Cornish
Farmyard
The fossil fuel industry will inevitably find ways to lower prices and increase sales and so the current crisis in maintaining the comfort and utility of existing dwellings and community buildings may pass. Nevertheless, the sudden unaffordability for energy for domestic use has increased interest in a Low Energy agenda for Dwelling and Meeting. This project shown here is a Cornish Farmyard built in local brown granite. The 120 m.2 Cowshed has a small upper storey gallery and bedroom and 2 ground floor bedrooms, The 90 m.2 Bull shed has an upper floor bathroom and 2 ground floor bedrooms and the 28m.2 Pig Shed ( previously 3 pig sties ) a single room that will sleep 4. The 25m.2 Muck Shed in the centre of the Farmyard is used communally and is unheated. Despite the use of biomass as background space and hot water heating the three dwellings used 5000 kWh between Nov’22 and Mar’23 down from 7.000 kWh for the same period the previous year when a newborn baby was in residence but daytime electricity was 1/3rd. the price.
The interior of the Cow Shed showing the North-facing sliding doors to the lawn the biomass boiler stove that heats a 300 litre. heatstore and underfloor heating network. The home office gallery can be seen above the kitchen table with its ‘paddle’ stair access. There are two bedrooms on the ground floor and another beyond the gallery. The floor, walls and roof soffites were all finished in timber planks on polyisocyanurate insulation boards to above Building Regs standards in 2015. Their performance is disappointing relative to the later Bull Shed which has additional layered foil insulation and is more airtight as a consequence of having plastered walls and ceilings.
The interior of the Bull Shed showing the plastered walls and double insulated flue to the biomass boiler that is a more than adequate space heater for the main room. Because of its enhanced insulation, lower volume and glazed areas and better airtightness the Bull Shed is easier to heat using mostly night-rate electrical energy for space and hot water heating during the winter. For much of the year solar hot water heating is adequate without supplement.
The Farmyard’s Pig Shed has a volume of 60m.2 i.e. 1/17th of the volume of the Holyrood shed -yet it has a heat demand scarcely 50% of the Holyrood shed. The comparison is a stark illustration of the greater thermal efficiency of deep plan multi-storey dwellings.
Water Source Heat Pump (WSHP) Discussion
Our tenants in the Cow Shed and Bull Shed lead busy lives and do not have the time to tend a biomass stove for a few hours each day. They need hot water in the morning and warm, dry rooms all day and night. As a result they use, in total, as much as £ 500 per month of electricity in the six months the houses are heated and the solar collectors do not provide much hot water.
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This is a cost we would like to reduce. Our '12-7' tariff reduces the price of electricity by about 30% but is not particularly convenient - except for charging an electric car. A heat pump with a Coefficient of performance between 3 and 4 should do more than halve the electricity costs. Were both biomass boilers scrapped then a new Heat pump installation could attract a grant of £ 15,000.
But we are not keen to become entirely dependent on electricity for heating as HMG seems happy to allow it to be priced extortionately. We would prefer to maintain an alternative energy supply and forgo the grant, which would in any case require expensive and pointless alterations to the heating system installed in 2012, in order to meet the geeky grant conditions.
Muck Shed Exterior
Muck Shed Interior
We have investigated Air Source Heat pumps but too many users tell us that at freezing temperatures they have a Coefficient of performance close to 1 because they need to defrost themselves.
We are fortunate that we have a 35 m.2 approx. body of rainwater in a brick cistern below the Muck Shed. The cistern is at least 100 years old and has a vaulted brick roof. It is located below the boarding seen in the Muck Shed interior. We hope to use the plentitude of stored water during winter to supply low grade heat to a KENSA 'shoebox' WSHP serving existing underfloor heating circuits in the Cowshed and the oversized radiator circuit in the Bullshed.
We are assuming heat to the 35 tonnes of water in the cistern will be replenished through its 27 m.2 of perimeter brick walls and 20 m.2 concrete base at a rate of 6 kW ( we assume wet ground to water interfaces have a ‘U’ value of over 20 W/ m.2 K).
The adjacent diagram and heat loss calculations show the configuration proposal that is currently being costed for implementation in 2025. However, WSHP alone costs £ 6 K. Underground ducting and new pipework will cost at least another £ 6 k.
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Assuming the heat pump operates at a 6kW rating with a Coefficient of performance of 3 using off-peak ‘12-7’ electricity for 7 hours a day for 200 days, then it will produce 200 day x 7 hr x 6 kW = 8,400 kWh / yr. at an energy supply cost of 200 day x 7 hr. x 2 kW = 2,800 kWh. This represents £ 840 p.a. at 30 p./kWh.
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If the same heating was provided by direct electrical boilers or convection heaters then it would cost three times as much at £ 2,520 p.a. The projected annual saving of £ 1,680 p.a. will mean the cost of the WSHP installation will have a payback period of about 8 years.
We are also looking into any rental value our wild 1.0 ha. field might have as Biodiversity Net Gain. It has not been treated with insecticides, herbicides or artificial fertilizers for 10 years and supports abundant worms, insects, frogs and toads, rabbits, foxes and badgers and a great variety of birds including a resident buzzard family and swarms of visiting swallows.
1,000 sapling were planted by the Woodland Trust in 2013. There are 12 indigenous tree species and many of the trees are beginning to mature. The field is also surrounded by fine existing Gorse and Hawthorn Cornish hedges and Blackthorn hedgerows.