Our heat pump is now one year old and we have a complete year of data to report/study/ignore/geek out over. See for yourself.
The graphs are from the MELCloud app – our system only has the standard metering provided with the heat pump – Mitsubishi call this ‘indicative data only’. For all but 4 days at the start of Dec 21 the heating has been running in room control mode with ‘auto adaptation’ turned on. There’s a couple of things to note in the graphs.
In May and June last year we were using the immersion heater powered from solar to heat our hot water – this was old thinking from before we had the heat pump when we heated our hot water for free from solar. What’s better than free? Eventually we realised that the heat pump heats water at 200-300% efficiency in summer so using it to heat our water meant we could export a bit more solar power and get paid a few pence to offset the standing charge!
Secondly the heating side of things seems to use loads of energy during the summer and produce no output. Working the numbers through it looked like heat pump was reporting using around 2.3 kWh per day during the summer – that’s 100 W which seems awfully high for standby. We couldn’t see this consumption in our electricity bill so spoke to Mitsubishi in the UK about it. Seems they are aware of a bug in the heat pump metering – told us the actual standby consumption is around 25W, 600 Wh per day For that we get continual monitoring of external, hot water and room temperature and a wireless connection to the MELCloud servers. We’d like it to be lower but it’s not that different from the Sky box! They couldn’t say when/if the bug was going to be fixed. Seems a bit daft to us to have metering which is wrong – it doesn’t matter in the winter when the heat pump is on most of the time – the error is in the noise – but in spring/summer/autumn the numbers are rubbish. Come on Mitsubishi get it fixed.
From the input and output energy we can work out how well the heat pump is performing – the Co-efficient of Performance (CoP), defined as output heat energy/electrical energy consumed – shown in the graph below.
The figures heating figures for May – September are omitted as due to the metering bug they are meaningless. We strongly suspect the lower CoP numbers in April and October are also caused by the metering bug – as the external temperature increases so should the CoP.
Metering bug aside the heat pump is delivering around 4 kWh of heat for each kWh of electricity – a result with which we are very happy. The hot Water CoP is much lower, that’s due to having to raise the flow temperature to 50C rather than the 35C typical for heating. Also in winter the hot water is heated overnight – when the external temperature is usually lower – so we can use the much cheaper overnight rate electricity.
Big picture summary – very happy
- House is more comfortable than when it was heated with oil
- Spend less on electricity than we would have on oil – Solar and battery helps
- No oil level monitoring and reordering
- No oil tank – more space in garden
- More visibility of temperatures, history, performance – geek on!
- Full control when away from home via the MELCloud app
Irritation
- The metering bug – it needs to be fixed