Phase Change Materials (PCM)

Phase Change Materials (PCM)

University of Minho5/11/2015Master of Sustainable Rehabilitation and Construction Group:Rita CorreiaAhmad Alshaghel

Outline Introduction What is a PCMPCM physical principle and behaviorWater as a PCMPCM ClassificationPCM general applicationsPCM applications in building Case studyPCM role in sustainability PCM challengesFurther researchConclusionsSuggestions

Introduction

Human comfort requirements and associated consequences

Environmental ImpactEconomicalImpact

Economical Impact instead of Cost Money !!!3

Introduction Energy consumption

Energy production is the main pollution source in the world!Energy for heating, air conditioning and ventilation

Introduction HVAC needsGreenhouse gas emissionsClimate changesAir pollutionEconomical costsHVAC impacts

What is a PCMDefinitionAphase-change material(PCM) is a substance presenting a high heat of fusion, and capable of storing and releasing large amounts of energy. Heat energy is absorbed or released when the material changes from solid to liquid phase and vice versa, thus, being classified as latent heat storage (LHS) units.

PCM physical principle and behaviour

Latent heat

Latent heat

PCM physical principle and behaviour

Latent HeatSensible HeatPCM physical principle and behaviour

Water as a PCM

Water as a PCM

Heat (energy) is transferred into the ice.The heat is used to break the bonds between molecules, not to increase the average kinetic energy of the molecules.Since the bonds among the ice molecules have been broken, water is formed. The water molecules, at this moment, have the same average kinetic energy as they did when they were ice.

Since the ice and water molecules both have the same average kinetic energy, they are at the same Kelvin temperature.

Changing levelsWater as a PCM

PCM classification

PCM application in buildingORGANICINORGANICAdvantages availability in a large temperature range freeze without much super cooling ability to melt congruently self nucleating properties compatibility with construction materials no segregation chemically stable high heat of fusion safe and non-reactive recyclable high volumetric latent heat storage capacity low cost and easy availability sharp phase change high thermal conductivity non-flammableDisadvantages low thermal conductivity, low volumetric latent heat storage capacity flammable (depending on containment) high volume change super cooling segregation

B. Zalba et al. / Applied Thermal Engineering 2 (2003) 251283Inorganic PCMsPCM classification

Organic PCMsPCM classification

PCM general applications

Commonly used PCMs PCM general applications

PCM application in buildingTemperature controlHuman comfort

PCM application in buildingTemperature ranges - Comfort zone

PCM application in buildingThermal loads in buildings

PCM application in buildingInsulation Improving thermal massPCM materials help avoiding peak temperatures by

storing the excess heat during the day

and releasing it during the night

PCM application in buildingHeating and cooling systems - Energy storageHuge energy savings

PASSIVE SYSTEMSAutomatically release the heat or cold stored

ACTIVE SYSTEMSRequires: fans, pumps, control system

Advantagestored energy available when needed

PCM application in building

PCM integrated into the building structure PCM application in building

PCM integrated into the building structure PCM application in building

PCM integrated into the building envelopePCM application in building

PCM application in building PCM in other building components

PCM application in building PCM in other building components

. A prismatic pane in the outermost air-gap reflects the solar in summer and transmits it at altitudes below 35 in winter. The storage material is a salt hydrate PCM (with a storage capacity equivalent to about 20 cm concrete). During night time the stored heat is delivered to the interior during recrystallization. The salt hydrate is contained in a Polycarbonate box. The interior toughened glass pane could optionally be coated with a screen printing. The whole system appears as a translucent wall.

PCM in separate heat and cold storage devices

46 % Savingscompared to traditional best practicePCM application in building

PCM in HVAC systemsPCM application in building

Fixed-bed Tubes

Heat Exchanger, stackable & wall Mountable PCM-Filled Profiles

PCM application in building PCM in building Example of energy savings

Which PCM for building? Depends on the application!Different temperature ranges needed PCM application in building

Operational needs PCM propertiesPCM application in buildingThermal Phase change temperature High enthalpy volume near temperature of use High thermal conductivity in both phases Chemical Stability No phase separation Compatibility with container materials Non-toxic Non-flammable Non-polluting

Physical Low density variation High density Small or no sub cooling

Economic Cheap Abundant

Direct application Raw material

PCM Integration methodsPCM application in building

Macro Encapsulated PCM

Microencapsulated PCM honeycomb wallboardMicroencapsulated PCM

Shape-stabilized PCM

PCM Integration - MicroencapsulationPCM application in building

PCM Integration Shape-stabilizedPCM application in buildingParaffin as dispersed PCM and (high density polyethylene) HDPE or other material as supporting material

No need for special latent storage device or containers to encapsulate the PCM

it has the defect of rigidity- Supporting material absorbs the paraffin in liquid state (Ex. HDPE) graphite or carbon fiber acts as a thermal conductive component The paraffin and supporting material are mixed evenly and co-extruded The shape of the product-plate, rod, pellet, etc. varies according to application In order to prevent the possible leakage of paraffin, a surface treatment, such as grafting and cross-linking is carried out Particles (at the order of magnitude of tens of micrometer) are dispersed evenly in the polymer matrix The polymer network stands still to support the shape The concentration of the paraffin defines the heat storage capacity (80% - Optimal value)

Shape-stabilized PCM

Case Study

Microencapsulated PCM in Office Blocks, Germany

Case Study 2 comparable rooms in different floors, 1 ceiling with PCM material, the other with conventional plaster

Case Study

The air temperature was recorded at three different heights (0,1 m, 1,1 m, 1,8 ) temperature sensor for the surface temperature on the surface of theThe area of the test roomswas 45 m and with the net height of 3,2 m the resulting air volume was 144 m

No cooling

Case Study

The study took place between 17.08. 2004 and 20.10.2004

PCM role in sustainability Sustainability DimensionsPCM ImpactEnvironmental

Important Energy Savings

Social

Improved Human comfort

Economical

Energy Costs Reduced

PCM ChallengesImproving long term stability of used PCM materials and containersHeat transfer enhancement (limited PCM heat conduction)Increasing thermal storage capacityReducing production costsImproving and developing composite PCMsImproving integration methodsFinding additives to help improve and/or preserve desired propertiesRaising market availability and diversity of PCM solutionsLife cycle analysis for better sustainability assessmentsSafety and long-term operation behaviorEvaluate the overall thermal comfort effect of phase change materials in real life buildingsPotential for natural, renewable and recyclable PCMPCM other than solid-solid (new integration techniques) Further research

Conclusions PCM capacity for buffering the natural temperature day cycles leads to a smaller demand of energy during the traditional energy-peak periods, diminishing the need for non renewable energy sources and their associated storage problemsIn terms of energy storage systems, PCM provide solutions requiring much less volume than existing classic systemsPCM materials present great advantages in buildings and is suitable for use in any region with climates with high demands in cooling and heating

SuggestionsPCM gained a lot of interests in the last few decades, and innumerous studies about their applications in buildings have been done.This renders difficult for us to make interesting suggestions on other potential new applications that havent already started to be studied, so the suggestion we can make is to keep developing market products and keep researching for new efficient materials with potential for building application.Here is a nonexhaustive list of possible applications found in studies:

PCM combined with:solar collectorsgeothermal systemsheat pumpsTES tanksunder floor heatingHeat exchangers

Directly in building materials:concrete blockslight weight blocksclay Brickscement, lime, gypsum mortarsgypsum, clay wallboardstiles, roofing, paintPCM in building components:Windows, insulation panels, trombe walls, Cork agglomerate compositeCoconut oil as a PCM

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