Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Heat Pumps – The Well-Tempered Future of A/Cs

spectrum.ieee.org

Post reply on HN
Print view View original

381–390 of 406 posts

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#381

Post by triceratops »

mindslight wrote: post #215
triceratops wrote: post #167

Earlier quoted context omitted.

End-to-end efficiency calculations are tricky and depend on a lot of variables.

Sure, but that doesn't mean you can throw your hands up and make an argument comparing nameplate efficiencies of things with different energy sources. I'm well aware the figure in my above comment could be off by a decent amount due to transmission efficiency, what specific plants are generating marginal power, etc. But it's at least framing the comparison right.

Even in your worst case scenario, heat pumps are about as efficient end-to-end as a natural gas furnace. And renewable power is only going to become more common over time so it could get better.

To a consumer, comparing nameplate efficiencies as you say makes the most sense. I can easily find out how much a joule of electricity and a joule of natural gas cost me. Then multiply those with efficiency to see which is cheaper.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#382

Post by rapjr9 »

kelnos wrote: post #331
rapjr9 wrote: post #272

Earlier quoted context omitted.

This seems to be a much more reasonable unit, 10,000 BTU, does both heating and cooling via a heat pump, and it costs $700, although there are a lot of negative reviews: https://www.amazon.com/dp/B09ZCZSSV8 $5000 is ridiculous for the Gradient Comfort 8000BTU window unit. The Soleus is the only other heat pump window unit I've seen for sale. Midea makes some A/C's that are more efficient because they use an inverter,…

It's that cheap because it's garbage. All the 1-star reviews (26% of all reviews) I looked at said various variations on the unit failing after some small number of months, and the return/replacement process is awful. Seems like the manufacturer just makes junk and hopes they can still keep the money by making it hard to return.

Have you ever looked for a product and found that ALL of the brands get poor reviews? Air conditioners are kind of like that, maybe half of them get a lot of poor reviews. Somehow air conditioners have seen a race to the bottom in terms of quality and features. The basic technology has also not changed in decades. Seems ripe for disruption. The Midea air conditioners are at least more efficient. There are a lot of commonly known problems with the basic design of window air conditioners though (uneven air distribution, creates drafts, mold, noise, temperature control). Maybe those problems are just too difficult to figure out? Maybe it's a problem of expectations, air conditioners have always had the same prices and features so no one will pay any more, even for a better product?

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#383

Post by Alupis »

tcfhgj wrote: post #332
Alupis wrote: post #314

Earlier quoted context omitted.

I am not aware of any such system in the US. What do you mean by "modulate"? Your utility provider decides how much heat your home gets? That's a very strange concept.

No, they decide how many energy the heat pump currently uses for heating.

That means they control how much heat you get. Otherwise, they would always run in a more efficient/lower-energy demand mode... think about it.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#384

Post by mindslight »

triceratops wrote: post #381
mindslight wrote: post #215

Earlier quoted context omitted.

Sure, but that doesn't mean you can throw your hands up and make an argument comparing nameplate efficiencies of things with different energy sources. I'm well aware the figure in my above comment could be off by a decent amount due to transmission efficiency, what specific plants are generating marginal power, etc. But it's at least framing the comparison right.

Even in your worst case scenario, heat pumps are about as efficient end-to-end as a natural gas furnace. And renewable power is only going to become more common over time so it could get better. To a consumer, comparing nameplate efficiencies as you say makes the most sense. I can easily find out how much a joule of electricity and a joule of natural gas cost me. Then multiply those with efficiency to see which is ch…

I did not put forth a worst case scenario. I put forth an example of doing proper comparison.

Based on a figure I just saw from someone else describing their setup (1.75 COP at 5 deg F), and taking into account transmission losses etc, the worst case would seem to be significantly less efficient than burning natural gas directly in a condensing furnace.

This isn't meant as some sort of knock against heat pumps! In fact I'm tentatively planning to add a heat pump to my own home within the next several years. Focusing on a worst case is still not an overall comparison of performance, but rather just one data point in the evaluation of a given design.

Multiplying the cost of the energy source by the nameplate efficiency is indeed another sensible way of comparing across technologies. But that isn't what you did in your original comment, where you juxtaposed two different types of efficiency numbers. That was my only point in my original comment.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#385

Post by nielsbot »

rayiner wrote: post #268
lsaferite wrote: post #186

Earlier quoted context omitted.

I live in FL and we have a backup resistive heating element that kicks in as needed. Mostly only comes on a few days in the year or for short bursts when there's a cold snap that the heat pump can't keep up with.

This is fine until everyone in your neighborhood has one and it causes a brown out. (Peak amperage for the heating strips on my heat pump are three times as high as for the heat pump itself at maximum cooling load.)

You can upgrade your home electrical service and the power company handles all that for you.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#386

Post by DropInIn »

bill38 wrote: post #365
_fizz_buzz_ wrote: post #339

Earlier quoted context omitted.

Not a handy man, but we build power electronics and a lot of customized stuff. I also often give quotes that are really high for stuff that we don't actually want to do. It's kind of better than saying we cannot do it (because then they will never ask again) and if they agree to it we make a lot of money. For larger investments it makes sense to get a second quote.

Don't you think that if you give a really high quote, the customer will never ask you again too ?

What are the rates for both choices?

One has a lower rate of "undesirable outcomes" and thus when the option's binary like that then the choice is clear.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#387

Post by gizmo686 »

glogla wrote: post #341
gooseyman wrote: post #309

Heat pumps are great, but it’s the dc inverter and advances in compressor efficiency that is really the biggy on energy usage here. Every one of these “heat pumps are the future” articles is so soft on data, and they often fail to explain the basics or a simple “why.” Once we get past the clickbait heat pump articles, we can actually make an impact.

I think the consensus on why heat pumps _should_ be the future is that you can power them with low carbon electricity, as opposed to literally world destroying natural gas.

A quick Google search says that natural gas -> electricity has an efficiency of about 44%, with an additional 5% loss during transmission. Lets call this about 40% efficiency for getting energy from natural gas to your electric heat pump.

A heat pump operating at 250% efficiency will use just as much natural gas as a furnace operating at 100% efficiency.

Modern heat pumps can often exceed 250% efficiency, making them use less natural gas, even if they are ultimately powered by a natural gas burning power plant.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#388

Post by tcfhgj »

Alupis wrote: post #383
tcfhgj wrote: post #332

Earlier quoted context omitted.

No, they decide how many energy the heat pump currently uses for heating.

That means they control how much heat you get. Otherwise, they would always run in a more efficient/lower-energy demand mode... think about it.

Its only for a restricted time frame

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#389

Post by simonblack »

bobmaxup wrote: post #346
stephen_g wrote: post #315

Earlier quoted context omitted.

Yes. Although I have noticed that some people here in Australia go from the belief that "air conditioners use a lot of electricity" so therefore have the misconception a (resistive) electric heater must be cheaper to use than the reverse cycle AC (heat pump). So there is a bit of an education gap even here where they are quite ubiquitous! I also do want to get a heat pump dryer (it's next on the list after my recentl…

> have the misconception a (resistive) electric heater must be cheaper to use than the reverse cycle AC You'd think costs would educate. Do people not talk about living expenses much?

Electrical bills come every three months. ALL electricity use is lumped together. So it's a bit hard to disect out what each usage-type is costing, unless you use one of those meters and study up average use over a period. Even then, some things like water heating and even aircons, are directly wired into the mains switchboard, so you would need an electrician to separate out those circuits for measuring. So it just doesn't happen.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#390

Post by simonblack »

fomine3 wrote: post #244
simonblack wrote: post #142

Earlier quoted context omitted.

Ditto Australia. We've been using 'reverse-cycle air-conditioners' for heating in Australia for decades. I'm puzzled as to why there is any debate at all on their use for heating. A heat-pump is far more efficient for obtaining heat than direct resistive heating using electricity. Many houses here use no other form of heating at all. And then at the press of a button, we get cooling in summer too. What's not to like?…

Heat pump dryer system is state of the art for efficiency. I saw some complains by American that it takes too long time for drying, but I don't know why they need to dry things so frequently.

I was thinking about this anomaly yesterday. Then I remembered that most US electrical outlets are at 110 Volts instead of the more usual world-wide standard of 220 volts. So most stuff in the US is under-powered by EU or Australian standards. Being under-powered, it would take longer to dry your clothes.

(That's also why they don't seem to use electric kettles in the US commonly as is normal in 220 volt countries)

Post reply on HN