ᐅ Vestaxx window heating – experiences?

OWLer schrieb:

Every time I read this topic, my resting heart rate noticeably rises. For me personally, discovering this thread while researching window heating would have been enough to completely remove the system from the project requirements. I still haven’t seen a clear and transparent calculation. What I have seen are lengthy texts filled with lots of numbers that don’t always fully match from one text to another. The forum allows for uploading screenshots, and here I would like to see clear data sets compared side by side, where input parameters and results can be clearly understood. I expect both from a managing director with a degree and 25 years of professional experience in electrical engineering.

And then there are always these outliers appearing here and there. How are we supposed to argue reasonably? The only conclusions I’m left with are either a lack of expertise or that facts are intentionally withheld or distorted for marketing reasons. Of course, you can measure a building’s energy consumption including all distribution losses with a heat meter. What else would you measure? Or to put it differently: the heat, including all transmission losses, stays within the building system and is therefore used effectively. It contributes to heating the building structure. Gross equals net. Why should I care about what reaches the person?

I install a heat meter in the hydraulic system: gross consumption.
I install an electric meter before the heat pump including the circulation pump (which is all-in-one for monoblock systems): electrical consumption.

Mixing both to calculate yearly performance factor / COP or whatever is, in my opinion, still irrelevant, since it is already included in the gross/net consideration via the heat meter.

So far, my question seems to have been overlooked. @Vestaxx GmbH how about providing clear and manageable profitability calculations?

Basically, it bothers me that you are using “20-year-old” heat pump data from Fraunhofer to base your arguments on, and that a new homeowner should make their comparison only on that. Otherwise, by analogy, we would also have to use 20-year-old insulation standards and compare those as well. The dogmatic view that the annual performance factor is 4-5? Impossible! No, it actually is possible! Source: me!

Since elsewhere the transmission heat loss to the ground was mentioned again, you also have that in your system, right? How am I supposed to sell the system to my wife, and especially to my mother-in-law? Your floor then would only have (estimated) a maximum surface temperature of 20°C (68°F). So I can just subscribe to the “Snocks subscription” and keep slippers ready?

Vestaxx GmbH schrieb:

And what about the argument: what happens if you (Vestaxx) are no longer around in 20 years? Where will we get a replacement glass?

That is a really important question, because in my personal opinion, your customers will genuinely care about this issue.

OWLer schrieb:

Basically, what bothers me is that people here argue using “20-year-old” heat pump data from Fraunhofer with a dogmatic attitude: Seasonal Performance Factor (SPF) 4-5? Impossible, source: me! Yes, it is possible, and new home buyers should base their comparisons only on current figures. Otherwise, by the same logic, we would also have to rely on insulation standards from 20 years ago for comparisons.

I have demonstrated our example with a heat pump achieving an SPF above 4 from 2020 using actual data. In my opinion, the response was evasive and flavored with the comment “heat pump owners are all being fooled,” which, with some imagination, can be interpreted as “the poor fools.” When responding in a similarly confrontational way, it quickly becomes “too personal,” yet that reply contained only vague statements and no data. So I guess we’ll wait until Monday to see if RotorMotor’s example can be factually and numerically refuted. 🙂

kati1337 schrieb:

Are the 25k included already based on solid data?

No, I just took the figure from V. to keep the discussions as short as possible.
He estimated 40k for the heat pump and 10k for Vestaxx, and I added another 5k for the BWWP.

kati1337 schrieb:

That difference even seems quite large to me, but I’m not exactly sure.

Same here. But you can find prices for underfloor heating between 50 and 100€/m² (around 5 to 10 USD per square foot), so that would be about 7,500 to 15,000€ (approximately 8,000 to 16,000 USD).
Then a heat pump for 15k€ (about 16,000 USD) including installation.
With some small extras, it’s more like 30k€ (around 32,000 USD).

In comparison, V. has 10k€ (about 11,000 USD) and BWWP, so the difference is probably closer to 15k€ (about 16,000 USD) rather than 25k€.
But of course, all just estimates. I thought the 17 years looked okay. So it’s more like 10.

kati1337 schrieb:

The heating system may eventually wear out and need to be replaced, but the underfloor heating usually stays intact. That means the costs for the underfloor heating should really be considered separately.

Yes, I think the heat pump needs to amortize within 20 years, and probably 50 years for the hydraulics?
That doesn’t seem to be an issue. And rising electricity prices only shift the balance toward even faster amortization.

Vestaxx GmbH schrieb:

I’m eager to answer this immediately

Sure, but please no long paragraphs—just corrections or critiques on specific numbers.
And if you’re going to take the trouble, please provide evidence instead of repeatedly claiming that a heat pump only has a seasonal performance factor of 3, when there are plenty of examples and studies showing 4 or 5 for new builds!
A study from the Fraunhofer Institute already gives an average of 3.1 for air-to-water heat pumps in older buildings, and they operate with significantly higher flow temperatures.

Vestaxx GmbH schrieb:

...
And then there's always the fear: What if we’re no longer around in 20 years? In Europe, there are 10 other manufacturers that produce heating glass panels. I would be more concerned about whether replacement parts for my heat pump will still be available in 20 years and what they might cost.

...

I find that interesting. Ten other manufacturers of heating glass panels? Are they mainly focused on other countries? If so, why? Does that mean the German (quite large) market has not been relevant so far? Or are you relatively small compared to other suppliers within Germany?

Vestaxx is (almost) the only provider in Germany as far as I know. Heated glass has been around for quite some time; Interpane already offered such glass before 2010 and still has it in their product range today. However, it is only offered for rooms with a low heating load or without conventional heating systems. The main application (also by other specialized suppliers) is, to my knowledge, rather for conservatories, roof windows, and similar areas (for example, to ensure snow clearance or prevent window condensation). There are also suppliers offering up to 300 degrees Celsius (572°F) – for example, a sauna with panoramic views in a mountain hotel at 2,500 m (8,200 ft) altitude as a use case.

Otherwise, yes, the heating works. Just spread the typical upfront costs of a heat pump over its lifespan. And that simply needs to be calculated. With a service life of 20 years—and yes, that is coming or has already partly been mandated—the requirement for photovoltaic systems / solar panels can make it an alternative. Overall, as a user, I would say: initially, keep your distance until Vestaxx evolves from a startup to a mass-market supplier (which didn’t work out for Interpane either). Photovoltaic leasing models can also be worthwhile but are initially calculated favorably there as well… It’s no different here.

“Don’t trust any statistics you haven’t manipulated yourself” – be careful when buying heating systems.

kati1337 schrieb:

I supported our example with a heat pump having a seasonal performance factor above 4 from 2020 using actual data. The responses felt vague to me and were mixed with the comment "heat pump owners are all being misled," which could be interpreted as "the poor fools" if you let your imagination run.

That’s exactly what bothers me, and that’s why I gave the detailed note to "Kill your darling." Here, someone seems absolutely convinced of their product and clashes with anyone who questions it or raises concerns.

This annoys me so much that I actually fired up Excel again.

The results over typical financing periods, which also correspond to the expected lifetime of the heat pump, don’t surprise me at all. I see all my claims and warnings about the system confirmed. If someone asked me, I wouldn’t recommend the window heating system to anyone.

Since sustainability was also mentioned, I did a quick rough cross-check for that as well. I assumed about 2.5 kg of CO2e per kilogram of German steel, and 2 kg CO2e for the PE floor heating pipe 17x2 mm (0.7x0.08 inches). Production overhead was estimated at 25%.

By the way, I’m also an engineer @Vestaxx GmbH, and I occasionally deal with calculating CO2 footprints at work, so I confidently say these are solid reference values based on my long professional experience.

The CO2e of the German electricity mix is, of course, problematic. There were ambitious goals before the war, which I now seriously doubt since East German lignite plants are still running. I assume the government will reach less than 25% of the 1990 target only by 2040, a full 10 years later than planned.

So I simply calculated the emissions from electricity. Unfortunately, I have serious doubts it will go as well as hoped.

The sobering outcome with my chosen input parameters is that over a 15-year lifetime, we emit 16 tons of CO2 including manufacturing and operation. The longer this window heating system runs, the worse its CO2 balance becomes.

The window heating system’s balance is significantly worse than the heat pump’s, naturally due to efficiency differences.

And please don’t argue with free photovoltaic. I already disproved that argument in the first calculation. Over the financing period, there are no meaningful cost differences, so photovoltaics should be considered as an add-on in both cases. Furthermore, from November to February, 63% of the days receive no direct sunlight on the photovoltaic panels. Two thirds of the heating then come from the electricity mix, and for the remaining third, it’s usually so overcast that even 15 kWp of south-facing photovoltaics can’t cover the base load of the house without heating. A few sunny days can balance that out if there’s no snow on the panels.

Photovoltaics and heating should be viewed strictly separately. So, in my opinion, it’s highly misleading to advertise the heating system together with “free photovoltaics.”

Since I’m not done yet, I’ll review my heating load calculations again and raise a few critical questions about heating the basement and my bathrooms, where I can’t install large window areas.