Screens & Feeders

Perlite and the electric company

We love living in the Sonoran Desert of Arizona. But the temperature gets high in the summer – as does our electric bill. To help reduce the cost, my son-in-law Rob helped me blow insulation into our attic, doubling the original thickness. My wife Pam and I also replaced our halogen lights with LEDs, cutting down both electric usage and the heat generated by the lights.

Apparently we are not the only people doing this. Our electric company recently added a lost fixed cost recovery (LFCR) charge to our electric bill because customers have taken so many energy-saving measures that usage has significantly dropped. The electric company can no longer meet its fixed operating costs, so we get to help it out.

Well, a rock called perlite is just waiting to exacerbate the problems of the electric company. Perlite consists of a glassy volcanic material, which, upon rapid controlled heating, “pops” into frothy, low density particles. Somewhere between 7000 and 12,000 tonnes of expanded perlite is produced in Australia every year for use as lightweight aggregate, insulation, soil amendments and numerous other applications. With a density between 6m3 and 33m3?per tonne, that’s a lot of perlite.

{{image2-a:r-w:300}}So here is how perlite can help reduce electrical usage. Different types of insulation can give different building envelopes (the physical separator between the interior and the exterior environments of a building) similar insulating values.

However, the quantity of heat it takes to increase or decrease the temperature of the entire building envelope (thermal mass) can vary greatly. For example, an adobe or concrete structure has much more thermal mass than a framed wood wall of equal thickness. Thermal mass reduces temperature variations, resulting in decreased energy consumption in some climates.

Researchers are investigating ways to increase thermal mass by incorporating phase-change materials (PCMs) into the building envelopes. The most recognisable PCM is paraffin wax. Others are chemical or organic materials, many with unrecognisable names. Most PCMs for building applications change from a solid to a liquid (melt) near room temperature – somewhere between 20°C  and 30°C.

It takes a large amount of energy (called the latent heat of fusion) to weaken the molecular bonds of a PCM in order to make the jump from an ordered state (solid) to a disordered state (liquid). So, when the temperature surrounding the PCM rises to melting point, the PCM needs large amounts of energy (heat from the atmosphere) to melt. As it melts, it consumes heat while maintaining a near constant temperature. This keeps the building cool. When the local temperature falls back to the “freezing” point, the PCM will discharge heat, maintaining the temperature of the space until the PCM has fully solidified. In summary, the PCMs incorporated into the building envelope absorb the higher exterior temperature during the day and dissipate that heat to the interior at night when it is cooler.

The US Department of Energy tested an attic insulation consisting of perlite (a carrier) embedded with a PCM consisting of hydrated calcium chloride. That PCM changes phases from solid to liquid at 28°C. As it melts it absorbs heat from the hot attic before the heat can penetrate into the home. When attic temperatures cool at night, the PCM solidifies and releases heat back into the attic, moderating the cooler outdoor temperatures.

Some day in the future, perlite infused with PCMs may reduce home heating or cooling loads, thereby producing energy savings for the consumer, a reduction in the need for new utility power plants – and perhaps yet an additional LFCR charge.

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