Energy storage
Prof Phil Banfill
Urban Energy Research Group
P.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 storage
Aims to reduce energy consumption by smoothing out the
fluctuations – whether electrical or thermal energy
temp
Heat surplus
Desired temp
Heat deficit
time
Ambient temp
Energy storage
Aims to reduce energy consumption by smoothing out the
fluctuations – whether electrical or thermal energy
temp
Heat surplus
Store this heat
Desired temp
Heat deficit
time
Ambient temp
Exposed thermal mass smoothes
fluctuations
simple model: mass = storage
solar
gains
internal gains:
lights, appliances,
cooking,
hot water,
occupants
ventilation
losses
T
inside temperature
fabric
losses
Thanks to Paul Tuohy
thermal
storage
outside temperature
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
simple model
solar
gains
internal gains:
lights, appliances,
cooking,
hot water,
occupants
ventilation
losses
T
Comfort?
inside temperature
fabric
losses
thermal
storage
outside temperature
Comfort depends on Tsurface and Tair
Standard
House
Passive
House
T
from EIV
simple model: mass = storage
low thermal mass:
surface temperature
is responsive to solar
gains and heating
2 days in October
high thermal mass:
surface temperature
less responsive to
solar gains and
heating
T
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?
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 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