TBOE radiators in new build incorrectly piped

[Chuck]

Regards to the Delta Temperature.
The Exchanger has flow temperature set to 75 degrees. The return temperature using thermal camera is 50 degrees, I assume this is actually much more like 70 degrees as the incoming temperature was read as 53 degrees.

Don't assume things that are central to the diagnosis of a problem.

The fact that the flow temperature was 'set to 75 degrees' does not mean the flow temperature *is* 75 degrees, particularly if your measurements say it's 53 degrees.

If you don't trust the temperature measurement, get another one made using a proper pipe thermometer. Alternatively, press your thumb onto the pipe and count in seconds how long before it's painful enough to make you pull it off. If you only get to one it's 75°C but if you get to more than ten it's 50°C.

 

[John.g]

Thanks. You guys are brilliant offering great advice. Also you have common sense unlike the cowboys I am dealing with. As we are in our defects period I will fight to get this resolved. I will keep you guys updated but this could take some time.

I asked them how long would it take to swap the pipes and they said 2 hours. So do not understand why they simply won't just swap the feeds around.

Got a few temperatures last night with "old" temp scanner but good enough I think for comparison purposes.

 

[ImranF]

I think a comparism between TBOE and BTOE would highlight what happens if you plumb it incorrectly.

 

[John.g]

Anything in the interest of science.
All temps taken after 40/45 mins, the BOE gave the fastest warm up from cold.

View attachment 37621

 

[chris watkins]

Anything in the interest of science.
All temps taken after 40/45 mins, the BOE gave the fastest warm up from cold.

View attachment 37621

View attachment 37622

I don't supposed you took the flow & return water temps of each one do you John? only what would have told us the heat out put. Interesting to see the heat distribution across them & the mean water temp 51.53 top, 60.93 middle & 59.2 bottom

 

[John.g]

They were pretty close to the sketch, ie, BTOE 65/56, BOE 65/58 & TBOE 64/54.

 

[chris watkins]

They were pretty close to the sketch, ie, BTOE 65/56, BOE 65/58 & TBOE 64/54.

So pretty conclusive without it being carried out in a climate chamber.
BOE = 7, BTOE = 9 & TBOE = 10 & flow was only 64 so would have had the smaller differential between the water to air.

 

[John.g]

Yes, Probably not thermodynamically very accurate but I just averaged all the temps and the BTOE was 51.5C="31.5 deg rad" or 55% output of a 50 deg rad, the TBOE was 59.C="39.1deg" rad or 73% & the best (marginally, apart from the quickest heat up) was the the BOE, 60.9C="40.9deg" rad or 77%.

 

[Chuck]

Yes, Probably not thermodynamically very accurate.

If the flow rate was the same in each case, it would more accurate to infer the emitted power from the fact it's proportional to deltaT. If this is correct, there is only a 10% advantage for TBOE over BTOE at deltaT = 9 °C. The heating engineers the OP is arguing with are claiming TBOE vs BTOE makes an insignificant difference and this result supports them; if the OP's radiators are running at deltaT = 3 °C rather than 10 °C the difference will be even smaller.

 

[chris watkins]

If the flow rate was the same in each case, it would more accurate to infer the emitted power from the fact it's proportional to deltaT. If this is correct, there is only a 10% advantage for TBOE over BTOE at deltaT = 9 °C. The heating engineers the OP is arguing with are claiming TBOE vs BTOE makes an insignificant difference and this result supports them; if the OP's radiators are running at deltaT = 3 °C rather than 10 °C the difference will be even smaller.

I wouldn't mind betting the 3 °C was not as per the design. With these communal systems the heating pant is invariable N.gas powered & capable of condensing so the design should be very much that of the domestic gas boilers system.

 

[John.g]

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?.

 

[Chuck]

I wouldn't mind betting the 3 °C was not as per the design.

I agree. The deltaT = 3, which I inferred from post #20 seems far too low. The flow temperature, if it is 53 not 75 is also too low and is where I'd look. Anyway, I'm repeating myself so I'll shut up now.

 

[SJB060685]

Johng that’s very informative

 

[John.g]

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).

 

[SJB060685]

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.

 

[SJB060685]

Don’t worry I was reading it slightly wrong. I know your numbers are estimates but the output is 77% of 41 not 71%?

 

[John.g]

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.

 

[John.g]

Don’t worry I was reading it slightly wrong. I know your numbers are estimates but the output is 77% of 41 not 71%?

NO, its (31.5/41)^1.3 and not (31.5/41), see above.

 

[SJB060685]

So what does your symbol of ^ mean. Sorry but maths was never my strong point, I’m but a humble Hoover man lol

 

[John.g]

"^" is to the power of, you have heard of "squared", 2 squared is 2x2 or 4 but if you were to do this calculation in a spread sheet, you would enter = 2^2, and so on,

 

[SJB060685]

Yes I get you but my maths wasn’t adding up lol

 

[SJB060685]

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

 

[chris watkins]

On the N.gas designs (with DHW cylinder) I use (70+50/2)-21 (or 22 bathrooms) 39 (38) against the rad manufacturers stated outputs of 50.
Do you think your results would differ much with the higher temps ?

 

[SJB060685]

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.

 

[John.g]

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.

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%