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Heating and cooling: Helium heat pumps

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  1.  
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2023
     
    Has anybody come across helium heat pumps? Are they real? Are they anywhere near production?
  2.  
    Heat pumps using non-condensing fluids (air, helium, nitrogen etc) have been around for decades, they are basically a Stirling engine running in reverse with the gas being compressed by the piston, instead of the gas driving the piston. The problem is they are a bit mechanically complex, and the sensible heat capacity of the gas carries less heat than the latent heat capacity of a condensing refrigerant, so they are only used for niche products. Eg here is a helium deep-freezer https://www.amazon.co.uk/Twinbird-SC-DF25-Digital-Portable-Capacity/dp/B008B88YXS

    Last few years, there has been some interest in using acoustic standing waves to compress the gas without needing pistons. There are some tech startup companies making bold claims about their progress on this, they get themselves in the press from time to time.

    Meanwhile the EU is looking to restrict the best refrigerant (R32) having already restricted the previous best refrigerant (R410A), both because of GWP, so the industry is complaining but looking to move over to Propane heat pumps.
    •  
      CommentAuthordjh
    • CommentTimeAug 26th 2023 edited
     
    Thanks for the confirmation. I see that https://www.amazon.co.uk/Russell-Hobbs-RHTTFZ1B-Energy-Freezer/dp/B00FLTUUYQ/ supposedly uses half the power for about 30 x less cost (well 28 x ), so I suspect there must be some pretty special requirements to justify the use of that niche product!?

    As I remember there are good reasons why Stirling engines are not used more widely, and I expect they apply to reverse uses too. So I shan't hold my breath. But maybe somebody has/will developed some new technology.
    • CommentAuthorowlman
    • CommentTimeAug 26th 2023 edited
     
    Still very much on the drawing board I think.

    https://www.equium.fr/en/home#Nos-objectifs
  5.  
    I found a couple of articles where the helium heat pump ...sounds...very good with prospects to ...scale... up to commercial domestic production in a couple of years. With luck they will hit the right...note... in the market place.

    https://www.pv-magazine.com/2023/01/02/residential-thermo-acoustic-heat-pump-produces-water-up-to-80-c/

    https://www.express.co.uk/news/uk/1805122/heat-pump-technology-helium-europe

    Whilst there is a projected life of 30 years, running at 30 bar will they need a 5 year pressure vessel inspection?
    But if they really do go to 80deg. at a cop of 3 - 4 then they promise to be a drop in replacement for the several gas combies around the country.

    (Is there a DIY opportunity for my old HiFi speaker set?)
    •  
      CommentAuthordjh
    • CommentTimeAug 26th 2023
     
    Why is helium 'magic'? Why couldn't they use nitrogen or oxygen? For house heating/cooling applications I mean, obviously not for very cold applications.
  7.  
    As I remember from my diving knowledge using heliox ( helium / oxygen mix) as a breathing mix has problems because helium has a much greater thermal conductivity than nitrogen which means that heat loss for divers can be (is) a problem. Another feature of helium of making you sound like Donald Duck is probably not an issue for heat pumps !!

    I suspect that this conductivity is the reason that helium is used.
  8.  
    Sensible heat capacity kJ/kgK:

    Hydrogen 14.3
    Helium 5.2
    Nitrogen 1.0
    Oxygen 0.9

    So Helium can transfer a lot more heat than nitrogen or oxygen can. (Hydrogen is better still, but difficult to handle). Also the speed of sound is much faster in light gases like Helium, IDK if that helps with the acoustics idea.

    But:
    Latent heat capacity kJ/kg:
    Propane 428
    R-32 382
    R-410A 275

    Condensible gases can transfer a lot more heat than Helium can. So heat pumps nearly always use the Rankine cycle (with condensing) and not the more efficient Stirling cycle (without) . That's good, because Stirling machines are more mechanically complex, two pistons instead of one, heat exchanger inside the compressor instead of outside in a fan unit, etc.

    But:
    Condensible gases have a narrow range of temperatures over which they condense. A propane heat pump cannot condense at say 95⁰ to directly replace gas-fired water heaters, because it hits its critical temperature. In principle a Helium one could get to -200⁰ or +2000⁰, no thermodynamic limit as doesn't need to condense. Same reasons, the 28x cheaper freezer cannot get as cold as the Helium one can, for storing vaccines etc.
    • CommentAuthorRobL
    • CommentTimeAug 27th 2023
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>
    But if they really do go to 80deg. at a cop of 3 - 4 then they promise to be a drop in replacement for the several gas combies around the country.
    </blockquote>

    As far as I am aware, there is a thermodynamic limit on the COP - here's a link confirming as I understand it:
    https://physics.stackexchange.com/questions/350074/is-there-some-theoretical-maximum-coefficient-of-performance-cop-for-heat-pump

    So at an outdoor temp of 2degC,and a radiator temp of 80C, the best COP that you could get is:
    COP = (273+80) / (80-2) = 3.5. Of course this is with magic pumps, compressors, heat exchangers etc - don't hold your breath!

    At present, the vaillant arotherm range claims COP=4 at A2/W35. Theoretically it could get (273+35)/(35-2) = 9.3. So it could get a little better, especially as that 4 ignores practical stuff (another pump, zombie losses, defrost cycles, additional heat exchanger) which will only pull that 4 down lower, as many people experience.

    I think heatpumps are a mature technology. 10% COP improvement here and there maybe - but more significant would be better controls, auto WC, ways to stop poor installs.
    •  
      CommentAuthordjh
    • CommentTimeAug 27th 2023
     
    Fascinating. I have a book about Stirling engines published in 1991. It discusses a heat pump built in 1978 that was powered by a helium-filled Stirling engine. But the Stirling engine was used in the forward direction and the heat pump was a Rankine cycle unit. It also mentions that a solar-powered Stirling engine driving an electricity generator had an efficiency of 30% compared to a solar panel's then max of 15%.

    I see the latest Ecodan is a CO2 heat pump :bigsmile: But the COP doesn't look very impressive. Haven't looked far enough to see why anybody would want one.
  11.  
    The CoP is the relationship between heat gathered from the air or ground (diffuse solar energy) versus electricity which is increasingly derived from wind or PV (diffuse solar energy). So the CoP is becoming meaningless as a measure of green-ness.

    Instead it's an economic relationship between spending money on insulation versus heatpumps/radiators versus more renewable generators. All are needed, but the balance might be different in different houses.

    In many existing houses, a CoP of 2 with a flow temperature of 80⁰ might be cheaper and more doable than ripping out floors and radiators to get up to CoP>3. In new houses, a CoP of 1 might be more economic. In some places, energy storage (battery or hydrogen) might be good even with CoP <1.
  12.  
    Posted By: djhFascinating
    For maximum geekiness, I like the Vuilleumier cycle which is a Stirling engine and a heat pump in a single refrigerant cycle, with no external drive. You put a small amount of heat into it, and a large amount of cold, and you get them both out as warm.

    Posted By: djhCO2
    Also lots of fun. A CO2 heat pump is half a Rankine cycle, but is supercritical in the other half, so it runs by evaporating but never condensing the CO2. This means it can deliver higher temperatures than the condensing point.
  13.  
    So are the helium heat pump articles all hype to get the next round of venture capital or will they actually work as promised and become the next generation of HP that will give a drop-in for conventional CH systems in the typical UK house ??
    •  
      CommentAuthordjh
    • CommentTimeAug 27th 2023
     
    Posted By: WillInAberdeenI like the Vuilleumier cycle which is a Stirling engine and a heat pump in a single refrigerant cycle, with no external drive.
    There's a photo in the book of one such produced in 1967 using helium as the working fluid, but using an electric motor to overcome mechanical losses and an electric heater (since it was a research/test device). It could freeze to 77 K with a COP of 0.8 (or slightly better at a higher pressure).

    the CoP is becoming meaningless as a measure of green-ness
    It isn't yet though and probably not for a significant time. I think it is a useful measure of the quality of a design/implementation as various losses are overcome.
    •  
      CommentAuthordjh
    • CommentTimeAug 27th 2023
     
    Electricity won't be carbon neutral until the production of new electricity generation is carbon neutral. So that includes steel production, cement production, global shipping and various other areas that need 'neutralising' first. Hence my scepticism about time scales and claims of forthcoming climate-neutrality for electricity. Quite apart from the cost and practicality issues of greatly increasing generation.
  16.  
    Posted By: djhElectricity won't be carbon neutral until the production of new electricity generation is carbon neutral. So that includes steel production, cement production, global shipping and various other areas that need 'neutralising' first.

    Is this rather than todays calculations which tends to say carbon neutral after x years because it takes that long to pay back the carbon cost of producing the kit.
    E.G. my EV has only been charged at home where my PV has produced enough to cover all the electricity for the household over the year.
    So carbon neutral has to account for the production of the EV and the PV and the grid import balanced against grid export ( = net zero but some dirty power stations) My brain hurts thinking about those calcs. but surely that is a valid account of carbon neutral in X years.
  17.  
    This argument still gets trotted out by those opposed to electric cars and/or wind farms, so fortunately lots of people already thought about it and spotted the logical fallacy!

    We should indeed consider the embodied carbon (of heating/transport/whatever). But when that is used to argue for delaying change to wait for 'something better', then we also need to compare the embodied and operational emissions for the 'carry on as we are' option.

    So we should definitely think about the embodied carbon of PV powered EVs, and whether waiting for better designs would mean less embodied carbon (it would). But we need to compare those to the embodied and operational carbon of sticking with diesel-burning cars whilst we are waiting, including making the diesel refineries, and the diesel transport ships, and the dockyards they are built in. When people add all that up, the embodied carbon of the EV is vanishingly small by comparison.

    Same when comparing manufacturing heat pumps vs manufacturing rendered EWI vs manufacturing wind-powered panel heaters - all have non-zero embodied carbon. But those who say that is a reason to stick with gas heating a bit longer, while we wait for better designs, usually haven't thought about the embodied carbon of building gas pipelines and LNG ships!

    Various LCAs say the embodied carbon for building a wind farm is in the region 6-15 g CO2/kWh. The embodied carbon of the natural gas supply chain is 12-40 g CO2/kWh. Both are vanishingly small compared with burning the gas, ~200 g CO2/kWh.

    So if a homeowner can only afford to fit a heat pump today without fitting underfloor insulation and bigger radiators, and so gets CoP of 2 and consumes more wind power, that's still better than him/her staying with gas heating for another decade while they wait for the insulation and radiators to become affordable, even if that would get them to CoP of 3.5!
    • CommentAuthorowlman
    • CommentTimeAug 28th 2023 edited
     
    <blockquote><cite>Posted By: WillInAberdeen</cite>This argument still gets trotted out by those opposed to electric cars and/or wind farms, so fortunately lots of people already thought about it and spotted the logical fallacy! ............................

    So we should definitely think about the embodied carbon of PV powered EVs, and whether waiting for better designs would mean less embodied carbon (it would). But we need to compare those to the embodied and operational carbon of sticking with diesel-burning cars whilst we are waiting, including making the diesel refineries, and the diesel transport ships, and the dockyards they are built in. When people add all that up, the embodied carbon of the EV is vanishingly small by comparison.

    Same when comparing manufacturing heat pumps vs manufacturing rendered EWI vs manufacturing wind-powered panel heaters - all have non-zero embodied carbon. But those who say that is a reason to stick with gas heating a bit longer, while we wait for better designs, usually haven't thought about the embodied carbon of building gas pipelines and LNG ships!



    Surely, the refineries and tankers and dockyards and gas pipelines and LNG ships are already built and therefore only need maintenance.
    The solar panels and wind turbines which don't last forever are an addition, and will still need maintenance, albeit arguably less.
    Trashing one technology in favour of another must lead to greater embodied energy and minimises the energy gain of the new. When another "new" technology arises do we go through the whole cycle again?
    •  
      CommentAuthordjh
    • CommentTimeAug 28th 2023
     
    The point about electricity not being carbon neutral is that it means that efficiency measures such as heat pump COP are not meaningless or obsolete. It is still important for carbon emission reasons, as well as the obvious one of cost, to minimise the electricity we consume.
  20.  
    An example may help:

    If a heatpump creates 3 units of heat from a unit of wind power that has embodied carbon of say 10g per unit, then that heat has an embodied carbon of 10/3 = 3.3g, and by displacing gas heating (say 200g per unit) that will save us (200-3.3) = 197g.

    If a better heatpump creates 4 units of heat, same maths, we save 198g of carbon.

    So that improvement in CoP means that we save 198g, instead of 197g.

    That measure of improvement sounds meaningless and obsolete to me. If everyone carries on burning gas for years while they are waiting for that improved CoP to arrive, then it's downright damaging.


    Back on topic:
    Here's a helium acoustic heat pump that NASA built for the space shuttle in 1991, expecting it to be "an excellent candidate for ... residential air conditioning applications". The design is explained nicely. https://ntrs.nasa.gov/citations/19920013477
    30 years later... please everyone don't hold off from installing your heat pump because you are waiting for helium to arrive!
    • CommentAuthorbhommels
    • CommentTimeAug 29th 2023
     
    Just to deflate the hopes further for domestic heat pumps running on Helium: Helium is a non renewable resource, and already very scarce due to competition from all kinds of other, mostly very useful, applications.
    Wikipedia paints a rather non alarmist picture of He supplies:
    https://en.wikipedia.org/wiki/Helium#Occurrence_and_production
    whereas other outlets ring the alarm bells:
    https://www.4he-resources.com/Helium%20supply.php
    •  
      CommentAuthordjh
    • CommentTimeAug 29th 2023
     
    Ours mains supply is not produced exclusively by wind turbines though, that is my point. So examples pointing out how much better things will be once it is are not terribly helpful. And I'm not suggesting that anybody delays installing a heat pump in order to wait for a better one. I'm simply saying that the COP of a heat pump is still a relevant measure in evaluating them. And not meaningless.
  23.  
    Posted By: djhI'm not suggesting that anybody delays installing a heat pump
    nobody does, but that's the unintended consequence:

    - everyone emphasises a need for high CoP (the MCS, funding schemes, installers, mfrs)
    - for very many households it's impractical or unaffordable to replace radiators, pipes, cylinder, insulation to get low flow temperatures (MCS rules require <55⁰ in midwinter) in order to get those high CoPs
    - so they are put off installing a HP now, and are sticking with gas 'a few more years' while waiting for something better to come along (helium anyone?)


    Thats a shame, because there are plenty heatpumps on the market now, that could be drop-in replacement for condensing gas boilers with CoP ~2.5 at 65⁰ midwinter flow, and better in shoulder months. But people are not allowed to install like that.


    The point is that electricity doesn't have to be 'produced exclusively by wind turbines' for a HP to be much greener than gas, we're already well past that point.

    Using Nat Grid's intensity forecast for next 5 years (IE the wind farms currently in construction) and CoP = 2.5, would reduce carbon by 150g/kWhth compared to gas, cf 165g at CoP=3.5. But only if people install them now, rather than waiting five more years...

    Obvs it is best to get the best CoP that is economically possible in each home, and for many homes that can be >4 at reasonable cost. But the 'best shouldn't be the enemy of the good', and if some homes can only get 2.5, then that's already better than nothing.
    •  
      CommentAuthordjh
    • CommentTimeAug 30th 2023
     
    I have no idea what 2.5 has to do with anything. I simply object to you stating that COP is meaningless. But since you seem to now agree that it isn't, I'm done.
  25.  
    As I mentioned, 2.5 is the CoP available with present models if people just install them like gas boilers, instead of worrying about CoP.

    165g is a CO2 reduction that we give out grants for based on good CoP; 150g is a reduction that we ban due to insufficient CoP. The distinction between 165g and 150g is meaningless, AFAICS.
    • CommentAuthorcjard
    • CommentTimeSep 10th 2023
     
    Move into politics; get it changed?
    • CommentAuthorSimon Still
    • CommentTimeSep 15th 2023 edited
     
    <blockquote><cite>Posted By: WillInAberdeen</cite>Meanwhile the EU is looking to restrict the best refrigerant (R32) having already restricted the previous best refrigerant (R410A), both because of GWP, so the industry is complaining but looking to move over to Propane heat pumps.</blockquote>

    The Economist has a sci/tech piece on heat pumps last week which covered propane. The disadvantage is that it's flammable so there are currently limits on the amount of gas you can use in a split system (and reducing gas required hasn't been a technology objective up to now with existing gases.)

    Viessmann, Bosch and Mitsubishi already have mono block propane systems on the market and propane has the advantage that it's easier to produce high temp (70C) output.

    Octopus launched a new British designed and made heat pump today
    https://octopus.energy/press/octopus-energy-unveils-next-stage-in-smart-heat-revolution-at-energy-tech-summit/
    • CommentAuthorGarethC
    • CommentTimeSep 15th 2023
     
    Iirc propane's supposed to be better at low temps too?
    •  
      CommentAuthordjh
    • CommentTimeSep 16th 2023
     
    Posted By: Simon Stillreducing gas required hasn't been a technology objective up to now with existing gases
    That's not quite true I think, since some advertise 'no F-gas licence required' because of the low volumes of gas.

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