Vestaxx window heating - experiences?

Calculating the inefficient heating system as worthwhile with a photovoltaic system is an "interesting" approach.

Photovoltaics are actually always worthwhile. To portray the inefficient heating system as more worthwhile than another is, with all due respect, not reasonable.

Hello Andreas,

I really like that you as the manufacturer of the system face the open questions and critical comments. I will take a look at your figures in Excel this evening.

But:

I would advise them not to rely on the numbers from the brochures, but on independent studies from recognized institutes. For the air-water heat pump, an average annual performance factor of 2.6 is given there). In addition, there is an efficiency rate of 70% (Source: TU Berlin - Hermann-Rietschel-Institute) and we end up below 2!

Here I wanted to stop reading already because of gross nonsense. So we are not supposed to rely on datasheet specifications here, but just believe you? My heat pump had an annual performance factor of 5 for heating operation in the last 11 months.

If you want to refer to studies, then don’t hide half of it. The annual performance factor of 2.6 refers to the Fraunhofer study as far as I know. But there is also to be read in a press release:

The average annual performance factors of air/water heat pumps at 15 measured systems range between 2.5 and 3.4. A comprehensively renovated building achieved an annual performance factor of 4.1. The annual performance factor describes the ratio of generated heating heat to the used driving energy.

In the study, only 5 (?) houses were built >= 2005 and in total only 16% of the examined buildings have pure underfloor heating. The rest operate exclusively or partially with radiators.

Thus, in no case comparable to modern KFW55 houses – which are compared with the 30kWh/sqm.

On one hand, I am not supposed to believe all brochures, on the other hand, I use unrenovated old buildings for the comparison annual performance factor determination.

Let’s look at the annual balance: The house produces more energy than it consumes in the year -> called a plus-energy house!

So heat pump houses with photovoltaics are plus-plus-energy houses? They do even more plus?



For me still an absolute case of "Kill your Darling" in the product development phase, as only sensible for absolute passive houses.

Hello,

since I have come out, it would also be nice if you introduce yourself in more detail.
What do you do professionally and in which industry do you work? But of course, you don’t have to.
What I would be interested in is where you read off your annual performance factor of 5 or how you calculated it.
Maybe you can present something about that sometime.

But we can abbreviate the topic of the annual performance factor (study 1 here - study 2 there), since it is actually completely irrelevant for the consideration when looking at the full costs. Because always talking only about the - admittedly low - consumption of a heat pump is not even half the truth.

Example(s):
If you buy a car for €40,000 that consumes little fuel, you also deduct all costs (depreciation, maintenance, operating costs, etc.) compared to the tax and can calculate 30 cents/km.
Or even better, the example of a photovoltaic system: What does the kWh generated by it cost? -> Investment costs : energy generated within a service life of 20 years (photovoltaic systems last up to 40 years and longer - but let’s leave that aside). From this, a kWh price from the roof of about 9 - 11 cents is calculated.

Given the current circumstances, consumers will be very interested in what the kWh of heat will cost them in the future. And that is where our system comes in. Full costs = investment plus operating and maintenance costs, and this is considered over the service life. In our webinar, we go into this in detail and show that even if the electricity supplier were to provide electricity free of charge for the duration (a little dream), the full costs are over €1/kWh.

I am very interested in talking about using a heat pump in a zero-energy house - but you surely didn’t mean that - or did you? Speaking of a plus-plus energy house in combination (the investment costs are again not considered) is nice, but not backed up with numbers. You are welcome to do that next time.

I notice you are a heat pump fan and that is good – really. I am by no means a heat pump critic (aside from the annual performance factor and the fact that you don’t say that it is measured at the heat pump outlet and distribution losses are ignored). In my view, the heat pump makes sense where the specific heating energy demands are quite high, because it helps save there. But in a low-energy building with a HWB of around 30 kWh/m²a, one saves – happily with an annual performance factor of, let’s say, 6 in a 150m² house annually 4,500 : 5 = 3,600 kWh per year.

In contrast, with a direct electric heating consumption of 4,500 kWh per year but through the photovoltaic system (same investment as with an air-to-water heat pump) one gains 13,500 kWh in the same period, thus a positive balance of almost 10,000 kWh per year. And every kWh of that is used – whether in the house or by a third party somewhere in the grid.

Everyone can decide freely: Either not save 3,600 kWh or rather generate 13,500 kWh.

Have a nice evening.
Best regards
Andreas

... oh, one more remark about "Kill your Darling":

We are no longer in the product development phase but have, in total, around 200 references including very happy customers (I am happy to arrange meetings or visits), some of whom have been using the system through their 5th winter already. And these are not absolute passive houses but a colorful mix of various house types (KfW55, KfW40, and KfW40+).

Whoever tries to sell a heating system using a technology (the photovoltaic system) that has nothing to do with heating probably has few arguments for the heating system itself. Understandably so, because a COP of 0.92 is clearly much less than 4 or even more, which other modern heating systems achieve today.

So again, the photovoltaic system must (because it is not a heating system) and can (through loans and so on) be calculated completely on its own and you will find that it almost always pays off.

When it comes to heating systems, you can gladly make the comparison: air-to-water heat pump vs direct heating, or air-to-water heat pump + photovoltaic against Vestaxx + photovoltaic. But the photovoltaic only provides the environment there, just like the size and insulation of the house. Unfortunately, the comparison is currently especially difficult because no one can predict the electricity price. With low electricity costs, I even see a chance for direct heating systems.

You can also take a look at the environmental balance. That is, how high the energy expenditure is for the manufacture and installation of the systems compared to the consumption over the lifetime. But I consider the statement that direct heating is cheaper than an air-to-water heat pump and therefore you can invest in other profitable ventures to be of little use.

I know, many will now again demand the annual performance factor=4.

If that is already known, it should be done as well. According to a large database, the average for air-to-water heat pumps in 2021 was 3.73. We are talking about new buildings here, otherwise I am curious how the calculation looks for a direct heating system in an old building. ;)

In addition, there is the efficiency of 70% (Source: TU Berlin - Hermann-Rietschel-Institut) and we end up below 2!

Unfortunately, I could not find that now. Does that apply to a new building?

Aha - some will now say. 3,000 kWh more than with heat pump! I told you!!!

Here you could already start and say 1,000€ more per year at 35ct/kWh. With an additional cost of 25k€, the amortization for an air-to-water heat pump is 25 years. At 60ct/kWh about 14 years. If you take photovoltaic electricity at 8.2ct/kWh it is 100 years. However, it can be said with certainty that in winter, when the heating is active, hardly any electricity comes from the roof. So the direct heating benefits especially little from photovoltaics.

(leaving aside the annual performance factor and that it is not mentioned that this is measured at the heat pump output and distribution losses are ignored).

With windows, I understand that losses go outside. But where do the losses of an air-to-water heat pump go? Into the technical room? They can go there, it is inside the house.

Or better yet the example of a photovoltaic system: What does the generated kWh cost? -> Investment costs : generated energy within a period of 20 years (photovoltaic systems last up to 40 years and longer - but let’s leave that aside). This results in a kWh price from the roof of about 9 - 11 cents.

Really nice that you are such a fan of photovoltaic systems, but it just has nothing to do with heating.

Anyone trying to sell a heating system through a technology (the photovoltaic system) that has nothing to do with heating probably has few arguments for the heating system itself.

You have it or you definitely do not want to understand it, so here is a very simple explanation for everyone else again:

A house basically has 3 energy demands that must be met: heating demand, hot water, and household electricity. For conversion, the residents need converters (heating systems) and energy. For the purchase, they have a budget -> here simply €40,000 (no matter how it is financed – why they have to finance the costs for the photovoltaic system and not the same costs for the heat pump themselves, you will have to explain to us here. But you do not respond to questions – unfortunately.

So – now they can do it smartly and get a simple heating system (infrared panels or heating windows WITHOUT maintenance costs). Or they decide on a highly complex heating system with annual maintenance costs. With the IR heating system there is simply €30,000 left, which they can sensibly invest in an energy generation system. I think that is – among many others – the best argument for the maintenance-free heating system.

The low COP of 0.95 (according to the latest measurements from TU Berlin) compared to that of a heat pump with 4 I have never denied anywhere – but that is not the point. A photovoltaic system is not a heating system either, but an energy generation system and I believe nowadays every homeowner would like to have a large photovoltaic system to be less dependent than they are at the moment and unfortunately probably will remain. And – I gladly agree – it is always worthwhile!

Air-water heat pump vs direct heating or air-water heat pump + photovoltaic against Vestaxx + photovoltaic. But the photovoltaic system only supplies the environment, just like the size and insulation of the house. Unfortunately, the comparison is currently particularly difficult as no one can predict electricity prices. With low electricity prices I even see a chance for direct heating systems.

Unfortunately wrong. The higher the electricity price, the more important it is to generate as much of it yourself as possible. And I repeat again: a pure heat pump system has no energy generator when the same budget is assumed. But you haven’t really looked at my calculation. Numbers don’t lie and please comment on the numbers in my first message here on the forum so that everyone can understand.

One can also gladly look at the environmental balance. That is, how high the energy expenditure is for the manufacture and installation of the systems in comparison to consumption over the lifetime. But I consider the statement that a direct heating system is cheaper than an air-water heat pump and therefore one can invest in other worthwhile things to be little constructive.

Thanks for this easy opportunity. Then tell us what CO2 footprint a heat pump with about 2 km of piping in a house has. What our heating glass has per m² I can gladly share: 3 grams of zinc oxide as a heating layer on the glass, 2 m of copper tape, and 2 grams of silver conductive adhesive. Basically, compared to a heat pump, about a factor of 10,000 smaller. And then the photovoltaic yield directly from the sun compared to electricity for heat pumps from the power mix. Mega own goal!

And direct electric heating in old buildings only makes sense if the house was insulated beforehand to new-build standards. But I have not made this topic an issue and I would always advise against it if the house is not insulated.

Here one could already start and say €1,000 more per year at 35 ct/kWh. With a €25,000 price difference, the payback for an air-water heat pump is 25 years.

Now it’s getting really interesting. So – you calculate 3,000 kWh x €0.35/kWh = €1,000 savings. And so the heat pump amortizes after 25 years. How do you get a price difference of €25,000? An air-water heat pump including everything today costs about €40,000. And then the payback you calculate so simply and without maintenance and repair costs is 40 years!!! Unfortunately, most heat pumps do not last longer than 15-20 years. So after 20 years you have to buy a new heat pump again. Just not at today’s price anymore.
How you come to 100 years at 8.6 cents (which by the way is only the remuneration price for the fed-in electricity and not for the electricity used in the house) you must explain to us.

With windows it is clear to me that losses go outside. But where do the losses of an air-water heat pump go? Into the technical room? They can go there, after all it is inside the house.

No – not into the technical room but where the heat is distributed – that is why they are also called distribution losses. So through the floor and indeed with a huge surface area against the colder ground. This is directly comparable to a window via the U-value. We can gladly calculate it sometime. But that would go too far right now.

Really nice that you are such a fan of photovoltaic systems, but it just has nothing to do with heating systems.
Well – if you consider heating systems do not need energy – maybe. But unfortunately, heating systems always need energy and WE generate that with photovoltaics, so our heating is also a solar heating system. Because when you look at a system you consider all components and do not leave out what you do not like.

I would find it fair if you would share more about your system with a seasonal performance factor of 5 from the last 11 months and respond to my questions. Run an energy calculation for such a house and show it to us. As written above: numbers are verifiable and you have not said a word about the full cost calculation. Also references with satisfied customers do not interest you.

It is actually not worth it, but I face any reasonable argument with numbers that can be proven.