Solar heat

Design aims: groundhouse is easily heated and cooled using the sun and thermal mass.  Solar hot water gain is maximised

  • glass south face maximises direct solar gain throughout the year
  • large 11m2 solar hot water roof array maximises indirect solar gain for both water preheating and piped underfloor heating
  • massive earth rammed sub floors and walls give high thermal mass, combined with high performance underground and roof insulation, gives stable  year round temperature
  • lean burn wood burner provides back up heat

Glass South Face – the entire front face opens onto the terrace.  Each room is glazed with operable windows for ventilation which sit over the top of trifolding doors supplied by Kloeber. These were selected for their durability and strength.  All glazing is double glazed to reduce heat loss.  The back skylights and air vents are triple glazed poly carbonate from ubbinck and all vents are gravity operated using yatching cleats and heavy organic bamboo cotton mix curtains from oecotextiles are used to reduce nighttime heat loss – further by the thermal drop down blind in the kitchen from luxaflex.

Solar Hot Water – a very large array is installed for heating water directly from the sun.  This is included in the design on the front of the building.  The Solex system uses black silicon tubing to carry the hotwater and a covering of glass tiles fitted to nulok roofing bars.  The result is 11m2 of roof which harvests hot water free from the sun.  Water is carried off the roof through an armacell stainless steel insulated pipe designed to carry high temperature water to the hot tank.  Key to the design is the very large domestic solar hot water tank supplied by Akvaterm.  At 1000 litres, the tank is 5 many times bigger than a conventional tank.  This enables the groundhouse to store plenty of hot water during sunny days, and retain a supply for cloudy days.  In practice, the house delivers plenty of solar hot water for showers for over half the year and during the winter, the hot water tank simply boosts the temperature to whatever you need using the inbuilt electric immersion heater.

Underfloor Heating – this simply enhances the heating efficiency already achieved by the ‘glass and mass’ passive solar design.  The systems works automatically, and kicks in after the solar hot water from the roof has first brought the domestic hot water tank up to temperature,  pumping hot water through the polypipe underfloor heating pipes.  The suns energy is taken off the roof and ‘injected’  deep into the large thermal mass of the floor and subfloor.  This performs extremely well and even during winter months, when the sun shines, water at 30-35 degrees C has been warming the floors. No energy is wasted from the roof.  It is simply stored throughout the year directly in the thermal mass, warming the floors and warming the home.

Exterior walls – construction follows the tried and tested ‘earthship’ rammed earth wall building technique using tyres as formers for the rammed earth.  Around 150 tonnes of rammed earth is created for the external walls. The result is a wall which is both indestructible and structurally stable.  The rammed earth is also enclosed in 100mm of underground insulation which acts as a ‘blanket‘ enabling the walls to act as giant storage heaters for the building.  Foamglas is the main underground insulation selected because of its stability and high recycled glass content. Damp proofing is achieved using visqueen ecomembrane, with its high recycled content, providing a permanent 0.5mm barrier around the wall and under the floors.

Internal Walls – constructed from solid upright timbers bolted to the floor and ceilings.  One side is skinned with fermacell, providing a very strong and stable structural ‘plasterboard’ made form recycled paper.  The walls are infilled with lime using a shuttering technique.  Although very time consuming, the result is a 90mm thick solid wall that provides both thermal mass and acoustic insulation between rooms.  It also provides an attractive timber and lime face to one wall of the bedrooms.

Floors – all floors are ‘warm’ earth cement floors.  The floor construction starts with laying of the sand blinded damp proof membrane, followed by the foamglass insulation.    On top of this is 175mm of compacted earth topped with 60mm of truck poured concrete subfloor across the entire building.  Before the concrete pour goes down, the underfloor heat pipes are laid, with one loop for each room and separate controls in the utility room.

Burners - the above design features achieve average temperatures which fluctuate around 19 degrees meaning little back up heating is required. On colder cloudy winter days back up heat is provided primarily by the Hwam stove specified by euroheat.  This self regulates, burns wood very economically and gives out a lot of heat.  The roundroom also contains a small esse stove specified by firesonline to heat this large room separately.