Roch Mill – Going Green


The Granary and Roch Mill have gone GREEN! We’ve been building up to this for years, the creation of an eco friendly house and holiday cottage. First it was the reed bed for sewage treatment, then under-floor heating (and insulation) to improve heating efficiency, then the introduction of log burning stoves.

In October we completed the installation of a 12kW heat pump and solar hot-water panels for our central heating and hot water. And in early December we installed 4kW of Solar PV panels to help offset our electricity usage. Though not yet energy neutral we are close to being cost neutral. The massive increase in efficiency offered by the heat pump and solar hot water panels means that our electricity costs are completely offset by the Feed-in-tariff income from our PV panels.

Project detail

Underfloor heating pipes in the garden room at Roch Mill providing eco friendly heating. Located near Solva, St Davids and Newgale, Pembrokeshire Coast National Park, South West Wales
Underfloor heating pipes in the garden room at Roch Mill providing eco-friendly heating. Located near Solva, St Davids and Newgale, Pembrokeshire Coast National Park, South West Wales

2011 finally saw the completion of our major building works at the mill, which included the construction of a plant room to house our eco-friendly, renewable energy systems. For years we’ve planned to introduce a heat pump to drive the central heating system but other projects took priority. Nevertheless, early on in our Roch Mill reconstruction project, we determinedly installed under-floor heating pipes. At the time, 12 years ago, there was little knowledge locally about such systems and lots of doubters. But we were insistent. Anticipating the later introduction of a heat pump we knew that under-floor heating was the only sensible option. So, unable to find a plumber willing to take on the task, we did it ourselves – and it really wasn’t that difficult.

Being of traditional random rubble construction Roch Mill and Granary are very difficult to insulate properly and the high temperatures required to drive a conventional radiator system just exacerbate the problem. What we didn’t properly think through was the location of our interim boiler and hot water tank. These we placed at the back of the house (where the bathrooms and kitchen are located). So it was in or near this location that the heat pump needed to be installed.


Had we gone straight to a heat pump system at the start it would have presented little extra difficulty. But, by the time we’d finished all the other building work there simply was no way in which we could easily feed the heat pump’s ground loop pipes through to the heat pump. In the end, we had to dig up the patio, burrow under the house and water-wheel, dig a trench through the bottom of the pond (!) and excavate half a mile of trench 4 to 5 foot deep! AND we had to build a new plant-room to house all the heat pump and solar equipment. Oh yes, we also put solar hot water panels on the roof to pre-heat the incoming mains water.


Being a water mill the house is very close to water: the Brandybrook river; a big pond; the mill leat and its tail-race. Water provides an ideal heat exchanger for the heat pump and where possible is often preferred over a conventional ground source. In our case access issues prevented us from relying entirely on a water source but it seemed sensible to gain what advantage we could.

Our heat pump supplier was unable to offer an off-the-shelf solution so we designed a special stainless-steel heat exchanger that could be placed in series with the ground loop but located in the tail-race.

To enhance heat transfer we placed it directly under the water wheel so that it would be constantly presented with a fresh flow of “warm” water. Of course, the water is no warmer than environmental conditions will allow but by constantly washing fresh water over the heat exchanger we can flush the cooled water away and thereby enhance heat flow into the ground loop. We have yet to finish building the water wheel buckets so at the moment the heat exchanger is not functioning as effectively as it will when the water flows. However, even so, this simple stainless steel box is currently generating about 80% of the heat energy being pumped into Roch Mill and Granary. And I’m writing this in January!

No doubt you’ll be wondering “how on Earth did you dig a trench under the pond?” The answer is “Martyn” – ace digger driver and expert Mr. Fixit.

He first lowered the pond water level by about half a metre then created a temporary dam using some exposed sediment. Next, the trench was quickly dug, the pipes laid and the trench filled in again. Whilst the pond level was low we decided to undertake some other long-awaited tasks.

A high priority was to dig out all the bull rushes that I had misguidedly introduced three years earlier. Everything people say about this plant is correct. Elegant in flower and attractive in a corner of the pond it may be, but it spreads so quickly by both runners and seeds. I expect to be donning waders to pull out the sprouting new shoots as they appear throughout the summer.


More excitingly we installed a mini water wheel in the pond outflow and it adds a really nice feature to the garden. We were lucky to ‘rescue’ this wheel from a local private museum when it became surplus to requirements several years ago. We didn’t have anywhere in mind to position it at first and it sat forlornly on our drive for far too long so it’s great to see it in use again.

Digging a pond through the pond might have been the most technically challenging element but we still had two quarter-mile trenches to dig. These had to go through the meadow, across our moor, back down the driveway, into the wheel pit, under the house, under the patio and back to the plant room which houses the Nibe heat pump – simple!

And, with the trenches filled in, everything put back in place, some new gravel and a tidy up, it all looks pretty okay once again.

Finally, to offset some of our electricity usage, in early December we installed 4kW of solar PV on the back roof of the garage block. Unfortunately, the location is not ideal. Being situated deep in the Brandybrook valley we don’t see any sun here between November and February, but we’re confident that the capital cost will be justified in the long run.

Finally, after more than twelve years and a huge amount of disruption, late last year we finally put the finishing touches to our Roch Mill project. Well almost!


Roch Mill and Granary Project finished providing an eco friendly self catering holiday cottage
Roch Mill and Granary Project finished, providing an eco-friendly self-catering holiday cottage.
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