Energy storage

Prof Phil BanfillUrban Energy Research GroupP.F.G.Banfill@hw.ac.uk OCTES workshop, 31st 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 storageAims 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 storageAims 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

fabric losses

thermal storage

ventilation losses

internal gains:lights, appliances,

cooking,hot water, occupants

outside temperature

solar gains

inside temperature

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

2 O c t o be r d a ys – low m as s

s u rf ac e te mp

s o la r g a in s

a ir te mp

2 O c t o be r d a ys – h ig h m as s

s u rf ac e te mp

He a t lo a d s

o u ts id e te mp

simple model

T

fabric losses

thermal storage

ventilation losses

internal gains:lights, appliances,

cooking,hot water, occupants

outside temperature

solar gains

inside temperatureComfort?

Comfort depends on Tsurface and Tair

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

2 O c t o be r d a ys – low m as s

s u rf ac e te mp

s o la r g a in s

a ir te mp

2 O c t o be r d a ys – h ig h m as s

s u rf ac e te mp

He a t lo a d s

o u ts id e te mp

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

2 O c t o be r d a ys – low m as s

s u rf ac e te mp

s o la r g a in s

a ir te mp

2 O c t o be r d a ys – h ig h m as s

s u rf ac e te mp

He a t lo a d s

o u ts id e te mp

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 reactionsThe important parameter is the energy

density = heat change x density

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

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 listening

P.F.G.Banfill@hw.ac.uk

@HWUrbanEnergy