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Heat and Power Sources for Buildings. Overview energy requirements of buildings traditional energy sources carbon emissions calcs LZC energy sources –low-carbon.

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Presentation on theme: "Heat and Power Sources for Buildings. Overview energy requirements of buildings traditional energy sources carbon emissions calcs LZC energy sources –low-carbon."— Presentation transcript:

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 space heating hot water electricity – lighting – appliances – cooling –… also for space heating and hot water Energy Required

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

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 % 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 kgCO 2 /kWh (DEFRA)

8 Emissions how do we calculate emissions? example – natural gas: CH 4 + 2O 2 CO 2 + 2H 2 O (16) (44) or 1 kg 2.75 kgCO 2 /kgCH 4 or x (12/44) = 0.75 kgC/kgCH 4 (CO 2 and Carbon coefficients resp.) energy content of nat. gas 93MJ/m 3 or 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 CO 2 /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 CO 2 /kWh

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

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

15 CHP –the CHP prime mover depends upon the application 1kWe >1MWe Stirling ICE (gas) 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/m 2 falling on a 1m2 panel will generate 72W typical energy yields are ~100kWh/m 2 /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 buildings 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 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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