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Comment by marcinzm | Hacker News Reader

That's not a heatwave by US standards, that's a pretty common summer day for a decent chunk of the US. Arizona can get to around 50C.

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I think you know that heat waves are defined relative to the local climate. And recall that all but the southern part of Germany is north of the US-Canada border. AZ should be considered uninhabitable (in a sustainable sense) even outside of heat waves.

A reasonably modern air conditioner to cool your house in Phoenix a few months in the summer is more efficient than many of the common ways you'd heat a house from potentially well below freezing in the winter in many other places.

And much of our power comes from solar (which is maximally available at the time cooling is maximally needed) and nuclear, while serious heating is often literally burning fossil fuels in your basement.

Yes, if I want to be locked inside 24/7 it turns out it does not matter much specifically where I do that.

What does it take to spend a vacation day outside working in your garden? At 30F that's just a thick jacket away, what kinda clothing can make your body work at 120F and sun?

I actually believe that the opposite is true. It takes much more energy to cool off a home with AC than it does to heat a home in cold weather.

I think you are confusing the efficiency of heating sources vs the inefficiency of A/C. However A/C just moves heat, it doesn't have to create it. This is why in climates in which they are appropriate heat pumps can be even more efficient than other forms of heating.

I will say there likely isn't a ton of good hard data on this for another reason, and that is that humidity plays a role, both in what temperatures are comfortable and maybe in some forms of temperature management.

The work put into the compressor and fan motors has to be rejected along with the heat that is transported by the refrigerant.

Huh? That hard data was half of my undergrad courses in mech

No it doesn't. An AC essentially transfers more heat energy out than electricity it consumes. Most heating generates exactly as much heat as energy consumed (electric heaters, burning fuels, etc.). Heat pumps are an exception but they don't work well before freezing temperatures.

Typical energy efficiency of heating is comparable to AC. The baseline solution is using waste heat from electricity generation and industrial processes. Geothermal heat pumps have become popular in the past decade or two, and lake/seawater heat pumps are seen as the future of district heating systems in dense cities.

The big difference is insulation. On the average, houses that need heating are better insulated than houses that need air conditioning.

Yeah the defrost cycle limits the heat pumps heating ability, but AC units have a similar limit wrt how much they are able to lower the temperature of the air. AFIAK they can do about 20 F. At this point you need to do some math and add additional units and run them 24/7 nullifying this benefit.

Geothermal heat pumps and good insulation solve both.

It is counterintuitive but A/C in general has a much smaller footprint than heating.

I agree that your solar-powered cooling is a giant improvement. But the water situation still seems totally unsustainable.

And where does your water come from?

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