Hacker News Reader

Author might be forgiven, considering the quality of available information online:

> Heat pumps offer an energy-efficient alternative to furnaces and air conditioners

> Because they transfer heat rather than generate heat, heat pumps can efficiently provide comfortable temperatures

https://www.energy.gov/energysaver/heat-pump-systems

> heat pumps tend to be more energy efficient than an AC

https://bkvenergy.com/blog/heat-pump-vs-central-air/

Of course those sites don't cite a source. It's probably AI generated. Apparently this is a widespread confusion.

My guess is they are comparing heat pump for both heating and cooling to conventional furnace/AC system, not just "for cooling" only.

Ground-water heat pumps can passively cool making them more efficient than traditional AC

I can't say I agree with this author, but this problem goes back many years: https://www.treehugger.com/why-are-there-so-many-fist-pumps-...

People seem to think heatpumps are some mystical woo-woo new-wave energy healing device or something like that. It's an air conditioner. That's it.

Not in the sense most people use the word "AC" or air conditioner.

If you mean it by what it actually does, it conditions the air to be cooler or warmer or have less relative humidity, then yes. In typical NA applications anyway if we are talking a specific kind (ones you hook up to potentially existing forced air system ducts or mini split types with in room units blowing conditioned air).

We heat with our mini split in winter and we cool with it in summer. And I'm in Canada so it gets pretty cold in winter. And if I said we had our "air conditioner" running in winter people would look at me strange.

A heat pump isn't more efficient than an air conditioner at cooling, because they're the same thing except a heat pump has a reversing valve.

For heating, running your air condition with a reversing valve so it cools outside and heats inside is often more efficient than a furnace, so that is nice... But irrelevant if we're talking about it being too hot.

And how does any of this apply to my comment? I said nothing about any of that.

I was commenting on the use of the word "air conditioning" for heating. Which is technically true but not used in that way by like literally anybody. In any regular use of the word AC it implies cooling.

Again, to be clear, yes the phrase is usable both ways. No regular person will use it that way. Get used to it instead of making technically correct points that don't help anyone.

They don't claim heat pumps are more efficient than plain AC at cooling. Their parenthetical remark about people should ideally get heat pumps, links to an article about why people should get heat pumps. And why? Because they can have lower ghg emissions than natural gas furnaces and resistance heating through efficiency and the ability to use renewable electricity.

Seems pretty clear they understand heat pumps.

You're correct, but OP's misunderstanding stems from the fact that the parenthetical isn't just a tangent, it's a non sequitur. Humans tend to assume that an utterance is relevant to the topic at hand and in particular to the surrounding context [0].

This parenthetical was inserted arbitrarily in order to plug an article that has little relationship to the surrounding text, and OP understandably interpreted it as though the writer thought it was relevant.

[0] See the Gricean maxims: "I expect a partner's contribution to be appropriate to the immediate needs at each stage of the transaction." https://en.wikipedia.org/wiki/Cooperative_principle

> stems from the fact that the parenthetical isn't just a tangent, it's a non sequitur.

It's not a non sequitur to point out a superior alternative like that. If air conditioning is on-topic, heat pumps are either on topic or a tangent.

> All the while, fiercer heat waves will require more energy-hungry air conditioning to keep people healthy. (Though ideally, everyone would get a heat pump instead.)

Juxtaposed with "heat waves will require more energy-hungry air conditioning", heat pumps are a non sequitur. A nonzero percentage of those energy-hungry air conditioners are actually heat pumps running in air conditioning mode.

"Everyone should get heat pumps instead" of what? Instead of a heater. As OP says, heat pumps save no energy during the summer, so they're entirely irrelevant here in a "though" clause.

> A nonzero percentage of those energy-hungry air conditioners are actually heat pumps running in air conditioning mode.

Wouldn't that percentage be... 100%?

Fair enough!

> "Everyone should get heat pumps instead" of what? Instead of a heater.

You almost understand. The author is saying that if you're installing or upgrading your air conditioning, you should take the opportunity to also replace any heating system that isn't a heat pump, rather than only upgrade half of your HVAC system.

I understand that that's probably the connection the author was desperately reaching for, but what they were actually saying is "we have some other content over here that I'm obliged to plug, so here's a plug". And since the plug was the point, little effort was made to make the connection make sense.

In the abstract you are correct but in practical application, products sold as air conditioners and products sold as heat pumps are designed and sized very differently, resulting in different consumption/efficiency for the same home.

I imagine every heat pump can cool a house, even though every “air conditioner” cannot.

If you have a gas furnace to heat the house, then it might not make sense to pay extra for a heat pump that works in both directions (to heat and cool a house). So you would just buy a heat pump that works in one direction to cool the house, aka an air conditioner.

But if you buy a heat pump to heat the house, you might as well have the unit be capable of running in reverse to also cool the house (since you have no other way to cool the house).

I wouldn't really say very differently. Residential AC and Heat Pumps are available in pretty the same spec range. You can make an AC by removing/replacing some parts from a Heat pump and that's what some manufacturers do, meaning they're literally almost the same (except for the reversing valve, accumulator, outside meter and defrosting and some other small stuff)

> Heat pumps and air conditioners are identical, with the sole difference being that the heat pump can _also_ function as a heater/furnace.

That's a pretty huge difference from the user's point of view.

Take an existing house that does not have cooling, and has either fossil fuel heating or electrical resistance heating. The owners want to add cooling.

If they get an AC for that then later decide they want more efficient heating in winter the cost of doing that (whether by getting a new efficient heating system or by making the modifications necessary to add heating mode to their AC) are likely to be quite a bit more than than the extra it would have cost to get a heat pump instead of an AC when they were just trying to add cooling.

I wonder if some of the confusion stems from a seemingly common conflation of heats pumps and mini-splits. Mini-splits are not heat pumps per se though most of the former tend to be powered by the latter. And all other things being equal, mini-splits tend to be more efficient than centralized ducted systems since you're heating/cooling a smaller volume. But I agree that it's not clear the author understood the difference.

You can have heat pumps that don't use air as a medium.

never heard of a ground source air conditioner.

The “air” in “air conditioner” is describing what the function is. It’s conditioning the air. Plenty of ground source/geothermal air conditioning. It’s just a nomenclature thing.

Have you ever tried contacting an HVAC company and asking them to convert your AC to a heat pump so that you can use it to heat your house in the winter? I did, they told me that it was a nice idea in theory, but that it was the kind of work that nobody did unless they were teaching a class or something. The way to go is to just tear out my AC and have a heat pump installed. Nevermind that an AC is technically a heat pump.

So in practice, they're quite different.

> heat pumps provide no advantage

If you're worried about carbon emissions, heat pumps provide an advantage over AC / fuel-burning furnace combo's. I assume this is what the article was talking about.

> Have you ever tried contacting an HVAC company and asking them to convert your AC to a heat pump so that you can use it to heat your house in the winter?

Of course not, that's like asking your car mechanic to convert your ICE car to an EV.

While the principle of operation in a heat pump and AC unit is exactly the same, an AC-only unit is missing hardware to be able to be used to provide heat, and it's not just a matter of replacing a part or adding an optional feature. It would require major surgery.

It's basically two 3-way valves to flip which coil has high pressure and which coil has low pressure. If you get freezing temperatures, you may also need to do something to manage the icing that would happen outside, which may be via a suitable sensor to detect that state and running it in reverse for a calculated duration or such to melt the ice off.

It's really not much that needs to change. Efficiency may not be too good in heating mode, though, but in spring and fall it should work much better than a furnace.

Is there not a difference of capacity?

It takes more energy to bring a house up to 20°C in -15°C weather in a reasonable amount of time than it does to bring down the indoor temp of 20° from an outdoor temp of 35°C.

Their point still stands, which is that a heat pump provides no advantage in the summer, so the article was wrong in indicating that it did. But yes, not all ACs can be run as a heat pump.

I don't know where you get your ACs, but any I've seen installed this side of the turn of the century has a heating setting.

I use the AC unit (air to air heatpumps) in my attic mostly for heating in Winter and it works fine. The big downside is noise, (air to water) heatpumps let you move the noisy bit to another space which increases comfort.

You can build a silent-enough forced convection condenser to put in the room and put the noisy part away, without water, and cheaper than the passive convection water setup.

For cooling you can't use the typical passive convection radiators anyways, so might as well invest their cost into making the cooling and heating refrigerant coil silent...

Also c.f. a normal domestic fridge: no noise beyond the piston compressor.

Forced air is however going to cost you quite a bit of efficiency. And in mid-winter just the airflow is noisy enough, not just parts of the unit.

In theory such a thing is possible. In fact, I've even sketched out what I'd need to do to my one to convert it. I may still do it as a science project -- it's an old unit (~2007), so if I destroy it it's not the end of the world.

I can completely understand why no HVAC company would want to touch such a project. It's entirely experimental, would take a skilled technician, and has a high chance of not working perfectly. They would much rather slap together 2-3 installs in the time it would take to plan and assemble your science project. Remember that most of their techs are literally just installers, and there's a huge incentive to "rip out and replace" rather than "diagnose and repair".

If you could find a retired HVAC tech, you might be able to convince them to help.