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    The state of Phase Change Materials in Australian building design

    Warren McLaren

    What keeps you comfortable? But is not air conditioning. Nor insulation, as you know it. Phase Change Materials.

    They sound like something from a science fiction movie like, Hyper Drive, Warp Speed or Temporal Agent. Even a simple explanation does nothing to dispel that notion.

    Materials that store (and release) heat, all the while retaining a near constant temperature. They do it up to a dozen times more effectively than other ‘thermal mass’ mediums, such as water and masonry. And they keep doing this for decades, with no powered input, nor maintenance. Just the sort of thing you’d expect to find aboard the Millienium Falcon or the Enterprise. But increasingly Phase Change Materials (or PCMs for those who prefer TLAs) are being teleported into our buildings.

    Water is the classic PCM. At room temperature it’s a liquid. Heat it enough and it turns to a gas — water vapour or steam. Cool it sufficiently and you have a solid — ice, snow, frost. Gas. Liquid. Solid. These are three primary states or ‘Phases’ that most of us are familiar with. (There is technically a fourth state, known as Plasma, when a material becomes responsive to electromagnetism, i.e. lightning.)

    Heaps of energy is inherent in these changes of phase. Much of it expressed as heat. PCMs that can capture and store that heat have great potential in architectural design. They equip designers with the opportunity to eliminate, or at least reduce, the inclusion of electricity guzzling air conditioning systems.

    Image: Charles Sturt.

    In 2009, Charles Sturt University's Thurgoona campus at Albury (pictured above) was apparently the first in the world to use phase change materials in their concrete flooring. PCMs were also integrated in the plasterboard ceilings. Such attributes helped the site score six green stars and 'world leader' status from the Green Building Council of Australia. Speaking of six star buildings, the first one in Victoria to rate such a thing for Office Interiors was the offices of architectural firm Umow Lai. They picked up a maximum of five innovation points for their use of phase change materials to control temperatures in a meeting room, without resorting to mechanical cooling and heating systems.

    It was around 2004 when Phase Change Materials really started to make inroads into architecture. About this time the world’s largest chemical company, Germany’s BASF, introduced their Micronal product. They encased a paraffin wax storage medium inside a microscopically small acrylic plastic sphere. When temps rise, the wax in the spheres starts to turn to a liquid —changing its phase — and in the process absorbs heat. When the mercury drops the wax starts the process toward solidify again and releases all that stored heat.

    Click to enlarge image^

    Now you may be thinking, “Big deal, that’s what ‘thermal mass’ materials have always done.” True, but never as effectively as this.

    When incorporated in a plasterboard, known as SmartBoard by Knauf (pictured left), BASF reckon that 5mm of their product has the thermal mass properties equivalent to “a 140mm thick concrete wall or a 3650mm thick brick wall.” Furthermore, they explain that one of the unique characteristics of Micronal PCM is that 1g of the stuff is equivalent to a surface area of 3sqm. The product has been tested for 10,000 phase changes, without loss of effectiveness, which is said to correspond to a life cycle of about 30 years. Based on such testing, BASF are confident their Micronal PCM is durable for the lifetime of the building.

    Depending on the intended end use, materials may be impregnated with a PCM graded to a set nominated heat storage temperature: usually 21, 23 or 26°C. Regardless of the start temperature BASF suggest that a “cooling effect of about 3 to 4 degrees Celsius [is] achievable.” They also note that “conventional air conditioning systems which are usually designed to create a temperature difference of 6 degrees Celsius.”

    The capsules are described as “mechanically practically indestructible” and being only 2-20µm in size (1mm = 1,000µm), there is no loss of heat exchange function to substrates that are cut or drilled. As the Charles Sturt Uni example above indicates, Micronal is also able to be mixed with concrete.

    BASF’s gargantuan size hasn’t completely frightened other players off the field. 

    Image: Wilmott Dixon.

    That other chemical giant, DuPont, entered the fray with their Energain product (pictured above). Their paraffin wax PCMs (60 per cent) are mixed with a ethylene copolymer (40 per cent) and sandwiched between two sheets of 100 μm aluminium sheet to create a panel a smidge over 5mm thick. These panels are suitable for use in partitions, walls and ceilings installed behind plasterboard. In buildings with air conditioning DuPont posit that their Energain panels “can reduce costs by an average of 35 per cent and help to reduce heating bills in the winter by up to 15 per cent.” In another comparison the company indicate that, “material analysis of equal volume has shown that concrete offers only approximately 17 per cent of the energy capacity.” Thus, panels of PCM can overcome the lack of thermal mass in lightweight buildings, as Energain starts absorb heat at 22°C.

    Phase Change Energy Solutions proffer another option. Unlike BASF Micronal and DuPont Energain, BioPCM doesn’t use paraffin wax or rigid panels. Rather it is created with the waste product derived from the manufacturing process of soy, palm, coconut oil. These “acidic fatty esters are then blended with a nano scale thickening agent made of spherical bits of silica.” The final result is a gel, which is contained within a multitude of pockets in a flexible roll of plastic film. This allows BioPCM to be easily installed in new structures, but also by home owners as a retrofit.

    The company based in USA, with an Australian office, believe their product, which resembles a rolled sheet of pills for a giant, makes a significant difference to indoor temperature variations. In one test a control building without BioPCM exhibited a temperature swing of 13°C, compared to only a 3°C variance in the identical structure that otherwise deployed BioPCM. Architectural firm Positive Footprintsworked with BioPCM for their 9-star reverse brick veneer residential project in Victoria.

    And whilst BASF Micronal can be combined cement to form a phase change concrete floor BioPCM can be install directly under timber floor boards. In doing so, Phase Change Energy Solutions maintain such flooring delivers more effective thermal mass than concrete, but with just two per cent the weight of concrete.

    Below: Click on the image to see a case study where BioPCM was used in place of bricks for a reverse brick veneer walling system. Image: Sollar Sellew by Positive Footprints.

    Tate Access Floors also use PCMs in flooring, but with a couple of twists. Firstly their EcoCore panels (pictured above) are used for raised access floors, that allow for an office’s services, like cabling and air conditioning, to be hidden underneath. Secondly, they advocate a perimeter placement of the panels on sunward side of building. As heat enters the office, the phase change materials mixed with structural cement and contained within steel welded shells absorb this increased temperature. Tests performed by Tate suggest their system can reduce air conditioning demand by 17.7 per cent, when contrasted with a typical concrete slab floor.

    Floors and walls aren’t the only building products utilising phase change materials. One of the more intriguing adoptions of PCMs is GlassX’s Crystal product (pictured below), which the Swiss firm believe “makes it possible to replace solid walls with glass elements.” Crystal is essentially a quadrupled glazed window. Positioned between two of the panes is a translucent salt-hydrate PCM. The 79mm thick glazing unit is credited with absorbing “about the same amount of energy as a 400 mm thickness of concrete.” But here is the extra kicker: with the PCM in its crystalline state, the panel transmits between up to 28 per cent of visible light, and up to 45 per cent in its liquid phase. Thus, a thermal mass external wall that allows the passage of diffused sunlight.

    Phase change IGUs can be employed more incongruously across a glazed building than other materials. Image: GlassX.

    We’ll conclude with yet another variation. Perth-based Phase Change Products have their High Efficiency Thermal Air Conditioning (HETAC) system regulated by phase change materials in a storage tank connected to an air conditioner. (click to enlarge image)

    Warm building air is transferred to the tank, where the biodegradable, non-toxic PCMs suck up the heat. In the evening the AC systems cools down the PCM storage tank preparing it for the next day’s heat exchange. It results in a 50 per cent energy saving, compared with conventional air conditioning.

    As we readily say, the above is but a taster, in this case, of the many innovative applications that Phase Change Materials can configured for. Science fiction made architectural reality.

     

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