Energy storage Prof Phil Banfill Urban Energy Research Group OCTES workshop, 31 st October 2012

Urban Energy Research Group 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

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

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

Exposed thermal mass smoothes fluctuations

simple model: mass = storage T Thanks to Paul Tuohy

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

simple model T Comfort?

Comfort depends on T surface and T air T from EIV Passive House Standard House

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

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

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

Energy density - materials  Sensible heat  Stone, concrete etc MJ/m 3 °C  Water 4.15 MJ/m 3 °C  Latent heat  Eutectic mixtures, salt hydrates, organics (incl. waxes) up to 100 MJ/m 3  Chemical heat  Absorbents etc MJ/m 3 °C

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

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.

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.

Thank you for