Building Material Absorbs and Releases Heat 98
Zothecula writes "Researchers at the Ningpo, China campus of the University of Nottingham (UNNC) have created a new heat-regulating material that could be used to cut the heating and cooling costs of buildings. The non-deformed storage phase change material (PCM) can be fixed so that it starts absorbing any excess heat above a pre-determined temperature and releasing stored heat when the ambient temperature drops below the set point. The researchers say the material can be manufactured in a variety of shapes and sizes, even small enough so that it can be sprayed as a microscopic film to surfaces in existing buildings."
Re:Absorbs AND Releases? (Score:5, Informative)
If it performs a phase change at a specified temperature, it means that there is a lot of extra thermal "capacitance" at one particular temperature. If we can choose that temperature to be, say 20 degrees C, this is useful. It would be a bit like water ice. As the freezer temperature falls from +1 to -1 degree, the ice releases a *lot* of stored heat (latent heat of fusion).
So, yes, this is a bit like building a large stone structure, which stays at a constant comfortable temperature by averaging out cold nights and hot days...but we don't need so much mass, and we can choose the temperature we want.
Unless... (Score:5, Informative)
Yes, every material absorbs and releases heat.
The interesting bit here is something different though. I have never seen that someone wants to use a phase change material for buildings, but why not? For coffee cups this already works nicely. The walls of the mug contain a material that is undergoing some phase transition (liquid to solid, different crystalline structure, magnetic, etc.) at a temperature that is slightly below really hot coffee but still a nice drinking temperature.
What happens is the following: the thermal energy of the coffee gets absorbed quickly by the material, therefore cooling it down fast from really hot to a lower temperature. The material can store a large amount of thermal energy and releases it slowly so that the coffee stays at a constant temperature for much longer (gizmag article [gizmag.com]).
For a whole building this makes a lot of sense as well. It more or less acts as a large thermal reservoir, so that your wall temperature does not increase during the day and falls too much during the night. You could achieve a somewhat similar effect by using 20 inch stone walls but this might be a bit easier to incorporate into modern buildings.
The important part is the phase change (Score:5, Informative)
This is useful for maintaining a consistent temperature inside when the outside temperature is bouncing above and below the temperature of the phase change (say, between day-time and night-time) rather than always needing to heat when it's cold and cool when it's hot. The PCM "building material absorbs and releases heat" automatically, in theory lowering your energy bills.
The neat thing--and yes, this IS neat--is a) this material is tunable; you can set the phase transition temperature at time of manufacture and b) it doesn't turn into a liquid, but rather changes between two different solid phases, which is nice for things like, you know, walls, that you'd like to stay solid.
And you were all so excited by this idea when Wozniak was pushing it in 2007; he'd latched onto a certain species of wood whose sap underwent a phase change at 72 degrees. Build a house out of that, and it will tend to keep the inside temperature at a Woz-friendly 72 degrees.
Re:The important part is the phase change (Score:5, Informative)
Re:Absorbs AND Releases? (Score:3, Informative)
Nothing new here.
Phase change applications were fairly commonly installed in houses back in the late 70s. Usually a liquid to gel phase change but some were liquid to solid.
The problem then as now, was finding something that changed at the desired temperature, because any time you have to concentrate the heat to reach the the temperature where phase change occurred you lost much if not all of advantage of using these materials. (You essentially ended up running a air-source heat pump to concentrate hot house air into the material).
Being able to set the phase change point is all well and good if it works, and you can plan AHEAD to have your building to be at certain temperature, or can use the material to collect direct solar radiation.
By the way, there is nothing that says a phase change necessarily makes for a "lot of extra thermal capacitance". Its true of water, (something like an 80 fold increase in heat/per-weight-unit going from ice to water or back, IIRC), but not all materials have this property. Presumably materials selected for this use would be good at this. This was not the case back in the day when I last worked with phase change material for residential use. It was pathetic compared to water.
Re:Unless... (Score:2, Informative)
It's been done for a long time.
Southern yellow pine resin has its phase change at about 71F. The first reference in google is from 2007 but it's been know about for a long time before that,
Re:Limited utility (Score:5, Informative)
It has limits, but it can save a LOT of energy. In some environments such as a desert, the average temperature is quite nice, but unfortunately it swings from freezing to over 100, so you need a good thermal mass to enjoy that average.
In other cases, the average temperature will not be comfortable, but a thermal mass can still save energy. For example when heating is needed, you can run a heatpump during the warmest part of the day when it runs more efficiently and rely on the mass during the coldest part.
All that said, thermal mass is nothing new, but the phase change at a useful temperature is an improvement on it.