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