I’m Trystan’s father in law and the owner of system A above so thought I would add a few findings related to the above posts. My 11.6kw Altherma Monobloc has been in for 13 months and I have been optimizing it constantly since the install. In common with many above comments while my install was good the set up/programming left by the installers was useless. Luckily I have another 8 yr old Daikin split system installed elsewhere so I have taught myself how to program these units.
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DHW - COP is poor with a low tank temperature rise. Plotting kWh into the tank vs temp rise of the tank shows a flattish line kWh vs tank dT. Conclusion - as Matt has found - except when it is very cold use ‘Reheat only’ and set the reheat hysterisis about 10c (eco temp 44 and you still get warm enough water down to 34). When it is very cold (below 5c outside) then you do not want house heating to be interrupted randomly so go to Schedule (only) with DHW coming on at circa 1pm when the ambient temp usually peaks and COP will be best.
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Like Matt I have found that the WD curve is not helping me as a) 37c flow temp gives me a COP of around 5 (outside = 10-12c) and 32c gives me a COP of 4. Possibly due to much lower radiator efficiency at the lower flow also b) when the ambient is below 4c and defrosting starts to bite big time into the average output a higher flow temp of say 40c might make the unit frost up faster. So I am sticking with 37c fixed with just 1degree of modulation. I should add that I am using room temp control 17c night, 19c most of the day and 21c evenings. The 17c switches it off at night except for very cold nights
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Defrost is a serious output limiter for these and I suspect many other UK installed heatpumps. Last winter my 11.6kW unit struggled to average much over 7.5kW when the ambient was below 4c. My house needs 9.9kW at -2c so I needed supplemental heat for a few days. Had I installed a 16kw I suspect it would not have changed this 7.5 kw as the evaporator sizes are much the same across the 9 to 16kW range. As you need the max output at the lowest ambients I cannot see the point in building a range of units like this. As mentioned above I am hoping that a lower target flow temp of 37c max will improve the COP at lowest temps and tweak the output a little higher with longer times between defrosts. But then isn’t the amount of heat drawn out of the outside air related (proportional??) to the moisture frozen out of that air - so it might not work.
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I’ve experimented with a range of flow-return dTs from 4 to 10c and optimised at 6c for my system. The HPCs achieve this easily with the fans on low. I did not see any COP gain from 4c or 5c dT.
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I had serious pump/pipe/rad valve noise issues at highest flows (I only have the one pump on the ASHP) so have limited the pump to 70% which is OK. This works well as my max flow x 6c dT x specific heat = my design output at design temp (around 10kW)
Overall I’m happy with the SCOP I have been getting and am hopeful that I can tweak it higher from now on.
Hope this helps