Environment

New technique stores summer heat until it's needed in winter

New technique stores summer he...
Though still in the prototype stage, EMPA is currently looking for commercial partners to assist in creating a compact version of the system for household domestic use
Though still in the prototype stage, EMPA is currently looking for commercial partners to assist in creating a compact version of the system for household domestic use
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Though still in the prototype stage, EMPA is currently looking for commercial partners to assist in creating a compact version of the system for household domestic use
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Though still in the prototype stage, EMPA is currently looking for commercial partners to assist in creating a compact version of the system for household domestic use

Making the move away from using fossil fuels for heating is a necessary part of creating a sustainable future, but it's often a difficult ask for many people when turning up a thermostat on a gas or electric heater provides instant, trouble-free warmth. If people are to be convinced to switch to more renewable sources, it makes sense that there need to be easy-to-use systems available to encourage them to do so. A group of Swiss researchers claim to have come up with a process that stores heat captured during summer for easy, flick-of-a-switch use in winter, with the added benefit that the captured energy can be physically transported anywhere it may be needed.

Created by researchers working at EMPA (Eidgenössische Materialprüfungs-und ForschungsAnstalt or, in English, the Swiss Federal Laboratories for Materials Testing and Research), the new system uses concentrated sodium hydroxide (NaOH) as the thermal storage medium, and a collection of largely off-the-shelf components to capture, convert, and release heat energy on demand.

To achieve this, the researchers rely on the fact that when water is poured onto dry sodium hydroxide an exothermic reaction ensues, where the chemical energy contained in the NaOH is released as heat. As NaOH is also extremely hygroscopic (that is, having a great attraction for dragging in and holding water molecules from the surrounding environment), more heat is produced from water condensing from vapor in the air and the sodium hydroxide solution is heated even further. In this way, large amounts of heat may be liberated from NaOH simply by the addition of water.

Conversely, if heat energy (collected from the sun, for example) is fed into a solution of sodium hydroxide diluted with water, the moisture readily evaporates and the NaOH solution becomes more concentrated and, therefore, effectively stores the supplied energy. This concentrated mixture may then be kept stored for many months (even years), until the heat is once again liberated when the NaOH is exposed to water again. The solution can also be easily transported in tanks to other areas where heat energy is needed.

In practice, the storage medium is a viscous liquid composed of a 50 percent NaOH solution that is made to trickle along in a spiral pipe (created from heat exchangers normally found in instantaneous water heaters), where it soaks up water vapor along the way and then conveys the generated heat into the pipe. The heat is then free to radiate, convect, and conduct into the area requiring warmth.

During this process, the sodium hydroxide solution cascades down the outside of the heat exchanger spiral, where it is diluted to around 30 percent in the steamy atmosphere of the inside of the system, and the water temperature within the pipe rises to around 50° C (122° F). Which, in a happy coincidence, makes it ideal for under floor heating.

The reverse of this process – passing heat through the medium to store energy – has also been demonstrated in the system. Specifically, the moisture from the NaOH solution evaporates when heat is applied, which is then siphoned off and condensed. The solution that exits the heat exchanger is now back up to 50 percent strength, and "charged" with heat energy. The researchers suggest that the heat for this step could be renewably produced using solar collectors (similar to those used in solar-powered air conditioning systems).

The heated water generated in the process of condensation is then transferred to a geothermal probe (generally loops of pipes embedded vertically in the ground) for storage and retrieval. After the stored condensation's temperature has dropped to somewhere between 5 and 10° C (41 to 50° F) it is returned to the apparatus to drain the store.

Though still in the prototype stage, EMPA is currently looking for commercial partners to assist in creating a compact version of the system for household domestic use.

The EMPA heat storage device is one of three competing systems in the COMTES project, which has the goal to develop and demonstrate compact seasonal storage of solar thermal energy.

Source: Empa

16 comments
VincentWolf
Just keep the mixture out of your eyes or your blind for life. It's a dangerous soup to be sure.
Bob
This process is easily contaminated by CO2 so it may be short lived unless it is filtered air and guess what makes the best CO2 filter?
Guy Macher
What's the energy density of this system?
McDesign
I've always felt that the world didn't have problems with heat or water - just a transport problem. Whether you want heat, a heat sink, or water, it's always available - just maybe a long way away.
Bruce H. Anderson
I wonder how this compares in overall energy use to a geothermal (well water or buried glycol tubes) combined with a heat pump. Perhaps with NaOH (commonly known as Caustic Soda or Lye) being highly reactive its intensity can overcome the cost of the raw material, stainless plumbing, pumps, and solar panels.
MBadgero
The old technique was called Passive Annual Heat Storage. It just used insulation, dirt and PVC pipe.
CraigAllenCorson
An even better heat source than solar to "recharge" the NaOH would be a heat pump, thus enabling the same system to both heat and cool.
Rorschach
" 50° C (122° F). Which, in a happy coincidence, makes it ideal for under floor heating???" Under floor heating at those temperatures is not likely to make anyone happy. Even wall mounted radiators run on a maximum of 35° C. The efficiency of underfloor heating lies in its substantially lower inlet temperatures.
myale
So the 50 % solution is tricked along a pipe where it absorbs the water - to increase its temperature - so it then goes back to a tank - where it needs to be regenerated back to the 50% - with the water it absorbs being removed - so it then goes back into the pipe - where does the water come back from in the pipe?
Ken Brody
Just use a ground source heat pump and forget about the caustic lye. If you need a hole in the ground, you might as well (pun intended) use it.