ᐅ Vestaxx window heating – experiences?

Just to be clear, I prefer underfloor heating in general.
In previous posts, I mentioned that with a heat pump, much of the system technology for hot water is already included.
I would always build a heat pump combined with a large photovoltaic system because I can afford it.
I do not want infrared heating, window surface heating, or warm air heating.
I don’t have to sell anything or promote anything as healthy.
But the fundamental statement that it is better to invest in energy generation than in energy saving—I do believe that.
It’s great for those who can do both.

RotorMotor schrieb:

I just don’t understand how anyone can say heat pump OR photovoltaic.

Photovoltaics should always be installed first, and then you decide whether to heat with an air-to-water heat pump, ground-source heat pump, direct electric heating, etc.

It’s quite simple – because we don’t say that!!! We say heat pump for 40,000 € or direct electric heating with photovoltaics combined with an air-to-water heat pump and possibly a battery, also for 40,000 €. Then calculate the annual costs for each system. Actually very straightforward.
Give me the parameters you can define, and I’ll gladly do the calculation. Not everyone here can, but everyone can review my calculation and point out any mistakes in the analysis, if there are any. 😉

Photovoltaics always make sense – that’s true. But they’re not free. That means maybe heat pump + photovoltaics = 60,000 €. Worthwhile? Definitely yes. But then you need to have 60,000 € available. And you have to look at the full cost calculation – then the kWh price could increase again.

Christian 65 schrieb:

Perhaps there was a temptation to attract interest using the buzzword “energy saving.”
In this case, that isn’t even true.
If the less catchy phrase “energy generation versus energy saving, which makes more sense” had been used,
the petty calculations would have been unnecessary.

By the way:
Twenty years ago, I thought it was a good idea to irrigate my garden with a 12m³ (420 ft³) cistern.
The investment was €6,000.
For a quarter of that amount, I could have also drilled a well.
Stormwater discharge fees amount to €1.50 per square meter (10.7 sq ft) of sealed area x 200 m² (2,150 sq ft) = €300 for the roof surface.
Savings with the well: €4,500
Annual discharge fee: €300
Payback period: 15 years without interest.
Clever??

Where in this context did I use the word “energy saving” for the system I presented???
Saving money is correct, and generating more energy than is saved by the heat pump is also correct.

Suggestion:
Provide me with new build parameters (living area in m², specific heating demand in kWh/m², number of occupants, and optionally various electricity prices), and I will calculate the household’s energy costs in a simple and transparent way. You are welcome to review the calculations and point out any errors. That’s all I can offer for now.

Christian 65 schrieb:

Just to be clear.
I generally prefer underfloor heating.
I mentioned in previous posts that with a heat pump, much of the system technology for domestic hot water is already included.
I would always build a heat pump combined with a large photovoltaic system because I can afford it.
I don’t want infrared heating, window panel heating, or warm air heating.
I don’t have to sell anything or justify anything as healthy.
But I do believe the basic statement that it’s better to invest in energy generation than energy savings.
Nice if you can do both.

Now I’m with you and congratulate you on being able to afford a heat pump with photovoltaics—I truly wish you all the best with that. I have mentioned several times that this system is excellent. But not every building family can afford it, and that’s why we offer a solution. It doesn’t rely on wishful thinking—it calculates facts that anyone can verify.
Here’s the offer again: Give me the parameters of your new single-family home build, and I will calculate everything clearly. Then anyone can have a look and try to find faults (if they can). 😉 I notice that not many feel confident about the calculations. It’s not easy, but anyone can follow the logic. So my offer still stands.

The problem with the calculation is that it relies on too many assumptions. How efficient and large is the house? A small one built to EH40 standard will have a different calculation than a larger building constructed according to the building energy law. At least for underfloor heating, the costs do not increase linearly with the area. An EH40 house is also more expensive compared to one built to the building energy law standard, so what price is being factored in for that? Looking at what has been charged for upgrades in our area, it’s quite surprising. Especially if you want to market a system based on price, it’s difficult to assume a high energy standard. It might actually be cheaper to build according to the building energy law and then use photovoltaic panels and a heat pump instead of EH40 with electric heating and photovoltaics.

What is a realistic COP? For new builds, you should probably expect more than 3.5 in most cases, except perhaps in areas like the Black Forest highlands or similar. At our altitude of 660 meters (which is already above average for Germany), that value should still apply.

Then there is the part that gives me the most trouble in making a useful assumption...there are day and night cycles, weather conditions vary daily, and solar gains (which reduce heating demand) and electricity from photovoltaics are strongly correlated. For all three factors, I have to apply a deduction to the photovoltaic yield, and probably a significant one. In winter, it’s dark for longer than it is light, and with three days of fog, you still need heating. During these periods, photovoltaics effectively provide no benefit. And especially a large system quickly produces surpluses on mild, sunny days. Simply subtracting 100% of the photovoltaic yield from heating electricity is definitely not correct—but what exactly should be assumed? That also depends again on the specific system size, the energy standard, the house size, and personal decisions such as the size of the window fronts.

Lastly, the question of electricity price. Two years ago, 30 cents per kilowatt-hour was assumed, and it was thought prices would remain stable for the coming years. Today, we’re just hoping prices still start with a 3, and it’s completely unclear where they will go in the next few years.

WilderSueden schrieb:

The problem with the calculation is that it relies on too many assumptions. How efficient and how big is the house? A small one rated EH40 will have a different calculation than a large one built to the Building Energy Act standards. At least for underfloor heating, costs don’t increase linearly with the area. An EH40 house is also more expensive compared to the Building Energy Act version—what price is being factored in for that? When I look at some of the upgrade costs we’ve seen, it’s quite shocking. Especially if you want to market a system based on price, it’s hard to assume a high energy standard because it might actually be cheaper to build according to the Building Energy Act and then use photovoltaic panels and a heat pump, rather than EH40 with underfloor heating and photovoltaics.

What COP is realistic? In new builds you should generally expect more than 3.5, except maybe in places like the High Black Forest and similar regions. We are at 660m (which is already above average for Germany), so that value should still apply.

And then the part I find hardest to make a sensible assumption about… there is day and night, weather changes from day to day, and solar gains (which reduce heating demand) and photovoltaic electricity production are strongly correlated. For all three aspects, I need to apply a significant reduction to the photovoltaic yield. After all, in winter there is more darkness than daylight, and with three days of fog you have to keep heating. During those times, photovoltaics practically do not contribute. And a large system will quickly produce surpluses on mild, sunny days. Simply deducting 100% of photovoltaic output from heating electricity demand is definitely not accurate, but what exactly to do? That again depends on the system size, energy standard, house size, and also personal choices like the size of the window front.

And finally, the question of electricity price. Two years ago, 30 cents per kWh was used and assumed to be stable for years. Today we’re happy if prices start with a 3, and it’s completely unclear where they will go in the coming years.

I understand all that, but you’re overcomplicating things here. If you don’t start with even a basic calculation, you can’t make informed decisions. Where else would the interested customer get their decision-making basis for a heat pump system? Just going by gut feeling and because it’s trendy isn’t sensible.

I suggest you simply provide appropriate values based on the parameters I mentioned, and I will create a straightforward, easy-to-understand overview calculation. Then you can comment where you think something doesn’t fit. Give it a try.

For now, I’ll do just one calculation: the annual energy costs the house—or better, the occupants—have to bear. This will be without interest, inflation, maintenance costs, etc. Let’s look at this together and evaluate it.

If we—maybe later—move on to a full cost calculation according to VDI 2067, it will become clear that the two systems differ by a factor of 2 to 3!!! That’s really striking! At that point, the uncertainties you mentioned above no longer have much impact. It basically comes down to one parameter that significantly influences the systems. Nobody really has that fully in mind, even though it’s extremely important and obvious for everyone. But I don’t want to get ahead of myself here.