Tame the gas monster with sensors, suckers and a spiffy new fan

More performance-tuning for your home and office

Solar thermal, pumping heat

Thanks to continuing government flapping on both solar PV (electricity) and solar thermal (for hot water) in the domestic FiT and RHI schemes, plotting some combined solar PV/T for the space left on our roof has been more ... um ... interesting than really necessary.

However, the nice man from Isoenergy came to visit and confirmed that we could probably do a ground-source heat-pump (GSHP) combi (to replace our ageing and not-massively-efficient gas combi) using a ~100m borehole (we don't have the lawn space for the normal pipe-runs), but for a kewl £17k or thereabouts. And that a good air-source heat-pump (ASHP) would not be much cheaper but would, as expected, be less likely to cut much footprint compared to gas. Ouch. I am keen to stop being committed to burning fossil fuel at home but there's keen and there's more than twice the cash per tonne of CO₂ avoided as even relatively-pricey solar PV.

However, if the heat-pump could be combined with solar PV/T to take away any need to import energy at all for hot water in the summer for example, and generate a trickle more 'leccy to spill to the grid, the numbers start to look at least competitive with solar PV, and might eat away another 500kg or more of CO₂ per year from our footprint, talking us firmly carbon negative for energy. (Plus we could disconnect gas entirely, which would save us £100 per year on standing charges alone!)

And like with my solar PV and MHRV I want a system that I can just forget about and let get on with the job, and that the rest of the family don't need a training course to manage. I can choose to take lots of meter readings if I want, but the basic kit must be reliable and almost entirely automatic. Just like in IT, being lazy and letting machines do the work can be a virtue; false heroics are not smart!

Off-grid SheevaPlug

At the start of 2011 I massively upgraded the batteries for the off-grid power system for my SheevaPlug Internet server and it coasted through December and January off-grid without a glitch.

December/January battery levels; the days without spikes over 14V were days without any sun to speak of (click to enlarge).

But that is 2kWh of effective storage or four biggish car-batteries in size for a device that uses about 0.1kWh per day; given that a typical UK household used 9kWh/day imagine what would be needed to take just one house off the grid and thus why grid-scale storage is so hard at the moment!

I hope to experiment with the Raspberry Pi and a network of temperature and humidity and maybe even CO₂ sensors this year, amongst other things, and may do some of the same for my kids' school... ®

References

• Passivhaus
• OWFS 1-Wire File System development site
• Vent-Axia HR25H single-room HR25H
• MHRV in our house
• UK heat-pump suppliers
• Rough numbers for a possible GSHP 'combi' system for us