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    • #30604
      Mark Siddall
      Participant

        David/Andy,
        Have you had a look at the Rehau website http://www.rehau.co.uk ? In the engineering section you will find mention of earth tubes and Ground Source Heat Exchange. Rehau have free software, you may be able to download it, or you may need to contact them (can’t remember) to size the pipe for both heating and cooling loads.
        To minimise health concerns these earth tubes are coated with a anti-microbial silver coating.

        Mark

      • #33474

        Not yet!

        I have used German rules of thumb in my house.

        David.

      • #33475
        Mark Siddall
        Participant

          Steve,
          I've re-diverted your query: For Gold Standard MVHR/ Silver Standard MV

          See https://aecb.net/forum/index.php?topic=717.0

        • #33476
          Mark Siddall
          Participant

            According to the rep Ground Source Heat Exchange (GSHX) has a COP of about 20. Thus in terms of efficientcy it far out stips GSHP systems (though it does not provide the same quantity of heat).

            The benefit of decoupled cooling using earth tubes is twofold:
            i) during the winter you have a thermally responsive building
            ii) again in the winter the earth tube provides frost protection to the heat exchanger of the MVHR system.

            Using lightweight structures and GSHX the opportunity to exploit passive solar is obviously diminished but there is always the debate about timber vs. thermal mass in this instance anyway…and this seems to me to come down to:
            i) how the house is occupied (both frequency and numbers) ii) whether you are in a region taht is subject to cloudy days for more than 2 days in a row (i.e. the heat from the solar gains disipates and additional heating loads are required to compenensate for this).
            From a brief play with the Rehau software a run of 20m can be used to provide both cooling and frost protection.

            The only problem is that in the summer the air is cooled to 16C which could be a bit to cool for introducing directly into the house. As a result I can envisage a secondary intake with a mixer to raise the summer intake temperature. (Proper modeling studies for this would need to be undertaken.)

            GSHX in the winter:
            The benefit of GSHX in the winter is the avoidance of frost protection (requires electric resistance heating, or reversable MVHR systems.)

            Mark

          • #33477
            Mark Siddall
            Participant

              David,
              A couple of questions on your decision to exploit GSHX within your house.

              1) What what was the principle purpose for your decision to use GSHX? Was it winter preheating (to avoid the heat exchanger freezing in sub-zero temps), or summer cooling?
              (The reason for asking is that the need for GSHX preheating in German/Austrian Passive Houses is driven by the harsh winters with prolonged periods of below sub-zero temperatures, the UK in contrast is not subject to the same prolonged extremes and as a result the need for winter frost protection is less. As a consequence alternative means could be considered in order to satisfy this requirement.)

              2) With regard to complying with AECB Gold standard, is GSHX, if used/sized for preheating, a cost effective means of limiting the CO2 emissions from frost protection, or is this an example of you using your house as an experimental test case?

              As a passing observation: If the GSHX is sized for summer cooling the utilisation factor increases and then, within the grander scheme of things, the whole thing becomes more cost effective (though no less costly).

              Mark

            • #33478

              The main purpose was to reduce the heating load; it complements a heat exchanger and has a slightly different effect from merely enlarging the h/ex. Frost protection is also useful. Any summer cooling is a bonus. I don't consider this very important now since high thermal capacity houses clearly stay more than cool enough for my tastes with a shorter list of features. But with climate change it may be very important in 2080.

              David.

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