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Green Building Bible, Fourth Edition
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Renewable Energy: GSHP Carbon footprint

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    • CommentAuthorrevor
    • CommentTimeNov 14th 2020
     
    I guess suitability of using existing piping will depend on the permeability of the pipework and valves etc. Hydrogen is a much smaller molecule than hydrocarbons so may find its way through polymeric materials such as plastic gas pipes. I once worked in a chemical plant that used hydrogen in pretty large quantities and as I recall all pipework was stainless steel but we were using it under pressure. A later job as a lab technician using bottled gasses we used special tubing the exact nature I do not recall. I reckon that the switch to hydrogen will be a long and expensive one and will require a new complete infrastructure to deliver the gas to point of use. I do not see any benefit in using electricity to make hydrogen to then burn that in homes. Surely better to use the electric that buildings are already connected to. But as a convenient source of power to large vehicles as previously mentioned where batteries (as current technology) would not carry the required energy per Kg I can see it working.
  2.  
    Some folks on here will be delighted to hear that the Smart Meters currently being rolled out in the UK are not thought to be suitable for hydrogen. A second national programme of gas meter replacements would be needed, before the grid could supply hydrogen.

    If someone flogs you a 'hydrogen ready' gas boiler without
    including a 'hydrogen-ready' gas meter, then it's just a methane boiler!

    https://www.sgn.co.uk/about-us/future-of-gas/hydrogen/h100-nia/domestic-metering-solution
    • CommentAuthorEd Davies
    • CommentTimeNov 14th 2020
     
    Going back to the original question:

    Posted By: revor… and how about the embedded energy used in making the HP.
    To a very rough approximation, the cost of an item can be used as a proxy for its embodied energy. Not terribly accurate but it gives an idea particularly when the things are made of similar materials, are about the same size and made in similar factories, such as an oil/gas boiler or a heat pump. An oil or gas boiler is, I think, likely to cost something in the region of £1000 whereas a functionally equivalent air-source heat pump [¹] will cost about twice that assuming you don't bother with the MCS BS.

    Given that heat pumps are probably still priced a bit higher as being less mass-market items that would indicate that the embodied energy is likely no more than about 50% more than that of an equivalent fossil burner, if that much. By the time you take into account the extra infrastructure needed to support combustion (oil tank or gas pipes) it seems to me it's not likely a difference worth worrying about.

    [¹] probably a bit lower power and running at a lower temperature (at least for space heating) but expected to run for a somewhat larger fraction of the day.
    • CommentAuthorrevor
    • CommentTimeNov 15th 2020
     
    I have found this carbon footprint calculator.

    https://www.carbonfootprint.com/calculator.aspx

    and filled it in and was alarmed when it came out at 8.1 tonnes until realised it is shared between 2 of us. There is no way to input things into the calculator one may do to lower footprint, other than do less of the stuff that contributes to the CO2. e.g I have planted about 400M of hedgerow grow veg sell at gate to locals. The total CO2 for the house is 1.6 tonnes CO2. Hopefully before long should be generating from our PV and will contribute an estimated 5229Kwh annually and save 2.75 tonnes CO2 somewhere. If I substitute the LPG for a GSHP with COP of 3 my house CO2 comes down to 1.1 a saving of 0.5 tonne. The cost of my Solar PV is roughly about the same as would have cost me for a GSHP not including the RHI which probably would not get, as would have, like everything else, put my own in anyway. So solar PV is a far better contributor to reducing my CO2 than HP by a big factor (5.5). Also interestingly I could save 0.45 tonnes pa by becoming vegetarian. Swop car for EV save another 1.6 tons less whatever C footprint of the EV is. All this off course dependent on how realistic the calculator is.

    An advantage of my LPG boiler is I can run it for short periods of time as can get 27kw into my thermal store when I want quickly, and just heat top part of store where the DHW HE draws water off. A 5 to 10 min burst is enough and would take one standard immersion heater 9x as long. I think will stop beating myself up by having gone the LPG route.
  5.  
    Revor, I'm sorry but I think they are using carbon intensity figures from some time ago (2.75/5229 would be 525g/kWh but the actual figures this year are well below 200 now). This means that heat pumps and EVs are more beneficial now, unfortunately it means that solar PV is less beneficial now, as the grid electricity which the PV is displacing, is less carbon intensive than it was back then.

    Edit to add: that website allows you to overwrite the g/kWh with up to date figures. If you input 0.17kg/kWh, then 5229kWh of PV would save 0.89t of CO2.

    Then they calculate that 1000kWh of LPG contributes 0.21t of CO2 whereas a GSHP (COP4) using 250kWh of electricity contributes 0.04t of CO2, so an 80% reduction. This is all in line with our previous discussion.

    Further edit to add: your house has excellent insulation and you are using remarkably little LPG, you certainly should congratulate yourself not beat yourself up! A GSHP would be overkill for such a low heat load.
    • CommentAuthorrevor
    • CommentTimeNov 16th 2020
     
    That input of .17g/kwh actually reduces my electric carbon footprint so house reduces to 1.43 tonnes. My original argument for the LPG was precisely the point you make it would have been overkill and an "overly engineered" costly solution. Coincidentally I have just ordered 2 X 46 kg bottles of gas this morning to replace those that went on stream on the 2nd February. Our solar thermal panels have been great providing all our hot water needs apart from an occasional 5 min burn on the boiler and according to my records 4 occasions. My PV carbon saving figures came off a quote an installer prepared for me 12 months ago. Had a look at the CI figures north Scotland currently 0 as mainly wind with hydro. Does not take into account the embedded energy though, but I get the drift thanks.

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