On 27/10/2024 17:57, PeterC wrote:
> Toolstation is selling Drayton TRVs that are self-balancing.
Hmm, not seen those before - quite a good idea if they are reliable,
> Seem to be for
> low flow temperatures as the manual goes up only to 20C Td.
Not sure I follow the logic? The temperature drop or "delta"(Td) across
the rad is not directly related to the flow temp. Normally a system is
balanced to achieve a similar drop across each of the rads. With
traditional (high flow temp) boilers, that was normally about 11 deg C.
This prevented the primary water's return temp being dropped too far,
since that could allow condensation of water out of the flue gases to
occur, and that would cause rapid corrosion of the boiler.
With condensing boilers you don't have to guard against allowing
condensation of the flue gases in the boiler (in fact you want quite the
opposite since you get more boiler efficiency with larger return
temperatures). Hence condensing boiler installs tend to be tuned for
larger a larger Td. That usually means a lower flow rate through each
rad. In turn that means lower output from the rad. One of the reasons
that larger rads are preferred for condensing boiler systems.
> The manual is
> rather complex - I'm sure that some here will understand it though.
> https://www.toolstation.com/drayton-auto-balancing-rt414-trv/p30659
It seems to make sense once you realise the he "Q dot" column is
nominal the power output of the rad. This is one of the specs that the
manufacturer of the rad will tell you. (note they may quote more than
one value for different flow temp and Td values)[1].
So decide what Td you are going to use for your wattage radiator, then
lookup the valve setting in the table.
So say you have a rad with a 1kW output at a Td of 15 deg, and you plan
to run the drop at that 15 deg, then you need a valve setting of 6
according to the table.
[1] If you don't know the value for your rad, just look through a online
catalog of rads and find those with a similar size and construction as
yours and see what figure they quote for that.
--
Cheers,
John.
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