Vestaxx window heating - experiences?

So - now come with your full cost calculations.

I had that already a long time ago:

One could already start here and say €1000 more per year at 35ct/kWh. With a €25k surcharge, the payback for an air-water heat pump is 25 years. At 60ct/kWh about 14 years. If you take photovoltaic electricity at 8.2ct/kWh it’s 100 years. Here one can certainly say that exactly in winter when the heating is active hardly any electricity comes from the roof. So direct heating benefits from photovoltaics particularly little.

As you can see, it strongly depends on the electricity price. But that cannot be determined without a crystal ball. Since I rather expect electricity prices to continue rising, I would tend to install more efficient heating systems or even better build the house completely passive. And here we apparently agree:

How will the electricity price develop? Will it fall back to pre-Ukraine levels? I don’t think so.

The photovoltaic price was stable for a long time but is currently actually rising. The kWh price from a photovoltaic system was thus quite calculable. It ranged between 9 - 11 cents/kWh, depending on system size. And this price does not change once the system is set up. One can even decouple from the Renewable Energy Act feed-in tariff and go into direct marketing. The market price for the kWh was e.g. about 31 cents/kWh in July 2022.

The thing is that you always turn on the window heating exactly when there is no sun anyway. Therefore this argument falls away, doesn’t it?!

One thing should not require any numerical examples from a person of clear mind: that energy is conserved, no more and no less. It cannot be "produced," only "converted" and "used." It is given as a gift exclusively in the form of [solar income]. Even a heat pump cannot generate energy; Kelvin is not a cryptocurrency. A windowpane always sits at an interface and cannot do otherwise than radiate heat supplied to it in both directions. The efficiencies of different energy conversion processes may vary - but anyone who believes that one or another process can perform magic has certainly smoked too many chemtrails.

So - I know my colleagues very well ;o) and there is definitely no Christian among them. Maybe it is not your real first name either, then unfortunately I can’t help any further.

I know - it is certainly not common to reveal your profession, place of residence/work here, but that might help driver55 with his assessment.

I’ll start: I am now 61 years old, living near Bielefeld, working in Berlin, studied electrical engineering with a specialization in energy technology, was employed for 25 years in middle and upper management of 3 companies (2 window systems companies, thin-film solar producer), voluntarily gave up these well-paid jobs and have been passionate about the window heating system since 2014.

Rotormotor: I already had that a long time ago.
-> What you are calculating there I cannot follow and unfortunately it is not a full cost accounting according to VDI 2067.
Basically, it includes: investment, operating costs over the lifetime, maintenance costs, inflation, and interest.

But at least you calculate that the heat pump has a payback period of 25 years – it just does not last that long, ergo -> after 60 years it is still not economical and must be subsidized with taxpayer money.

Rotormotor:
Since I assume electricity prices will continue to rise, I would rather install more efficient heating systems or even better, build the house completely passive.
-> With rising electricity prices, one should generate the electricity oneself and building the house passive is great. With today's insulation standards, we are already close. The less a heat pump pays off in these houses. I have been trying to illustrate that the whole time.

Rotormotor:
The thing is that you always turn on the window heating exactly when there is no sun anyway. So this argument falls away, right?!
That is again absurd. So you always turn on your heating in winter only when the sun is not shining. OMG!
A heat pump system runs through the winter months because underfloor heating is far too sluggish for reasonable control. A floor slab has about 1000 kg/m² mass – glass heating panel about 10 kg/m². And again: the system makes sense because we do not only supply the heating panels in winter (of course not completely – I never claimed that) but photovoltaic delivers energy all year round – and the household power demand from the grid is significantly reduced.

11fant: A windowpane always sits at an interface and cannot help but emit heat supplied to it in both directions.
-> For decades, the radiator was under the window – why actually? To reduce the discomfort of cold downdraft at the glass pane by the rising warm air. So it is actually only logical to put the heat source completely into the glass and thereby raise the comfort to the highest level. And of course a heat source radiates in both directions. Only with us (for other manufacturers, I cannot say) about 5% outward – and proven 95% inward. At 50/50 it would not be sensible. And whoever now comes again with ... the window is the weakest component regarding heat transfer ... should nicely separate U-value and efficiency. I can gladly write something about that again.

Basically, I now want to ask those who consider the heat pump system in new buildings (!) the very best and are firmly convinced that other systems are pointless at the same cost, to stop reading my threads – I will never convince you nor try to persuade you. No offense, it just takes too much of my precious time.

However, if you consider the heat pump a very sensible system in new buildings (!) but also want to look beyond the horizon into previously unrecognized fields of innovation, I am happy to continue the discussion here and answer any concrete questions (see all the questions from Rotormotor).

Einstein said: "The purest form of insanity is to do the same thing over and over again and expect different results."

Rotor motor: I've had that for a long time. -> What you calculate there I cannot follow and is unfortunately not a full cost accounting according to VDI 2067. Basically it includes: investment, operating costs over the service life, maintenance costs, inflation and interest.

If you are already so picky, it should be clear to you that this is not universally possible. Discussions like these are about estimates.

But at least you calculate that the heat pump has a payback period of 25 years - it just doesn't last that long, ergo -> after 60 years it is still not economical and has to be subsidized with tax money.

How do you know that it does not last 25 years? And even if you need a new compressor after 20 years, you can keep the whole other system (heating loops, valves, water storage, ...). You can probably assume costs between 2 and 5k€. So 2-5 years. ;) How long warranty do you give at Vestaxx? More than 25 years? What is included in the warranty?

So you always turn on your heating in winter when the sun is not shining. OMG!

How much of the required energy for the window heating can be generated by the photovoltaic system? Maybe 20%? But a very different comparison: electric underfloor heating instead of window heating. The underfloor heating has the same efficiency, is just as comfortable and is cheaper to purchase.

If you are already so picky, you should be aware that this is not universally possible. -> then just take the values you have available – I’ll let you have the annual performance factor of 10. But simply throwing a few numbers into the room that nobody (at least not me) can verify is not helpful. Maybe you have a heat pump and can share your consumption here (but please all of it).

How do you know that it doesn’t last 25 years? And even if you need a new compressor after 20 years, you can still keep the entire other system (heating loops, valves, water tank, ...). You can probably expect costs between 2 and 5k€. So 2-5 years. -> These are empirical values and VDI 2067 assumes them as such. Maybe they have no clue either ;o). And I never said that every heat pump breaks after 15 years. So if yours lasts 20 years, you believe you only need one compressor and will shell out a mere 2 - 5 k€ in 2042 for it. I wouldn’t want to have your faith ;o). Just this weekend, at a HOUSE fair, heat pump owners lamented their misery to me. And not because the heat pump or any component broke after 20 years. No – that was after the warranty period (3 years), and they were graciously refunded the pump (150 €) out of goodwill. Only the installation and removal (800 €) had to be paid by the user. Another had constant error messages and later figured out the cause himself. The manufacturer later had to sheepishly admit it. I gladly invite these two gentlemen here to the forum, so they can tell their stories themselves – after all, this is an experience-sharing group.

The warranty period for Vestaxx heating glasses is 5 years. Heat pump -> 2 years. The lifespan of insulated glass is 20 years. And now take a look at which glasses in old buildings are still perfectly fine after 30 years. They have no pumps, compressors, valves, etc. By the way, ours don’t either ;o)

How much of the required energy for the window heating can be generated by photovoltaics? Maybe 20%? -> That of course depends on the size of the photovoltaic system. I already did a calculation here. For the saved money of 25k€, you can nowadays get a 15 kWp system that generates at least 13,500 kWh per year. Since you rely so much on flat rates: about 2/3 of that is generated in the summer half-year and about 1/3 in the winter half-year. So in the winter half-year, there are about 4,500 kWh from the roof. The heating demand for new buildings is in this order of magnitude. Still, it’s not a direct 100% that flows into the windows, because naturally nothing is generated at night. But in terms of balance, the photovoltaic system generates exactly what the house needs for heating (room heat) in the winter half-year in the above example.

But a completely different comparison: electric underfloor heating instead of window heating. It has the same efficiency, is just as comfortable, and is cheaper to purchase. -> Hey – you’re already completely in the direct electric heating corner – great. ;o) I can’t say what efficiency electric underfloor heating has at the moment. That also depends on many parameters. It is as comfortable as any other underfloor heating, except that it stirs up fine dust and mites into the air. But who told you that underfloor heating is cheaper than window heating? 150 m² x 60 €/m² plus embedding in the screed plus connection. That is much more expensive than our solution. Sorry.