One of the most pressing challenges the world faces today is the increasing demand for energy against the backdrop of finite resources. The search for renewable sources of energy must go on, as must the development of new energy saving solutions which are effective, safe, economically viable, and have a positive impact on the Earth’s Ecological Balance. Phase Change Materials (PCMs) are INNOVATIVE, INEXPENSIVE and EFFICIENT
In the United States, nearly 50% of the energy dollars spent on commercial and residential structures are for Heating or Cooling the building. According to The US Department of Energy and officials at Oak Ridge National Labs, the use of properly formulated and placed PCMs within a structure can reduce the heating and cooling load by 40% to 60%.
The use of PCMs in buildings within the United States has the potential to save Quadrillions of BTUs of energy every year, reducing our dependency on foreign energy sources, and significantly reducing our carbon footprint.
Peak Load Benefits
Energy absorbed during the day by the PCM is gradually released at night over the following 6 – 8 hours. The result is that with large-scale use of PCMs in buildings on the grid, much less power will be consumed at present conventional peak hours and the peak load hours will be pushed back by up to 6 hours. This will result in savings to customers who purchase power during peak hours as well as present & future savings for the utility company in reducing the need for capital investments to increase peak-load capacity.
Ordinary thermal insulation such as fiberglass or cellulose, work by slowing the rate at which heat energy flows from a warm to a cooler area. The rate of heat energy flow is controlled by two factors:
1. The (Delta T) between the warm and cool sides
2. The Thermal Resistance (R-Value) between the two sides
Conventional insulations used alone are not an efficient use of space between competing temperature zones. The solution is the introduction of PCMs into the barrier assembly, be it a wall, ceiling or containment unit.
The New Approach
If temperature difference (Q) can be kept low, then heat flow across an “R” Value is also kept low. If the temperature difference, sometimes called Delta T, (ΔT) equaled zero, then zero heat flow would occur. Using this new approach, zero heat flow conditions have been witnessed even when large temperature differences existed between the spaces. The old conventional way would require an infinite amount of “R” Value to accomplish this and is impossible to achieve utilizing conventional insulation.
Water has the ability to hold one BTU of heat energy per pound per degree F. Water in the solid phase (ICE) also has the same ability to hold one BTU of heat energy per pound per degree F. The strange and wonderful thing is that during the phase change from liquid to solid, water gives up 144 BTUs before it can pass from 32°F liquid to 31°F ice. This is 143 times the amount of BTUs it takes to change the temperature of water or ice by one degree F at other than 32°F temperatures. It works the same in the other direction from a solid phase melting into the liquid phase. This massive amount of heat storage capacity only occurs at 32° F and is called “Latent Heat Capacity”. Unlike Sensible Heat, Latent Heat does not cause a change in temperature of the substance.
Sensible heat is ordinary heat and it determines the temperature of a material. If you add thermal energy the temperature increases, if you remove the thermal energy the temperature falls.
Latent Heat is harder to understand. It is the heat that is released when a PCM changes phase from a liquid to a solid. To melt the PCM and change it back to a liquid requires the same amount of extra Latent Heat energy.
This means a small amount of PCM at the phase change temperature can CONTROL a relatively LARGE amount of energy and release it again at a CONTROLLED rate.
The interesting and most significant asset of PCMs is that the temperature of the PCM does not change during the phase change. Water is a good PCM which changes phase at 32°F. As long as there is a mixture of ice and water the temperature of the mix will always remain constant at 32°F. This is the reason you don’t want to remove the water from your cooler until ALL of the ice has melted.
Latent Heat Used to Control Heat Flow
The temperature difference across the internal “R” Value of a wall or a ceiling has never been challenged and was long thought to be immutable. By using Phase Change Materials (PCMs) it is possible to control this temperature difference for a time. The length of that time period is determined by the amount of PCM, the temperature difference and the “R” Values on both sides of the PCM.
Winner NET Zero Max for Innovation and Creativity RE:
The one that impressed us most, and was awarded the NetZeroMax Award for Innovation and Creativity, went to InfiniteR. InfiniteR is a thermal phase change product that will help to absorb heat at a low temperature and release it at a low temperature. We ended up returning to the InfiniteR booth several times. Please refer to the other posts on NetZeroMax related to InfiniteR. This is a new product and deserves closer investigation.
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