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

Pretty soon, heat pumps will be able to store and distribute heat as needed

sintef.no

Post reply on HN
Print view View original

181–190 of 243 posts

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#181

Post by leoedin »

elric wrote: post #174
5ersi wrote: post #109

It uses phase change (solid to liquid) to store heat at about 200 kJ/kg. Compare this to heating water in a boiler from 10c to 60c - stores 209 kJ/kg. So we already have an effective way to store heat which can work for decades without servicing and is also cheap to produce (in terms of money and energy consumption).

What about heat per unit of volume? Seems like the selling point is that a pretty small box can service a whole bathroom. Presumably it has a higher density than water and requires less insulation?

I think this is the most crucial part. External heat pumps are OK - people install air conditioners everywhere already - but most houses/apartments aren't set up for large water tanks. The interior heat storage needs to be comparable in size to the existing gas boiler.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#182

Post by cucumber3732842 »

wffurr wrote: post #110
AlexandrB wrote: post #82

Earlier quoted context omitted.

But dumping the waste cold air into the house when it's below 0C outside doesn't make much sense either.

You already dump waste hot air into your kitchen from the refrigerator during the summer. Is this much different? It does seem a little silly to have these chains of heat pumps all working in various directions. I read about "cold district heat" in a sibling comment which circulated lukewarm water to use as a heat sink or source with heat pumps. Maybe something similar could be done with a water or refrigerant loop t…

Everywhere in the country they have basements a huge fraction of them are unheated and probably hover around 38, 40, 35deg in the winter. You dump cold air into that and some % of pipes are going to freeze. And we're talking about a much bigger energy amount, water having high specific heat after all so it is a lot of "cold" being dumped in.

Now, this is of course no concern in the "my water heater is in my attic or attached garage" parts of the country such regulations come from...

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#183

Post by manmal »

tempestn wrote: post #126
manmal wrote: post #105

Earlier quoted context omitted.

Certainly not gas or oil, which are still cheaper to heat with than heat pumps.

Modern heat pumps are cheaper than oil for heating just about everywhere. They're cheaper than natural gas in most places, unless electricity prices where you live are particularly high.

Yes, and many places have high electricity costs. And btw, those are hard to foresee, so if you make a long term investment into a heat pump that is supposed to last 20-25 years, you have no idea how electricity prices will affect you. That's obviously true for gas and oil as well. I do concede that my original point was too blanket-y.

I have a heat pump btw., with COP 4.5 (below ground). Costs me EUR 2.5 - 3k per year to heat the house.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#184

Post by manmal »

yurishimo wrote: post #167
zobzu wrote: post #142

Earlier quoted context omitted.

in CA my natural gas is far cheaper than the heat pump sadly

In western europe today, I spend €10+ per day to heat my home (17 degrees mind you) with a gas powered boiler for radiators. I can run my mini-split on 18 degrees all day for a couple of euros. I moved here from the US in 2022 right after the full scale invasion of Ukraine so natural gas prices skyrocketed overnight. I don't really understand what the aversion is to forced air climate control here other than "it's no…

I don't buy your numbers. I'm in Western Europe myself, and have run those numbers multiple times. Kilowatt for kilowatt (COP adjusted) gas is always cheaper than a heat pump.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#185

Post by manmal »

Tor3 wrote: post #156
manmal wrote: post #105

Earlier quoted context omitted.

Certainly not gas or oil, which are still cheaper to heat with than heat pumps.

Hm? Around here oil was never been in the same (low) order of magnitude. Those who installed oil heaters many decades ago regretted it quickly. And it's been illegal to use them for a couple of decades as well now. Gas has never been an option in my region, there's no infrastructure for that. We have used gas in Japan until now, but even that we'll be phasing out (I live in two places)

> Those who installed oil heaters many decades ago regretted it quickly.

That really depends on the oil heater, no? You can't compare a heater from the 70s with a modern one. That's like saying I don't drive modern cars because cars in the 70s were unsafe and stank.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#186

Post by manmal »

pjc50 wrote: post #175
manmal wrote: post #105

Earlier quoted context omitted.

Certainly not gas or oil, which are still cheaper to heat with than heat pumps.

Oil heating has usually been the most expensive way to heat in the UK, on par with resistive-electric.

That's completely wrong.

Electricity (standard): 33.34 p/kWh

Heating oil (gas oil): 10.54 p/kWh

Kerosene: 6.20 p/kWh

Mains gas: 7.68 p/kWh

https://www.nottenergy.com/advice-and-tools/project-energy-c...

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#187

Post by DrScientist »

IshKebab wrote: post #159
Xylakant wrote: post #61

Earlier quoted context omitted.

it also reduces peak load - you can heat water up slower with a lower powered heater. I have a 35 liter warm water tank in my garden shed that pulls about 3.5kw - an equivalent on demand heater would need 14kw or more.

I don't see why that matters. You use the same amount of energy and the demand is smoothed out at grid scale (yes I know about tea in ad breaks).

You can get things like cheaper overnight tariffs when the demand is lower - if you have some sort of storage system - like a hot water tank - in effect the electricity company is distributing some of that smoothing function to things like hot water tanks, storage heaters or batteries.

If you have your own solar ( either direct solar water heating, or solar electricity generation ), the hot water tank is a simple, cheap, reliable energy store.

Sure capacity isn't that great - but pretty much every house in the UK used to have one, so it adds up.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#188

Post by leoedin »

coryrc wrote: post #108
DrScientist wrote: post #34

Earlier quoted context omitted.

Indeed. In the UK there was a unfortunate trend of ripping out these energy storage devices and replacing hot water tanks with on demand electric hot water heating ( only heat the water you need ). And new builds often have no tanks ( as it saves space in the new tiny homes ). Very short sighted in my view - a very simple way to store energy and everyone uses hot water directly.

They don't work well with heat pumps. Heat pumps lose efficiency as the differential increases, so if you try to store heat in a tank, you quickly drop capacity and efficiency. Versus resistance, which is exactly as efficient at 0°C and 1000°C, and why those storage heaters used to make sense. (And storage is directly proportional to temperature differential above interior ambient)

Every air-to-water heat pump install will have a hot water tank. So I'm not sure why "don't work well" is the term used.

It is true that heat pumps coefficient of performance drops as the output temperature increases. So you need a proportionally larger hot water tank to store the same amount of energy. So it is fair to say there are tradeoffs. But hot water storage is still a necessary part of most heat pump installs - because peak output of heat pumps tends to be below the heat demand of showers.

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#189

Post by leoedin »

modo_mario wrote: post #176
coryrc wrote: post #108

Earlier quoted context omitted.

They don't work well with heat pumps. Heat pumps lose efficiency as the differential increases, so if you try to store heat in a tank, you quickly drop capacity and efficiency. Versus resistance, which is exactly as efficient at 0°C and 1000°C, and why those storage heaters used to make sense. (And storage is directly proportional to temperature differential above interior ambient)

Isn't it better to heat the water up to a point (let's say 40 or 50 degrees) and to heat it the rest of the way with resistance heating? >Versus resistance, which is exactly as efficient at 0°C and 1000°C It isn't. The difference is smaller than for a heatpump tho obviously.

> It isn't. The difference is smaller than for a heatpump tho obviously.

Where does the energy go then?

Re: Pretty soon, heat pumps will be able to store and distribute heat as needed

#190

Post by IshKebab »

ifwinterco wrote: post #161
IshKebab wrote: post #159

Earlier quoted context omitted.

I don't see why that matters. You use the same amount of energy and the demand is smoothed out at grid scale (yes I know about tea in ad breaks).

Houses in the UK typically have 100A supply and the whole local grid is sized assuming people use relatively small amounts of electricity. If everyone gets an electric car and a massive heat pump, lots of local transmission will need upgrading

Right but unless everyone is drawing large amounts of power at the same time it doesn't matter if you use 1kW for 10 hours or 10kW for 1 hour. To the grid they look the same.

One interesting case where "at the same time" actually does happen is overnight car charging. Some chargers are configured to start charging exactly when a cheaper tariff kicks in, which causes big transient issues for the grid. I think modern chargers have a random delay to help with that.

Post reply on HN