thermostatic return valves on rads?

StephenB_2

Hang on. You get better regulation of the room temperature if you put the TRV at the return/cold end of the radiator, but it's not because you 'restrict the flow out of the radiator concentrating the heat inside the rad, as opposed to restricting the flow into it' as per moneysavingplumber.

If you put it at the feed/hot end of the radiator, a local combination of convected and conducted heat can fool the TRV into thinking the room is warmer than it is. You can end up with just enough flow for the TRV to keep itself toasty, with most of the radiator cold and the room colder than you want. You can't get this effect with the TRV at the cold end of the radiator.

SJB

moneysavingplumber

StephenB wrote:

Hang on. You get better regulation of the room temperature if you put the TRV at the return/cold end of the radiator, but it's not because you 'restrict the flow out of the radiator concentrating the heat inside the rad, as opposed to restricting the flow into it' as per moneysavingplumber.

If you put it at the feed/hot end of the radiator, a local combination of convected and conducted heat can fool the TRV into thinking the room is warmer than it is. You can end up with just enough flow for the TRV to keep itself toasty, with most of the radiator cold and the room colder than you want. You can't get this effect with the TRV at the cold end of the radiator.

SJB

What you say may be true in theory, and I have heard the theory before, but it is the effect of cranking down the lockshield at the flow side of the radiator in an attempt to achieve the correct differential that concerns me, as when the TRV is fully open at the return end with the lockshield restricted at the flow end, it has to have a different effect than the opposite arrangement would. As placing a restricted LS valve on the inlet to a cylinder coil would surely reduce the temperature of the water too early, as opposed to putting it on the return once it has been through the coil.

I'll make some technical enquiries and see what is said, but I may be wrong, it's happened before :rotfl:.

Just as an update, Energy Savings Trust Documents CE29 and CE30 don't specify a preference, it just informs that some are bi-directional and some not but all the schematics illustrated in the document do show the TRV on the flow side but that may just be for tradition's sake.

StephenB_2

Just to be clear, I'm more than happy to agree that some TRVs have a preferred direction of water flow. I'm just arguing that they regulate the room temperature better if placed at the cold end of the radiator.

As for your example of the coil, [EDIT that looks a bit combative, which was not my intention - I mean something like "to turn to your example of a coil"] the primary purpose of a lockshield valve is to restrict flow, and IIRC it doesn't make any difference from a 'thermal' point of view where in the circuit it is. There may well be another 'best practice' or 'tradition' reason for putting it in a particular place.

SJB

moneysavingplumber

StephenB wrote:

Just to be clear, I'm more than happy to agree that some TRVs have a preferred direction of water flow. I'm just arguing that they regulate the room temperature better if placed at the cold end of the radiator.

As for your example of the coil, [EDIT that looks a bit combative, which was not my intention - I mean something like "to turn to your example of a coil"]
SJB

No worries, I've sent you a private to continue this discussion before we get told off for arguing in public and not helping the OP .