps to calculate the energy usage for each user billing purposes.
 
If they are serious about accurate energy consumption then they would have to measure the deltaT as well. Is the bill presented as kWh/month? Or what and purely for comparison purposes you might like (or not) to post one period's usage.
Any circ pump visible there?.
 
They provided pay as you go meter. This is only for hot water and heating. I have standard meter for electricity.

For months where I don't use heating it costs £20 a month. During winter it cost me around £60 a month with the inefficient setup.

Basically this is for a family of 4.
Also I know they take £10 a month in service charges to cover for the gas in the central plant and for maintenance of everything including the unit in the flat.

This seems far more expensive then gas boiler.

I will look at the Meter and check the KW usuage. The rate is at 7.9p per unit used. I believe there is a daily charge of 20p a day. So around 6 to 8 KW a day usuage.

I am quite Fortunate, apparently one bedroom flat was paying more than us to assume something is wrong with his meter.
 
You are doing very well, I would have expected at least ~ > 30 kwh/day for HW+CH. If you are/were using say 7 kwh/day for HW only; this equates to a usage of 30 ltrs/person/day @ 60C or 50 ltr/person/day @40C, pretty normal/lowish usage IMO.
 
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