Sandy's Garden ... Hot Dig - ity

Not all of the pavement was speckled white. A strip of wet blacktop linked every one of the recently-installed metal lamp posts to its neighbours, a damp indicator of exactly where the cable trench runs, a power line which awaits being wired in to the lamps which it is designed to serve.

And that clearly-defined stripe reminded me of a sight with which I was very familiar some sixty-or-so years ago, when I was a student at Dundee College of Education and living in ‘digs’ in the Balgay Road area of that city.

The council house in which I lodged enjoyed the benefits of central heating, the source of this then-rare luxury being a nearby council-operated boiler house which fed hot water through underground pipes to every house in the scheme.

Heat leaking from these pipes soon melted any snow or ice which tried to form above their trenches, as well as ensuring that there were strips of pavement which dried almost as soon as rain stopped falling.

It was while my mind was focused on underground sources of heat that some advice from the Energy Saving Trust came to mind. I

Our government has committed to reducing so-called greenhouse gas emissions drastically in the not-far-distant future; and that this government target can only be met if we … all of us … reduce our greenhouse gas discharges, principally our emissions of carbon dioxide, much of which comes from our use of carbon-based fuels like coal, oil and gas.

And this is where my garden returned to prominence in my thinking. The Energy Saving Trust (EST) is, to quote Wikipedia, “an independent, not-for-profit organization funded by the government and the private sector.”

EST is, “devoted to promoting energy efficiency, energy conservation and the sustainable use of energy, thereby reducing carbon dioxide emissions and helping to prevent man-made climate change.”

It offers lots of advice about how we can achieve these objectives, including advice on how to heat our homes by harvesting heat from our gardens. This is how it works, according to EST. “Ground source heat pumps use pipes buried in the garden to extract heat from the ground.

A ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe, called a ground loop, which is buried in your garden. Heat from the ground is absorbed into the fluid which passes through a heat exchanger into the heat pump. The length of the ground loop depends on the size of your home and the amount of heat you need. Longer loops can draw more heat from the ground, but need more space. If space is limited, a vertical borehole can be drilled instead.”

Simple, yes? Well, not as simple as it might sound. Your garden might not be suitable, or big enough for a loop. If you’ve got to go vertical, you’ll need a borehole between 90m and 160m deep, say, between 300 and 500 feet in old money! That’s deep! And that’s expensive; you’re looking at £20 000 for that! I wonder if the council might build an eco-friendly boiler house nearby to supply every home in the neighbourhood?