Solar Electric Photovoltaic Array (PV): After much debate on the ideal location for a PV array with the NT internal architectural review board, it was concluded the only sensible place was up on the main mill roof clear of most tree solar shading and out of the reach of vandals and thieves. The rooftop positioning of the PV array was accepted only on the grounds that it could at some point be removed with negligible impact on the listed building historic fabric. For this reason the PV array was set up above the existing stone slate roof on proprietary 150mm ‘stand off’ Oatey integrated upstands and flashings. Proprietary stainless steel and aluminium rails formed a framework to support 24 No Kyocera 120Wp PV modules and 48 No Kyocera 60Wp PV modules. The total PV array rating was 4,320Wp connected in parallel to a junction box mounted in the roof attic space and hard wired to the public display switch gear exhibit.
Biomass Heating Systems: A 60kW peak downdraft log burning boiler was installed in the former engine house supplied by Econergy. The boiler has a batch feed hopper and is capable of operation under natural draught conditions. The boiler was oversized to allow once a day firing, and will operate at a higher than required temperature to minimise environmental effect. A single skin grade stainless steel flue exits from the stove outlet and runs inside a new lining in the existing tall mill chimney. This primary stove supplies hot water to a 1200 litre pre-insulated stainless steel accumulator tank located in the cafÃ© kitchen to provide 85 degree water for hot drinks and 65 degree hot water for washing up etc. The hot water for hot drinks is topped up to 100 degrees with an electrically operated instantaneous water heater at the cafÃ© serving hatch.
A 14kW traditional Swedish ‘Kakkelovn’ thermal mass log burning space heater stove was installed in the cafÃ© seating area by Oxford Stoves. It draws air from the room through a duct, past, but not through, the firebox and out through vents in the doorframe. The five-channel flue system was developed in 1767 by Cronstedt and Wrede in Sweden and is still the system in use in most stoves of this type to this day. While passing through this extended internal flue, the flue gases impart their energy to the thermal mass, dropping in temperature from the initial burn temperature of 900-1100 degrees C to less than 200 degrees before exiting to the chimney. After only one burn process at the beginning of the day the heat deposited into the thermal mass of the stove is emitted over a 12 hour long period during the rest of the day. The ceramic stove is the principal source of high-quality heat permeating throughout the walkers’ refuge cafÃ© space. This efficient heating system saves on the use of traditional precious fossil fuel, extends the life of the heating system output beyond the initial burn process and reduces indoor pollution.
To service the resident warden’s house a 20kW Warmsler biomass timber fuelled kitchen stove and combined boiler producing central heating, cooking and domestic hot water was fitted in the kitchen hearth. A 5kW clean burning Clearview Vision space heating stove was also fitted in the Warden’s living room as a social focus and to provide alternative viewing to the TV.
It was calculated that the annual fuel requirement for the whole project is 17 green tonnes. This can easily be met from arisings from the woodland management on the estate’s 66 hectares of mixed woodland under a new sustainable management regime.
Battery Storage: A battery store consisting of 24 No of lead-acid cells has a total available capacity of 48kWh. The store is utilised to â€œsmoothâ€ inputs and demand peaks, and to provide electrical energy to appliances in periods of low hydro and PV input. The battery cells are sealed gel, valve regulated maintenance free type. We are generally not keen on battery storage systems because of the environmental consequences of their future disposal but on this site we did not have the luxury of using the national grid for net metering or long term storage.
Renewable Energy Control System: A central feature of the public display of the sustainability exhibition was the renewable energy control system switch board and data logging panel, laid out to be easily interpreted by the lay public. The control panel was designed to be flexible, and automatically prioritises key loads in times of low energy input. The control system also incorporates easily understood status displays, easy to read metering dials and data logs giving staff the necessary information to manage the energy resource and avoid an embarrassing energy blackout during public visitor access times.
Solar Water Heating: An AES solar water heating system was integrated onto the end of the PV array to supply domestic hot water service to the warden’s cottage during the spring, summer and autumn months. The solar heated hot water flow and return pipes feed into a twin coil hot water cylinder, located in the warden’s airing cupboard.
Site Sewage Treatment System:
A private water supply and wastewater treatment system was the only practical option for this remote site but the autonomy brief also called for sewage solids to be treated rather than tankered away. Dry compost toilets were considered for the public but rejected by the client in favour of conventional looking but water efficient WCs. As well as the ‘no tanker’ brief, access to the public toilets is by a narrow bridge so a sludge-free system made sense.
The solution chosen was based around the Swedish Aquatron separator. This simple passive (non electric) device uses surface tension to separate the solids from the flushed water, for composting in one of two prefabricated bio-chambers located in the room under the toilets. These dry composting chambers are primed with worms to accelerate the decomposition process of the solid faeces. In time the dried out and fully composted solids will be returned to the woodland floor as a benign fertilizer. The separated urine and flush water liquid effluent from the Aquatron separator flows to an un-powered dosing device, which delivers pulses of liquid black water effluent along a below- ground infiltration trench. The sandy soil provides filtration and biological treatment without odour, pollution or energy use and not a reed bed in sight.
The visitor toilet Stable Block is served by robust but super-efficient 4 litre IfÃ¶ WCs with traditional leak-free siphons and IfÃ¶ Cero waterless urinals. When temperatures dropped to -13C this winter everything froze solid but the urinals continued to work without the risk of bursts or flooding. Once the WCs had thawed they worked fine with no leaks or damage to the tough and simple siphon.
Located across the river from the Aquatron system, the staff and cottage needs are served by compact compost toilets. The historic buildings precluded the use of larger vault type toilets, which are more robust but would have required excavation of the building floor. The warden’s cottage was fitted with a single Canadian Sunmar Excel dry compost toilet and the Toll House disabled toilet and staff toilets were fitted with Swedish Separrett dry compost toilets linked to a single fan assisted extract flue fed up through the existing chimney.
Locally Sourced Spring Water Supply:
Fortunately a reliable and pure spring was found on site that was just high enough to supply all the buildings by gravity without the need for pumps or treatment. New fence enclosure constructions protected the source from deer and sheep droppings and wandering dogs. A concealed and landscaped header tank was built to provide a small backup supply if short-term demand exceeded the springs natural supply flow rate. A below ground pipe safely delivers the drinking water to the mill and outbuildings. Finding a free flowing source of water pouring out of the hillside might seem to make water efficiency measures redundant, however dramatically reducing the water use simplified wastewater treatment and onsite disposal design. Low water use design strategy also demonstrated best practice to the visiting public and in addition provided performance and reliability advantages. With limited power, hot water was not considered feasible for the remote toilet block but the use of spray taps minimises the discomfort from washing hands in unheated water whilst also further reducing effluent volumes.