Controlled residential ventilation - frost protection and ground heat exchanger

Hello,
our controlled residential ventilation planning is moving into the next phase...

In a meeting with the planning office, it was mentioned that frost protection for the heat exchanger should be planned – I understood the reasons and causes for this.
Note: A gas boiler with underfloor heating will be used as heating, which is also responsible for the hot water.

Now unfortunately there are several methods to deal with this, the list is certainly not complete...

[*]Schedule the ventilation so that no icing occurs at too low temperatures (no additional investment costs, no ongoing costs)
[*]Install an electric preheater (about 1,500 watts) (additional investment costs approx. €400, ongoing electricity costs)
[*]Use the heat exchanger with the gas heating (additional investment costs approx. €1,000, low? ongoing costs for additional gas consumption)
[*]Install an air-ground heat exchanger (sucking air through pipes in the ground), additional advantage is slight cooling function in summer (additional investment costs of > €3,000 at Helios, almost no ongoing costs)
[*]Brine-ground heat exchanger (pumping cooling/heating fluid through the ground to preheat/cool) (additional investment costs of > €2,000 at Helios, ongoing costs for pump operation)

I just wonder: Which alternative is the "right" one?

I am still missing information / good links on alternative (3), I really couldn’t find anything.

If there is not much against (3), I find it the "most reasonable" solution because:
- the ventilation system creates a negative pressure in the house and the missing air comes in through the cracks
- generating heat with electricity is inefficient
- the investment costs for the ground heat exchangers put me off

What do you think??

Many thanks and sunny greetings from Hamburg – J

As a layperson, I do not know why icing can occur in the ventilation. I suspect it happens when the moist air from inside is blown out and cooled in the process. Regarding 1). If it is that cold, then the incoming air is very dry; maybe less air is needed to remove the moisture? Regarding 2) I wonder – isn't that a bit oversized? After all, it makes no sense to put more into the heating than the amount of heat you can recover?!