I raised balancing in an earlier thread but still can't get my head around it. I'm quite prepared to believe that I've missed something or got something wrong - but I can't see what it is. If you think that balancing is worthwhile and possible in an evohome system then please tell me where I'm wrong so I can stop thinking about it.
My view of the basic facts:
It's clearly possible to adjust the LSVs to give a 20degC differential with a fixed flow rate pump, with the TRVs fully open, and with a particular water-room differential temperature.
But, as TRVs close or as the rooms heat up this differential setting will be lost.
With an evohome system the HS92s are closing asynchronously by varying amounts, plus the modulating pump is changing the flow rate, plus the rate of loss of heat is changing as the rooms heat. Unless someone can explain to me how balancing can be maintained in any meaningful way in this situation I suspect that the real reason we adjust the LSVs is just to get a balance of flow when lots of rads are calling for heat.
Please explain what I've missed or got wrong!
My view of the basic facts:
- Lockshield valves (LSVs) in simple systems, without TRVs or multi-speed pumps, were set to balance the flow distribution to all rads. LSVs in condensing systems were also set to ensure the temperature of the return water was low enough to get the boiler condensing.
- Water in a rad loses heat in direct proportion to the temperature difference between the water and the room
- Water in a rad loses heat in direct proportion to the time it spends in the rad, and therefore inversely with the flow rate, but the flow also introduces new water
- LSVs are adjusted with TRV/HS92s fully open therefore TRV/HS92s can only reduce the flow thereafter
It's clearly possible to adjust the LSVs to give a 20degC differential with a fixed flow rate pump, with the TRVs fully open, and with a particular water-room differential temperature.
But, as TRVs close or as the rooms heat up this differential setting will be lost.
With an evohome system the HS92s are closing asynchronously by varying amounts, plus the modulating pump is changing the flow rate, plus the rate of loss of heat is changing as the rooms heat. Unless someone can explain to me how balancing can be maintained in any meaningful way in this situation I suspect that the real reason we adjust the LSVs is just to get a balance of flow when lots of rads are calling for heat.
Please explain what I've missed or got wrong!
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