Does a radiator like this make sense?

pieroabcd

On the TRV that I installed last year I had to set the right mode, iirc with a pin. 
I'll check the others

pieroabcd

Is it correct to say that the reason why closing the return valves make the hot water reach the radiators downstream (like at the second floor) is that the water that can't leave the radiator occupies all the available spaces, forcing the hot water from the boiler to go somewhere else?
After all water is incompressible. 

ThisIsWeird

pieroabcd said:

Is it correct to say that the reason why closing the return valves make the hot water reach the radiators downstream (like at the second floor) is that the water that can't leave the radiator occupies all the available spaces, forcing the hot water from the boiler to go somewhere else?
After all water is incompressible. 

Not sure I follow.

But in essence, if you have a too-open rad, especially (but not exclusively) near the boiler, it'll allow too much hot water to circulate straight back to the boiler, still hot, and the boiler will begin cycling in order to reduce its output. Boilers measure both the flow and return, and modulate accordingly. A too-open rad will give it a hot return, so it'll modulate down - and starve all the other rads.

Albermarle

ThisIsWeird said:

pieroabcd said:

Is it correct to say that the reason why closing the return valves make the hot water reach the radiators downstream (like at the second floor) is that the water that can't leave the radiator occupies all the available spaces, forcing the hot water from the boiler to go somewhere else?
After all water is incompressible. 

Not sure I follow.

But in essence, if you have a too-open rad, especially (but not exclusively) near the boiler, it'll allow too much hot water to circulate straight back to the boiler, still hot, and the boiler will begin cycling in order to reduce its output. Boilers measure both the flow and return, and modulate accordingly. A too-open rad will give it a hot return, so it'll modulate down - and starve all the other rads.

I presume as well, if a radiator has a NOT too open valve, it can only physically allow a certain amount of hot water flow through it, thus allowing more hot water flow to carry on through the system to the rest of the radiators. 

For sure if you have too many radiators with the lockshield valves too open, you can find the last one or two radiators in the system taking a long time to heat up, presumably because the hot water flow has got too weak. I suppose an easy solution would be to whack the pump speed up to full, but that puts strain on the pump/system and can be noisy.
Better just to balance the system better, even if only with the basic 'hand on the radiators' check to see how quick they warm up ( apologies to the purists !) 

pieroabcd

The delta of 12 degrees should be while still heating at not yet at temperature or when the radiator is fully hot at the touch?
Tonight I did a quick preliminary test. While heating (still lukewarm at the touch) the delta was around 11-12 degrees until the flow temperature reached 48 degrees. After that the difference fell by a lot: 52 degrees on the flow (reached slowly) and 50 on the return. The lockshield was at 1/4 turn, so I closed to 1/8, but even after 20 minutes the difference was the same.
The full balancing will have to wait a few days, unfortunately. 

FreeBear

The ΔT should be roughly flow temp x 0.3

So when at full temperature at 52°C, the return should be ~36°C. No good trying to balance the radiator(s) as the system is getting up to working temperature. And as mentioned up thread, if you can't get a ΔT15°C, then the pump speed is too high.

ThisIsWeird

pieroabcd said:

The delta of 12 degrees should be while still heating at not yet at temperature or when the radiator is fully hot at the touch?
Tonight I did a quick preliminary test. While heating (still lukewarm at the touch) the delta was around 11-12 degrees until the flow temperature reached 48 degrees. After that the difference fell by a lot: 52 degrees on the flow (reached slowly) and 50 on the return. The lockshield was at 1/4 turn, so I closed to 1/8, but even after 20 minutes the difference was the same.
The full balancing will have to wait a few days, unfortunately. 

It must surely be when the radiator is fully heated, and CH fully running.
Don't forget that when you tweak the l/s, any response will be sloooow. It's still getting heated all the time, but just not as quickly. 
Perhaps, with these rads that are clearly getting the most powerful supply, you can shut them off via their TRV for a half hour until they cool, then fully reopen and let it get back to temp again - that'll tell you if the l/s tweak was enough.
Yes, it's surprising just how near-closed some l/s will need to be.

Chickereeeee

Albermarle said:

Chickereeeee said:

EssexHebridean said:

We have a pair of them in our kitchen-diner and find they work really well for us - it’s a 12’ x 21’ space with 2 windows, patio doors, and 3 velux roof lights, high ceilinged too, but the rads are surprisingly effective. I too was concerned before we bought the house that they wouldn’t actually warm the place up and were more for show, but we’ve had no issues. Ours are black - no idea if that would make a difference - and ai have noticed that they never get really hot, but certainly still heat the room well. 

ETA - ours are taller than yours - roughly 7’ tall. 

Colour makes a difference. The worst  are chrome, which reduce heat output by about 40%. Black gives the best heat output.

Interesting.

I can only assume that the chrome finish is acting as a sort of semi insulator. In which case the radiator would use 40% less heat energy from the circulating hot water, otherwise you would be breaking the laws of physics !

No, different colours and textures have different emissivity for thermal radition. Chrome radiators are the 'worst' for output, matt black the best. No laws of physics are broken: it is similar to radiators with fins have a higher output than radiators without fins!

(If you doubt, look up a radiator design which is available in both black and silver, and compare stated outputs).

pieroabcd

I imagine that it's the reason why ovens are always black inside 

pieroabcd

I took only  partial  measurements for lack of time, but it's been quite revolutionary so far.



Before the test: all flow valves were mostly closed, except at the second floor where flows and returns were fully open. The return valves without TRV were closedi in large part, fully open at the second floor. The TRV were set at 3.

Now: all flow valves are fully open (except the T21 in the study that is back at 3 because it was too hot). The return  valves without TRV (taps) at the ground floor are mostly closed, 1/4 of turn only. The TRVs are set at 3.
The water temperature was the usual 60 degrees.

The temperature differences are not really satisfying, but I've stopped measuring them because after 30 minutes all radiators were HOT, even at the second floor. The only problem there is the cold bottom part of the radiator. Maybe sludge.

I've finally seen the TRV make a real difference. In the past they didn't, maybe because the flows were almost closed (opened only by 1/4 turn or so)? It's also fast: 5 minutes after turning down the TRV the rad temperature had adjusted.

The delay between the radiators coming up to temp is much lower than before. Now the columns ones at the ground floor heat up more or less at the same time and at the same temperature. The fastest of course is huge T22 in the kitchen.
The T22s at the 1st floor got very hot too, as fast as the others. In the past due to my previous meddling they got lot less hot, especially the one in the second bedroom that is slightly smaller.

Can I leave the flows fully open as they are now or could they create problems? The returns would stay as they are of course.

Maybe i could even lower the temperature to 55°.
The TRVs have no arrows.