Ive got a large, heavy & expensive but otherwise ordinary radiator to which I want to fit a Honeywell "Rondostat" digital TRV.
Sadly it has an LED display that can't be read with the 'stat in the traditional location at the bottom.
The question is if I re- arrange the hot water inlet to use the top tapping will the bottom half of the radiator still get hot ?
DerekG
Diagonal connections will give you the maximum heat output. The manufacturers heat ratings are all for diagonal connections because it makes them look more efficient.
Diagonal connections are the traditional way radiators are connected. Using the two bottom connections is just done to make the pipework look neater. And save a bit of pipe.
Does it make any difference whether the water goes in at the top and out the bottom, or vice versa?
Google suggests inlet at the top is traditional; with inlet at the bottom you can get a cooler lower corner at the other end as the hot water rises as it comes in.
And it turns out that top and bottom at the same end is actually even better than diagonal (and is used for quoted ratings). But the effects are small in modern systems.
ICBW but it seems to me it'll be better with hot fed in at the top. That way the top of the radiator will be hottest, and the outlet at the bottom coldest (which you want for boiler efficiency) and you'll also have the advantage of a counter current flow between the air and the water: the air will rise and be coolest where the rad is coolest, and hottest where the rad is hottest.
Andy
No difference at all. The outlet has to be at the bottom, but the inlet can be anywhere. If you feel a radiator with inlet at the bottom, you will see the hot water rises by convection to the top in the first vertical channel. It makes no difference if this happens inside the radiator or if you pipe it to the top outside the radiator.
The only time the inlet must be at the top is for a gravity fed system (no pump), to generate the dynamic pressure difference in the height of the radiator which generates the gravity flow.
When you are using top and bottom connections the (hot) flow must be at the top and the return must at the bottom. The logic behind this is that hot water entering at the top loses heat progressively and falls to the bottom of the rad where it is pumped out on the return.
If you reverse this then hot water entering at the bottom rises immediately (in the first few vertical channels) to the top of rad where it is pumped out (still hot) on the return. The result is a cooler than normal surface temp on the lower part of the rad resulting in reduced output.
This applies to both Top Bottom Opposite End (TBOE) and Top Bottom Same End (TBSE) connections.
This needs to be clarified as it doesn't fully answer GB's question. I once got a TIBO the wrong way round and I got a hot bottom entry area and hot at the top and everywhere else cold. I cannot stress that if choosing a top connection, it must be on the flow side and the exit must always be a bottom connection.
yes. hot water must go in at the top and out at the bottom. Also the connections should ideally be diagonally opposite each other (e.e "top left and bottom right", or "top right and bottom left").
Robert
Use more lube next time.
MBQ
More bollocks.
TBOE was traditional, but only whilst gravity circulation was in use. With any pumped system there is very little difference in the flow rates between TBOE and BBOE. The manufacturers' radiator ratings will be done with the pipe arrangement specified. There should be correction factors for other temperatures.
Not according to Faber & Kell's Heating and Air Conditioning of Buildings:
TBSE = 1.00 TBOE= 0.97 to 0.95 BBOE = 0.78 to 0.84
I am interested to find that TBSE is better than TBOE.
Robert
I think the book is dated and recent measurement won't support that. I saw figures (in the CIBSE magazine ISTR) circa 1984 that said BBOE > TBOE, but think I've seen contradicting numbers since. I don't think it's a precise s cience and the differences are marginal.
Why? How did the water pass from the hot bottom to the hot top, without wa rming the area of the radiator between them?
The head provided by a pump would be many times the head generated by gra vity circulation, so the water will still flow through the rad if connected bottom in top out. I can't imagine why anyone would intentionally do that, but it should still get hot and emit heat.
warming the area of the radiator between them?
gravity circulation, so the water will still flow through the rad if connected bottom in top out. I can't imagine why anyone would intentionally do that, but it should still get hot and emit heat.
The hot water will flow in the bottom, straight up the first channel, and out of the return (passing along the top if it's on the opposite side). The water in the rest of the radiator stays cold, and doesn't circulate, and most of the radiator remains ineffective.
warming the area of the radiator between them?
It warms a little bit of the vertical, not all of it. As FredXX found.
Andy
Thank you for expanding the TLAs since I couldn't quite work out where the Billion Barrels of Oil Equivalent (BBOE) fitted into the topic ;-)
Cheers
Dave R
TLAs? FLAs!! Surely?
ETLAs.
warming the area of the radiator between them?
So FredXX says, but I am asking the company to apply their wisdom and say why that should be; since I don't think it would happen unless there are some other factors involved. I have spent a lot of time designing, commssioning and balancing fluid systems. I can't see it happening, unless there's something else happening.
It is plausible with TBSE connections,
It is unlikey with TBOE connections. If you look at a TBOE radiator, there are equal flow distances between the inlet and outlet connections, regardless of which vertical channel the water passes through. You would expect there to be equal flow rates through all of the radiator channels, regardless of which connection was top or bottom.
The things that might cause it to happen, IMHO, are; radiator with some channels obstructed with rust or corrosion products (they often are); second-hand radiator with internal baffles/blanking; radiator airlocked; TBSE connections, especially with a CI sectional radiator (big waterways); CI radiators generally (negligible hydraulic resistance).
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