On 17/06/2020 12:50, wrote:
On Wednesday, 17 June 2020 10:48:02 UTC+1, Robin wrote:
On 17/06/2020 00:36, John Rumm wrote:
snip

Good, lets all stop talking about radiator efficiency.

agreed - it's not a good label for what's involved and I shouldn't have
stuck with it

You can talk about overall system efficiency, or radiator power...


and, I suggest, something that captures the way it's not only the
/quantum/ of the power that matters but also /how/ it is transmitted.
Location is (I hope) an uncontroversial example: the Wiki covers how
radiators under windows differ are different from those on internal
walls. That's captured - and quantified - in the "efficiency factors"
in EN 15316[1]. But there is also work which shows size and shape also
matter[3]. You'll not be surprised to learn that (for any given power)
big and tall is best



[1] I don't have the up-to-date ones but were e.g. 0.97 under a window
vs 0.94 on an internal wall.

[3] eg https://iopscience.iop.org/article/1...X/415/1/012034

All hot water radiators output their power almost entirely by convection.

Its typically about 80%/20% at a 70 degree flow rate.

Also worth considering is the effects of the adjacent wall. A radiator
will heat that by radiation, and you will get a boost to the rate of
convection from the "hot" wall.

(also counter intuitively, its common to place reflectors on outside
walls to reduce transmission through the wall - however in doing so, you
lose the convection boost you get from local heating of the wall
surface. It might save energy, but make the room actually feel less warm).


--
Cheers,

John.

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