Wiser iTRVs in flow or return?

[njknh]

I remember reading somewhere that the Wiser iTRVs have to be installed on the flow side of radiators although it does not state that anywhere in the Wiser documentation as far as I can see. When I asked Schneider about this they were quite categoric in stating that they could ONLY be installed on the flow side, but provided no further expanation and were non-committal about updating their documentation.

In my house about half the mechanical TRVs are on the return side & the valve bodies are all bidirectional. I don't know if my installers were particularly lazy or whether this is typical given the availability of bidirectional TRVs. Anyway, I did experiment with the Wiser iTRVs in both the flow and return and I couldnt detect any real difference - I did wonder if the iTRVs temperature measurement may be slightly better on the cooler return side, but I couldnt really see any reduction in temperature measurement error.

Do any other users have any experience of fitting iTRVs on the return side of radiators?

[PhilHornby]

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@njknh wrote:

I did wonder if the iTRVs temperature measurement may be slightly better on the cooler return side

I don't know if it would necessarily be that much better, but it might be a better match for whatever algorithm they've implemented?...

Do any other users have any experience of fitting iTRVs on the return side of radiators?

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I do - but they're in rooms that have RoomStats as well. I only rely on the iTRVs in rooms where precise temperature control is not particularly important: the Utility Room, the Hallway, the missus's hobby room - that sort of thing 😉 )

[SAtewart]

I have two valves on the return legs of the radiators. When the valves approach set point (i.e. driving the valve itself to a small flow opening), I experience a hammering action or oscillation that is annoyingly loud. You can prove this to yourself by adding a few degrees to the set point of a hammering valve.

The hammering stops but at the expense of tight energy efficient control. 

There seems to be an opinion that these valves drive fully open or fully shut. I really do not believe this to be the case, rather the iTRV motor modulates its closure to provide proportional with integral control of the temperature. (Look up PID control here link ). I'd agree with Phil Hornby and others that the iTRV temperature values are not accurate but the error seems to be largely constant so you can play with set point values to achieve real world room comfort.

I am resigned to moving the valve bodies to the supply side of the rads at some point during the summer.