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

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

#171

Post by jcattle »

gwbas1c wrote: post #136
mike-the-mikado wrote: post #98

Earlier quoted context omitted.

I would guess that is intended for a daily cycle, perhaps using air source heat pumps at times of day when the air temperatures are higher and electricity prices are lower, then using it as required. As it works on phase change (e.g. think of melting ice) heat is added (or removed) without changing the temperature of the store (which, I guess, might be hotter or colder than where the heat is extracted or used).

But how hot does the heat source have to be? Depending on the needs, resistive heating can get hundreds of degrees hot, but the best heat pumps that I know of can only raise the temperature about 60 or 70° f.

That's the whole point of this, no? Heat pumps can't heat up a large amount of water quickly (like resistive heating can). So if you have a solar peak at noon, where either yourself are producing cheap solar, or there's cheap solar on the grid in general, then you want to use that cheap energy to store heat for later use (like showers in the evening/morning).

So the way I see it, is that this material should be able to quickly store heat with the using the low temperatures that heat pumps provide, and be able to store it with minimal losses until it is needed.

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

#172

Post by ProllyInfamous »

moooo99 wrote: post #169
jcattle wrote: post #165

Earlier quoted context omitted.

Does heating water in a boiler work well with a heat pump? How about a release of energy 10 hours later (peak solar at noon, to first shower the next morning)? I actually don't know the answer. I'm just thinking that there must be more to it, if the answer was as simple as "just heat water".

It does. However, the hotter the water becomes, the less effective the heatpump becomes. With anything beyond 60C becoming very inefficient. With hot water tanks, they are unfortunately pretty badly insulated as well, with some of them loosing heat very quickly. Depending on how you plan on using that water, you also have to make sure the temperature never dips below ~60C to avoid legionella from spreading. I actuall…

I have two heat pump water tanks, one Rheem and one AO Smith (our local utility heavily-subsidizes these, with a net-cost less than a standard tank water heater).

They both are rated for annual kWH usage less than the US EPA yellow label can display (for their category of tanked water heaters, i.e. competing mostly with resistive heating models).

Annually water heating is about 3% of my energy consumption.

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

#173

Post by masklinn »

globular-toast wrote: post #168
matwood wrote: post #67

Earlier quoted context omitted.

I think a heat pump only for water isn't the right way to go. In the EU, new systems I see use a single heat pump for all heating and cooling in the house including heating water. I do miss my natural gas on-demand water heater from when I lived in the states though. Unlimited hot water was nice, and it took up almost zero space.

> I do miss my natural gas on-demand water heater from when I lived in the states though. Isn't that what we call a combi boiler in the UK (and Europe?) I've recently moved from having a big hot water cylinder to a combi. The space saving is nice, but there are downsides. Waiting for the hot water to come through is annoying and I'm often just wasting cold water waiting for it to come through hot. There is a "pre-hea…

> There is a "pre-heat" feature which would be nice, but then it would keep it warm 24 hours a day which is ridiculous. Maybe some better boilers can time the pre-heat.

Yeah one of my colleagues has a preheat which can be triggered manually and via automation. They also have a preheat loop which cycles hot water through the entire piping as the boiler is on an edge, so it takes ages for hot water to reach the far bathroom.

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

#174

Post by elric »

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?

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

#175

Post by pjc50 »

manmal wrote: post #105
stuaxo wrote: post #73

Earlier quoted context omitted.

What did you heat with before?

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.

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

#176

Post by modo_mario »

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)

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.

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

#177

Post by gwbas1c »

jcattle wrote: post #171
gwbas1c wrote: post #136

Earlier quoted context omitted.

But how hot does the heat source have to be? Depending on the needs, resistive heating can get hundreds of degrees hot, but the best heat pumps that I know of can only raise the temperature about 60 or 70° f.

That's the whole point of this, no? Heat pumps can't heat up a large amount of water quickly (like resistive heating can). So if you have a solar peak at noon, where either yourself are producing cheap solar, or there's cheap solar on the grid in general, then you want to use that cheap energy to store heat for later use (like showers in the evening/morning). So the way I see it, is that this material should be able…

> Heat pumps can't heat up a large amount of water quickly

No, it's about temperature difference. My heat pump water tank heats about as quickly as resistive water tanks; but it could never heat to hundreds of degrees.

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

#178

Post by gwbas1c »

tootie wrote: post #133
gwbas1c wrote: post #90

The article omits some critical details: It says this is both a "heat pump" and also "storage" AND says that it will run when electricity is cheap or plentiful. Thus: 1: Where does it pump the heat from? (Or is this not really a "heat pump" and instead is using resistive heating?) 2: How long does it store heat? Is this something that will store heat on a 24-48 hour basis, or will this store heat during the spring /…

Presumably it's air source and if it's indoors it will just be the air in whatever room it's in. That's how my ventless dryer works. I'm not sure what the implications are for taking heat from air that may have been heated by another heat pump are for efficiency. But also if it's summertime, they may be relieving load from your air conditioner.

> That's how my ventless dryer works.

Do you mean a heat pump dryer? Those aren't taking heat from the room; they work by sending the air inside the unit through a powerful dehumidifier. (I have one, it's very nice.)

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

#179

Post by gwbas1c »

hippo22 wrote: post #153
gwbas1c wrote: post #84

Earlier quoted context omitted.

You're about 20 years behind. My heat pump is working great at 0F. It's 7 years old.

It really depends on how well your home is insulated. Heat pumps don’t work well on old, poorly insulated houses in cold climates. If they can keep up, which is a big if, the price of electricity generally dwarfs natural gas, even if the heat pump is running at 250-300% efficiency.

To clarify my parent post: My house is also 7 (now 8) years old and has 6 inch (15cm) walls with air-tight walls. We built with solar, which got the cost of electricity down to an estimated 4-5 cents per kilowatt hour.

At that price, resistive heating cost about as much as what I paid for gas at my old house.

I went with a heat pump to hedge the bet. (I was also pointed away from geothermal.)

If the insulation wasn't as good, or electricity more expensive, I would have used a different heat source. I was looking at pellet furnaces at the time, but never seriously got into the research before the solar proposal came in.

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

#180

Post by TobTobXX »

raffraffraff wrote: post #160
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).

I don't know why these aren't used more in building fabric. There's a youtuber who makes these phase change solutions out of various salt mixes aiming for the correct change temperature for a specific application. Eg he made panels for his shed roof (keeps it cooler in sun, warmer at night). Obviously this works better to smooth out large, reliable daily temperature swings, and offers little to someone in a constantl…

The name of the YT channel is NightHawkInLight[0] btw. Absolutely worth checking out. He creates materials with extremely useful properties from household materials (eg. PCM (high heat capacity), highly reflective paintings, Aerocrete (high insulation/fire resistance), ...)

[0]: https://youtube.com/@Nighthawkinlight

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