Hacker News Reader

Comment by grey-area | Hacker News Reader

You should still feel some guilt for the heat pollution your air conditioning causes for those outside your house, esp. in an urban area.

View on HN

Can you please elaborate more on pollution from air conditioning equipment and heat pumps. I was thinking they are closed systems.

Sorry autocorrect changed heat pollution to ‘what pollution’, I’ve fixed that now.

There is some impact on others, particularly those without ac.

If you’re using rooftop solar then presumably the net heat generated by your aircon is the same as the amount your roof is no longer absorbing. Otherwise you just described a perpetual motion machine?

I imagine that absorption by the roof or panels is around the same - however the aircon moves heat from inside to outside, so you are moving heat outside for other people to deal with. In an isolated house it makes little difference. If every building has aircon in a city it does impact outside temperatures and adds to the heat island effect.

Right, but energy that would have heated the roof goes towards powering the aircon (which likely is on the roof itself), which then emits the same amount of heat, no?

Say a roof is absorbing 10000 watts. You install solar panels that absorb 2000 watts, used to power an airco. You now have your roof absorbing 8000 watts (released as heat) and ann airco absorbing (using) 2000 watts (also released as heat). Am I wrong? Seems like a conservation of energy problem. And you get a cooler roof so less airco demand too!

Ah, unless you refer to shifting the release of heat from inside to outside earlier in the day?

No the solar panels do not absorb only infrared or even mostly infrared.

OK, but I don't see how that addresses what I was getting at?

As a thought experiment, imagine you attach a heater to the solar panels (maybe it's a sunny day in winter). Do you get free energy for heat?

Nobody said there was free energy, but heat is not the only energy available. Here if you like in your analogy visible light is turned to outside heat and inside cool. But it’s simpler just to think about the heat inside the house - heat is being transferred from inside to outside.

In a country like Australia where building density is extremely low that’s a negligible problem?!

Sure if building density is low in your area and you have no nearby neighbours it probably doesn’t matter, you’d just be heating your surroundings a little.

Or, we could lobby politicians to actually improve the lives of their constituents by making climate control appliances so affordable and ubiquitous that it's no longer an issue and we can stop accidental deaths attributed to heat. More green spaces can also help mitigate the impact.

The reality is that a lot of old western europe was built for a climate that no longer exists. Houses are built to prioritize holding on to heat and rebuilding entire cities is definitely not possible if we're already bickering so much about adding heat pumps.

Yes, heat pumps may create a rise in temperatures in cities, but there are other things we can do as a society to also lower temperatures as to create a net-neutral impact.

Schemes like the Paris central cooling one are interesting here - there are other possible solutions in cities too.

And sure yes combined with other measures AC can be a net good.

This is heat that would have escaped the house anyway

No, air conditioning units generate heat (that is how they cool!) and do contribute to local warming. Without AC the house reaches equilibrium with outside. With AC the house is cooled and that heat has to go somewhere.

They don't generate heat in the sense that heat is generated from nothing. If the AC is being powered by solar, then the energy that is powering the heat pump has already hit the earth and has become part of that system. The energy that would otherwise have hit the roofing and been radiated is more focused around the radiators, but as soon as that dissipates into the air the difference to the local climate isn't any different.

If the roof was white and reflective then a lot more of that light would be reflected, but most roofing isn't.

Your logic isn't really compatible with the laws of thermodynamics.

Solar energy is not just infrared, and infrared is not what is used by PV solar. So not it’s not equivalent and anyway doesn’t in any way impact the extra heating effect of a new heat source on the ground.

Instead of generate heat you could say they move heat if you like, from inside to outside.

All absorbed light gets turned into heat, infrared or otherwise (I'm not sure why you brought up IR?); solar panels catch some of that spectrum. I'm not sure what argument you're trying to make here, particularly given the second paragraph seems to contradict the first; "extra heating effect" (from where does this "extra" come from?) vs "you could say they move heat if you like" which yeah, not really about what I like, that's just how physics works, can't get any more fundamental than the law of conservation of energy.

You said that AC/heat pumps "generate" heat and if they were powered by fossil fuels, in an roundabout way they do. But if they're driven by solar, there's no long-trapped energy being expelled and therefore no "extra" energy added to the system beyond what the sun is providing.

Not all light is absorbed and turned to heat, much is reflected, for PV some turned to electricity.

I think we can agree energy is conserved. Extra heating effect OUTSIDE.

AC moves heat from inside to outside, ergo outside is hotter than it would be, this is not complicated.

Yes, for a time, there is a temperature difference between indoors and outdoors. Air conditioners push heat outside. But they reach equilibrium eventually. (At night, or I suppose in the autumn).

Similarly heat pumps (which is what air conditioning is) also push cold outside when you use them for heat, so the outdoor environment is colder than it would otherwise be, again until equilibrium is reached.

Similarly your refrigerator is cold inside but makes your home warmer.

My point was just that the -net- heat added to the city is zero if you’re using solar.

Right, but assuming conservation of energy holds then the net should stay the same, right? Unless solar panels have lower albedo than the roof they’re sitting on (considering how many roofs are flat black tar that seems unlikely…)

that's inconsequential to keeping my family cool on the third 43c degree day in a week

Reply on news.ycombinator.com