Marketing has clearly gone awry in the world of CO2 air supply heat pumps. It would be a painfully damaging stretch of the imagination to believe that there was anything cute about the Eco Cute. Perhaps painting large, sympathetic eyes and covering it in fluff might work?
Setting aesthetics aside (although why environmentally-friendly products often look butt-ugly is perhaps a discussion for another time), does the Eco Cute deliver on the Eco part of its name?
I’ve discussed how heat pump technology can heat water and homes using less energy and emitting less CO2. There are claims that the Eco Cute can reduce CO2 emissions by up to 50% under certain conditions. Whether the Eco Cute is really this effective is debatable, but it is certain that heat pumps generate more heat than the amount of electrical energy added.
But the Eco Cute is a CO2 air supply heat pump. That name seems to suggest that it uses CO2 to emit less CO2. Sounds like devilry.
To break through the confusion, let’s explore why CO2 got such a bum rap.
CO2: Philanthropist or Racketeer?
Carbon Dioxide has a nasty reputation. It’s considered an environmental criminal, going on a rampage warming up the globe.
Poor Carbon Di. It never meant for things to get like this. It started out with good intentions. It was, after all, always busy helping keep the planet warm by stopping the radiation from the sun from all bouncing back out into space.
It didn’t work alone, either. It worked as part of team with some other gases in the atmosphere. Big-name gases like Water and Methane. These guys, and a few (but highly influential) others formed the GHG Gang.
Without the work of the GHG Gang, the Earth would be a frozen inhospitable place. People would be begging for global warming, assuming we’d had a chance to evolve at all.
But Carbon Di just worked too hard and did its job a little too well. Instead of keeping the Earth at a pleasantly comfortable temperature, Carbon Di just kept pumping out there into the atmosphere. Carbon Di kept landing all the Total Combustion deals, spreading its wealth around, heating the Earth.
Now the Earth is getting too hot. Carbon Di went too far, and so the IPCC issued an arrest warrant.
The minor players in the GHG Gang are also fugitives from the law, but the real kingpin—Water—is keeping a mysteriously low profile. Perhaps Water has better biological contacts or something?
Gas Gansters can be rehabilitated though. Perhaps not the most morally bankrupt ones, like Mustard Gas, but CO2 started out a good guy. Some would argue Carbon Di still is a good guy, and has been unjustly persecuted. Regardless of your viewpoint on whether or not it’s doing anything wrong, it is obvious that Carbon Di is an overachieving Earth-Heating workaholic.
All that’s needed is to get our workaholic warming gas interested in something else. Something like refrigeration.
Putting Carbon Dioxide to Work
It might seem a little insane to think of CO2 as a refrigerant. CO2 causes global warming and refrigerants make things cold—but that’s the heat pump magic for you.
Under normal circumstances (and by normal I mean conditions under which life will not be crushed, incinerated, or freeze-dried) CO2 is a gas. By increasing the temperature and pressure, it is possible to turn it into a super-critical fluid. It’s neither a gas or a liquid, but it still flows. The diagram shows the sort of temperature and pressure that the CO2 needs to be put under to make it supercritical.
Turns out that this super-critical fluid has some very handy physical properties, making it an excellent refrigerant for use in heat pumps.
Since the supercritical CO2 is cycled around the closed pipes in the heat pump, none of it is released to the atmosphere. That’s not to say that some might not leak out, but none of the CO2 is intentionally emitted from the heat pump. Thus the CO2 in the heat pump contributes very little to the global warming problem during its lifetime.
Competitors to the Eco Cute heat pumps use other refrigerants, such as HFCs. Although HFCs have an engineering advantage in that they can operate at much lower pressures than super-critical CO2, they have an environmental disadvantage. They have a significant Global Warming Potential (GWP). The most popular refrigerant, HFC-134a, has a GWP of around 1300 times that of CO2.
Since heat pumps don’t intentionally discharge their refrigerant to the environment, a refrigerant with a higher GWP isn’t a huge problem until the end of the heat pump’s life. When the heat pump is disposed of, that refrigerant has got to go somewhere. Even attempts to reclaim and recycle it will result in some losses to the environment. HFCs are clearly going to have a bigger impact than CO2.
These days engineers need to take the treehuggers a lot more seriously, so have found ways to overcome the challenges posed by the higher pressure operation of CO2 refrigerants. The solution could be the Eco Cute.
Now if they could just get it to actually look cute…
 Cute is apparently phonetically similar to the phrase meaning “supply hot water” in Japanese.