ᐅ Vestaxx window heating – experiences?

Christian 65 schrieb:

Don’t talk nonsense.

Nonsense?

Christian 65 schrieb:

What does reality look like?
A family takes out a mortgage loan with 3.5% interest and 2% repayment.
And now another €23,000 is added on.
On the same terms that everyone hopes for.
And as a result, the payment increases by €1,265/year.

That’s the reality for most people.

Haha, yes, exactly.
You HAVE to repay 2%! Anything else isn’t possible.
2.3%? Out of the question! 2.25% repayment? Absolutely no go for @Christian 65.

Let’s be factual: Nowadays, nobody calculates with straight percentage numbers for repayment rates anymore.
So it’s basically about comparing €1,500 electricity costs to the repayment on the "heat pump loan."
And of course, you could pay off the heat pump plus underfloor heating more slowly, but then you’d still save money every month compared to electric heating through radiators, where you can’t just tell the utility company that you’d rather pay less.

Christian 65 schrieb:

Basically, I’m talking about the fact that there are different ways to heat a house and spend money on it.
And every decision can be understood on a case-by-case basis.

No, not every decision can be understood.
That would imply that all were real choices and carefully considered.

Christian 65 schrieb:

Out of about 400 property buyers I have advised over the last 25 years, the main question for a large proportion was:
Can I afford this?

In which area did you provide advice?

Christian 65 schrieb:

And for them, savings of around €20,000 can play an important role and lead to choosing a less energy-efficient yet initially cheaper solution.

Ah, so it’s better to pay €1,500 more for electricity every year than to pay €1,500 in loan installments over 20 years and then save significantly after that?

Christian 65 schrieb:

Among the roughly 400 homebuyers I have assisted over the past 25 years, the main question for most was:
Can I afford this?
Not, how can I best save energy.

Is that a contradiction? The financial burden always includes the mortgage payment plus additional costs and reserves. So, you don’t necessarily save anything by keeping the mortgage payment low with the cheapest but inefficient solution, only to pay four times more for heating. Various example calculations have already shown that even in relatively inexpensive cases, the savings from underfloor heating are offset over the next 15–20 years by electricity costs. In the end, nothing is saved; the expenses are just shifted to another category.

profil65 schrieb:

The crystal ball says that in 20 years, there might be much better and cheaper photovoltaics that deliver significantly more electricity under unfavorable conditions. And there might be affordable, efficient electrical storage systems worth installing, as electricity rates can vary significantly depending on supply...

That’s a different matter. If affordable photovoltaics become available in 20 years, I can always install more on the garden shed and carport. If they tolerate shade well, even on the north side. The current photovoltaics on the south side should still be generating electricity then. And a battery storage system could still be added later for relatively low cost.
From an energy standpoint, we are slowly reaching the physical limits. You can’t have less than zero heating demand. Considering that many buildings from 1970 start at around 300 kWh/sqm (30,000 BTU/sqft), the current 25–45 kWh (2,500–4,500 BTU/sqft) are already very low. Slightly less than that puts you in passive house territory (depending on the exact definition). Then, waste heat from the stove, TV, occupants, etc., is enough to keep the house warm. This range also shows why the "future-proof house" from 1990 with 120 kWh (12,000 BTU/sqft) represented the typical technology level at the time but was far from the theoretical optimum.

kati1337 schrieb:

When we built our first house, we were concerned about this too, but now (after having observed the installation) – what could happen to underfloor heating that is completely embedded in the screed? Specifically regarding the pipes? If a pipe in the screed does break (which is unlikely), usually homeowner’s insurance covers such damage.
I see the risk mainly with the pump or similar components, which are located above the floor and can be replaced.

I would be less worried about individual suppliers – if the window heating system becomes widespread, there will likely be more providers in 20 years.
Choosing window heating carries the risk that switching later to a system with underfloor heating might involve significant costs. Therefore, it might be more interesting for renovations than for new builds. Often in existing buildings, the problem is that underfloor heating is not installed. Retrofitting it is expensive.

Underfloor heating pipes undergo constant expansion and contraction—only by a few millimeters, but over the years, leaks can develop. Pumps, compressors, and valves are naturally more vulnerable and require more frequent replacement. These parts aren’t necessarily expensive themselves, but the replacement can easily cost around 800 to 1,000 € (approximately 870 to 1,090 USD). This always needs to be taken into consideration.

What interests me about your cost breakdown is how much you pay annually for maintenance.

Why would a customer want to switch from window heating to underfloor heating? What would be the point? But no matter. I’m about to finish the calculations for the example house provided by Rotormotor. Take a look at it—maybe then it will be clearer what I’m trying to demonstrate.

WilderSueden schrieb:

Is that a contradiction? The costs always include the loan installment plus additional costs and reserves. So, you don’t necessarily save anything by keeping the installment low with the cheapest but inefficient solution, only to have four times higher heating costs. Various example calculations here have already shown that even in relatively affordable cases, the savings from a window heating system over the next 15-20 years are offset again by the electricity costs. In the end, nothing is saved but just shifted to another category.

That’s different. If a cheap photovoltaic system becomes available in 20 years, I can still install more on the garden shed and carport. If it is very shade-tolerant, also on the north side. Today’s photovoltaic panels on the south side will likely still produce electricity then. And the battery storage could still be retrofitted later at low cost.
From an energy perspective, we are slowly reaching the physical limits. Less than zero heating demand is simply not possible. If you consider that many buildings from 1970 have around 300 kWh/m²a and today’s 25-45 kWh/m²a are already very low, going a bit lower would mean reaching the Passive House standard (whatever exact value you consider as the threshold). Then the waste heat from the stove, TV, occupants, etc. is sufficient to keep the home warm. This range also makes clear that the "future-proof house" from 1990 with 120 kWh/m²a may have represented the usual technology of that time but was far from the theoretical optimum.

I will try to explain it simply:
Basics from RotorMotor:
150m² (1615 ft²) with 40 kWh/m²a (12,900 kWh/year) → 6,000 kWh/year heating energy demand / electricity price 35 cents/kWh / 4 occupants (assumed)
What was forgotten? → Hot water (produced by the heat pump as well) → 4 occupants approx. 2,000 kWh (rounded up to 12.5 kWh/m²)
House electricity for 4 people → approx. 4,000 kWh
Users thus need energy for space heating (6,000 kWh), hot water (2,000 kWh), and household electricity (4,000 kWh). All approximate!
Together, this adds up to about 10,000 kWh of energy annually for the house mentioned above.

Heat pump system
Total cost including everything → €40,000
This is the basis for the following calculations.
Seasonal performance factor (SPF) → I’ll assume 4.

System with heat pump
Space heating 6,000 kWh / 4 = 1,500 kWh
Hot water 2,000 kWh / 4 = 500 kWh
House electricity 4,000 kWh
Annual energy demand for the house = 6,000 kWh
Annual energy cost 6,000 kWh x $0.35/kWh = $2,100

System with window heating, hot water heat pump (HPWHP), and photovoltaic
Space heating 6,000 kWh with window heating (€10,000)
Hot water with HPWHP (SPF = 4) (€5,000) = 2,000 kWh / 4 = 500 kWh
Annual energy demand for the house = 10,000 kWh
Annual energy cost 10,000 kWh x $0.35/kWh = $3,500

Oh no 😕 you are all right! Our system costs $1,400 more per year!

Or? What haven’t I considered yet? → Out of the €40,000 investment, €25,000 remain.
This allows for a 15 kWp photovoltaic system, which under poor conditions produces around 13,000 kWh annually.
So, already 3,000 kWh more than the house’s calculated annual consumption → plus-energy house.

What happens to the 13,000 kWh?
The HPWHP needs energy all year, fully covered by the photovoltaic system → 500 kWh
The heated windows require 6,000 kWh, but perhaps only about 1,500 kWh are covered by the photovoltaic system in winter.
About 50% of household electricity, i.e., 2,000 kWh, is covered by the photovoltaic system.
So, in total, 4,000 kWh of the photovoltaic system’s electricity goes to the house at zero cost ($0.00/kWh).
The user therefore still needs to buy 6,000 kWh per year.

At this point, both systems are even. What did I still forget?

Ah yes – from the 13,000 kWh, 13,000 kWh – 4,000 kWh = 9,000 kWh remain.
Currently, these have a guaranteed tariff of €0.086/kWh (8.6 cents/kWh) for 20 years from the government (Renewable Energy Act feed-in tariff).
The market value of this electricity was about $0.32/kWh in July 2022 — good for direct marketers.

Back to the example house above. 9,000 kWh x €0.086/kWh = €774 feed-in remuneration per year.
The house with Vestaxx window heating thus saves about €774 per year in energy costs compared to the house with a heat pump.
With this money, the user can buy €774 / $0.35/kWh = approx. 2,200 kWh.

This and nothing else is what I am trying to demonstrate continuously here.

RotorMotor schrieb:

Vestaxx GmbH schrieb:


I’m trying to keep it simple but calculating a bit differently than RotorMotor:
Basics from RotorMotor:

150m² (1,615 sq ft) with 40 kWh/m² per year -> 6000 kWh/year heating energy demand / electricity price 35 cents/kWh / 4 people (assumed here)
What was forgotten? -> Hot water -> 4 people approx. 2000 kWh (according to the building energy regulation 12.5 kWh/m², rounded up)
Household electricity for 4 people -> approx. 4,000 kWh

So users need energy for space heating (6000 kWh), hot water (2000 kWh), and household electricity (4000 kWh).
Together that’s 10,000 kWh energy per year for the house mentioned above.

Heat Pump System
Costs including everything -> €40,000 and this is the basis for the further comparison calculations.
Coefficient of Performance (COP) -> I’ll calculate with 4 here. (I could also use 10 – it would hardly make a difference)

System with Heat Pump
Space heating 6,000 kWh / 4 = 1,500 kWh
Hot water 2,000 kWh / 4 = 500 kWh
[U]Household electricity 4,000 kWh
Annual energy demand of the house = 6,000 kWh
Annual energy cost 6,000 kWh x $0.35/kWh = $2,100

System with Window Heating, WWHP and Photovoltaics
Space heating 6,000 kWh with window heating (investment = €10,000)
Hot water with WWHP (COP = 4) (investment = €5,000) = 2000 kWh / 4 = 500 kWh
Household electricity 4,000 kWh
Annual energy demand of the house = 10,500 kWh
Annual energy cost 10,500 kWh x $0.35/kWh = $3,675

Crap 😕 you’re all right! Our system needs $1,575 more per year!

Or? What have I not considered so far? -> There is still €25,000 left for investment.
That covers a 15 kWp photovoltaic system, which under poor conditions produces around 13,000 kWh per year.
So already 3,000 kWh more than the house’s energy consumption annually -> Plus-energy house

What happens with the 13,000 kWh?
The WWHP needs energy all year, fully covered by photovoltaics -> 500 kWh
The heating windows require 6,000 kWh, but maybe only about 1,500 kWh is covered by photovoltaics in winter.
About 50% of household electricity, so 2,000 kWh, is supplied by the photovoltaic system.
So, together 4,000 kWh from the photovoltaic system are used in the house at zero cost.
The user still needs to purchase 6,500 kWh per year.

At this point, both systems are roughly equal. What else have I missed?

Oh yes – from the 13,000 kWh, 13,000 kWh - 4,000 kWh = 9,000 kWh remain.
Currently, there is a guaranteed feed-in tariff of 8.6 cents/kWh for 20 years from the government (Renewable Energy Act compensation).
The market value of this electricity was about 32 cents/kWh in July 2022 – good for direct marketers.

Back to the example house above. 9,000 kWh x $0.086/kWh = $774 feed-in revenue annually.
The house with Vestaxx window heating therefore has about $774 less energy costs per year than the house with the heat pump.
With that money, the user can buy 774 / 0.35 = about 2,200 kWh.

This and nothing else is what I try to represent here continuously.

Sorry – I made a small mistake above – forgot 500 kWh for WWHP, but it doesn’t affect the overall picture.

… and now you can try calculating the above with a COP of 10 and/or an electricity price of, say, 50 cents/kWh.
The heat pump house will never become a plus-energy house and amortization no longer applies.

The main advantage is the photovoltaic system and looking at the overall energy balance!
The house above has 40 kWh/m²/year, which today in new builds goes down to about 25 kWh/m² and below.
Maintenance costs for the heat pump and possible component replacements were not considered.

It would be even better with direct electric heating compared to a heat pump.

Oh man, it’s the same nonsense again about justifying an inefficient heating system through photovoltaic panels...

Instead of addressing my calculation directly, it’s suddenly being ignored that a photovoltaic system is also used with the air-to-water heat pump, even though we had already agreed that it always makes sense.
It would be just like saying: I have 25,000€ (about $27,000) left over and will buy an electric car to save thousands in diesel fuel.
That’s nonsense! Such investments must be evaluated separately and strictly.

It’s a cheap trick to keep pretending that you can only afford a photovoltaic system if you use direct electric heating.
With every message, this approach makes the company less credible to me!