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Comment by seydor | Hacker News Reader

Aren't heat pumps the same as air conditioning? I have one

This feels like a US vs rest-of-the-world thing. In the US, “central” air conditioning is usually one-way and paired with a furnace for the winter. The main alternative is window ac-only units which are removed in the winter.

Mini-split heat pump units that heat and cool are everywhere in Asia and parts of Europe but are still relatively uncommon in most of the US. I installed one last year and had to shop around for an installer, several of which tried to talk me out of it. If this is what you think of as “air conditioning” then you’re right. Most Americans would think of a central air system that cannot heat.

Minisplits are becoming very common in the older cities - NYC, Boston - where they're much easier to retrofit into plaster-and-lathe walls.

In regions like the Southwestern US, where furnaces are not needed, AC units are heat pumps. The US is large enough to defy most generalizations.

They’re the same core concept. There are generally two major differences:

* a heat pump has a switch valve for coolant. This allows it to move heat in either direction.

* while not strictly necessary, heat pumps typically have a variable rate compressor. They scale to match load.

Some heat pumps will also have a supplemental electric heat element when conditions are extremely cold.

> When it’s cooling your house, it’s just a normal AC. But did you ever think “When it’s cold outside, why can’t we just turn the AC around and air-condition the outside, so it heats up inside?” Well, it turns out you can! And that is how a heat pump works. It just moves heat from the outside of your house to the inside, just by turning the air conditioning in reverse.

That's what most air-conditioning does in europe, it is also used for heating

Probably location dependant but numerically I'd guess most ACs that Europeans have interacted with are in cars, which only very recently started using heat pumps for heat in the EV era.

That dpends where you are in EUrope. Lots of housing have AC in the Mediterranean countries, and even in the famously AC-deficient UK pretty much every office building and supermarket will have AC.

I wouldn't say most air-conditioning in Europe includes heat pump heating, in fact for most of Europe I'd say its not super common.

Germany is in Europe. Only 4% of residential heating is from electrical sources, which is both heat pumps and resistive heat. 51% of household heating is from natural gas, 20% is from heating oil, and 18% is from district heating.

https://www.statista.com/statistics/1189752/household-heatin...

Here's iea's residential heating sources in 2020. Italy (also in Europe) sourced 60% of its energy for residential heating from gas. Hover over electricity and see how low of a percentage it is in most countries.

https://www.iea.org/data-and-statistics/charts/proportion-of...

Yep, most people have "heat pumps" already .. in their car or refrigerator ;)

> Aren't heat pumps the same as air conditioning? I have one

not even remotely

I ma fairly sure that in europe A/C and heat pumps are the same (cooling/heating)

Then you are incorrect

That’s a stretch.

Do explain

They’re actually nearly identical in concept.

An air conditioner is actually just a one-way heat pump. The major difference is heat pumps can run in reverse.

Actually an AC unit is a heat pump, just a one directional one that moves the heat outside.

It depends. Window or floor units that are portable are not usually heat pumps. They use a different cycle with the refrigerant. Ductless splits and central air are often heat pumps.

How so? Anything using vapor compression refrigeration should technically qualify as a heat pump. They may not move the heat as far, but that shouldn't matter. A swamp cooler isn't a heat pump, but the units you describe would seem to me to obviously qualify.

You can buy portable window heat pumps from several companies. They’ve been around for a while.

Sure, there might be some in some markets, but when I go to the store around here practically none of them are heat pumps. They're rare to find shopping around for some reason.

Like, look at this list. How many will heat? Probably none.

https://www.lowes.com/pl/Window-air-conditioners-Room-air-co...

I can walk into a dozen stores selling window AC units around me with hundreds in stock ready to go today. If I want one with heat near me, I'll have to custom order online. Thus, the vast majority of window AC units you'll encounter in most of the US are cooling-only unless the person knew they could order one which does heat from someplace else online.

Home Depot seems to carry the LG window heat pumps in stores.

I do agree that it’s odd that most units can’t heat and that the heat pumps are so poorly advertised.

> They use a different cycle with the refrigerant.

No, every major consumer air conditioner and every major consumer heat pump on the market that I'm aware of uses the same cycle (the vapor compression cycle). The only difference between a vapor compression cycle AC and a vapor compression cycle heat pump is which of the two loops is being used as a heat sink and which as a heat source. You could in theory do this by simply reversing the flow direction in the refrigerant loop, but in practice the better approach is to do the same thing with valves, allowing the compressor to always operate with the same flow direction.

It's important to distinguish between the heat pump itself and the heat exchange medium used to transport that heat into a given space though. If you try to connect a heat pump meant to replace a radiator system in an old (or european) dwelling, the radiators we're really designed for cooling, and you may have performance issues. But that has nothing to do with the heat pump itself.

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