8 ms·

Thermo acoustic heat pump boosts performance without refrigerants

32 points by anjel 3y ago

ChoGGi 3y ago
Seems nice, but I don't see mentions of drawbacks?
- c_o_n_v_e_x 3y ago
  The article mentions using helium as the working gas... which there's a global shortage of. Also, Helium is an escape artist, extra thought must be given to your design to prevent leaks.
  - extraduder_ire 3y ago
    Is there a specific reason helium has to be used? These things would be amazing if nitrogen, or some other cheap gas could be used instead. I'm also wondering how heat is moved in to the unit, and out of the unit. Since normal heat pumps gain a lot from doing the compression/evaporation right where the heating/cooling is needed, but what I get from the article is that this focuses on heating water.
    - chipsa 3y ago
      One of the key design parameters is the thermal diffusivity of the gas. The greater it is, the deeper the stack can be, and the better it performs. Helium is about 190, while nitrogen is about 22. Next best to helium is hydrogen, but that has a bunch of other tradeoffs in terms of use. Among other things, it's very hard to seal high pressure hydrogen, and it's notably explosive in almost all concentrations with air. As for moving the heat, since it's using water as a heat medium, it just moves the water to the hot or cold spot on the internal stack to heat or cool as appropriate.
  - waste_monk 3y ago
    Good deal on helium here if you're buying in bulk: https://news.ycombinator.com/item?id=37391584 https://news.ycombinator.com/item?id=37391584
- hyperhello 3y ago
  “can produce about 3 to 4 kW of heat for every kW of power drawn into the system” Doesn’t that produce perpetual motion, given a cold reservoir?
  - toast0 3y ago
    That's most likely a misleading statement of the coefficient of performance... 3-4 kW of heat delivered into the conditioned space with 1 kW of electricity from the grid (or wherever) is pretty reasonable for a heatpump, given appropriate conditions. The downside is probably cost of manufacturing. Ben & Jerry's prototyped thermoacoustic cooling in 2004 [1], but now their "Cleaner Greener Freezers" are refrigerant based, although they're using a hydrocarbon refrigerant rather than a traditional hydrofluorocarbon. I'm not sure which specific refrigerant they're using, but based on the timing, it might be R441a, which was the first hydrocarbon refrigerant approved for sale in the US and is a mixture of ethane, propane, butane and isobutane. [3] [1] https://www.npr.org/2004/04/28/1861434/ben-jerrys-uses-sound-to-chill-ice-cream https://www.npr.org/2004/04/28/1861434/ben-jerrys-uses-sound... [2] https://www.benjerry.com/values/how-we-do-business/cleaner-greener-freezers https://www.benjerry.com/values/how-we-do-business/cleaner-g... [3] https://www.acr-news.com/hydrocarbon-refrigerant-r441a-gets-first-roll-out-in-the-usa https://www.acr-news.com/hydrocarbon-refrigerant-r441a-gets-...
  - p1mrx 3y ago
    No, because 1 kW of heat would produce much less than 1 kW of electricity.
    - hyperhello 3y ago
      Is that so? I would have thought if you heated boiling water you’d turn the excess heat energy into steam pressure or something.
      - p1mrx 3y ago
        A steam turbine is (to some approximation) an inverse heat pump. You can use the temperature delta from an electric heat pump to run a turbine and generate electricity, but the laws of thermodynamics guarantee that the power output of the (heat pump + turbine) system will be less than its power input. The best you can hope for is to approach 100% efficiency.
garyclarke27 3y ago
Sounds too good to be true, but great if it is. Current generation of Heat Pumps are Too expensive, Too Noisy and not that effective in Northern Climes
- Glench 3y ago
  This is just pure nonsense. Maine is the US state with the highest rate of heat pump installs: > In a state with fewer than 600,000 occupied housing units, the agency has already given out rebates for 116,000 heat pumps > “If they really didn’t work in the cold, you would think people would stop buying these things, but they haven’t,” said Michael Stoddard, executive director of Efficiency Maine. Source: https://www.washingtonpost.com/climate-environment/2023/02/07/maine-gas-industry-heat-pumps/ https://www.washingtonpost.com/climate-environment/2023/02/0...
- getwiththeprog 3y ago
  Heat pumps have been standard and cheap to run and effective in all ways, In Australia for more than 20 years now. Proven and reliable.

32 points by anjel 3y ago

ChoGGi 3y ago

Seems nice, but I don't see mentions of drawbacks?

c_o_n_v_e_x 3y ago
The article mentions using helium as the working gas... which there's a global shortage of. Also, Helium is an escape artist, extra thought must be given to your design to prevent leaks.
- extraduder_ire 3y ago
  Is there a specific reason helium has to be used? These things would be amazing if nitrogen, or some other cheap gas could be used instead. I'm also wondering how heat is moved in to the unit, and out of the unit. Since normal heat pumps gain a lot from doing the compression/evaporation right where the heating/cooling is needed, but what I get from the article is that this focuses on heating water.
  - chipsa 3y ago
    One of the key design parameters is the thermal diffusivity of the gas. The greater it is, the deeper the stack can be, and the better it performs. Helium is about 190, while nitrogen is about 22. Next best to helium is hydrogen, but that has a bunch of other tradeoffs in terms of use. Among other things, it's very hard to seal high pressure hydrogen, and it's notably explosive in almost all concentrations with air. As for moving the heat, since it's using water as a heat medium, it just moves the water to the hot or cold spot on the internal stack to heat or cool as appropriate.
- waste_monk 3y ago
  Good deal on helium here if you're buying in bulk: https://news.ycombinator.com/item?id=37391584 https://news.ycombinator.com/item?id=37391584
hyperhello 3y ago
“can produce about 3 to 4 kW of heat for every kW of power drawn into the system” Doesn’t that produce perpetual motion, given a cold reservoir?
- toast0 3y ago
  That's most likely a misleading statement of the coefficient of performance... 3-4 kW of heat delivered into the conditioned space with 1 kW of electricity from the grid (or wherever) is pretty reasonable for a heatpump, given appropriate conditions. The downside is probably cost of manufacturing. Ben & Jerry's prototyped thermoacoustic cooling in 2004 [1], but now their "Cleaner Greener Freezers" are refrigerant based, although they're using a hydrocarbon refrigerant rather than a traditional hydrofluorocarbon. I'm not sure which specific refrigerant they're using, but based on the timing, it might be R441a, which was the first hydrocarbon refrigerant approved for sale in the US and is a mixture of ethane, propane, butane and isobutane. [3] [1] https://www.npr.org/2004/04/28/1861434/ben-jerrys-uses-sound-to-chill-ice-cream https://www.npr.org/2004/04/28/1861434/ben-jerrys-uses-sound... [2] https://www.benjerry.com/values/how-we-do-business/cleaner-greener-freezers https://www.benjerry.com/values/how-we-do-business/cleaner-g... [3] https://www.acr-news.com/hydrocarbon-refrigerant-r441a-gets-first-roll-out-in-the-usa https://www.acr-news.com/hydrocarbon-refrigerant-r441a-gets-...
- p1mrx 3y ago
  No, because 1 kW of heat would produce much less than 1 kW of electricity.
  - hyperhello 3y ago
    Is that so? I would have thought if you heated boiling water you’d turn the excess heat energy into steam pressure or something.
    - p1mrx 3y ago
      A steam turbine is (to some approximation) an inverse heat pump. You can use the temperature delta from an electric heat pump to run a turbine and generate electricity, but the laws of thermodynamics guarantee that the power output of the (heat pump + turbine) system will be less than its power input. The best you can hope for is to approach 100% efficiency.

garyclarke27 3y ago

Sounds too good to be true, but great if it is. Current generation of Heat Pumps are Too expensive, Too Noisy and not that effective in Northern Climes

Glench 3y ago
This is just pure nonsense. Maine is the US state with the highest rate of heat pump installs: > In a state with fewer than 600,000 occupied housing units, the agency has already given out rebates for 116,000 heat pumps > “If they really didn’t work in the cold, you would think people would stop buying these things, but they haven’t,” said Michael Stoddard, executive director of Efficiency Maine. Source: https://www.washingtonpost.com/climate-environment/2023/02/07/maine-gas-industry-heat-pumps/ https://www.washingtonpost.com/climate-environment/2023/02/0...
getwiththeprog 3y ago
Heat pumps have been standard and cheap to run and effective in all ways, In Australia for more than 20 years now. Proven and reliable.