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

251–260 of 406 posts

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

#251

Post by tharkun__ »

sokoloff wrote: post #247
tharkun__ wrote: post #235

Earlier quoted context omitted.

Agreed. Ours is at least 5 years old if not more now and was way cheaper. That said there is a difference between mini-split and something you hook up to internal ducting where your furnace used to be and prices have increased in the meantime. That said there was basically no difference in putting in an A/C only unit vs a combination. Technology wise it's the same so to speak just running in reverse in winter vs summ…

Mechanically, there’s a reversing valve and defrost elements and controls to turn an AC into a heat pump. (So, it’s small, but not zero, mechanical differences.)

Thabks for the assist on the tech!

And I can definitely attest to the heating element aka defrost. We don't have actual resistive heat in the pump as we have the baseboards anyway but the lower the outside temp goes the more it has to defrost the outside as it freezes up. As winter goes by, icicles form underneath the outside unit where the defrosted ice drains out and refreezes.

It's actually amazing that the thing can extract heat from -10C air outside to heat up air that's already 21C inside to heat it up even further!

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

#252

Post by coderenegade »

ori_prior wrote: post #245
danans wrote: post #241

Earlier quoted context omitted.

Not only that, but since a heat pump is at least 3x as energy efficient as the most efficient gas furnace, using one results in about 1/2 the E2E CO2 emissions as the gas furnace when the grid electricity being consumed is natural gas based. If you live in an area with abundant zero emissions electricity, then you are heating without any C02 emissions at all. That said, we should do both heat pumps and insulate bette…

Your numbers are off. Thermal power plants typically do have a thermal-to-electric efficiency of around 30% (40% max), so with your heatpump having an electric-to-thermal efficiency of an assumed 300%, you end up with basically no difference in CO₂ emissions. Note that there are some misleading efficiency claims for gas plants around 60%, but those are not for thermal-to-electric efficiency but for generating electri…

60% would be terrible thermodynamic efficiency for a cogeneration plant. Modern CCGT systems crack 60% thermodynamic efficiency for just the electricity generation. With cogeneration, system efficiencies are typically in the 70-80% range.

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

#253

Post by zip1234 »

spiderice wrote: post #249
ashayh wrote: post #232

The article mentions the most important point towards the end: “The better you insulate, the less heat you need in the first place,” No heat pump will help if your house is leaky or under insulated.

You’re describing my situation. How do you de-leakify a house?

- spray foam around/behind outlets on exterior walls (major leak point) which can be done often by just removing the outlet covers

- spray foam around windows (requires removing trim)

- caulk joints/spray foam rim joist in basement/crawl space

- spray foam around any attic can lights/duct work

- make sure ducts and air returns are sealed properly

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

#254

Post by sokoloff »

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.

If I’m doing 3 loads of laundry for the family, I don’t want a 2.5-3 hour dry cycle to make laundry take all day (or make me do laundry of half the days of the week).

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

#255

Post by sokoloff »

__MatrixMan__ wrote: post #115
jillesvangurp wrote: post #97

Earlier quoted context omitted.

This persistent myth just needs to go away. People use heat pumps all over Scandinavia, including in the arctic circle. They are extremely popular there. They were early adopters of this technology there decades ago. There are two popular varieties: - Ground source heat pumps. Those work pretty much anywhere; just dig below the perma frost and you are good to go on the northern tip of Canada, Alaska, Norway, or where…

I've been on zoom calls with two separate co-workers who are all bundled up because their heat pump can't handle the weather. It doesn't mean that the technology is inadequate in principle--probably their systems have some problem that competent HVAC installers know how to avoid. But its an unfortunate fact that there are places in the US where installers that recommend heat pumps can't be found for 100 miles. It doe…

> heavy snows cause power outages in places where tree limbs fall on overhead lines. If gas outages happen... well I've never experienced one.

If I lose power, my gas boiler does me no good. A gas boiler will use pumps (and likely a power vent). A gas furnace will use a fan and a power vent.

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

#256

Post by tapoxi »

spiderice wrote: post #249
ashayh wrote: post #232

The article mentions the most important point towards the end: “The better you insulate, the less heat you need in the first place,” No heat pump will help if your house is leaky or under insulated.

You’re describing my situation. How do you de-leakify a house?

Some home energy companies will do a free audit, in my case it's Mass Save. My in-laws on a limited income even got new windows and insulation for free.

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

#257

Post by ori_prior »

coderenegade wrote: post #252
ori_prior wrote: post #245

Earlier quoted context omitted.

Your numbers are off. Thermal power plants typically do have a thermal-to-electric efficiency of around 30% (40% max), so with your heatpump having an electric-to-thermal efficiency of an assumed 300%, you end up with basically no difference in CO₂ emissions. Note that there are some misleading efficiency claims for gas plants around 60%, but those are not for thermal-to-electric efficiency but for generating electri…

60% would be terrible thermodynamic efficiency for a cogeneration plant. Modern CCGT systems crack 60% thermodynamic efficiency for just the electricity generation. With cogeneration, system efficiencies are typically in the 70-80% range.

60% is feasible for e.g. nuclear and gas, if you use more than one turbine and there is a big constant temperature differential. This typically isn't the case for gas plants which are intentionally variable and often intended to be cheap to build. While at peak temperature, they might run at peak efficiency around the theoretical maximum of 60% (thermal to electric) with a multi-turbine assembly, typically efficiency is far lower because gas plants usually don't run at peak efficiency and only have one turbine.

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

#258

Post by nerdbert »

thrashh wrote: post #240
nerdbert wrote: post #211

Earlier quoted context omitted.

> Fun fact, a resistive heating device is a rare case of something being 100% electrically efficient in that all the energy it uses will be turned into heat My understanding is that you get considerably more heating per watt-hour with a heat pump than with resistive heating, though. I get that it's not creating that heat but moving it, but still that seems like even more efficiency from the perspective of energy cons…

Well the word “efficient” always needs context. You have to define the goal first before you can define efficiency. OP said electrical efficient so the goal is conversion of electricity to heat and it’s 100% efficient. Even an electric heater compared to a propane heater is more electrically and energy efficient, but it’s not as storage-efficient (because fossil fuel gases have much higher energy density per volume A…

> OP said electrical efficient so the goal is conversion of electricity to heat and it’s 100% efficient.

I am not an engineer and I am only nitpicking to have fun, so don't engage me if it's not fun, but doesn't some of the energy go into degradation of the materials used to build the device?

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

#259

Post by philipkglass »

ori_prior wrote: post #245
danans wrote: post #241

Earlier quoted context omitted.

Not only that, but since a heat pump is at least 3x as energy efficient as the most efficient gas furnace, using one results in about 1/2 the E2E CO2 emissions as the gas furnace when the grid electricity being consumed is natural gas based. If you live in an area with abundant zero emissions electricity, then you are heating without any C02 emissions at all. That said, we should do both heat pumps and insulate bette…

Your numbers are off. Thermal power plants typically do have a thermal-to-electric efficiency of around 30% (40% max), so with your heatpump having an electric-to-thermal efficiency of an assumed 300%, you end up with basically no difference in CO₂ emissions. Note that there are some misleading efficiency claims for gas plants around 60%, but those are not for thermal-to-electric efficiency but for generating electri…

Modern combined cycle gas turbines offer thermal-to-electric efficiency over 60% (on a lower heating value fuel basis) at full design load, e.g. this General Electric system at 64%:

https://www.ge.com/news/press-releases/ha-technology-now-ava...

Approximating natural gas as 100% methane, that means the thermal-to-electric efficiency on a higher heating value basis is more like 57-58%:

https://en.wikipedia.org/wiki/Heat_of_combustion#Heat_of_com...

Neither of these efficiency measures include district heating with waste heat.

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

#260

Post by throw0101a »

tharkun__ wrote: post #235
newZWhoDis wrote: post #224

Earlier quoted context omitted.

Almost certainly. Proper/modern heat pumps do not need heat strips until -20F or so

Agreed. Ours is at least 5 years old if not more now and was way cheaper. That said there is a difference between mini-split and something you hook up to internal ducting where your furnace used to be and prices have increased in the meantime. That said there was basically no difference in putting in an A/C only unit vs a combination. Technology wise it's the same so to speak just running in reverse in winter vs summ…

> That said there is a difference between mini-split and something you hook up to internal ducting where your furnace used to be and prices have increased in the meantime.

Generally true, as the mini-splits (have) tend(ed) to operate down to lower temperatures, but the heat pumps that look like 'traditional' outdoor A/C units are getting down there as well: for example this Lennox unit can work down to -4F / -20C:

* https://tech.lennoxintl.com/c03e7o14l/viu12ch2uv/ehb_sl25xpv...

That'll provide pretty good coverage of the year in many parts of North America before something like a gas furnace needs to kick in. (Speaking as someone who lives in Canada.)

Post reply on HN