Energy storage Prof Phil Banfill Urban Energy Research Group P.F.G.Banfill@hw.ac.uk

1. Energy storage Prof Phil Banfill Urban Energy Research Group P.F.G.Banfill@hw.ac.uk OCTES workshop, 31st October 2012

2. Skills/Experience in retrofit and new build: • Building simulation and modelling, including district and regional scale • Climate projections • System and equipment integration • Energy monitoring and analysis / metering • Retrofit measures - domestic and non-domestic • “Soft Landings” initiative - users and commissioning • Life Cycle Assessment - environmental impacts • Whole Life Costs • Thermal comfort • “Solar cities” initiative • £3.5m research project funding since 2004 Urban Energy Research Group

3. Energy storage Aims to reduce energy consumption by smoothing out the fluctuations – whether electrical or thermal energy Heat surplus Desired temp temp Ambient temp Heat deficit time

4. Energy storage Aims to reduce energy consumption by smoothing out the fluctuations – whether electrical or thermal energy Store this heat Heat surplus Desired temp temp Ambient temp Heat deficit time

5. Exposed thermal mass smoothes fluctuations

6. simple model: mass = storage T Thanks to Paul Tuohy

7. simple model: mass = storage low thermal mass: surface temperature is responsive to solar gains and heating T high thermal mass: surface temp less responsive to solar gains and heating

8. simple model T Comfort?

9. Comfort depends on Tsurface and Tair Standard House Passive House T from EIV

10. simple model: mass = storage low thermal mass: surface temperature is responsive to solar gains and heating 2 days in October T high thermal mass: surface temperature less responsive to solar gains and heating

11. simple model: mass = storage low thermal mass: surface temperature is responsive to solar gains and heating Faster response to heating system? T high thermal mass: surface temp less responsive to solar gains and heating Better storage of solar and internal gains?

12. Types of thermal storage • Sensible heat – i.e. elevated temperature, thermal mass • Latent heat – by change of phase • Chemical heat – by exo- or endo-thermic chemical reactions • The important parameter is the energy density = heat change x density

13. Energy density - materials • Sensible heat • Stone, concrete etc 1.5-3.5 MJ/m3°C • Water 4.15 MJ/m3°C • Latent heat • Eutectic mixtures, salt hydrates, organics (incl. waxes) up to 100 MJ/m3 • Chemical heat • Absorbents etc 100-200 MJ/m3°C

14. Phase change materials • Phase change materials as room linings can make a difference • Wax impregnated gypsum wallboard

15. Potential applications / systems • Room linings – products already available but issues of phase change temperature. • Storage tanks = “heat batteries” but issues of heat exchange, size, location.

16. Conclusions • Low thermal mass buildings respond faster to heating and occupancy • High thermal mass responds slower but stores the internal gains • Heat can be stored in various materials with a range of efficiencies – significant amounts of material are needed for the effects to be worthwhile. Issues of cost.

17. Thank you for listening P.F.G.Banfill@hw.ac.uk @HWUrbanEnergy