Heat pump running costs – Hitachi Yutaki ASHP

Published July 17, 2012 by Sean

So, the heat pump installation detailed here has been running for 6 months now, and it is probably reasonable to present some comparative data against what I had before, 4 storage heaters and an old poorly insulated immersion cylinder, plus an electric shower. I don’t have good detailed data for the previous years, just my utility bills (mostly my readings, not estimates) so I’ve put that into imeasure and let it do a regression against degree days to come up with a set of estimated points. I also have accurate readings for the month prior to installation and a period of tweaking of the settings.

Headline numbers (at todays unit prices, all E7 tarrif):

2010: 7861 kwH (£1089)
2011: 9389 kWk (£1300)
2012: 6969 kWh (£965)  – extrapolated
2012: 3873 kwH (£536) – to date

This isn’t too conclusive, there is a saving – partially offset by not making good use of E7, and of course weather in each year will have an effect.

For the detailed readings, the imeasure website will plot actual usage against estimated. This shows that the storage heaters had appalling regulation (down to me deciding when to turn them up/down), but week of 12 Dec was most expensive (radiant heaters, doors open, install in progress). The system was unstable for the first couple of weeks and didn’t always heat, it wasn’t till the end of January that I got the settings about right (saving 50 kWh/week). End of march, the fuse blew whilst I was away, and recently there is no heating load so the savings have faded away.

Heat pump tracking accuracy – click for larger image

Comparing against the trend for earlier years, it seems that my adjustments to the settings have mostly resulted in savings in the 0-60 degree day weeks (that’s weeks where the day averages 7.5 degrees roughly). which is all but 2 or 3 weeks of spring 2012.

ASHP heating/energy load for H1 2012. Click for full size image.

This saving is roughly 50 kWh/week, so it seems reasonable that I’m saving 20% of my energy usage, have a significantly more comfortable house, but probably won’t save too much in energy bills (unless the renewable heating incentive actually materialises). There is probably scope for additional improvements to the system – hopefully my more accurate monitoring will help with this.


Filed under Heating

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