Hacker News Reader

Comment by throw0101d | Hacker News Reader

CO2 as a refrigerant isn't new:

It's just not as prevalent in the residential HVAC market (which this product serves?), and more in the commercial/industrial space (probably because of the higher pressures needed to get into a liquid state).

View on HN

It's useful though, as I think (correct me if I'm wrong) that the gases generally used in HVAC tends to have much worse warming effect than co2 per volume.

We do need heat pumps deployed at large scale, but sometimes I worry we don't understand they need to be handled with care at the end of their life

If it is outside you can just use propane as refrigerant. Low warming value and it leaking to outside doesn't matter, not gonna catch on fire.

There are indoor devices using propane but they generally come with caveat "must be installed on room at least this m3", precisely so if it leaks it doesn't get to density that allows explosion

I believe there are propane using split AC systems where propane is used only in the outside unit. The outside unit has a heat exchanger transferring the heat to some glycol-water solution which is what then circulates through the inside unit.

I currently have R410a heat pumps with minisplits, when they're off warranty sometime in the future I might consider putting propane in them. The main question would be whether the oil used with R410a is compatible with propane as a refrigerant.

This is probably a little bit "dangerous" in the sense that I'll have high pressure propane in the line sets and minisplits inside the house, but it's a very small volume of propane and not really any more dangerous from a fire perspective than my propane fired condensing gas boiler.

[edit] a little internet sleuthing indicates that hydrocarbon refrigerants "might be" compatible with basically any oil, so I can probably just continue using whatever oil is in it.

Yes, that dangerous effect is indexed as GWP - global warming potential.

CO2 has a GWP of 1 in this context, while other refrigerants are worse - for example, R32 has a GWP of 675 (so 675x worse if it escapes), not sure about R290 (Propane), which I believe is either about 40 or 14…

Regarding EoL: At least around here, household appliances such as fridges are brought to a recycling yard and are properly taken care of in that regard… and as for heatpumps - those are only to be installed by certified professionals, for this very reason.

Per the latest IPCC report, GWP of propane is estimated to be 0.02, previously it was estimated to be around 3.

R32 also got rated higher: GWP went from 675 -> 771

So it went from three times worse to 98% better?

R32 is on the safe side of common refrigerants. R410 just started its phase out in the US and carries a GWP of >2000.

The global warming potential of hydrocarbons as such is generally overblown, since they oxidize into CO₂ in the atmosphere with a half-life of a decade or two.

That's true, old school refrigerants like R-12 are awful. The downside of modern replacement refrigerants are high operating pressure (>100 bar for R-744/CO2) or high flammability for natural refrigerants like R-290 (Propane) and R-600a (Isobutane). But these are solely engineering problems, and I'm happy to know that my R-290 heat pumps at home (Panasonic L & Wolf FHS) and A/C (Midea Xtreme Save Blue) aren't awful to the environment, once they reach EOL.

The neat thing about propane as a refrigerant is that it's a really powerful one, actually rather better than R12 in practical applications.

If you replaced an R134a fill with R290 you'd need about half as much gas and if it got out, it's got a Global Warming Potential of 3, making it three times as bad as carbon dioxide and about 475 times better than the same amount of R134a.

Even in a very large air conditioning system like in my elderly Range Rover, the 500g or so of propane it would need is about the same as the engine sucks up in about four miles.

The effect of that escaping into the atmosphere is about as bad as the amount of petrol you spilled the last time you refilled your lawnmower.

If you're worried about the ZOMG IT IS GAS IT WILL MAKE A GINORMOUS EXPLODISHION aspect like a lot of people are, ask yourself this - how many aerosol cans are in your car right now? Tin of deicer, tin of magic tyre inflater, maybe a tin of air freshener or WD40 or something? You're already carrying more propane around with you, rattling around loose at your feet.

And you can just replace r134a with r290? No need for compressor configuration, change of seals or anything?

Mostly yes, you need to vacuum it down well and make sure you have compatible oil in the compressor. Some types of plastic tubing aren't particularly compatible but for cars it's okay.

Yeah, ammonia can also be used, it's, IIRC, more efficient to use it and a bit safer because you don't high pressure, buuut enough ammonia in the air will suffocate you.

It's lighter than air so it will go away by itself if allowed to. For a purely exterior instalation it's much better than anything else.

I feel like potential suffocation is not what I'd be most concerned about if I were in an atmosphere with high concentrations of gaseous ammonia.

I have a heat pump that uses R290 (propane) (as well as an CO2 one for hot water) and would take that any day of the week over ammonia! The charge of propane is pretty tiny and the safety standards extremely strict, so not really concerning in terms of flammability, ammonia I would consider far, far more dangerous.

> enough ammonia in the air will suffocate you.

It will suffocate you on account of all that blood pulp in your lungs. And eyes, and nasal mucosa...

Having a high pressure ammonia leak indoors is a death sentence for anybody in the same room. Same building, if it's large enough...

The “common” places I’ve seen ammonia refrigeration in use are hockey rinks and cold storage warehouses. I assume it’s used in industrial installations as well for heat rejection.

I always wondered why we don't see more Sterling Engine based heat pumps. IIUC they can use almost any gas including air.

Because they're sensible heat machines, instead of latent heat machines. In a perfect frictionless vacuum, both of these can achieve the same theoretical efficiency. In practice, not so much. In particular, the isothermal heat exchange of the ideal Stirling cycle requires heat exchangers with no thermal resistance (and therefore no temperature difference). A latent heat pump has a much easier time to very closely approximate isothermal heat exchange because condensation/evaporation temperatures at a given pressure are essentially constant.

What is the back of the envelope efficiency penalty we're talking about here?

https://www.sciencedirect.com/science/article/abs/pii/S01407...

Looks like 30-50% less efficiency.

Thank you!

Would mandating the use of CO2 as a refrigerant also somehow economically motivate efforts to capture more CO2 out of the atmosphere, in a kind of virtuous cycle? Or would there be a Cobra Effect in there somewhere? I'm not familiar with the industries that refine and bottle the stuff.

No, neither - the amount of CO2 that'd be needed for use as a refrigerant is insignificant. There's already a lot of CO2 produced as a byproduct of industrial chemical processes like petroleum refining. Some of it is captured for reuse (e.g. in drink carbonation); most of it is released to the atmosphere.

This has the useful property of being regulation-exempt because it's already literally everywhere. Unlike "F gases", which have much more serious greenhouse effects and are regulated in the UK (and elsewhere): https://www.gov.uk/government/collections/fluorinated-gas-f-...

You could install your own CO2-based heat pump in a way you wouldn't be allowed to do with a F-gas based one.

OTOH, CO2 uses much higher pressures and so I'm more willing to DIY a F-gas based one. CO2 if there is a leak can cut a limb off. F-gas is generally not that high. I wouldn't want a leak/mistake, but CO2 is less personally forgiving.

There are resident systems, and they're of exactly the type listed in the article (i.e. water heaters). Residential... area heating pumps, so to say, are moving towards propane (afaik). I've been looking into getting a propane monoblock air-to-water pump, with an antifreeze loop towards an indoors heat exchanger / water tank.

Trends for new refrigerant depends on country... some to R-454B, and some to Propane, doesn't seem like C02 is very common which is a pity because I love the idea of a non-toxic non-flammable super cheap refrigerant.

This is for the Japanese market so perhaps the cons of the C02 systems are outweighed by the safety aspects.

CO2 does better with large temp deltas, like hot water tanks. Radiators don't produce large deltas - the inlet to outlet diff is typically under 10 degrees. But they run at higher pressures, making the manufacturing more expensive.

There is no reason not to use propane or butane, they have low global warming potential and is cheap. The fire risk is overstated, no one thinks twice about carrying a lighter in their pocket.

I heard CO2 is a gas with a powerful green house effect. What happens at the end of life of these units I wonder? What if they leak and it gets into the atmosphere!

CO2 has a surprisingly feeble greenhouse effect.

Almost anything else you could use as a refrigerant is worse.

Even water vapour is a worse greenhouse gas.

Edit: wait, have I been whooshed? Apologies if so... ;-)

Maybe but at this point I no longer think it's fair to be quite this dry on something that quite so many people would be legitimately sincere about anyway so I wouldn't exactly apologize for being the victim.

> Maybe but at this point I no longer think it's fair to be quite this dry on something that quite so many people would be legitimately sincere about

Yeah, but I'm from the UK so I should be able to detect dry humour. It's something that Americans don't really get.

You know, like affordable healthcare.

I apologise, I am at the dry humour stage of climate grief.

Take heart in the thought that this is going to ease off a bit in a couple of years when the current solar cycle dies down and the sun is not dumping about 5% more energy into the atmosphere than normal.

So, in the US, for instance, the average person leads to the emission of 16 tonnes of co2 per year. The amount of co2 in your domestic heat pump (which… doesn’t weigh multiple tonnes) is more or less immaterial, even if it does leak.

> I heard CO2 is a gas with a powerful green house effect.

Compared to other refrigerants it's a paradise:

* https://www.epa.gov/hfcs/technology-transitions-gwp-referenc...

* https://en.wikipedia.org/wiki/Global_warming_potential#Calcu...

Reply on news.ycombinator.com