TBOE radiators in new build incorrectly piped

[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.