Relative efficiency of finned vs unfinned rads.

[bripl]

thank you kev i was looking for a diagram,drayton and honeywell as well as danfoss do the trv bigger orifice for the water i think long time since i fitted some

 

[Malcolmkeith]

Fundamentally I can't see why a TRV does not work with a one pipe system. What is the difference between a TRV and a manual valve? I can turn off any radiator with a manual valve without a problem. I actually fitted a TRV to one rad I had to replace which had rusted through and it worked fine, but I notice in the small print for most TRVs that it says suitable for 2 pipe systems so I expect there is a problem -but what is it?

 

[kevplumb]

cos on a one pipe system all that takes the water into the rad is convection

hence the need for a bigger orifice

bripl's explaination makes perfect sense to me

 

[Agile]

There are a few one pipe systems made in copper which have been agumented whilst retaining the one pipe flow.

A useful addition is to fit a gate valve in the flow pipe between each rad connection point. This can be closed slightly to cause some addition flow through the rad other than convection and this will make a TRV more viable.

The TRV manufacturers have to cover themselves and the later TRVs have a pretty high flow resistance and the new models with fancy adjustments must be even worse.

Tony Glazier

 

[Malcolmkeith]

cos on a one pipe system all that takes the water into the rad is convection

hence the need for a bigger orifice

bripl's explaination makes perfect sense to me

You are forgetting the pressure difference along the pipe. According to Myson
"The pressure drop across a single panel radiator is similar to that of an equal length of 15mm copper tube. For a double panel radiator, assume the radiator is two lengths of 15mm pipe connected in parallel. "
Imagine a single pipe system of 15mm diameter with a double panel radiator connected to it (i.e in parallel). There will be more flow through the radiator than the pipe. This will happen with cold water! You don't need heat.