Good Thinking

Electricity-free air con: Thermoacoustic device turns waste heat into cold using no additional power

Electricity-free air con: Ther...
SoundEnergy's THEARC-25 thermoacoustic cooling system is claimed to take heat and turn it into sound, before then turning that sound into cold – all without moving parts, and without any additional energy required
SoundEnergy's THEARC-25 thermoacoustic cooling system is claimed to take heat and turn it into sound, before then turning that sound into cold – all without moving parts, and without any additional energy required
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SoundEnergy's THEARC-25 thermoacoustic cooling system is claimed to take heat and turn it into sound, before then turning that sound into cold – all without moving parts, and without any additional energy required
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SoundEnergy's THEARC-25 thermoacoustic cooling system is claimed to take heat and turn it into sound, before then turning that sound into cold – all without moving parts, and without any additional energy required
The SoundEnergy design accepts waste heat or solar heat at the red pipes and pumps out cold at the blue pipes
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The SoundEnergy design accepts waste heat or solar heat at the red pipes and pumps out cold at the blue pipes
SoundEnergy's THEAC-25 prototype successfully provided a 25-kilowatt cooling effect in testing. The production design will be much more streamlined
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SoundEnergy's THEAC-25 prototype successfully provided a 25-kilowatt cooling effect in testing. The production design will be much more streamlined
Diagram showing the connections required: heat must be pumped in, excess heat must be sent to a heat sink, and cold must be pumped out the other side. So the global process isn't entirely energy-neutral, but the cooling system itself requires no electrical input
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Diagram showing the connections required: heat must be pumped in, excess heat must be sent to a heat sink, and cold must be pumped out the other side. So the global process isn't entirely energy-neutral, but the cooling system itself requires no electrical input

Beginning with the principles of the Stirling engine, SoundEnergy's THEAC thermal acoustic engine takes heat – either industrial waste heat or solar heat – and turns it into powerful cooling without requiring any other power source. This completely renewable technology could prove highly disruptive.

The THEAC system uses no mechanical moving parts, no refrigerants, no CO2, no precious metals or materials. Instead it uses Argon gas, which is plentiful and has zero global warming potential, and is totally sustainable, relying solely on the energy of incoming heat to produce cold. The technology is also claimed to make about as much noise as a running shower, and is scalable, way up from the company's 25-kW demo unit, which can produce cooling temperatures as low as -25° C (-13° F).

How on Earth does it work, then? Through the principles of thermoacoustics, it turns out, which we can only explain up to a certain point. Thermoacoustic effects have been observed for centuries, particularly by glass-blowers, who noticed that occasionally when they were blowing a hot bulb at the end of a cold, narrow tube, a loud, monotone sound would be produced. Experiments in the 1850s figured out that the temperature differential was key, and that the volume and intensity of the sound would vary with the length of the tube and the size of the bulb.

Sound, of course, is merely an audible vibration of the air, consisting of pressure peaks and troughs. Gases expand and contract with heat, meaning that a temperature differential can create a pressure differential. This is the principle behind the operation of the Stirling engine, and it's the source of the pressure waves that were causing sonic oscillations in the glass tubes.

1850s Physicist Pieter Rijke was able to demonstrate that adding a heated wire screen a quarter of the way up the tube would greatly magnify the sound – it was effectively giving extra energy to the air in the tube at its point of greatest pressure. Further experiments showed that taking away energy by cooling the air at its points of minimal pressure would have a similar amplifying effect on the thermoacoustic wave.

SoundEnergy's THEAC-25 prototype successfully provided a 25-kilowatt cooling effect in testing. The production design will be much more streamlined
SoundEnergy's THEAC-25 prototype successfully provided a 25-kilowatt cooling effect in testing. The production design will be much more streamlined

The SoundEnergy device uses heat differential to create an acoustic wave in an infinite loop tube, and amplifies that wave until it reaches a high intensity. Then, just as the heat differential was converted into a pressure differential, the pressure differential is converted back into another heat differential, this time in reverse.

In an interview with Forbes magazine, SoundEnergy CFO Roy Hamans says "this huge mechanical power will be transformed into a delta T [another temperature differential] down in the last two vessels by connecting them in reverse. The sound waves produce cold by distracting the heat from the particles like in a classical Stirling cycle."

As odd as it sounds, what you get is a fixed system without moving parts that can accept heat and pump out cold. The heat can come from anywhere – excess industrial heat or that coming out of a cruise ship motor are prime candidates, but like with a Stirling engine, the source isn't important and can just as easily be supplied by the Sun under the right conditions, using vacuum tube collectors. The cold can be used to cool whatever needs cooling, be it fresh produce, cold storage, or any number of industrial cooling purposes. Excess heat that can't be converted to cold is sent away to a water/glycol heat sink to be dispersed.

Diagram showing the connections required: heat must be pumped in, excess heat must be sent to a heat sink, and cold must be pumped out the other side. So the global process isn't entirely energy-neutral, but the cooling system itself requires no electrical input
Diagram showing the connections required: heat must be pumped in, excess heat must be sent to a heat sink, and cold must be pumped out the other side. So the global process isn't entirely energy-neutral, but the cooling system itself requires no electrical input

Or, of course, air conditioning – a huge global energy drain that only stands to increase as global temperatures slowly rise and more households and offices start running air con more of the time. It's easy to see how the SoundEnergy THEAC system could be a significant and disruptive technology, with a potential ability to reduce global energy usage while efficiently scavenging waste heat at an efficiency of 40-50 percent.

This kind of thermoacoustic cooling has been in development since the mid-70s and 80s. A similar thermoacoustic refrigeration device was used for cryogenic cooling on Space Shuttle Discovery all the way back in 1992 – in this case, with a moving loudspeaker diaphragm. But thus far, nobody seems to have made it into the kind of commercial success that could make it a world-changing device. So hopes are high for SoundEnergy's efforts to get this gear out to market.

The company has already made its first couple of sales – one to tech-hungry Dubai – and says that large units will cost around US$50,000. Prices are expected to drop as production scales up, and the company says it's possible to create residential/consumer products at much lower prices. Each system should have an expected lifespan of around 20-30 years, which is certainly better than a conventional air con unit.

Source: SoundEnergy via Forbes

21 comments
KaiserPingo
Great !
watersworm
Indeed a potential Great world-changer ! Let's hope it'll be cheaply downscaled
myale
Did I miss the data - i.e. does 1 degree of heat produce 1 degree of cooling? or how many kilo watts produce what cooling potential? - so if I take a room at 25 degree C can I cool a same size room to 0?
CLERKY
Errrrrr ... etc ...... Was this not done in 1950's in Brit (at least) military aircraft? (Not forgetting also, ye Vortex Tube used for heating).
paul314
Any word on efficiency? How many watts across what kind of temp difference does it take to produces how many btu/hr of cooling? (Or whatever units you prefer) It's nice to hear that it doesn't use moving parts, but, for example, is that 25-kw number quoted the in or the out?
guzmanchinky
Aww man this is great news!
toyhouse
What an awesome development! Disruptive tech indeed but much needed.
nigeltech
WOW
Douglas Bennett Rogers
Doesn't look like a replacement for a home air conditioner but a replacement for an ammonia absorption unit. Needs a boiler or process heat to work. Both of these will work with solar thermal. PV's have about 90 % waste heat but at too small a thermal gradient.
SatoruRyu
While this is interesting an efficiency of 40% pales in comparison to absorption chillers whose coefficient of performance is almost double for single stage absorption chillers to 3.5 times higher efficiency in two stage absorption chillers. Evaporation is simply superior as a cooling function hence why it's favored. I will concede based upon basic material properties the thermoacoustic cooling system should theoretically have a longer lifespan and longer maintenance cycles. Yet, if they can't outright demolish the upfront pricing I don't foresee this becoming mainstream.