What is the real story around heat pumps?

[pcprogrammer]

Seems that most heat pump engineers suggest that over-zoning causes problems.  You want the heat pump to be providing constant heat to all rooms, with some exceptions for times when you are out of the home for instance.  So my little trick of not heating rooms (via home automation) when unoccupied, and zoning rooms to different temperatures, would be not recommended.  This is because the heat pump will need to work very hard to get that room up to temperature after returning home or to change temperatures according to the schedule, which means the COP will fall dramatically for the whole house during those periods. 

The general principle of low temperature design is to have the system running more or less continuously keeping the radiators 'ticking over', whereas typical gas/oil boiler CH systems rely on cycling the boiler.  In the boiler case, you oversize the boiler slightly so that even if it is -10C outside and +10C inside the home can get up to +20C within about an hour.   A heat pump would probably struggle with that.

That is what I'm finding more and more, that it is better to let it run continuously at lower temperature. I will have to discuss this with the companies we invited for the quotes.

With underfloor heating it is in it's nature to be very slow. We have been away several times over the years near the end of the season to return to a cold home. About 12C inside and it would take the whole day to get the rooms with the underfloor heating back up to temperature. On the one hand the wood burner setup that takes several hours to heat up the first tank to >40C and on the other hand the slow process of the underfloor heating.

It would be nice to return to a home at set temperatures after a 10 hour drive from the Netherlands.

[nfmax]

It would be nice to return to a home at set temperatures after a 10 hour drive from the Netherlands.

What you need in that case is remote control - probably via the Internet in this day & age.

[pcprogrammer]

It would be nice to return to a home at set temperatures after a 10 hour drive from the Netherlands.

What you need in that case is remote control - probably via the Internet in this day & age.

Won't be necessary when the system keeps on running when we are not there, and with the old system it would not help either because the wood burner can't start it self and the storage tank won't be full.

It is the whole point of the discussion that a heat pump system needs to run constantly to maintain its performance ratio's.

[zilp]

It is the whole point of the discussion that a heat pump system needs to run constantly to maintain its performance ratio's.

If you are away for multiple days, it shouldn't hurt to let the temperature drop (and probably save energy overall), you'd just have to have it start heating back up a day or so before you return. But varying temperatures throughout the day probably/usually isn't a good idea (in that it either just doesn't work, or you'd have to increase temperatures so much that you get a bad COP, and you'd have to oversize the heat pump, which is also expensive and decreases the COP).

[zilp]

There is also the option of opening all the zones and use the adjustable return valves to control the flow.

Yep, that is the ideal way to do it where you don't need to regularly change room temperatures.

Have the system regulate the temperature output of the heat pump to maintain a livable temperature in the rooms. Incorporate the outside temperature in the equation and see what it does.

Well, that is sort-of what your regular heat pump will do by default. Specifically, it will set the source temperature target  based on the outdoor temperature and will then adjust the compressor speed to hold that temperature, and if the temperature rises some hysteresis above the target (i.e., when the minimum compressor power is too much), switch off the compressor and let the temperature drop. And for controlling the temperature inside, you then can have either individual per-room controllers that asjust the flow per room, and/or a room thermostat that influences tha target source temperature/causes the compressort to be shut off when the target room temperature is reached.

Another option is the use of a controllable variable speed circulation pump. When only a few zones are open reduce the flow with the pump.

Well, yeah, that's essentially what a constant-pressure pump does.

However, you also have to be careful that you don't go under the minimum flow required by the heat pump, which tends to be relatively high, as you are otherwise likely to get rapid cycling of the compressor, which is neither good for the compressor nor for the COP.

[tszaboo]

It is the whole point of the discussion that a heat pump system needs to run constantly to maintain its performance ratio's.

If you are away for multiple days, it shouldn't hurt to let the temperature drop (and probably save energy overall), you'd just have to have it start heating back up a day or so before you return. But varying temperatures throughout the day probably/usually isn't a good idea (in that it either just doesn't work, or you'd have to increase temperatures so much that you get a bad COP, and you'd have to oversize the heat pump, which is also expensive and decreases the COP).

you would think that in this century there would be an easy way to control the temperature.
I had to deal with a Dutch temperature controller for gas heating. It had settings for only two temperatures, one for heating, and one for "set back temperature". So I tried placing the setback during the day, when I'm at work. It was impossible. The setback temperature was hardcoded to be at the end of the day, because you are surely not going to heat during the night, and it's impossible that someone else will have a different schedule or requirement for heating.
Now I have a google Nest thermostat, where you can set the temperature, but the measurements on it are just plain off. Because they put the temperature sensor next to the Wifi, and it heats up. And the wall behind it heats it up, where all the heating system stuff is. You would think that this would be an issue that they resolved during development of the product, but no. Ah but you see, it's possible to connect an external temperature sensor to the thermostat, and use the value from that. If you live in North America, not possible in Europe.

[Marco]

It's designed to be a very efficient system, with the water temperature barely above the setpoint. The higher the temperature difference, the lower the efficiency of a heatpump. You can find some data here: https://en.wikipedia.org/wiki/Heat_pump#Performance, but keep in mind these are going to be the cutting edge numbers that are not really afforable.

I know, that's why I said it's the control system. It needs headroom power, because the thermal loss of the house obviously isn't static ... if it took days to heat up the house to setpoint at 0 degrees ambient due to lack of power, it wouldn't be able to get to set point at all at minus 10 ambient. That's almost certainly not the case, the control loop is the limiting factor in letting it respond faster. It values efficiency over response time, but you can probably hack it if you have different priorities.

[Marco]

Seems that most heat pump engineers suggest that over-zoning causes problems.

They are biased towards modern homes. Those homes might drop only a degree overnight with heating off ... so yeah, easiest to just keep everything equilibrium.

For me it's more like a degree every 30 minutes, the potential gains from lowering temperature during the night and working hours are far different.

[Marco]

Not going to happen. Fans make noise.

Below 800 rpms it's pretty much inaudible.

[zilp]

Because heat pump actually doesn't solve the problem. The problem is that we need energy to heat our homes during the winter. And it doesn't matter where it comes from.

Except ... it does?! I mean, I don't really understand what you are trying to say here, but I would think the whole reason for switching to renewables is that it does matter where our enery comes from?!

My house heating comes from a waste energy of a power plant, how much is the efficiency of that?

There is  no efficiency for that. But there is an efficiency for that power plant as a whole. And if you feed that power plant with methane from P2G, you get an efficiency that you can compare to directly using renewable electricity. And it's going to be atrocious.

You might compare 70% and 500% and say 500% is better. But 70% is during the summer, and 500% is during the winter. If the energy for that 70% conversion is provided by free (as in beers) solar energy, your efficiency doesn't matter one bit.

While you are right that I simplified quite a bit, your conclusion doesn't exactly follow.

If we all install solar panels, the upfront cost is 5-10K per house, depending on how big your roof and ambitions are. And it's getting cheaper. And we already see that it can cover 100% of our usage during certain days the summer. In these days electricity is cheap, sometimes even free.
You take this electricity, run it through P2G and make gas out it, that you burn during the winter.

OK ... and what is going to be the price of a kWh of methane from a P2G plant that sits idle 95% of the year in order to produce methane from free electricity the few hundred hours a year that that is available?

And mind you, if a kWh of electricity can make 4 kWh of heat in a heat pump, while your P2G plant needs 6 kWh of electricity to create 4 kWh of heat in a gas heating system, even if your P2G plant somehow magically was free, that gas is more expensive as soon as the electricity used by the P2G plant is more than a sixth of the average market price. So, "cheap" electricity really doesn't cut it, it has to be almost free for this to be economical, especially when considering that the plant probably isn't actually free in reality.

Either you have a plant that's idle most of the time, which is going to make the gas expensive, or you increase the load, which requires feeding increasingly expensive electricity into it, which is going to make the gas expensive, too.

Plus, there are limits to how much renewable electricity we can generate here. Like, people here in Germany use roughly 500 TWh of heat for heating homes per year. That's roughly 2.5 times the amount of renewable electricity generated last year. So, to feed those P2G plants for that purpose alone, we would have to install ~ 3.5 times what we already have in solar and wind. And then, the demands for transportation and industry comes on top.

Maybe, just maybe, it makes more sense to install 125 TWh of solar and wind and then use heat pumps to turn that into 500 TWh of heat?

Gas storage is a solved issue, unlike seasonal electricity storage.

Well, true, but also misleading.

For one, we don't need seasonal electricity storage. The wind doesn't stop blowing in the winter. Actually, you generally have more wind during winter than during summer. And also, funny enough, wind correlates with heating demand, because wind cools houses.

Then, there is a type of renewable energy source that doesn't depend on direct sun or wind that can be used to provide energy when both of those are in short supply. It's called a heat pump. It can be -10 °C, no wind, no sun outside, and my heat pump still manages to move multiple kW of renewable energy from the outside into my home, using relatively minor amounts of electricity for the purpose. I mean ... how about we use that rather than trying to generate tons of electricity that we then don't really know how to store, other than using rather inefficient methods?

And what is great about heat pumps is that they can run both with renewable electricity, but also with electricity from gas power plants, say. And that's where electrolysis and P2G come in: If you run a P2G plant 24/7, the capital costs per kWh aren't that high, so you can slowly fill gas storage all year. And the releatively little time per year when both sun and wind are lacking, you can then burn that gas in peaker plants (which also are relatively cheap to build) to fill the gaps. So, you have your heat pump running most of the time at ~ 400% efficiency, and only a few days a year, you feed it with electricity from P2G methane at a total efficiency of, let's say, 100% (those usually will be colder days, so probably not peak COP). This way, the inefficiency of the conversion process doesn't really matter all that much.

Oh, and those P2G plants then also can contribute to grid stability by shutting down production when needed. Because one alternative to storage is to have variable loads. With those, you can add generation capacity that doesn't just sit idle most of the time (which would be a waste of capital), which then still is available to keep vital things running in critical situations by shutting down some variable loads as needed.

Plus you use CO2 in the process, that you can capture for free at power plants, during the winter. In fact the price of CO2 could be negative, since the power plant doesn't have to pay the carbon tax if it captures the CO2. There just isn't an large industrial process that uses that much CO2 as we make now.

Except there won't be any power plants to provide CO2.

Mind you that we can't emit any more CO2, so burning fossil fuels, capturing the CO2, using that for P2G, and then burning that P2G gas and releasing the CO2 into the atmosphere afterwards is not a solution, as the CO2 would still end up in the atmosphere, and CO2 emissions would only be halved at best (because the carbon would essentially be used twice before being released).

So, the only way to implement this without CO2 emissions would be to implement a closed loop. But mind you that that then would mean that you would have to burn the gas as you are generating it in order to get the CO2 back to feed into the P2G plant. Which is obviously economical nonsense, are you are then trying to feed electricity back into the grid that you just bought it from, with additional costs and energy losses from your conversion processes. Well, or you could try storing the CO2 for half a year or something ... which would double the amount of gas storage you need. Or something.

Also, systems for capturing CO2 aren't free either.

This is just the most sensible way of handling the issue for the next decades.

If you ask me, that sounds more like a more uninformed way of handling things.

[pcprogrammer]

There is also the option of opening all the zones and use the adjustable return valves to control the flow.

Yep, that is the ideal way to do it where you don't need to regularly change room temperatures.

The way it is now the rooms are basically always on the same temperature setting. The only exception is my upstairs hobby space, where I will raise the temperature in case of prolonged stay in the room. It has 4 big radiators and heats up quick even with low water temperature. When I'm up there just to solder some wires or change some components on an experiment, I just leave the temperature as is on 16.5 degrees Celsius on the sensor.

I will have to experiment when the heat pump is installed to see what works best.

Have the system regulate the temperature output of the heat pump to maintain a livable temperature in the rooms. Incorporate the outside temperature in the equation and see what it does.

Well, that is sort-of what your regular heat pump will do by default. Specifically, it will set the source temperature target  based on the outdoor temperature and will then adjust the compressor speed to hold that temperature, and if the temperature rises some hysteresis above the target (i.e., when the minimum compressor power is too much), switch off the compressor and let the temperature drop. And for controlling the temperature inside, you then can have either individual per-room controllers that asjust the flow per room, and/or a room thermostat that influences tha target source temperature/causes the compressort to be shut off when the target room temperature is reached.

The guy who gave the quote for the De Dietrich heat pump explained that the idea was to set the heat pump controlled by outside temperature at, for example, 35C output water when >10C outside and 55C when <-10C outside. Also something to experiment with.

[zilp]

The guy who gave the quote for the De Dietrich heat pump explained that the idea was to set the heat pump controlled by outside temperature at, for example, 35C output water when >10C outside and 55C when <-10C outside. Also something to experiment with.

Well, yes, that is something to experiment with, but heat pumps are optimized for particular temperature ranges, so you probably should try to find out the minimum temperature that you need to keep the house warm before selecting the heat pump. 55°C is at the high end of what "regular" heat pumps can provide, and rather inefficiently so, so, if you really need 55°C, you might need a high temperature model. However, if you can reliably keep the house warm at 40°C, a "regular" model might do the job just fine.

[Siwastaja]

There is an off-the-shelve solution for that. It is a simple mixer unit with it's own pump that takes in hot water from the hot water source and mixes that with the cold water coming from the tubes that make the underfloor heating system. These have been in use for decades.

That doesn't solve the problem. The problem isn't that the water is too hot for the under floor heating, the problem is that the high temperature is inefficient to generate with a heat pump, and it's kinda bad to have your heat pump generate 55 °C at great expense and then cool it back down to 30 °C.

Yes, shunting down to lower temperature distribution makes the whole system have the worse COP of the higher temperature. For small differences, maybe 10degC worst case, between the two distributions, it's not a big deal, but for anything bigger, it is. The (somewhat complex) solution is to use two separate (large enough, say at least 100-200 liters) reservoir tanks and a valve which redirects the heatpump to alternatively heat one of the tanks to different temperature than the other; e.g., for half an hour heat tank 1 with setpoint of +30degC, then for half an hour turn the valve to redirect water to go to tank 2 with setpoint of +40degC.

This is what the usual air-to-water installation would do anyway, alternating between the heating circuit water and domestic hot water, latter being almost always significantly hotter (and thus lower COP, but still more than 1). In this case you would just have a third storage tank.

Another alternative is a single tall enough storage tank so that different water temperatures get layered, then you don't need 2 (or 3) physically separate tanks. The upmost part of the tank, just below the domestic hot water heat exchanger pipes would have direct electric heater elements installed for those days when it's too cold outside for the poor compressor to make +55..+60degC water which you really want to have to prevent legionella in DHW. But most of the year in French climate, the compressor would be doing +60degC just fine.

But, OP said they have low temperature radiators so the difference to underfloor circuits might be low enough so that the compromise from just shunting down the floor circuit is not too bad, in the end if SCOP goes down from 3.27 to 3.15 then who cares if you have simpler and cheaper installation. And for those not afraid of tinkering (and a tiny little bit of noise), adding PC fans to the radiators indeed would work to reduce the water temperature needed.

[tszaboo]

Maybe, just maybe, it makes more sense to install 125 TWh of solar and wind and then use heat pumps to turn that into 500 TWh of heat?

You see, this is where everything falls apart. I got 1 KWh of solar today on my panels, while regularly get 25KWh during the summer.
If you turn the 1KWh into heat with a heatpump, you get 4-5 KWh of heat. If you do the same with P2G, for a summer day you get ~15KWh, if you burn the methane. If you burn the methane in a power plant, and use a heatpump to heat your house, from the same summer day, you get ~60kWh heat.

Mind you that we can't emit any more CO2, so burning fossil fuels, capturing the CO2, using that for P2G, and then burning that P2G gas and releasing the CO2 into the atmosphere afterwards is not a solution, as the CO2 would still end up in the atmosphere, and CO2 emissions would only be halved at best (because the carbon would essentially be used twice before being released).

So, the only way to implement this without CO2 emissions would be to implement a closed loop.

Nobody talked about carbon capture. It's a farce, on the scale of solar roadways, and it's never going to work. But the same goes for "net zero" it's bullshit real world doesn't work that way. We don't have to emit zero CO2, we just have to be more efficient in the emissions, and do it in a way that doesn't cripple the economy completely. That's what net zero would do and the WEF if we let them.

Even if you had a magical hat, and pulled out hundreds of millions of heatpumps, we wouldn't have the capacity to install them, and when we did, we wouldn't have the necessary power plants supply it.
P2G has the largest effect with the least amount of effort. It's the hybrid car of electricity. And it's going to happen whether or not you like it, naturally, because it makes sense market wise. You make profit with it, since electricity is sometimes free, and CO2 has negative price. The banning of fossil fuels for home heating is the government again interfering with our life (they did that here), policies by people who have no basic understanding of the issue. I just watched a youtube video, American politicians on a committee (who were making a bill) were asked how much CO2 is in the air, and their answer was 3-5%. And these idiots are supposed to tell us what to do.

[pcprogrammer]

I have been looking at the temperature data in my database of the last couple of months and see that the radiator in the worst room can keep up with 40C on the input and outside temperature ~-2C. It does not clime up to the set temperature, but also does not drop below the trigger point. So with continuous pumping 40C water through the system it might be fine on the coldest days.

This season we only had 4 nights with temperatures below -4C on my outside sensor. Since it is place against a house wall in a secluded place it is not very accurate and the real low might have been below -6 according to the weather reports.

But still not a lot of really cold days.

I'm going to do an experiment the next couple of weeks where the water temperature on that radiator is limited to 35C and see if it will keep the room on temperature. Is just a simple change in the database done via my website to configure the system.

[zilp]

You see, this is where everything falls apart. I got 1 KWh of solar today on my panels, while regularly get 25KWh during the summer.
If you turn the 1KWh into heat with a heatpump, you get 4-5 KWh of heat. If you do the same with P2G, for a summer day you get ~15KWh, if you burn the methane. If you burn the methane in a power plant, and use a heatpump to heat your house, from the same summer day, you get ~60kWh heat.

Nah, best case 36 to 45 kWh, assuming the same COP of 4 to 5. Gas power plants have terrible efficiency. First, you lose 40% in the conversion to methane, then you lose another 40% when burning it in the power plant, so the round trip loses 64% of the energy. And that is with the best, most modern combined cycle power plants, simple gas power plants have ~ 30% efficiency, so you would lose 80% of the energy. And also, that is ignoring the energy expended in order to compress the methane for storage and afterwards for expansion.

Also, I don't really get what your point is here. I mean, that is exactly what I wrote would be a part of the optimal approach!? Obviously, we will be burning P2G gas when both sun and wind don't supply enough power in order to keep heat pumps running. Or are you suggesting that it would be more economical to use electricity from such a lossy process rather than wind power that can be used directly when that is available?!

Also, the coldest days tend to be sunny, BTW. When you have a closed cloud cover, that keeps the heat in. When there are no clouds, that's when it gets cold.

Nobody talked about carbon capture.

I have news for you:

https://www.eevblog.com/forum/chat/what-is-the-real-story-around-heat-pumps/msg5343137/#msg5343137

Let me quote:

Plus you use CO2 in the process, that you can capture for free at power plants, during the winter. In fact the price of CO2 could be negative, since the power plant doesn't have to pay the carbon tax if it captures the CO2.

So ... I guess "Nobody" is an alias of yours?

But the same goes for "net zero" it's bullshit real world doesn't work that way. We don't have to emit zero CO2, we just have to be more efficient in the emissions, and do it in a way that doesn't cripple the economy completely. That's what net zero would do and the WEF if we let them.

I am not sure what your point is here!?

Even if you had a magical hat, and pulled out hundreds of millions of heatpumps, we wouldn't have the capacity to install them, and when we did, we wouldn't have the necessary power plants supply it.

What makes you think that we'd have the capacity to install 500 TWh annual solar and P2G capacity? (Well, for Germany, I assume the situation would be similar in the Netherlands, just scaled down.)

But also ... yeah, we totally have, and obviously so. Heating systems last on average, say, 20 years. So, every year, 5% of all heating systems are being swapped out, and we do have the manpower for that. Now, you replace it with a heat pump instead of a new gas burner, and in 20 years, you are done. At the same time, you keep building out renewables. Now, thanks to heating with heatpumps, the primary energy demands shrinks significantly, and you only need to add 125 TWh in order to replace the 500 TWh of natural gas. And as that whole thing progresses, the CO2 emissions go down continuously.

P2G has the largest effect with the least amount of effort. It's the hybrid car of electricity. And it's going to happen whether or not you like it, naturally, because it makes sense market wise. You make profit with it, since electricity is sometimes free, and CO2 has negative price.

Have you even read what I wrote? I mean, yes, P2G will happen. I wrote as much. In fact it is already happening. But the idea that we will add 3.5 times the renewable build-out we currently have plus huge P2G capacities in order to then feed the resulting gas to home heating systems at a large scale because that makes sense market wise vs. installing heat pumps ... that's just insane. And no, you still don't make a profit by building a huge chemical plant that converts energy into a more expensive form just because "electricity is sometimes free". That is not how any rational investor calculates expected returns.

The banning of fossil fuels for home heating is the government again interfering with our life (they did that here),

Erm ... wasn't that the point of haveing a government, that it bans people hurting other people?! So ... what's your complaint there?!

policies by people who have no basic understanding of the issue. I just watched a youtube video, American politicians on a committee (who were making a bill) were asked how much CO2 is in the air, and their answer was 3-5%. And these idiots are supposed to tell us what to do.

OK ... and how are some clueless US politicians relevant to anything you are saying here? Is there any logical connection between "some US politicians have said dumb shit" and "therefore, P2G is an economically useful path to zero CO2 emissions in the Netherlands" or "therefore, heat pumps aren't a useful solution for the Netherlands"?

[zilp]

I have been looking at the temperature data in my database of the last couple of months and see that the radiator in the worst room can keep up with 40C on the input and outside temperature ~-2C. It does not clime up to the set temperature, but also does not drop below the trigger point. So with continuous pumping 40C water through the system it might be fine on the coldest days.

This season we only had 4 nights with temperatures below -4C on my outside sensor. Since it is place against a house wall in a secluded place it is not very accurate and the real low might have been below -6 according to the weather reports.

But still not a lot of really cold days.

I'm going to do an experiment the next couple of weeks where the water temperature on that radiator is limited to 35C and see if it will keep the room on temperature. Is just a simple change in the database done via my website to configure the system.

If you haven't yet, you maybe want to also add sensors to the return pipes, as the spread is required to calculate the energy going into a loop. If the return adjustment valves have a built-in flow meter (probably?), that would be all you need to calculate the power at least roughly. Also, it gives you an idea as to how much the power can be increased with increased flow.

[tszaboo]

Plus you use CO2 in the process, that you can capture for free at power plants, during the winter. In fact the price of CO2 could be negative, since the power plant doesn't have to pay the carbon tax if it captures the CO2.

So ... I guess "Nobody" is an alias of yours?
[/quote]
That's not carbon capture. Carbon capture is a very inefficient process where they take CO2 from the atmosphere and compress it down. This is taken from an output of a power plant.

Now, thanks to heating with heatpumps, the primary energy demands shrinks significantly, and you only need to add 125 TWh in order to replace the 500 TWh of natural gas. And as that whole thing progresses, the CO2 emissions go down continuously.

You need 125 TWh during the winter, from renewable, without mass storage. Good luck with that. From solar alone, it takes maybe 25 times as much panels to have the same capacity as during the summer. Not to mention the simple fact that the sun doesn't shine during the night, so what's your plan for that, battery storage? You are waaay off, because you calculate in watthours per year instead of watt of installed capacity. You cannot put electricity in a bucket. I hope this image will tell you what the problem is. If it doesn't then just think about the reliability of a completely renevable electricity based heating system. Meanwhile you can store as much gas, as you want.

[nctnico]

How energy efficient would it be if we all move from north to south & vice versa twice a year in order not to need heating? 

[zilp]

So ... I guess "Nobody" is an alias of yours?

That's not carbon capture. Carbon capture is a very inefficient process where they take CO2 from the atmosphere and compress it down. This is taken from an output of a power plant.

It's just that that is exactly what carbon capture is:

https://en.wikipedia.org/wiki/Carbon_capture_and_storage

What you apparently mean is usually called carbon removal:

https://en.wikipedia.org/wiki/Carbon_dioxide_removal

You need 125 TWh during the winter, from renewable, without mass storage. Good luck with that. From solar alone, it takes maybe 25 times as much panels to have the same capacity as during the summer.

I mean ... are you really unaware that wind power exists? Especially so, given that I have already told you that the yield curve of wind power is inverted vs. solar, so ... why the fuck are you now presenting a graph of solar yield?! Yeah, solar won't provide the power we need for heating in winter, who would have thought?!

Not to mention the simple fact that the sun doesn't shine during the night, so what's your plan for that, battery storage?

I mean, I guess you don't know this, so: The wind does indeed blow during the night. You can test this yourself by going outside during the night if you don't believe me.

You are waaay off, because you calculate in watthours per year instead of watt of installed capacity. You cannot put electricity in a bucket.

No, I am not waaay off, just because I simplify things a bit. Obviously, we don't need just any random 125 TWh at arbitrary times. For heating, we need primarily wind power. And possibly some hydro power, where possible. Then, we need to make more biogas for storage and use in gas power plants (Germany composts most of its organic garbage, so there is quite a bit of potential there if we were to ferment it instead). And then some P2G for the gaps. Some of that probably imported from elsewhere.

What certainly does not make sense is to instead install 700 to 800 TWh of solar capacity plus the matching P2G plants in order to generate and store 500 TWh of methane for use in gas fired home heating systems during the winter.

I hope this image will tell you what the problem is.

Given that there is no wind power mentioned in that image ... no, it obviously doesn't?

If it doesn't then just think about the reliability of a completely renevable electricity based heating system. Meanwhile you can store as much gas, as you want.

Who cares that you can store as much gas as you want (which, by the way, isn't true either - currently existing storage volume in Germany for natural gas is not sufficient for the amount of natural gas Germany burns during a (cold) winter, for example) if it is more expensive than the alternative?

Also, a completely renewable electricity based heating system is perfectly reliable. Because P2G is a part of the equation. It would just be dumb to run it all on P2G exclusively, and even dumber to just burn it in heaters, instead of extracting the majority of the required heat energy from the environment (thus obviating the need for storage), using primarily cheap wind energy to drive the process (also doesn't need long-term storage), and then using expensive P2G electricity when that isn't sufficient to make the whole thing reliable.

Installing hundreds of TWh of solar on every roof in order to avoid installing heat pumps doesn't solve any problems, not even the man power problems.,

[Siwastaja]

I have been looking at the temperature data in my database of the last couple of months and see that the radiator in the worst room can keep up with 40C on the input and outside temperature ~-2C. I

Note that in need of varying distribution temperatures, if most of the house could use lower distribution temperature and it's just one room which needs higher, it will likely be more energy efficient to just run the whole system at the lower temperature and add a small extra direct electric heater to the room in question; especially if you can allow the room to temporarily cool down a bit.

This season we only had 4 nights with temperatures below -4C on my outside sensor. Since it is place against a house wall in a secluded place it is not very accurate and the real low might have been below -6 according to the weather reports.

But still not a lot of really cold days.

This is still all easy-peasy to any half-decent air-to-water heatpump. I mean, my cheap heatpump is still doing quite acceptably (COP well over 1.5) at -15degC out / +40degC water. At my place it really starts to struggle i.e. need extra source of heat at -18 / +42, at which point marginal COP is 1.0 (that of added power) and actual COP not much over 1.0.

It's a nice micro-optimization if you could lower the distribution temp to +35 but this is not a dealbreaker question.

I was thinking about the noise. Ground source heatpump produces compressor noise, air source unit fan + compressor noise. The fan noise is almost never heard inside, unless you have something like a vent hole right next to the unit; it's the compressor noise that's bad. So the ground source pump is not necessarily completely silent to you either. If it's in cellar, made of concrete or stone, it will be completely silent of course. OTOH, if your house has brick walls and you pick a wall with no nearby windows or vent holes, and air source unit is ground mounted (not wall mounted) then it will be completely silent, too. One option which is not unrealistic at all, and applies equally to ground and air source units, is to improve the sound insulation. Compressor is normally wrapped in soundproofing (and thermally insulating) material, but the sheet metal case tends to have completely uninsulated spots which sometimes even tend to resonate, adding some bitumen-based sound insulation boards is not too far-fetched. And of course mounting the unit with dampers to prevent vibrations from propagating to the mounting base.

[pcprogrammer]

The De Dietrich heat pump for geothermal has a lot of sound insulation by the looks of what is given in the manual, and if needed additional sound insulation can be added to the basement.

The question about performance has been satisfied and it is clear that there won't be that much difference between air to water and ground to water, so fear of sound is now basically our only choice factor.

I'm also looking in to the possibility to control the heat pump with my own system, and that seems to be a bit tricky due to proprietary interfaces and protocols.

[tszaboo]

So ... I guess "Nobody" is an alias of yours?

That's not carbon capture. Carbon capture is a very inefficient process where they take CO2 from the atmosphere and compress it down. This is taken from an output of a power plant.

It's just that that is exactly what carbon capture is:

https://en.wikipedia.org/wiki/Carbon_capture_and_storage

What you apparently mean is usually called carbon removal:

https://en.wikipedia.org/wiki/Carbon_dioxide_removal

You need 125 TWh during the winter, from renewable, without mass storage. Good luck with that. From solar alone, it takes maybe 25 times as much panels to have the same capacity as during the summer.

I mean ... are you really unaware that wind power exists? Especially so, given that I have already told you that the yield curve of wind power is inverted vs. solar, so ... why the fuck are you now presenting a graph of solar yield?! Yeah, solar won't provide the power we need for heating in winter, who would have thought?!

Not to mention the simple fact that the sun doesn't shine during the night, so what's your plan for that, battery storage?

I mean, I guess you don't know this, so: The wind does indeed blow during the night. You can test this yourself by going outside during the night if you don't believe me.

You are waaay off, because you calculate in watthours per year instead of watt of installed capacity. You cannot put electricity in a bucket.

No, I am not waaay off, just because I simplify things a bit. Obviously, we don't need just any random 125 TWh at arbitrary times. For heating, we need primarily wind power. And possibly some hydro power, where possible. Then, we need to make more biogas for storage and use in gas power plants (Germany composts most of its organic garbage, so there is quite a bit of potential there if we were to ferment it instead). And then some P2G for the gaps. Some of that probably imported from elsewhere.

What certainly does not make sense is to instead install 700 to 800 TWh of solar capacity plus the matching P2G plants in order to generate and store 500 TWh of methane for use in gas fired home heating systems during the winter.

I hope this image will tell you what the problem is.

Given that there is no wind power mentioned in that image ... no, it obviously doesn't?

If it doesn't then just think about the reliability of a completely renevable electricity based heating system. Meanwhile you can store as much gas, as you want.

Who cares that you can store as much gas as you want (which, by the way, isn't true either - currently existing storage volume in Germany for natural gas is not sufficient for the amount of natural gas Germany burns during a (cold) winter, for example) if it is more expensive than the alternative?

Also, a completely renewable electricity based heating system is perfectly reliable. Because P2G is a part of the equation. It would just be dumb to run it all on P2G exclusively, and even dumber to just burn it in heaters, instead of extracting the majority of the required heat energy from the environment (thus obviating the need for storage), using primarily cheap wind energy to drive the process (also doesn't need long-term storage), and then using expensive P2G electricity when that isn't sufficient to make the whole thing reliable.

Installing hundreds of TWh of solar on every roof in order to avoid installing heat pumps doesn't solve any problems, not even the man power problems.,

Honestly your straw man arguing style is very exhausting to reply to. A few things that make your plan unviable is the simple facts that during summer there will be so much excess electricity, thats not even funny. Your own government is betting on power to gas, with short term plans for a 100 TWh  a year.
And banning fossil fuels and forcing people to install heatpumls is again the government forcing something on the people. But there has been enough research on the subject, so instead of typing here a wall of text like you, I'm just going to link those studies.
https://www.google.be/url?sa=t&source=web&rct=j&opi=89978449&url=https://cris.vtt.fi/files/53434850/1_s2.0_S0306261921010643_main_1_.pdf&ved=2ahUKEwjz-ejbtrmEAxWpgf0HHV51A0E4ChAWegQICBAB&usg=AOvVaw0ryS1moGd9X6JepJADaAOX

[Zero999]

I appreciate there's a political element to this. Governments are try to push heat pumps, in favour of oil and gas, to cut emissions. Understandably many people are fed up because they don't like being told what to do, which is why there's some push back against heat pumps. Personally speaking, I won't get one in the foreseeable future, because it isn't economical for me. Natural gas is much cheaper than electricity, even taking into account the lower energy consumption, it doesn't add up.  I don't have any problem with them and certainly aren't against the idea of getting one in the future. Heat pumps are viable where electricity is cheap, such as near a hydroelectric or nuclear power station. Areas where electricity is expensive need more investment in nuclear power, then people will choose heat pumps for economic reasons.

Politics aside, are there heat pumps which use natural gas or oil, rather than electricity? It won't give the same COP but might be more economical. That might also suit me, although my energy usage is fairly low, so not worth it, until I need a new boiler.

[Siwastaja]

I'm also looking in to the possibility to control the heat pump with my own system, and that seems to be a bit tricky due to proprietary interfaces and protocols.

Look at terms like "EVU" or "smart grid" or "SG" or "SG-ready", which is a simple two-bit digital on/off control, allowing increase/decrease of setpoint. If even that isn't supported, then you most likely still have a simple on/off logical control you can interface to, and possibly another to prevent usage of aux resistive heating.

No one actually interfaces the RS485/CAN buses of these heatpumps, even we doing this thing professionally have postponed such feature creep and still offer simple on/off control as the primary means and dedicated our efforts elsewhere (e.g. support gazillion of solar inverters instead of gazillion of heatpumps).

One option is to use relays to add resistors in series/parallel with the thermistor used to by the heatpump to measure reservoir tank temperature, this way you can cheat setpoint finetuning without having to figure out an interface to actually control the setpoint (or more specifically, curve parallel shift).

Be careful with your control, though - if you prevent heating for too long, creating large dip in temperature, then after releasing the control the heatpump's internal logic might decide that using resistive support heating is a great idea, ruining your COP.