For those not familiar, r744 is a type of refrigerant, similar to r134a and r404a. In any refrigeration system (A/C units, refrigerators, freezers, heat pumps), a type of refrigerant is required to move heat out of the target location (but heat pumps can reverse direction to move it into a living space to provide heating). Note that this is a closed system and had nothing to do with sequestering CO2 or anything, it just uses the specific properties of the gas to move heat. If I recall correctly, this refrigerant has been used in the industrial space for many years already for related cooling applications but is now being marketed as a something that EVs can utilize for cooling battery systems because it’s thermo profile allows it to be used very efficiently in this particular use-case.
The other thing I want to point out is that the linked article is coming from a website who’s domain is r744.com so they may have some vested interest in publishing this research. That is to say, I don’t believe this to be fluff or misleading specifically, just something to keep in mind.
R744 is just the refrigeration industry's name for CO2.
A wide range of substances can be used as refrigerants - basically anything that can be boiled and condensed. This includes the more commonly used ones such as r134a (tetrafluoroethane), r717 (ammonia). Even water can be used as a refrigerant (r718). It's just an industry naming convention for different chemicals.
>Note that this is a closed system and had nothing to do with sequestering CO2 or anything
Surely the fact it is a closed loop does mean it is sequestering co2.
In fact I'd go further and suggest that the best way of sequestering co2 is in ways where the sequestration is purely incidental, because then there's an economic imperative to do it.
It won't be permanent sequestration, though, or even necessarily long term. When these units are retired, their contained volume of CO2 will be reintroduced to the air, one way or another. In terms of scale, even several kgs of CO2 per person taken as a sum would still be a rounding error.
I suppose technically you are correct: a vanishingly small amount of CO2 is captured temporarily in units like these. It just doesn't matter for the issues where we need it to matter.
Well assuming we don't find anything better than heatpumps then homes will have a heatpump forever, so while your current heatpump might not sequester its co2 permanently, your heatpumps and your childrens heatpumps will effectively sequester co2 permanently.
An LED bulb saves ~5kg of CO2 a year v an incandescent. Is switching to that led bulb worth it? or is it too small to matter and not worth doing?
With current industrial processes, they usually will use some chemical reaction to create new CO2 because the can be certain of its purity. Most methods of capturing
CO2 involve changing the chemical.
Good to see heat pump tech being pushed forward in all sorts of applications. I didn't even think about using CO₂ in car applications.
I have a CO₂ heat pump hot water system (integrated by this Australian mob - https://reclaimenergy.com.au/ - but I think the heat pump unit is an OEM Japanese one) and it uses a ridiculously small amount of energy compared to my old conventional electric system (somewhere between 1.2 and 2kWh typically vs 4 to over 6kWh per day - and the new system also has a tank 2.5 times bigger than the small one I had before, which is so much better, and I probably use some more hot water than I did previously since it’s available). I have solar and it’s timed so it basically always is entirely, or almost entirely powered from that, so it’s gone from using more power from the grid than the rest of my usage combined, to now using almost no power from the grid.
Yes, it was a bit pricy but should only take a few years to pay back.
The whole tank thing is really holding me back from moving away from natural gas. With gas you have unlimited hot water when you need it, it never runs out. I hate planning things in advance. And you're not wasting energy keeping it hot when you don't need to. And no wasted space for a big tank.
If they ever manage to make electric water heating efficient enough to just heat on demand I'd probably use it.
Of course it is more efficient with electric but I hardly use any gas anyway, my bill is like 15€ a month including fixed supply charges. There's just no return there for a big investment. And I can never have solar so free electricity is not a thing (I live in a big city and don't own the roof of the apartment building)
> If they ever manage to make electric water heating efficient enough to just heat on demand I'd probably use it.
It's more a matter of efficiency than throughput. Mark-one googling suggests that a shower head might have a flow rate of 2 gallons per minute (0.125L/s). Suppose that the incoming water supply is at 10C, and the target hot water temperature is 43C (110F) for a shower.
The necessary heat flow rate is 33C * 0.125L/s = 4.125 kilogram-degrees per second. Multiply that by the specific heat of water (4184 J/kgK) to give a net energy flux of 17.3kW. On a 240V circuit, that would require 36A of current for electric resistive heating, a hefty circuit indeed.
I'm having trouble sourcing a reliable comparison, but the calculated 17.3kW draw appears to be larger than a typical natural gas stovetop with all burners on.
> There's just no return there for a big investment. And I can never have solar so free electricity is not a thing (I live in a big city and don't own the roof of the apartment building)
You might not personally have free electricity, but utilities are experimenting more with time-of-use billing. Hot water tanks allow heating demand to be time-shifted from use.
The finances clearly don't make sense for you right now, but there might come a time when electricity at some part of the day is cheaper (heating equivalent) than natural gas.
Resistive heating is considered to be 100% energy efficient in heat conversion when measured on a watt-per-watt basis.
That's to be expected as they are essentially entropy production systems.
However, heat pumps are more than 100% efficient on a watt-per-watt basis as they are not directly converting electricity into heat, but rather are moving heat from one area to another.
Heat pumps currently are between 150% to 400% efficient on a watt-per-watt basis, which could mean that your ideal hot water heater could run on as little as 240v/10a, or 120v/18a (120v/20a breakers are common in kitchens, to power microwaves and refrigerators, so this wouldn't be a huge stretch for a hot water system, either).
Additionally, the state of the art is always improving.
Recent heat pump advancements have been made with CO2 for use in electric vehicles that may push past the 400% efficiency rating, which could make it even lower than that.
> However, heat pumps are more than 100% efficient on a watt-per-watt basis as they are not directly converting electricity into heat, but rather are moving heat from one area to another.
To reactivate this dead thread: I thought of that, but I don't think it's an argument in favour of on-demand electric heating. A heat pump capable of delivering ~16kW of heat equivalent on demand would be something like 50,000BTU/hr, or larger than many whole-home air conditioning systems.
Instead, a heat pump hot water heater would be far more appropriately sized to work with a high duty cycle at lower intensity – a hot water tank.
> You might not personally have free electricity, but utilities are experimenting more with time-of-use billing. Hot water tanks allow heating demand to be time-shifted from use.
> The finances clearly don't make sense for you right now, but there might come a time when electricity at some part of the day is cheaper (heating equivalent) than natural gas.
Understood. And yes I can get time of use billing here already. Some of my friends are really into it, they schedule their whole day around it with planning and automation. They watch and analyze the prices like greedy traders watching the stock market lol.
But personally I don't care and I don't want to. I want to live my life as I see fit and I want my systems to adapt to me, not the other way around. I want to shower when I need and wash when I need fresh clothes, I hate planning days ahead of time. So I'm on fixed billing.
Even if time of use billing becomes a mandatory thing I'll just disregard it and do whatever I feel like. My energy use is so low it's never going to be something I want to worry about.
Unfortunately, residential electrical service in the United States is 120/240v single phase (technically it is split-phase, two 120v legs 180 degrees out of phase with each other plus a center-tapped neutral) in almost 100% of cases. It would be cheaper to just buy a 240v single-phase instant hot water heater than to buy a three-phase water heater and a VFD to convert the single-phase to three-phase. It’s definitely worth doing a three-phase water heater if you have three-phase electrical service though.
I have always had tank-type water heaters and I don’t recall ever running out of hot water (family of 4). Is this actually a problem people have or is it just a tankless water heater industry talking point?
Nope it’s a real problem, an undersized tank, high usage devices (eg a big bath tub) or just low temperature set on the unit for safety’s sake can cause the hot to run out.
Modern tanks have a label on them that will let you know how many gallons of hot water it can deliver in its first hour of usage, some of those numbers are much lower than others.
The good thing about the heat pump I've got is that it's also surprisingly quick to heat up. If you do run out (I never have, but I experienced the speed the first time it was turned on when it was installed) you can go and press the 'Boost' button on the controller and you will have 50L in 20 minutes and a full tank (mine is 315L) in 3 hours.
The system also heats the tank to at least 60 degrees C at the sensor point (about 2/3 of the way down) at least once every 24 hours and then has a tempering valve on the output for safety. That way you don't have scalding water at the point of use, but do have lots of hot water available and no issues with Legionella bacteria.
I have a large 2-person tub, even though I have a 80 gallon water heater (double normal size) it cannot fill the tub. That is a rare use case though, and I don't use the tub very often so I'm not sure I'd recommend it to someone thinking about that. (when my wife and I want to relax it is nice).
As a kid my family had off-peak water heating, 200 gallons of water heaters, that were only turned on for a couple hours at midnight. We ran out of hot water about every 5 years - when mom did a lot of laundry and we all took long showers/baths on the same day. One time the breaker blew and we suspect it was 2 days before we noticed.
you can run the tank hotter and use a mixing valve to deliver hot water at a safe temperature. Let's you have a smaller, more efficient tank and also ensures your water heater is hot enough to never get infected with the bacteria that causes legionnaire's disease. Double win!
Various places will have different-sized water heaters installed. As a child, I lived in one place that had a measly 20 gallon electric heater. It sucked, badly. Dad showered first, then I got woken up to shower - barely any hot water.
Ah, interesting, apparently it is manufactured by Sanden, yes. I thought they were different because you can also buy Sanden branded heat pumps here in Australia too, and I assumed that since Reclaim also sell commercial ones made by Mitsubishi Heavy Industries I though the domestic one might be Mitsubishi too.
I'm in Launceston, Tasmania and have access to no-interest credit up to $10k over three years for energy efficiency improvements including heat pump hot water.
Our electricity use is dominated by heating and hot water, and the next step I've been wanting to take is heat pump hot water.
I'll have a read of the link you provided when I get home.
Yeah, it’s been good. I think you should be able to get it installed for something like $5K after rebates.
My situation was a bit weird since I bought it in late 2021 directly from Reclaim (for about $4600 with the 315L glass lined tank), it sat in storage for a bit while I was doing other work on the house and then I had it installed more recently (cost $950) and then am claiming the STCs myself (which are worth about the same as the installation). It would be much easier to just have it done by an installer who orders it, installs it and claims the credits as part of the deal…
I have often dreamed about solutions for this, but at the end of the day I'm not sure that your average household would really have enough coincident demand for heating and cooling to make it worth it... Definitely for larger buildings it makes a lot of sense though (and there are chillers that have heat recovery now for this kind of thing)
I was not thinking of running heating and cooling at the same time. Simply that if you run a heat pump in reverse, you can use it for cooling. So you should be able to use the same device for heating in winder and cooling in summer. Even portable aircon's do this.
The tricky part here is that you want heating to transfer heat to water, because radiators are much nicer than heated air. These Co2 based heat pumps are good because they can heat to a higher temperature which is necessary if you want to use your existing radiators or your house is difficult to insulate.
But I'm not sure it would work well to use 'radiators' for cooling. Apart from any other reason, you won't want to risk freezing them.
CO2 heat pumps are an interesting trade-off. I think Sanyo used to make them and they work well but never get the best SCOP values, tho I don't think they are far off.
Their major benefit obviously is that the refrigerant has a GWP of 1. Instead of several thousand for the mainstream gases.
So say an air-to-air home heat pump with about a kg of refrigerant could release couple of tons of CO2e in case of a leak or an unknowing/caring worker cutting the pipes without properly collecting the gases during the dismantling.
This could easily negate the lifetime atmospheric CO2 savings of that heat pump.
Whereas in case of a heat pump using CO2 it would be a non-issue.
That's not exactly how I understand it - my understanding is that they are generally very good in terms of COP but the trade-off is that they operate at much higher pressures than other refrigerants (including the ones we're phasing out), so material properties, servicing, etc. are more challenging.
(of course, it's more complicated than that because COP changes depends on input and output temperature, both in absolute and relative terms, and different refrigerants can be better for colder inputs or hotter outputs etc., but I am talking in general).
It’s not really about price, you can get refrigerant grade CO2 for about $2/lb while other common refrigerants can range from $4-$14/lb. The problem is making sure equipment is certified to handle r744 because it does have a different thermo profile, expansion ratios, and critical point. As you can imagine, manufacturers of more expensive refrigerants are probably not super eager to push a cheaper, easy to capture or manufacture alternative that is effectively not patent-enforceable.
The manufacturer of the heat pump system is rarely the maker of the refrigerant but they maintain a close relationship with them. That relationship would be harder to maintain if they suddenly decided to use a very common substance rather than the Dow, Carrier, or Honeywell r410a. It’s likely these companies would be happy to sell r744, but the margins are not going to be as good.
AFAIU the main challenges is that the thermophysical properties of CO2 are different than for the usual fluorocarbon refrigerants, so it needs a different design taking that into account (among others, needs to handle much higher pressures).
The advantage of the fluorocarbon refrigerants is that the current automotive one, R1234yf, is mostly a drop-in replacement of the previous R134a, which in turn was mostly a drop-in replacement for the freon refrigerants (R12) that were banned due to destruction of the ozone layer. So going down this path manufacturers can basically slightly tweak their original designs, potentially originally dating back to the beginnings of the automotive AC era. So saves on R&D costs. The downside is of course that these fluorocarbon refrigerants are very expensive compared to CO2, and the ever tightening F-gas regulations around the world meaning there seems to be a never-ending rat race where a fluorocarbon refrigerant gets banned, necessitating the development of a replacement which is more expensive, and then in turn gets banned in a decade or so. Rinse and repeat.
Looking at the tradeoffs of CO2, r744, I don't see it gaining adoption.
Quick search shows 10x pressure vs r134a. That pressure difference is significant on size, weight, maintenance of parts. Also at non-low ambient temps it's apparently less efficient so the useful range is quite limited.
>Also at non-low ambient temps it's apparently less efficient so the useful range is quite limited.
Surely it depends on efficiency curves, and local climate.
If it's marginally less efficient above 0c and much more efficient below then it would still be a win in many climates.
Further, the very coldest days tend to be less windy, and also tend to be the days when you want most heat so if your generation backbone is based on wind, co2 would still be the best choice, if only to minimise demand at the worst possible points.
> Surely it depends on efficiency curves, and local climate.
Yeah and i'm still trying to understand the enthalpy curve of the two systems but at the same given temp it's way further along the X-axis for 33'C[0][1].
33'C is a pretty common for a huge chunk of the earth.
If it was way cheaper to implement then of course cold locations would work really hard to adopt it. but with 10x pressures, there's no way, right?
“ A CO2 heat pump uses carbon dioxide as a refrigerant. Carbon dioxide is a naturally occurring gas, and it has a very low boiling point. This makes it ideal for use in a heat pump. When the carbon dioxide is compressed, it becomes a liquid. This liquid then evaporates, and as it does so, it absorbs heat from the surrounding air.”
Wait - a highly efficient heat pump technology for EVs using the exact same gas EVs were created to avoid? And they say God doesn't have a sense of humour!
In a personal car sized vehicle it's probably less than 1 kg, circulating in a closed system. The only time it will enter the atmosphere is in case of a leak, or when doing some service on the AC unit where the refrigerant parts need to be opened.
I would guess that as opposed to the fluorocarbon refrigerants there is no need to capture the gas, as there's already plenty of CO2 in the atmosphere? Might need to ensure proper ventilation though, 1 kg of CO2 in an enclosed garage might increase the CO2 level uncomfortably high..
Through the magic of dimensional analysis we can see that 1kg of CO2 is approximately 22.7 moles. Coincidentally, 1 mole of gas at STP is 22.7 liters. So 515 liters of CO2, which is a fair volume - half a cubic meter. Not enough to raise the CO2 level of a garage dangerously (assuming a standard garage is 4m by 7m by 3m) but a substantial jump - 1% or so, so you'd notice it.
The other nice thing is that it's rare to have people suffocate due to high CO2 levels - it quickly becomes uncomfortable and people move to fresh air, unlike e.g. pure nitrogen, because the body is adapted to detect and alleviate high CO2 levels as a proxy for low O2 levels.
Fortunately our bodies are very well equipped to detect high CO2 concentrations (in our bloodstream - but that tracks outside concentration pretty reliably) - you will feel like you're suffocating and have an irresistible urge to move to fresh air.
Unlike other gases (CO (without the 2), helium, argon, even nitrogen) that we don't "feel" at all, so they can displace oxygen and cause us to lose consciousness or even die, without much warning from our bodies.
The other thing I want to point out is that the linked article is coming from a website who’s domain is r744.com so they may have some vested interest in publishing this research. That is to say, I don’t believe this to be fluff or misleading specifically, just something to keep in mind.