Posted by: @bobtskutter

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Swapping the radiator for a fan coil might not give you additional heat output because it's not the radiator that's causing the "restriction".

Absolutely, I am very aware of that! Moving to a fan coil is an (major) aesthetic improvement, but only once I know it will have adequate flow.

I am still trying to think of a way of making a diagnosis ie where is the obstruction, and what is it. I know how to drain the system and so also know it is not a trivial undertaking, and I would prefer to know if possible what I need to fix while it is drained down. I am also not inclined to do it during one of the coldest month's of the year, in case something goes wrong!  

Naturally I was concerned that increasing the energy out (delivered to the house) by opening up the lock shield valves might increase the energy in (used). I now have enough data to be able to plot hourly energy in and mean room temp for hours at a particular OAT for before and after I opened up the valves. I have done this for year to date (note date time axis is categorical, they are just the hours that match the OAT criteria), for mean OATs of 5 (5.0-5.9, normal running) and 2 (2.0-2.9, defrost territory) , and marked when the valves were opened with a down pointing arrow: 

Interestingly, no obvious penalty, in fact very possibly (need more data, and there are things I haven't controlled for...) an improvement! In both charts the mean room temp improves a bit (as expected) and in both charts the energy in appears to fall. It's more marked at 5 degrees than 2 degrees OAT, but still present on both charts. Truly heat pumps are a miracle, that surpasseth all understanding...    

Posted by: @cathoderay

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Truly heat pumps are a miracle, that surpasseth all understanding...    

I've just remembered...two days after I opened the LSVs I dropped the weather compensation curve 2 degrees, and then 2 days later I dropped it by another 2 degreees. 

Posted by: @cathoderay

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I dropped the weather compensation curve

That'll do it 😉

Can you go lower?

Bob

Posted by: @bobtskutter

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Can you go lower?

Very possibly. The IAT is at the warm end of my preferred range, and it looks like we'll have fairly settled though cool weather here over the next few days so a good time to experiment. Watch this space... 

Posted by: @cathoderay

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Truly heat pumps are a miracle, that surpasseth all understanding...    

Somehow that feels like the basis of a motto/strapline. 

Without a doubt the combination of the nonlinear response to the main variables, the inherent complexity of the thermal dynamics of houses, contrasted with the extremely simplicity of the thermodynamics on which it is all based, really does make them fascinating beasts.

@cathoderay any updates in this mild spell are you boiling indoors yet?

Posted by: @judith

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any updates in this mild spell are you boiling indoors yet?

Thanks for asking. Yes, the indoor air temperature has certainly been more consistent, a bit higher by a degree or two despite the fact I have lowered the leaving water temperature by a few degrees. The Mark 1 Human Sensor (me) also reports good comfort levels. All in all a success, and I don't think my costs have increased greatly, if at all, the lower LWT appears, as expected, to mean better performance, with COPs at times in the 4-5 range. Sometimes I think we forget how much difference a change in COP can make. For example, a seemingly not very large change, at least in absolute terms, from a COP of 3 to 4.5 means, all other things being equal, including having the same heating load, the unit costs part of my electricity bill falls by one third - where I would have paid £100, I now only pay £66.66, not a trivial saving. 

Here's my chart for the last week. On Monday, I restarted the overnight setback (using room stat down to 16 degrees between 2100 and 0300), as I am interested to see how the now all valves open system copes with the recovery period after the setback. Previously it struggled, sometimes taking 12 hours or so to get back to temperature. On Tuesday morning, after a mild night, it recovered well, back to where it should be by 0700. Last night was significantly colder, and the recovery has been a bit slower, but by no means a disaster, despite being in defrost territory. Bear in mind this is partly managed by my auto-adapt script, which adjusts the LWT depending on how far the actual IAT deviates from the desired IAT. At the moment the script is set up to do one degree of LWT change for every degree of actual vs desired IAT deviation, up to a max of 3 degrees eg if desired IAT is 19, actual IAT is 17, deviation is 2 degrees and LWT increases by 2 degrees. These parameters are easily changed, by editing the script and restarting it. I am going to run the system as is for a week, and then see if it needs any tweaking. 

Note: subsequent comments here about setback running have now been moved to another thread here.