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Phase Change materials for cold storage applications
Peter Schossig
Fraunhofer-Institute for solar energy systems ISE
Preheat workshop at CETIATLyon, 4.07.2006
content
why cold storage with PCM
wall materials with PCM passive active systems
phase change slurries microcapsules suspensions emulsions
the pcm quality mark
conclusions
example: cold market in italy
• EU Study (EERAC) 1996: four times the floor area conditioned in 2020 ( for offices: 27% in EU, 80% USA, > 90% Japan)
• 2002 worldwide 15% of electricity for cold production (source: IIR)
sensible versus latent storage
for most PCM,
sensible heat < water
Why store cold with PCM?
cold applications often need small temperature ranges
cold demand is increasing
cold is often more expensive (~3 times)
load curve of cold demand is similar to load curve of electricity demand -> higher peak loads -> short time storage is helpful
more cycles can be reached than for long therm storage applications
cold production is more efficient at lower target temperatures
Phase change Materials in walls
lots of research in the 70´ies
direct immersion or macrocapsules
patents and papers, but no products due to:
leakage, interference with other material parameters
lots of work to integrate
risk of damage
low heat conductivity of PCM
one Solution: microencapsulation
Phase change Materials in walls
development project with the partners BASF, caparol, maxit and Sto with Fraunhofer ISE 1/1999 - 9/2004
funded by BMWA
used as normal materials at the construction site
measurements
two identical rooms measured without and with two PCM products monitored one year each
result: - 4 K difference reached- night ventilation essentiel
wall surface temperatures for 15 mm gypsum plaster with 20% PCM and 0% PCM
result:
products on the market
some products based on microcapsules (plaster, plasterboard, dispersion based plaster)
two companies selling macro-encapsulated PCM:
Dörken
Rubitherm
BASF: micronal
www.micronal.de
active PCM-systems
passive systems suffer from two limitations:
wall to air heat exchange coefficient
only cold source is night air at dry bulb temperature
solution:
active driven systems
enhanced heat transfer coefficient
any source can be connected
development project 9/2004 - 8/2007
BASF, caparol, maxit, BTU Cottbus, Fraunhofer ISE
funded by BMWA
Testrooms
Simulation tool
to calculate:
• comfort
• energy saved
• economie
needs::
• easy to use
• fast caculating
Simulation tool
should help to:
• choose the right system
• choose the right material
• determine the area needed
phase change slurries (PCS)
advantage : greatly enhanced storage/transport capacity in small temperature range, thus:
smaller storages
reduced losses due to isothermal storage
lower pumping energy due to lower mass flow
increasing the storage/transport capacity of a existing system just by exchanging the fluid
research-project 12/2001 - 11/2004 ; funded by EU
carrier fluid + PCM
e.g. water/water glycolas fluid und Paraffin-microcapsules as PCM
First results with 20 µm capsules (3 weeks of pumping)
Improvement with 5 µm capsules (6 month of pumping)
Heat capacity of PCS comp. to water
Small melting ranges
factor of 4 times better than water possible today
Subcooling increases the temperature
range of a PCS application
ready for demonstration plants/applications
30% 150 kJ/kg
0
2
4
6
8
10
12
14
16
18
20
0 2 4 6 8 10 12 14 16 18 20melting range [K]
storab
le heat
- fact
or to
water
[-]
50% 150 kJ/kg
40% 150 kJ/kg
35% 150 kJ/kg
standardisation
In 2004 german companies founded a quality mark group „PCM“
BASF, rubitherm, dörken, SGL, arcadis,…
ZAE-Bayern and ISE asked to develop standard procedures for measuring PCM properties
3 quality criteria: enthalpy stability conductivity
since may 2006 standard public, see www.ral.de
Conclusion The rising cooling market requires new techniques
to increase the efficiency of cooling for room conditioning
PCM and PCMS offer the possiblity to store heat at small temperature ranges close to the target temperatures needed for air conditioning
network load balancing/peak shifting possible with thermal energy storages
driven by developmenents in the cooling sector, PCM for heat storages may reach the market in future
First products on the market, but still research needed