CO2 Heat Pumps Found to Offer High Efficiency at Low Ambient Temperature
r744.com
r744.com
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.
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.
A heat pump locks away a few kg of co2. While (more importantly) lowering the other side of the equation.
I'm not advocating it as a one stop solution to climate change, just that it does in fact sequester a few kg of co2.
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.
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?
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.
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.
For context, 54 degrees for 30 seconds will cause full-thickness skin burn.
If it doesn’t for you, that likely is because of your settings
It does now.
It’s not as if someone from Apple did a quick fix is it?
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.
Thanks again.
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…
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)
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 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.
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.
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.
> 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.
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.
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.
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.
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.
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.
(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).
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.
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.
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?
[0] https://onlinelibrary.wiley.com/doi/full/10.1002/ese3.976
[1] https://onlinelibrary.wiley.com/cms/asset/cf698e11-dfed-489c...
“ 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.”
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..
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.
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.