Dyffryn Ogwen: warm rooms, healthy air, lower bills

I answered from general knowledge and had no access to local data. Treat every Ogwen-specific figure as an estimate to be measured.

1. Purpose and present arrangement

Purpose: every home in the valley has warm rooms, dry healthy air and bills it can bear. The valley ends up better at doing this than before, in skills, ownership and recorded knowledge.

Present arrangement: about 2,000 homes buy imported oil, LPG or grid electricity, and money leaves the valley every winter. The solid-stone terraces leak heat and hold damp. A 100 kW hydro scheme sells its output to the grid. The quarry pumps water out of its workings and discharges it. Bangor University sits six miles away, largely disconnected from the valley's winter problem.

2. The numbers, first

• Heat demand: assume about 2,000 homes at about 15 MWh a year each, which is about 30 GWh of heat. This is the main uncertainty, and a survey would settle it.
• Hydro output: 100 kW at a typical 40–50% capacity factor gives roughly 0.4 GWh a year. That is about 1–2% of the valley's heat need.
• Heat pumps: at a coefficient of performance (COP) of 3.5, 30 GWh of heat needs about 8.6 GWh of electricity. After halving demand through fabric work it is about 4.5 GWh. That is still more than ten times the present hydro.
• Winter peak: about 2,000 homes at 2–3 kW electrical each is 4–6 MW on a cold evening. The local network and storage must carry that peak.
• Mine-water heat: the temperature of the water is not what limits you; the flow does. If the quarry pumps or drains 100 L/s and you cool it by 4 °C, that is 100 × 4.186 × 4 ≈ 1.7 MW of heat. After the heat-pump work is added back, that supports roughly 500–700 homes at peak. The 100 L/s figure is my assumption, so it needs measuring.
• The sun and the rain: the rain that falls here (more than 2 m a year) is the flux arriving as water. It refills the workings, runs the hydro and keeps the mine water near a steady 9–11 °C. Low-grade heat is plentiful here. The scarce things are the demand peak, the network capacity and the fabric. The conclusion is that heat is not scarce in the valley. The leaking walls and the 4–6 MW evening peak are the real constraints.

3. Genuinely different arrangements

A. Valley fabric first, breathable. A local retrofit co-op insulates the stone terraces with vapour-open materials. These include wood-fibre or lime-hemp internal or external layers, lime plaster, and humidity-controlled ventilation. It works street by street with measured before-and-after data.

B. Ambient heat network (a "fifth-generation" cold loop). The quarry discharge, and where possible the flooded workings and the river, feed a shared low-temperature loop of about 8–12 °C. Each home has a small water-source heat pump. The loop can also carry heat between homes: a house that is warm and cooling can give heat to a neighbour who needs it.

C. Flux-matched electricity. More small hydro sites are added, and ideally some wind and solar. Each home gets a thermal store, so a hot-water cylinder acts as a battery. The co-op becomes a local supplier that shapes demand around its own generation.

D. Frame-breaker: sell warmth, not kilowatt-hours. Households pay the co-op for a guaranteed temperature and air quality, with a cap on their bill. This changes who has the incentive. The co-op now profits from every draught it stops and every COP point it gains. The retrofit stops being a cost the household bears and becomes the co-op's route to margin.

E. Frame-breaker: change the question. Make Dyffryn Ogwen the place that works out the pattern for slate towns and cold stone terraces everywhere (Blaenau, Nantlle, Llanberis, Corris and others, in Wales and beyond). The measured method, tools and training are the export. The valley is paid for the pattern as well as for its own heat.

Trade-off I'm treating as a signal. Fabric first versus network first look like competitors for the same money. They are not: the network is far cheaper and more efficient on a well-insulated home, and the insulation is far more valuable when the heat source is cheap. So fabric and network are sequenced and jointly planned street by street. The more insulated the street, the smaller the network pipe and heat pump it needs.

Pick: D as the organising frame (the co-op sells outcomes), A as the first move (it pays on day one), B as the backbone (with a proper source study), C to cover the electricity, and E as the long-term income and resilience.

4. What to return

1. Changed arrangements

1. A warmth-service co-op that owns the outcome.

• Change: the community body, or the hydro co-op, offers a "warm home" package. The household pays a fixed monthly sum that is lower than its present heating cost, and the co-op pays for the fabric work and the heat equipment and carries the technical risk.
• Physics: energy in is hydro and imported grid electricity. The loop is heat moving from the environment into the home through a heat pump. The leak is heat through the building envelope. The heat finally radiates to the sky from the roofs and walls, which is the normal route.
• Opens: a business model that pays for retrofit out of the savings, for tenants and low-income households who cannot lay out capital, and for local jobs that stay in the valley.
• Label: designed. Comparable service models exist (energy-as-a-service, heat-as-a-service in housing associations). A community-owned version in a Welsh-speaking valley is imagined.

2. A breathable retrofit programme with monitoring.

• Change: the retrofit uses vapour-open materials (lime, wood fibre, hemp-lime) and ventilation that responds to humidity. Every home gets cheap temperature, humidity and CO₂ sensors before and after. This guards against the main failure of internal insulation on solid stone, which is trapped moisture and mould inside the wall.
• Physics: the fabric work cuts demand, plausibly 30–60% on a solid-wall terrace. The leak is the remaining conduction, the draughts and the ventilation losses. Heat-recovery or humidity-controlled ventilation recovers part of that. Moisture leaves as vapour through the walls and through ventilation.
• Opens: healthy air as a measured result. It also opens a body of local trades (stonework, lime, joinery) and a data set that improves each next house.
• Label: prototyped elsewhere (retrofit pilots on solid-wall homes exist, with mixed results where materials were wrong). Observed working in some cases, with failures well documented.

3. A quarry-and-river ambient heat loop.

• Change: the quarry's pumped discharge, and later the flooded workings and the river, feed a shared low-temperature loop. Each home has a small heat pump on it. The first phase is one dense terrace plus the community buildings (school, leisure centre, health centre, chapel halls).
• Physics: the energy in is the low-grade heat the water holds (rain-refilled, at about 10 °C) plus the electricity for the pumps and compressors. The loop stays closed. The leak is heat from the pipes, which is small at these temperatures. The heat ends up in the buildings, then radiates to the sky.
• Opens: heat for homes that cannot take an individual ground or air source system, and the ability to share heat between buildings. It also converts a discharge the quarry already pays to pump into a useful asset.
• Label: designed. Mine-water heat networks are observed working at scale elsewhere (for example Heerlen in the Netherlands, and Gateshead and Glasgow in the UK). A slate-quarry version here is imagined until the flow and temperature are measured.

4. Winter-matched local generation and storage.

• Change: the co-op adds more small hydro sites, and possibly wind and solar. It places thermal stores in homes so heating can lean on the hours when generation is high. One flooded pit is studied as a small pumped-storage site. Nearby Dinorwig in Llanberis (a large pumped-storage plant) and the proposed Glyn Rhonwy pumped-storage scheme show that this geology and this terrain suit it.
• Physics: energy in is rain-driven hydro, flowing from the high rain-fed catchment. Water loops between upper and lower pits, losing about 20–25% per cycle to friction and electrical losses, and that loss is released as heat. Cold, still, dry spells reduce hydro output, so the system needs grid import or storage across them.
• Opens: local control over electricity, and more of the valley's money kept in the valley. It also helps the heat-pump peak.
• Label: hydro is observed working (Ynni Ogwen already exists). Home thermal stores are observed working. Flooded-pit pumped storage is designed elsewhere but imagined for Ogwen.

2. One step now

Pick one terrace of 15–25 homes with willing neighbours. Lend each household a cheap temperature, humidity and CO₂ logger, which costs about £10–20 each. Add a thermal-imaging walk-round and a draught check. Run a bulk oil and LPG buying scheme at the same time, which is the standard day-one saving for off-grid homes. In the same week, ask the quarry whether it will share the flow rate and temperature of its pumped discharge, and put a £50 temperature logger on the outflow.

It pays on day one in three ways. Households save on oil or LPG by buying together. They get a list of which draughts and rooms cost them most. They also become the first people in the valley with evidence about their own homes. The co-op or the regeneration body learns who qualifies for Nest and other grant schemes and becomes the coordinator. That makes it the natural owner of the next step.

3. One long route

Over 5–10 years, build the full valley arrangement:

• Retrofit the whole building stock by street using the breathable method.
• Run an ambient heat network from the quarry water, with extensions to the flooded workings and the river as the source study supports.
• Expand local generation and add storage.
• Move households to the warmth-service model, with the co-op as the energy company of the valley.

The long route waits on three things:

• A network source study. It must cover the quarry's flow and temperature all year, the water chemistry and fouling risk, and the legal agreement with the quarry owner over the water and its after-life.
• Trained local capacity. There must be enough retrofit and heat-pump installers and a reliable supply of vapour-open materials. Bangor University and a local training body (a college or an apprenticeship scheme) could grow this.
• Grid capacity and consents. The distribution network operator must be able to take a 4–6 MW peak, and planning must allow work in a sensitive landscape. The area includes the UNESCO World Heritage "Slate Landscape of North-West Wales", so the guardrail is to record before changing any tip, building or quarry feature.

Possible patrons are Welsh Government energy programmes (Ynni Cymru), Gwynedd Council, UK public funding bodies, the National Wealth Fund, a community share offer, the quarry operator (which gains a use for its discharge), Bangor University as a research partner, and housing associations.

The technology not yet built is a standard, low-cost, factory-made "terrace kit". It would be a heat-pump unit and plant room sized for small stone homes, tied to a thermal store. It would be designed by the valley and Bangor together, and it would be sold on to other slate towns.

4. One opening for the next person

Rerun this design against the public record, asking nobody. The 2021 Census for the Bethesda area, the EPC register, Natural Resources Wales's discharge permit for the Penrhyn adit and its hydro licences for the valley, Ynni Ogwen's published output and Ofgem's price cap are all free to read. Use them to correct the house count, the fuel mix and the hydro already in place, then run the warm-room service and the quarry-water loop across the whole plausible range of flow and temperature, since neither is published. End with the short list of measurements still needed, each with the threshold at which the design flips and who would plausibly pay for it.

Waits on a person

• A one-year, hourly record of the quarry discharge: flow in L/s, temperature, and a basic chemistry panel (pH, iron, sulphate, suspended solids). With it, anyone can compute the thermal capacity of the source and the likely fouling of heat exchangers, and size phase one. A student at Bangor could do this as a project. The question to answer is: "How many Bethesda terrace homes can the quarry discharge heat at winter peak, after fabric improvements, and where in the valley does the pipe route make that economic?"
• A measured fabric baseline. Use in-situ heat-flux readings on three typical Bethesda terrace types before and after breathable insulation. Publish the real U-values, the moisture results and the costs, in Welsh and English, so the next slate town can start from what was recorded here.

5. A changed premise

Proposed premise 13 (Sonnet 5.5, 2026-10-27): Sell the outcome, not the commodity.

When people buy the commodity (kWh, litres of oil, tonnes of anything), the seller profits from selling more of it, and the buyer carries every inefficiency. When the arrangement is paid for the outcome (a warm, dry room; clean water; a meal prepared), everyone in it gains by wasting less. This is why efficiency work that never pays under a commodity bill can pay under an outcome contract.

It opens the retrofit as a self-financing activity. It aligns the co-op with the household. It also makes consent, premise 12, part of the design: the household signs up for the warm room, a thing it already wants, and never for a technology. Dyffryn Ogwen: the CE Seed answer, short form. I answered from general knowledge only, with no tools and no local data, so every Ogwen figure below is an estimate to be measured.

Numbers.

• Heat demand is about 30 GWh a year, from roughly 2,000 homes at about 15 MWh each.
• The 100 kW hydro scheme gives about 0.4 GWh a year, which is 1–2% of that heat.
• Heat pumps at a coefficient of performance of 3.5 would need about 8.6 GWh of electricity. After halving demand through fabric work, about 4.5 GWh.
• The winter evening peak is about 4–6 MW.
• If the quarry discharge is about 100 L/s and is cooled by 4 °C, it gives about 1.7 MW of heat. That is roughly 500–700 homes at peak. The 100 L/s figure is my assumption.

1. Changed arrangements.

• Warmth-service co-op (designed, community version imagined). The household pays a fixed sum below its present heating cost for guaranteed warmth. The co-op funds the retrofit and carries the risk. This lets tenants and low-income households get retrofit without capital.

• Breathable retrofit with sensors (prototyped; observed working in some cases).

• It uses lime, wood-fibre or hemp-lime layers and humidity-controlled ventilation.

• Every home gets temperature, humidity and CO₂ loggers before and after.

• Demand falls plausibly 30–60%, and damp is measured rather than assumed.

• Quarry-and-river ambient heat loop (designed; mine-water networks are observed working at Heerlen, Gateshead and Glasgow).

• The pumped quarry discharge, at about 10 °C and refilled by rain, feeds a low-temperature loop.

• Each home has a small heat pump, and heat is shared between buildings.

• The Ogwen version is imagined until flow and temperature are measured.

• Winter-matched generation and storage (hydro observed; flooded-pit pumped storage imagined for Ogwen).

• More small hydro, and home hot-water cylinders used as batteries.

• A flooded pit studied as small pumped storage, with Dinorwig and Glyn Rhonwy nearby as precedents.

• Cold, dry, still spells still need grid import.

2. One step now. Take one terrace of 15–25 homes. Lend each household a £10–20 logger and do a thermal-imaging and draught walk-round. Start a bulk oil and LPG buying scheme, which pays on day one. In the same week, ask the quarry for its discharge flow and put a £50 temperature logger on the outflow.

3. One long route (5–10 years).

• Retrofit all the valley's streets, run the quarry-water heat network, expand local generation and storage, and move households to the warmth-service model.
• It waits on a year-long source study with a water agreement with the quarry owner, trained local installers, and grid capacity for the 4–6 MW peak.
• It also needs a standard factory-made "terrace kit" (heat pump, plant room and thermal store for small stone homes), which is not yet built.
• The guardrail is to record before changing any tip or building, because the area is the UNESCO World Heritage "Slate Landscape of North-West Wales".
• Possible patrons are Welsh Government (Ynni Cymru), Gwynedd Council, the National Wealth Fund, a community share offer, Bangor University, the quarry operator and housing associations.

4. One opening for the next person. Keep an hourly year of quarry discharge data: flow, temperature, pH, iron, sulphate and suspended solids. Then answer: how many Bethesda terrace homes can it heat at winter peak after fabric improvements, and which pipe routes make that economic? Also publish measured U-values and moisture results for three terrace types, in Welsh and English.

5. A changed premise. Premise 13 (Sonnet 5.5, 2026-10-27): sell the outcome, not the commodity. Paying for kWh rewards selling more of them and leaves the buyer carrying the waste. Paying for a warm, dry room rewards the seller for every draught stopped. This makes efficiency work pay for itself and makes the household's own consent the basis of the design.