Renewable Heat / Passivhaus Gary Wilburn Sustainable Construction Network
Heat - generating lowand zero carbon technologies
1. Ground source heat pumps (GSHP)I Ground remains at a fairly constant temperature (10-12°C) all year round at approximately 1.5 meters below the earth’s surface.I GSHP extracts heat from the ground to provide space (and water) heating to any building type.I Air source and water source heat pumps are also available.
GSHP: three main elements1. Ground loop. - Comprised of lengths of pipe buried in the ground, either in a borehole or a horizontal trench.2. A heat pump. - Evaporator - Compressor - Condenser.3. Heat distribution system. - Under floor heating or radiators for space heating and in some cases water storage for hot water supply.
Ground loopI Water (or other fluid) is circulated through pipes underground and passes through a heat exchanger that extracts heat and is circulated through a building (often underfloor heating, fan coils or oversized radiators).I Pipe work containing heat transfer fluid is either laid in ‘horizontal trenches’ or in a ‘vertical borehole’ and transfers the heat from the ground to be used for space or water heating.
GSHP EfficiencyI The efficiency of a GSHP system is measured by the coefficient of performance (CoP)I CoP= ratio of ‘units of heat energy output’ for ‘each unit of electricity used’ to drive the compressor and pumpI Typically every unit of electricity used to pump the heat, 3-4 units of heat are produced. Therefore, typical CoPs range from 3 to 4
2. Solar water heating Solar thermal hot waterI Converts energy from the sun to provide useful heat. Their most common application in the UK is to provide hot waterI Comprises of a collector with a heat transfer fluid mounted on the roof of the building. This fluid is heated by the sun and the heat is transferred by a heat exchanger to a separate water storage tank or a twin coil hot water cylinder inside the building, which is used to provide hot water
Solar thermal hot water: components1. Solar panelsCollect heat from the suns radiation and are usually fittedon the roof2. Heat transfer systemUses the collected heat to heat water3. Hot water cylinderStores the hot water that is heated during the day and supplies it for use later
Solar thermal hot water: types of system1. Flat bed panels - Realize temperatures of 35ºC - Good for supplying pre-heated water for a gas boiler or immersion heater - Commonly used and cheaper technology2. Vacuum tube - Suited to cooler climate due to reduced heatloss - Can heat water to 60ºC. May require no additional heating - Should be linked to a storage facility to store excess warmth in summer for winter season. - More expensive though generally claim to provide better winter performance
3. Biomass heatingAny biological mass derived recently from plant or animal matter, including: I Material from forests (roundwood, cutting residues and other wood brashings) I Dedicated crop-derived biomass (woody short-rotation coppice energy crops – willow and poplar, grass crops-miscanthus, timber crops) I Dry agricultural residues (straw, poultry litter) and: I Wet waste (slurry, silage), food wastes, industrial and municipal waste
Biomass: Low carbon source of fuelI Biomass is considered carbon neutral or low carbon if materials are derived from sustainable sources.I Some net emissions result from cultivation, harvesting, processing and transportation of fuel.I Local availability of fuel is important for reducing associated net carbon emissions.
Lifecycle Carbon Emissions comparisonI These figures include raw material supply, production, transport, energy generation and eventual disposalI Biomass more efficient when used for space heating as compared to electricity generationI Solid Biomass for heating typically gives reductions of about 90% as compared to fossil fuels
Passivhaus – a comfort standard? I No draughts I No cold radiant I No summer overheating I Fresh air always I Whole house warm - no hypothermia I Fuel Poverty eliminated
Passivhaus – Simplicity I Extra insulation I Extra panes of glass I Full ventilation system I And clever design… - Site layout - Insulation and thermal bridges - Solar gain and protection - Air tightness and ventilation
Retro-fit housing...I Passivhaus targets for a retro-fit homeI Prewett Bizley ArchitectsI 22 kWh / m2 achievedI Victorian terraceI MVHR and air tightness challengesI Owned by a Building Physicist!
Passivhaus ConstructionI Use of bioregionally sourced materialsI Manufactured, high quality solutionI Off-site modular formatI Maximising insulation, minimising energy useI Known technology and construction details
Charts created using heating system data created Elevation G (NORTH 1)by DSM in IES and lighting dataDomestic Retro-fit (after)
Paultons ParkWorking closely with the client team at Paultons, HPW have createda low carbon, wild flower roofed and naturally ventilated indoorplay areaThe building will form the centre piece to the new attraction at the wellknown amusement park for ‘Peppa Pig’ and his friends. With underfloorheating, wind catchers, super insulated building shell, rainwater harvesting,hybrid frame and locally sourced timber cladding the 10,000 sq.ft facilityis due to open in spring 2011