Energy storage
Prof Phil BanfillUrban Energy Research [email protected] 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
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?
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.
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