balancing sytem with valves on wrong way round

[slingo]

I have an open vented system with 17 radiators. I replaced some of the valves a couple of years ago with TRV's, replacing each main valve. Little did I know that when the house was built 10 of the radiators were installed with the lock shield valve on the feed side of the radiator. The TRV's I fitted are bi-directional.

Question is, is it possible to balance a system like this or will the valves have to be swopped on the radiators that are wrong?

To make matters worst the radiators are connected using micro bore, 8 mm for upstairs and 10 mm for downstairs. The Danfoss trv's I fitted will not simply swop ends as the back nut and olives are totally different. My worry is that if I have to change the valves I will have to renew the micro bore at both ends but there is not a lot of room between the wall and centre line of the rad valve to get an inline connector and an elbow in.

 

[Gasguru]

Doesn't really make any difference which end (although manufacturers make recomendations).

More importantly is not to have the TRV jammed in a corner or behind a door.

 

[croydoncorgi]

Why do you think the system is 'unbalanced'?

With a fully-pumped system and TRVs, even on microbore pipework, pump output should be adequate to get enough flow through all the rads without a lot of tinkering about (after all, once an area is warmed up the TRV will shut and the flows should re-distribute into other areas....).

What's actually going wrong?

 

[Agile]

On microbore the higher pipe resistance is in series with the valves and that will to a large extent perform and automatic balancing action particularly when the microbore is fed from a central manifold with very similar tube lengths.

It creates an analogy to a constant current in an electricial circuit.

Tony

 

[slingo]

I was under the impression that each radiator had to have it's lock shield adjusted to reduce the flow and therfore hold the water in the radiator long enough for it to give its heat into the room. I read somewhere that the outlet water should be 10 deg C lower than the inlet.

The system works fine I just wanted it to run efficiently. But if you guys think it is Ok I am more than willing to leave it as it could turn into the nightmare.

 

[Dan Robinson]

It should be an 11 degree drop for non condensing boiler and 22 for condensing... well thats what I was taught all those years ago.

It can be a black art though...

 

[croydoncorgi]

High flow rate through the rads will NOT have ANY effect on the rad surface temperature.

The objective of adjusting the flow rate is to get the correct temperature drop between the inlet and outlet of each rad. With a conventional boiler, this means (as Dan says) approximately 11 degrees drop Flow to Return.

For a high efficiency condensing boiler, the drop needs to be greater (usually around 20 degrees), so that the Return temperature to the boiler stays below approximately 50 degrees. A condensing boiler CANNOT condense UNLESS part of the heat exchanger stays COOLER than 56 degrees.

It is a Very Bad Idea to let the Return temperature on a conventional boiler go below 60 degrees - if condensation occurs, the heat exchanger will corrode and start to leak very quickly!

You'll gather from this that the rads which need most careful attention are those closest to the boiler and / or in the colder parts of the house - they'll be the ones which work with the TRVs open most, and therefore have most effect on the overall Return temperature.