"Heating and Cooling With a Heat Pump" - https://www.nrcan.gc.ca/energy-efficiency/energy-star-canada...
"Heat pump" - https://en.wikipedia.org/wiki/Heat_pump
I’ve lived in places with hard water and most people have a water softener right next to their water heater so that all water to all appliances in the house is softened.
Every dishwasher I’ve had in Europe has a salt compartment. I can’t remember the ones I had in the US to have a salt compartment. I’d wager the powder and pods in the US have some salt in them to make up for that?
Turn on captions if you're having trouble keeping up.
Lets do "special salt" first. What you need is Sodium Chloride. Commonly: salt. The manufacturer tells you to buy "dishwasher salt" but all that is, is a bag of salt. Why not say just "salt"? Well, the table salt you might buy comes in lots of fancy and/or tweaked varieties which are not ideal for the machine, yet they are more expensive. Instead of buying ten smaller packs of "Genuine Himalayan Rose Salt" for $1.50 each, you should buy the same amount of just regular sodium chloride labelled "Dishwasher salt" in your supermarket in one packet for like $1. As well as irrelevant or potentially undesirable minerals to make it pink (for some reason) salt for food might have a packaging stabilizer, an ingredient added to make sure it doesn't stick together, and iodine salts because sometimes humans don't eat any iodine and if they don't their thyroid gland doesn't work properly which is bad so some public health authorities have local salt tweaked to fix that (salt is chosen because it's really easy). So yeah, TL;DR it's literally salt, it's not special.
Now, do "the capsules have this". Well, they all say they solve this problem, but of course they say that, a manufacturer isn't going to advertise their product and say "This product is pretty bad really, you probably shouldn't use it". Every manufacturer of "flushable" toilet wipes says their wipes don't cause sewer blockages. The blockages happen. Maybe all the other brands are lying except yours?
Here's why they don't really solve the problem, what your dishwasher wants from salt is a source of ions to re-charge its water softener. Sodium Chloride is (if you remember chemistry class) Sodium ions and Chlorine ions, the softener wants the Sodium ions, it will swap them with the ions from the hard water, softening it. But how much softening is needed? With bulk salt in the machine you don't care. Once a month (or even once a quarter) check the salt, if it's low fill it back up, done. But in a capsule there must be enough softener for each load, or else it gradually gets worse.
Now, it can happen you live somewhere that the water is exactly as hard as the capsule manufacturer decided water should typically be, and for you they work perfectly. Most people don't.
It seems weird if "coarse salt" is significantly cheaper where you are than dishwasher salt, the main cost difference I'd expect is that the "dishwasher salt" manufacturer is like "This isn't food, so I don't need food inspections" which would make their product cheaper.
I checked my usual suppliers, if I want fancy salt, because I'm stupid, crazy or rich, I can pay up to £40 per 100 grams for special "black salt" which apparently has rare minerals in it and presumably is aligned with my spiritual ancestors or something?
If I'm content with just salt, NaCl, ordinary crystals of sodium chloride, that's £0.10 per 100g. I could put that in a dishwasher but...
If I want dishwasher salt, that's £1 per 1kg, which is the same ratio but larger sizes because unlike fancy specialist salt, nobody buys 100 grams of dishwasher salt.
However, do check your "coarse salt" is actually just salt, it probably doesn't matter, but the manufacturer doesn't design the machine to have, for example iodine in it, which is often in the table salt in places where iodine deficiency causes medical problem, or an anti-caking agent (to stop it forming "big chunks" when you want to sprinkle it on food) or other food ingredients.
Just verified, dishwasher salt is almost 5usd/kg. Coarse salt is .75usd/kg
Where exactly outside you tap in for that heat energy and how the outdoor heat exchangers look like varies depending on implementation, but the principle is the same.
Wouldn't it be more accurate to say that an air conditioner is a type of heat pump?
In terms of basic science, they are the same principle so "air conditioner" is a type of "heat pump".
But in terms of semantics that is understood by the general public for purposes of differentiating various HVAC equipment one can buy, a heat pump has an extra reversing valve to change the flow of refrigerant. A standard air conditioner doesn't have that extra feature.
When folks casually say "heat pumps", they're talking about a HVAC equipment category and not general science principles.
In Europe most units are reversible cold/heat unit so “air conditioning” means making air both colder and hotter. We would call the ACs the Americans have “air coolers”, if we needed to make the difference.
In this view air conditioners are a kind of heat pump.
There is a question around time to pay off though. If you run it one day a year, you may as well buy the cheapest possible thing.