PhilT

The figures vary a lot by manufacturer for example, at 35C the 10kW Vaillant Arotherm Plus SCOP is 5.03 vs the 7kW model at 4.36 (MCS test results). But my calcs look at this in a different way, by comparing an 11.2kW heat pump running comfortably within it's so-called "mid-range" capacity (c. 9kW ball park) vs the equivalent 8.5kW running flat out, at different ambient temps. So an over-sized heat pump could be more efficient or, at worst, no less efficient than the "perfect size" (for want of a better description).

Looking to upgrade to 15mm. I thought the 8mm microbore circuit was fed by manifolds, but removing the downstairs ceiling reveals instead a 15mm secondary circuit feeding short 8mm microbore feeds to the upstairs rads, and long 8mm microbore runs dropping down to the ground floor rads (see photo). This should make things easier because I won't have to hunt around for the manifolds, I can just leave the upstairs rad circuit as it is, run two new 22mm pipes dropping down from the primary circuit upstairs, just after the secondary circuit pump in the airing cupboard, and then connect new 15mm runs from the two central 22mm drop downs to the downstairs rads. Any issues with that approach?

The output ranges in that data table aren't exactly like for like, but it indicates that the larger unit is more efficient across the whole range of ambient temps, so a more cautious approach in selecting the 'next size up' should not significantly compromise efficiency and running costs.

It would seem that for modern scroll compressors, for a given range of output, a larger compressor is more efficient than a smaller one across the entire ambient temperature range. This is the Ecodan data table. The Vallant Arotherm+ shows a similar pattern when comparing the 10kW and 12kW to the 7kW model. Up front cost is obviously a consideration. 11.2 "Mid range " vs 8.5 "Max" @ 35°C In kW In kW Out kW Out kW COP COP 11.2 kW 8.5 kW 11.2 kW 8.5 kW 11.2 kW 8.5 kW % dIff. outside temp °C -15 2.7 3.4 6.7 7.3 2.5 2.15 16% -10 2.9 3.7 8.1 8.5 2.8 2.3 22% -7 3.0 3.6 9 8.8 3.05 2.45 24% 2 2.4 3.0 9 9.7 3.75 3.2 17% 7 1.9 2.3 9 10.5 4.8 4.55 5% 12 1.4 2.3 9 10.7 6.25 4.6 36% 15 1.3 2.3 9 11.5 7.05 4.9 44%

the counter argument is that at the coldest temps, for a given heat output, an oversized heat pump works more efficiently than undersized - manufacturer's data tables back that up. During the coldest days you could be using 10 x as much electricity as the mildest heating days. Think about the maths, for example, 10% more efficiency x 100kWh on the coldest days = a 10kWh saving, whereas 10% inefficiency x 10kWh on the mildest days means only a 1kWh loss.

Mitsubishi sent someone out to do mine for no charge to update to the firmware via the outside unit. It has made a significant difference especially in October, much longer runs at lower temp/power consumption and better control of room temp around the target. I'm running in full auto (room temp) mode using the Mitsubishi room controller.

could be - the specs say it has "low temperature protection", but that's a very short warming time and it happens every single discharge irrespective of temperature

At around 02:40, with consumption (orange) continuing at a background level, there is an unscheduled light battery charge (blue and red lines) but, bizarrely, in the first 5 minutes, the SOC (purple line) drops from around 17% to ZERO, WITHOUT ANY CORRESPONDING CHANGE IN CONSUMPTION OR OTHER OUTGOING POWER, then gradually goes up to around 6% SOC at around 03:20 at the end of this mysterious little charge cycle

Every time my battery charges and discharges, even though the minimum discharge level is set to 6%, it always overrides that and discharges to zero then recharges to 6%. Anyone know why that happens?

Gas plant efficiency is far worse than theoretical because of renewables fluctuations

if my calcs are correct a 20% glycol mix will reduce efficiency by around 2%. Important for fully informed choices. Water Cp 4.18 Fernox HP-5c @ 20% 4.085 -2.3%

yikes - storms mainly?

Surely it's similar to the English scheme whereby you can apply for the 7500 grant for a self build if it meets certain criteria

Going away soon. For a week's holiday at this time of year, how do people set their heat pump modes, temps and timings, and with what objectives in mind?