ᐅ Building a Single-Family Home in North Rhine-Westphalia

Alex85 schrieb:
The calculation is fundamentally wrong. The savings come from the thermal energy recovered from the air ventilated out of the room. With an open window, 100% of this energy is lost, and heating is necessary to compensate. A mechanical ventilation system with heat recovery returns 84%, or even more depending on the model, of the thermal energy back into the room.
However, this has nothing to do with the approximately 1.2 kWh of electricity needed to run the mechanical ventilation system for one day.

Of course, the calculation is fundamentally wrong, but in so many ways that, simplified, it ends up being correct again.

Where is the difference whether I use x amount of energy to blow air around or use x amount of energy to reheat cold air? x energy is and remains x energy. Heat recovery does not change that. The energy is consumed in both cases.

With the costs mentioned above (300–350 euros), I can heat my house (without mechanical ventilation).

The electricity required to power the controlled ventilation fan has absolutely nothing to do with the heat energy recovered through the heat exchanger. Your statements are fundamentally incorrect and not even slightly correct in any way.

It would be like saying the electricity used to operate a gas boiler’s control system heats the house, or that the starter motor of your car accelerates the vehicle to 100 km/h (62 mph).

The comparison is seriously flawed. Even the electricity used to start a car originally comes from gasoline. And you need gasoline to power the vehicle. So, you actually need a total amount of gasoline for the trip from A to B, including starting the engine. But let's leave that aside.

The issue is the amount of energy required to heat a house for one year.

Case 1 (with mechanical ventilation with heat recovery):
1500 kWh heating
500 kWh mechanical ventilation with heat recovery

Case 2:
2000 kWh heating

Now please tell me (based on this limited information) which house is "energetically/environmentally/economically better" (ceteris paribus).

I cannot, because both houses consume the same amount of energy. This is what I have been trying to point out here for hours.

The equation is still incorrect. The supplied auxiliary energy has no direct correlation with the recovered heat energy, so your statement is nonsense.

The question is whether mechanical ventilation with heat recovery saves heating costs compared to window ventilation. What you have been doing for hours is off-topic.

andimann schrieb:
50 watts running 24/7 adds up to about 110 euros in electricity costs per year. Plus the cost of changing the filters twice a year, we easily reach 200 euros annually.

Add financing costs of 100-150 euros per year (around 10,000 euros financed at 1-1.5%).

This results in total costs of roughly 300-350 euros per year.

Filter costs for 4 filters each of F7 and G4, if you buy an empty frame and the filters separately: 25 euros per year (quarterly filter change). I just took the first available offer on Amazon; there may be cheaper filters.

A mechanical ventilation system with heat recovery has an annual performance factor (seasonal efficiency) of about 15 to 20. For every 1 kWh of electricity consumed, you get 15 to 20 kWh of heat back.

Consumption is about 35 watts per hour, which corresponds to 306 kWh per year. Savings are therefore approximately 4,599 to 6,132 kWh. This aligns well with the practical experience that with a mechanical ventilation system with heat recovery, you can reduce the heating capacity by at least 2 kW (with a heat pump).

At a gas price of 4.82 cents per kWh as in our case, that means savings of 221.67 to 295.56 euros per year.
Electricity costs: 306 kWh x 26.54 cents (relatively expensive in our area) = 81.21 euros.

Electricity 80 euros, filters 25 euros, and financing 150 euros total 255 euros, meaning the system more than pays for itself at current prices and saves money as prices rise. Comfort, time savings, better indoor air quality, and more come free as added benefits.

In our case, the mechanical ventilation system also made solar water heating unnecessary. So we saved around 5,000 euros here (otherwise at least 3 solar collectors would have been needed).

Not to forget, those who heat with an air-to-water heat pump pay significantly more than 4.8 cents per kWh of thermal energy.

Caspar2020 schrieb:
Typically, 10-20% of the energy losses in a standard house are caused by traditional ventilation.

In a typical older house with double glazing and poor window frames, uninsulated walls, poorly insulated roof, etc., this 20% figure is accurate. However, in a modern house built to the 2016 energy-saving regulations standard, with maximum insulation but still relying on normal window ventilation, energy losses due to ventilation are at least 30%, and can be as high as 50%.