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Heat and Power Sources for Buildings

Heat and Power Sources for Buildings. Overview. energy requirements of buildings traditional energy sources carbon emissions calcs LZC energy sources low-carbon energy sources renewable (zero-carbon) energy sources. Energy Required. space heating hot water electricity lighting

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Heat and Power Sources for Buildings

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  1. Heat and Power Sources for Buildings

  2. Overview • energy requirements of buildings • traditional energy sources • carbon emissions calcs • LZC energy sources • low-carbon energy sources • renewable (zero-carbon) energy sources

  3. Energy Required • space heating • hot water • electricity • lighting • appliances • cooling • … also for space heating and hot water

  4. sources: boilers, chillers, electricity supply distribution: cables, ducts, fans, pumps, piping, etc. delivery: radiators, underfloor heating, lights, diffusers, etc. control: thermostats, dampers, valves, timers, PID controllers, etc. environmental system

  5. Traditional Energy Sources • space heating – gas, oil or solid fuel boilers, direct electric, electric storage heating • hot water - gas, oil or solid fuel boilers, direct electric heating • electrical equipment and appliances – power from the grid • … ultimate energy source typically fossil fuels

  6. Boilers • the main function of the boiler is to convert the potential energy of a fuel to heat • In the UK this is typically in the form of hot water or steam (larger systems) • boilers can be: • condensing (recover latent heat from flue gases) • combination (instant hot water) • typical device efficiencies range from 70-90% depending upon age, features and fuel type • fuels: natural gas, oil, solid fuel

  7. Grid • grid electricity ultimately comes from large central power stations: • combined cycle gas turbine (η=50+%) • coal/oil power station (η=35%) • nuclear power station (η=35%) • grid electricity carbon intensity: 0.53 kgCO2/kWh (DEFRA)

  8. Emissions • how do we calculate emissions? • example – natural gas: • CH4 + 2O2→ CO2 + 2H2O • (16) → (44) or 1 kg → 2.75 kgCO2/kgCH4 or x (12/44) = 0.75 kgC/kgCH4 (CO2 and Carbon coefficients resp.) • energy content of nat. gas 93MJ/m3 or 51.12 MJ/kg or 14.2 kWh/kg • so for an 80% efficient boiler, C emission for 1kWh of heat • C = (energy/(efficiency x energy content)) x carbon coefficient • C = (1/(0.8 x 14.2)) x 0.75 = 0.07 kg C/kWh = 0.24 kg CO2/kWh

  9. Emissions • Similarly …. • so for an 35% efficient coal power station C emission for 1kWh of electricity • C = (energy/(efficiency x energy content)) x carbon coefficient • C = (1/(0.35 x 10)) x 0.9 = 0.26 kg C/kWh = 0.94 kg CO2/kWh

  10. sources: boilers, chillers, electricity supply LZC sources: CHP, PV, solar thermal, etc. distribution: cables, ducts, fans, pumps, piping, etc. delivery: radiators, underfloor heating, lights, diffusers, etc. control: thermostats, dampers, valves, timers, PID controllers, etc. environmental system

  11. Low Carbon Energy Systems

  12. Combined Heat and Power (CHP) • CHP (combined heat and power) is the simultaneous generation of heat and power from a single conversion device • CHP technologies: • ICE – internal combustion engine • SE – stirling engine • gas turbine • fuel cell (SOFC)

  13. CHP • CHP is classed as low carbon as it makes use of the waste heat produced by a thermodynamic cycle • this is not done in conventional power generation – the heat is typically rejected to atmosphere

  14. CHP 83 waste 100 fuel 108 fuel 25 electricity 30% eff. power station 180 fuel total 10 waste 90% eff. boiler 65 heat 72 fuel 90% eff. CHP 7 waste

  15. CHP • the CHP prime mover depends upon the application 1kWe Stirling ICE (gas) >1MWe ICE (diesel) Gas turbine

  16. CHP • typical device efficiencies : 85-95% • heat/power ratios: • 8:1 stirling engine; • 2:1 ICE; • 1:1 gas turbine • fuel cell CHP is still a research area with lots of work to be done before these devices appear on the market

  17. CHP • CHP device coupled into heating system

  18. Heat Pump • heat pumps move heat energy from a low temperature heat reservoir to a high temperature reservoir (e.g. the building) using a refrigerant cycle • heat pumps can use the ground, water or even the air as the low temperature reservoir • the cycle is driven by a compressor, which consumes electricity

  19. Heat Pump • heat pump performance is measured using a quantity known as the coefficient of performance (COP) • COP = useful heat output ÷ energy consumed by compressor • so for a COP of 4 (typical) 1kWh of heat will require 0.25 kWh of electricity • the cycle can also be reversed to surplus heat from the house can be returned to the ground (e.g. summer cooling) • heat pumps (arguably) have the greatest carbon saving potential of any low carbon technology • if powered using renewable electricity heat pumps become zero carbon devices

  20. Heat Pump

  21. Zero Carbon Sources

  22. Photovoltaics • photovoltaic devices (PV) convert sunlight directly to electricity • PV is based on semiconductor technology • the most common material used is silicon • the basic unit of a PV system is the cell:

  23. Photovoltaics • individual cells are wired together and encapsulated in a panel • groups of PV panels installed on a building are called an “array” • silicon PV is typically 12% efficient • so an incident solar intensity of 600W/m2 falling on a 1m2 panel will generate 72W • typical energy yields are ~100kWh/m2/yr • conversion efficiency is dependent upon: • the PV material used • temperature • solar intensity • the load

  24. Photovoltaics • PV power is intermittent – the amount being produced being determined by the solar intensity • PV produced DC electricity – which can be used directly for battery charging • connecting to AC loads requires the power from the panel is inverted • PV is usually connected to the building’s electrical system via a power electronic interface • this maximises the PV efficiency and converts ac → dc

  25. Photovoltaics

  26. Micro Wind • micro wind power devices generate electricity from air flow around a building • typical devices are horizontal axis machines – smaller versions of large scale machines • typical device ratings are 1-5kW (@5-6 m/s) • however the rated wind speed is rarely achieved in urban areas in practice (2-3 m/s) • better suited to more isolated buildings or unobstructed air flow

  27. Micro Wind • flow in urban areas is highly turbulent and not ideal conditions for turbines • wind speed and direction can vary wildly in short distances • proper siting is critical to achieve the best yield

  28. Micro Wind • the best site for a turbine can be predicted …

  29. Other Zero Carbon • solar thermal • flat plate • evacuated tube • biomass/biogas boilers • hydrogen fuel cell

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