Significance of geothermal heat exchangers in controlled residential ventilation

Hello everyone!

A quick question about the usefulness of geothermal heat exchangers with a controlled residential ventilation system:

I understand that you should not let cold air into the house and that you should not blow the heat energy of the warm air outside. Heat recovery therefore seems sensible to me, even if it costs quite a bit in investment. Allegedly, up to 90% of the heat is recovered.

So why does a geothermal heat exchanger still make sense? Is it to keep the heat inside even more cheaply? The idea being that the earth warms the -10 degree cold air for free, while the heat recovery system requires electricity. Is it therefore the electricity consumption of the heat recovery system that you want to reduce? Is it worth it?

Or is it mainly about the possibility of being able to introduce cooled air into the house in summer? Usually, one reads that the winter use is the main benefit and summer use is only a small positive side effect.

Best regards

jx7

That is not allegedly but actually the case, I can see it every day based on the temperatures in the air ducts.

The geothermal heat exchanger prevents the system from freezing in winter without an additional heating coil in the intake duct. Without a heating coil and geothermal heat exchanger, the systems usually go into frost protection mode, the bypass opens, and cold air is blown in directly without heat recovery. This causes the house to cool down.

The geothermal heat exchanger ensures constant temperatures and the bypass stays closed.

In summer, you have the opposite effect.

Without a geothermal heat exchanger, the bypass is open again and warm air enters the house, gradually heating it up, even if only minimally, but in addition to the windows, etc., it can get quite warm throughout the entire house.

The geothermal heat exchanger counteracts this because pre-cooled air comes in, keeping the temperature in the house more or less constant.

Thank you for your response, Mycraft!

So I see three possibilities:

(1) Without heating coil, without ground heat exchanger => Higher heating costs when frost protection mode is active and uncomfortable indoor climate due to cold drafts. I will exclude this option.

(2) With heating coil, without ground heat exchanger

(3) Without heating coil, but with ground heat exchanger

(2) probably has lower investment costs compared to (3), but higher operating costs if the temperatures fall below a certain limit.

At what outdoor temperatures should one expect the heating coil to be used? Is there a temperature limit?

The ground heat exchanger is probably more worthwhile in cold regions where this temperature limit is often undershot, and less so in warm regions (e.g., on the Rhine), where this temperature is not often undershot.

Well, you can figure out the temperature limit yourself... I'm just saying as a little help....at what temperature does water freeze?

With an enthalpy exchanger, you can suck in air at -10 to -15 degrees cold - for this reason, I also forego the geothermal exchanger with us and place the system in the attic. For me, it has only had advantages in planning...

And you always have to consider the climate where you live - in the Berlin surrounding area, it gets really cold more often and for longer in winter (ok, except for the last few winters), but here in Münsterland, for example, you can count the deep frost days/nights on one hand per period. If it does get really cold for 2 days, you just turn the system off. For that, I gladly save myself the geothermal exchanger including the existing hygiene issues with incorrect planning of the same.

Or one uses a brine geothermal heat exchanger instead of a geothermal heat exchanger ("Erdregister"), then there are no problems with hygiene.