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Comment by tspike | Hacker News Reader

This is something I’ve been confused about. In common discourse, it seems that “heat pump” has positive associations with efficiency while “A/C” is associated with gluttony and waste. Aren’t they the same device? Why the difference?

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I think it is largely because people from colder climates understand the necessity of heating but think cooling is a luxury. They understand freezing risks, but might not have real appreciation of heat exhaustion or heat stroke.

Secondarily, many may lack the basic physics knowledge to think about both as heat transfer nor to recognize the most important parameters: temperature differential and isolation.

On the other hand, people may have some awareness of poor deployments of air conditioning into leaky and barely insulated structures in hot climates. These are indeed wasteful, but so would heating that structure if it were transplanted to a cold climate. But, it is the structure that is inefficient, rather than the heating or cooling method...

In common usage, the term "A/C" refers to a kind of heat pump that only does cold, whereas "heat pump" means one that does both hot and cold.

A refrigerator also has a heat pump, but we just call them refrigerators.

Part of the problem is in temperate climates, if you have "A/C" you probably _also_ have a furnace. They might run on different fuels (electric vs. natural gas) so it makes it harder to get a ballpark estimate for the overall efficiency.

I see. So this comes from a temperate climate perspective, where it's historically been the case that everyone _needs_ heat but cooling is an optional luxury. This perspective would seem to need revisiting with a changing climate and in a global context.

> In common usage, the term "A/C" refers to a kind of heat pump that only does cold, whereas "heat pump" means one that does both hot and cold.

Does it though? That seems to be some kind of subcultural jargon that matches neither common (which uses central heating and air conditioning for any central system that cools with a heat pump regardless of how it heats) nor industry usage. (My fairly nee system, marketed as A/C, has both a two-way heat pump and a gas furnace to back up the heat punp for heating.)

Why does anyone make A/C’s rather than just make Heat Pumps that run in both directions? Is there a cost difference?

Heat pumps are about 1.3x up front cost, but 0.75x over the life of the unit. New construction therefore tends to prefer a/c, but some federal and state subsidies are kicking in soon to sweeten the deal.

In really cold climates (e.g. Minneapolis, Montreal) heat pumps often also need a supplemental furnace or fireplace because the heat differential inside vs. outside exceeds what the pump can handle. Depending on your fuel source, you still come out ahead, but not as much.

I should note that I'm not an expert by any means; my brother in law works in this field and he gave me a crash course a couple weeks ago. So I probably feel like I know it better than I actually do.

[1]: https://carbonswitch.com/heat-pump-vs-ac/

I am aware there is a cost premium up front but I am wondering if this is just due to the production scale of AC units versus heat pumps or if there is something fundamentally, non-trivially more expensive?

The difference is mostly the setup. Most "A/C" I see are hung up on roofs and exposed directly to the sun. Kinda funny if you think about it. But the installation guys/company do not care. And most people have no idea that it's a heat-pump or how that thing works.

That must be a regional thing. In my area heat pumps and air conditioners are indistinguishable on the outside. They are usually installed behind or beside the house in an inconspicuous location, as close as reasonably possible to the corresponding interior coil and machinery.

My guess is that heating is perceived as a survival issue, and cooling is about comfort. Needs vs wants.

Isn't excessive heat is the leading cause of death in many areas?

Worldwide, ten to twenty times as many deaths are caused by excessive cold as are caused by excessive heat.

https://thebreakthrough.org/issues/energy/human-deaths-from-...

https://www.wunderground.com/cat6/Which-Kills-More-People-Ex...

Unsurprisingly, this seems to be a matter of debate:

> In a 2014 interview in the Washington Post of University of Miami climatologist Larry Kalkstein, who has published numerous research papers on weather-related mortality, weighed in on the matter: “Comparing apples to apples, which would be to evaluate acute or short-term responses to weather, I would always give the nod to heat-related deaths. However, if you are considering the seasonal differences in daily mortality, rather than just the “spikes” that we find with acute deaths, I can see why one can argue that winter (or cold-related) mortality is greater.”

https://www.wunderground.com/cat6/Which-Kills-More-People-Ex...

Edit: I see we are citing the same article :)

Yes, but I also cited another one, which takes the more general approach of estimating excess deaths per year associated with cold vs. heat. That article comes up with a factor of about 10 (4.6 million excess deaths per year due to cold vs. 0.5 million due to heat).

Note that this article also discusses other factors, such as seasonal changes in death rates due to diseases--but it, unlike the one you referenced, correctly observes that temperature is a factor in such deaths. The fact that flu season is worst in winter is because temperatures are colder than optimal in winter. So the increased flu death rate in winter should at least partly be counted as an increased death rate due to cold. The excess deaths methodology takes these kinds of things into account.

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