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LEAF Log stove project Technical team

LEAF Log stove project Technical team. Jacinta MacDermot Rob Gwillim Chris Laughton. RHI and log stoves. RHI =Renewable Heat Incentive Introduced in phases; Non-households first Household phase delayed till 2013 RHPP = Renewable Heat Premium Payment

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LEAF Log stove project Technical team

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  1. LEAF Log stove projectTechnical team Jacinta MacDermot Rob Gwillim Chris Laughton

  2. RHI and log stoves • RHI =Renewable Heat Incentive • Introduced in phases; Non-households first • Household phase delayed till 2013 • RHPP = Renewable Heat Premium Payment • Community groups and social landlords ‘competition’ • Biomass boiler - £950 grant (for homes without mains gas heating) • No log stoves !

  3. Why are log stoves not RHI eligible? Difficult to measure heat output Some wood fuel not ‘renewable’ Multi-fuel stove market saturated Air heating without using water – excluded Intermittent vs primary use Fossil fuel – user interaction Fossil fuel (ignition process, pumps, fans) Air emissions Perceived low efficiency

  4. Improving RHI compatibility- Heat measurement challenges Stoves emit most heat by convection and radiation Some stoves have ‘back’ boilers heating water Pump vs thermosyphon Surface temperatures at various temperatures Chimney losses Combustion air replacing room air Fuel temperature Combustion efficiency varies Calorific content and moisture content

  5. Improving RHI compatibility- Heat measurement experiment New and old stove installations Machynlleth and Newtown Provide logs of known moisture content Users measure the mass burned each load Temperatures of stoves and flue recorded Flue gas velocity/mass flow calculated at full burn Theoretical efficiency looked up Infra-Red images for spread of heat Theoretical radiant emissivity and convection rates

  6. Moisture content results

  7. Recording temperatures

  8. Infra Red Camera

  9. Temperature results

  10. Temperature vs fuel input

  11. Snapshot averages measured in operation • Flue temperature 133 C • Top of stove casing 136 C • Mid stove casing 106 C • Bottom of stove casing 71 C • Stove glass 150 C

  12. Average derived or manufacturer values at rated output • Stove efficiencies 75 % (probably gross) • Minimum flue draught 12 Pa • Mass flow-mass 7 grams/second • Flue speed 0.44 metres/second • 290 C

  13. Method A • Erhi = Eligible heat for RHI • Ein = Calorific value of wood • Effic = Efficiency of combustion net (lower) Method A Ein * Effic = Erhi Erhi Ein * Effic

  14. Method B • Ein = Calorific value of wood • Eflue = Lost energy up flue • Eair = Energy lost through combustion air change • Esundry = Energy lost from cold fuel, opening doors • Eelec = Pump or fan or ignition power • Erhi = Eligible heat for RHI Method B Ein – Eflue – Eair – Esundry – Eelec = Erhi Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Ein Erhi Eelec Eflue Esundry Eair

  15. Method C • Erhi = Eligible heat for RHI • Eemis = Energy emitted from stove as radiation • Econv = Energy convected from stove by hot air • Ewater = Energy circulated from the stove to water Method C Erhi = Eemis + Econv + Ewater Eemis Erhi Econv Ewater

  16. Method D • Erhi = Eligible heat for RHI • Eair = Energy lost through combustion air change • Esurfaces = Energy heating room surfaces Method D Erhi = Eair + Esurfaces Eair Erhi Esurfaces

  17. Proposals for improving RHI compatibility • For new stoves and chimneys or re-lined • For stoves tested to EN 13240 • Maintenance service agreement • Known wood supply to less than 25% MC • Primary heat source – not intermittent use • Not possible for appliance to be multi-fuel • Thermosyphon heat to be deemed • Recording method for proof of use

  18. Margins of error • Temp sensor calibration and insulation • Recording (logging) failures • Deviation of moisture content samples • Chimney calculation – Missing Appliance Data • Fuel not meeting manufacturer’s minimum • Non-compliant installations – Combustion air • Non-representative temperature locations

  19. The Solar Design Company 0845 519 7914 www.solardesign.co.uk

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