organic-organic eutectic organic-inorganic inorganic inorganic inorganic-inorganic .... fusion 1.9·105 J/kg, specific heat in the liquid and solid state equal to ...
Simple to use Non-corrosive p g No or low supercooling No nucleating agent recyclable
Generally more expensive Lower latent heat density quite broad melting g range g Often q High volume changes during phase changes Can be combustible Some react with ith concrete (béton)
Salt-based
Generally cheap Good latent heat density Higher thermal conductivity Well defined PC temperature Non-flammable g and recyclable y Biodegradable
Need careful preparation Need additives to stablise for long term use Prone to supercooling Can be corrosive to some metals
From Phase change materials: overview Centre for sustainable engineering
Building g applications pp UNDERFLOOR
AIR EXCHANGER
WALL
Applications pp polymers
Encapsuled in plastic or metallic packaging
aluminium
steel
Applications pp
Impregnation porous materials as panelboard and concrete
Macrocapsule PCMs Microencapsulated PCMs
15 mm thick board = 9 cm thick concrete wall
Schematic view of a lightweight g g wall
8 m
Images g from P. Schossig g et al article
SEM (Scanning Electron Microscope) image of PCM micro-capsules in gypsum plaster
Properties p of PCMs Thermophysical properties - melting temperature in the desired operating temperature range - high latent heat of fusion per unit of volume - high specific heat to provide additional heat storage - small volume change on phase transformation - small vapour pressure at operating temperature - congruentt melting lti off the th pcm for f a constant t t storage t capacity it
Properties p of PCMs Kinetic properties high nucleation rate to avoid supercooling of the liquid phase high rate of crystal growth
Chemical properties - complete reversible freeze/melt cycle - no degradation after a large number of freeze/melt cycle - no corrosiveness to the construction materials - non-toxic - non-flammable non flammable
Stability y of PCM Stability of the proprieties of PCM after many cycles of charging and discharging must be guaranteed. guaranteed 20 years
7300 cycles
The major problem in using salt hydrates as PCM is that most of them melt incongruently.
The thermal capacity p y of p pure salt declines q quickly y from an initial value of 238 kJ/kg to 63 kJ/kg after 40 cycles.
Stability y of PCM Several technique to become stable the PCM has studied :
Calorimeter analysis allow to measure the thermal proprieties of Phase Change Material
provide in a short time, time the Accellerate cycles allow to provide, behavior of the PCM after many cycles of fusion and solidification
Measurement technique q DSC (Differential Scanning Calorimetry) Measure the temporal p variation of the thermal energy gy exchanged with the sample of PCM. The output of the measurement is the energy gy time diagram g (thermogram) Use a very small quantities of sample (1-10 mg)
TA (Thermal Analysis) Measure the temporal variation of temperature in the sample of PCM. The output p of the measurement is the temperature p - time diagram Use small or big quantities of sample (10 g – 10 kg)
Calorimeter analysis
Wall Application pp A PCM layer can be placed within wall constructions to increase the thermal mass of the house The room air temperature p results more comfortable and less varied
The energy consumption for both air conditioning and heating will decrease
Wall Application pp –1 A PCM layer can be placed within the wall close to the external layer DAY The PCM layer in warm days store a great deal of the energy that flows through the wall NIGHT The PCM layer release energy stored in the day outside and inside the building
Wall Application pp –2 A PCM layer can be placed within the wall close to the external layer with a ventilated air chamber DAY The PCM layer in warm days store a great deal of the energy that flows th through h the th wallll d due iin particular ti l tto th the solar radiation NIGHT The PCM layer release outside the energy stored in the day The ventilation in the chamber evacuates part of the energy stored
Wall Application pp –3 A PCM layer can be placed behind a glass and a air chamber
DAY The PCM layer is directly irradiated to solar radiation and store the energy NIGHT The PCM release the energy store in the day within the building If the energy want to be evacuate outside, the air chamber will be open and becomes ventilated
Wall Application pp –4 A PCM layer can be placed within wall constructions to increase the thermal mass of the house The PCM is contained to the internal finish The PCM exchange energy with the internal room Store energy when the air temperature is higher than the temperature of fusion Release R l energy stored t d when h th the air i temperature is lower than the temperature of fusion
Wall - confrontation
Glauber salts Na2SO4·10H2O melting temperature 32°C, density 1450 kg/m3, latent heat of fusion 1.9·105 J/kg, specific heat in the liquid and solid state equal to 3.6·10 3.6 103 J/(kg J/(kg·K). K).
Paolo Principi Dipartimento di Energetica Università Politecnica delle Marche Ancona (Italia)
Air temperature p (surface ( interne))
Thermal flow ((Wm-2) through g south wall
Underfloor applications pp Two PCM layer and plastic tube sandwich
time 2004/08/27 14:35:00
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Time
[ [°C]
Underfloor applications pp air temperature
50
45
40
35
30
25 BOX 3 BOX 4
20
15
10
5
0
time 40:00 2004/08/27 14:4
2004/08/27 11:50:00
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40:00 2004/08/26 21:4
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40:00 2004/08/26 04:4
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40:00 2004/08/24 18:4
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2004/08/23 17:10:00
2004/08/23 14:20:00
2004/08/23 11:30:00
[°C]
Underfloor applications pp surface temperature
80
70
60
50
40 R1 Box3 R1 Box4
30
20
10
0
time 2004/08/27 14:40 2 0:00
2004/08/27 11:50 2 0:00
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2004/08/26 21:40 2 0:00
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2004/08/23 22:50 2 0:00
2004/08/23 20:00 2 0:00
2004/08/23 17:10 2 0:00
2004/08/23 14:20 2 0:00
2004/08/23 11:30 2 0:00
[°C]
Underfloor applications pp surface temperature
50
45
40
35
30
25 R2 Box3 R2 Box4
20
15
10
5
0
Transparent p PCM façade ç panel p
Ceiling g air exchanger g
Ceiling g air exchanger g
NIGHT storing outside cooling
Night behaviour
DAY releasing stored cooling
Day behaviour
Ceiling g air exchanger g
Heat exchanging absorption
SOLID
LIQUID
release Daily cycle
The efficiency of PCM is associate with the heat exchanging
Heat exchanging Conduction Conduction Climate condition with temperature day - night
high
oscillation
of
Natural Ventilation The exchanging is facilitate with the natural air flow
Heat exchanging Artificial ventilation The changing and discharging is improved with mechanical system of ventilation
Hydraulic system The energy energ is carried through thro gh an system s stem with ith water ater or other liquid
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