Intriguing, but slow, geothermal heating proposals for Glasgow
No obvious follow-up stories after a couple of articles appeared in the media suggesting that old mine-workings below Glasgow could form the basis of geothermal heating systems for the city.
The diagram below is based on electricity generation, but it illustrates the concept. Ignore the turbine/generator, since the heated water would be sent to the properties, not utilised to drive the turbine
Due to the relatively low temperatures involved in the Glasgow proposals, rather than use the heat/water/fluid directly, as can be done in systems where the water or transport medium is at much higher pressure and temperature, the system proposed for Glasgow uses heat pumps to extract the energy from a loop that goes down into the workings and collects the heat, then transfers it to a second loop on the surface, which circulates around the properties to be heated by the transferred energy.
The idea is far from new, and used widely abroad, but it is relatively new to Scotland, with only a few existing schemes in place, and little experience.
This report sounds good, but is short on detail, noting only that the householder said their heating cost only “pennies”, and that the average heating bill was about £500 less than the Scottish average – but failed to give actual figures for heating under the system, or state the average it was referring to:
I’d guess this is why the news comes with a 3-year timescale just to carry out a feasibility study to research the concept, And it would seem we need the experience, as we may have schemes in place, but are finding problems with the installations.
While the underground water they raise for this system is only at around 12°C (up to 20°C according to one article), it seems that they are having problems with keeping both the electronics and water handling systems trouble-free – and that’s frankly a fairly ridiculous position to be in nowadays. Reliable electronics should be easy install, unless they are buying cheap junk, or using poor designs, and other countries have successful water handling systems in places, so they should not be “re-inventing the wheel”, but calling on the experience others.
This news item came with some surprise information for me, as I learned the system the comments about reliability (also the subject of the video in the report) was one I had unknowingly been walking past for years, in Glenalmond Street, Shettleston. I just thought the homes were a relatively recent development that had gone up a few years ago, and had no idea it contained a geothermal heating system within.
This pdf provides details the project:
As can be seen, some interesting points came out in the summary of the Glenalmond project (I’ve ignored/omitted those not related directly to the water aspect):
7 A water recycling system complete with storage tank and an independent feed system was installed to recycle some of the waste mine water, by feeding toilet cisterns. However ferrous-oxide compounds become brown and sticky when exposed to the air, resulting in blocked valves and discolouration of toilet basins. The decision was made to discontinue the system.
8 Returning water to the mine also proved difficult, as it is not always possible to find a void mine space, and boreholes may be easily blocked by rock falls and silting.
Although it has some problems, they seem to be relatively minor, provided they are dealt with at the start, and not as an afterthought.
STV also reported on the story, with a video explanation, but as with first article mention about, this second item also mentions great savings, but also fails to quote figures from the resident interviewed:
Ground heat is not only suitable for large-scale projects. Individual homes can benefit from a similar system which operates in a different way.
I used to spend hours in the university library, and unearthed a book by someone who had installed a ground-heating system, possibly as far back as the 1960s (I no longer have access to this book), from which he was able to heat his water and his home for about a third or less than it would have cost otherwise. I forget the exact figures, as this was some years ago, so they would be irrelevant today, given the horrendous price increases of recent years.
In this case, heat energy was drawn from the ground by pipes buried a metre or more underground. Water plus anti-freeze was circulated, and a heat-pump used to transfer the energy to storage, heat domestic hot water, or heat the house. The system described all those years ago managed more than 3 kW out for each 1 kW used to power it. Modern systems can now be purchased ‘off the shelf’, and do no better. In fact, having read some journals and studies, they do a considerably worse. While good systems manage a similar 3:1 ratio, it looks as if many have been installed by cowboys. The use of poor contractors has led to bad reports for many of these systems, and manufacturers withdrawing their hardware from some contractors. Unfortunate, as their get-rich-quick tactics reflect badly on the system.
As well as ground heat extraction, it is also possible to extract heat from the air. Although this appears simpler, it’s not as good, since air has less energy than ground to give up, and the condensation on the exchange matrices freezes and cuts off the air flow if care is not taken and protection circuits are included. Ground systems can freeze, but their design and capacity means this does not stop them working. Freezing can be minimised if the pipes are buried deeply (if possible). The account in the book I referred to noted that the pipework froze toward the end of each winter, but did not stop the heat exchanger working. The only effect was to reduce its efficiency, since the available heat energy was also falling.
I always wanted to build one of these systems, and while I might have the ground, have no access for a digger to tear it up to bury all the pipework, and doing it by hand is not really a good idea, well, not while having to do a full-time job. Now I have the time, but not the inclination – having recently had to dig up and replace about 10 metres of water main, the thought of having to dig at least 20 times more than that no longer appeals.
I can’t wait for the results of the Glasgow mine feasibility study, really I can’t. But three years is just too long for this basic step.
I will have forgotten all about this story by then (and suspect everyone else will too! )
On the other hand, heating costs might have become even more frightening by then, and everyone will be on the edge of their seats waiting for the study to be published.
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