Geothermal heat exchanger for controlled residential ventilation in new construction

Hello everyone,
I am considering installing an air-to-earth heat exchanger in a new central ventilation system for a single-family house under construction. I am interested in whether the increase in comfort and energy savings are really noticeable and measurable in everyday life – for example, noticeably cooler supply air in summer and lower heating costs in winter.

However, there are frequent reports of hygiene problems with air-to-earth heat exchangers, such as condensation and dirt deposits in the pipes.
Does anyone have practical experience or well-founded theoretical knowledge on this?
Is the benefit worth the effort and risk, or would you rather advise against it because modern heat recovery systems are sufficient anyway? And cooling in high summer is then done via the underfloor heating system?

Best regards

Hi,

we installed about 40 m of KG2000 pipe with a diameter of 200 mm in the garden as an air-to-ground heat exchanger. It is smooth inside and laid with a slight slope towards the house so that condensate can be collected and drained there.

The first F7 filter is of course located at the outside air intake and thus before the heat exchanger. Otherwise, it would quickly get clogged.

There is already a noticeable effect. Don’t expect a real cooling function, but in the height of summer you no longer draw air with +35 degrees into the house but only +22 degrees, and with that you at least don’t heat up the house any further. You also extract some humidity from the air by cooling it from 35 to 22 degrees.

In winter, you can completely do without the preheating coil and similar gimmicks. Even in very severe frost of -15 degrees, the air arrives at the house with positive temperatures.

So it works really well for us.

Best regards, Andreas

Well, I wouldn't install something like that for hygienic reasons. The advantage is extremely small, because a central controlled residential ventilation system always has a heat exchanger, which recovers heat in winter and correspondingly "recovers cold" in summer. This means that hardly any heat enters the house through the controlled residential ventilation system even in summer. The humidity also condenses accordingly in the heat exchanger. That means you can only get very little out through a pipe in the ground, and you might potentially bring mold and such into the house. Cooling via underfloor heating works very well for us!

Hi,

the one that recovers heat in winter and accordingly also "recovers cold" in summer.

"Recovering cold" only works to a limited extent because a heat exchanger can never completely balance out the temperature differences.

In summer, the air inside the house is say 24 degrees, the outside air over 30 degrees. The heat exchanger can then maybe "cool" the supply air to 25-26 degrees, but there is still a positive heat input into the house. If you can use your underfloor heating as cooling, however, this will indeed no longer be decisive.

But what happens to you when you suck in air at -10 degrees in winter? Doesn’t the heat exchanger freeze up? Back then I didn’t want to install a preheater.

Best regards,

Andreas

"Recovering cold" only works to a limited extent because a heat exchanger can never completely compensate the temperature differences.

In summer, the air inside the house is, say, 24 degrees, the outside air over 30 degrees. The heat exchanger can then perhaps "cool" the supply air to 25-26 degrees, but there is still a positive heat input into the house.

I checked this for myself from last summer. Your figures roughly fit.
But with 24 degrees inside and 25 degrees supply air, we're talking about a delta T of just one degree!

That is a heating power of 50W at 150m³/h. 50W distributed over the whole house. A person present produces significantly more.
With two degrees delta T it would be 100W.
The cooling capacity of the underfloor heating at that moment was over 3500W for comparison.
So even if the geothermal heat exchanger gets rid of that one degree delta T, the effect would be unnoticeable.

But what happens with you if you suck in air at -10 degrees in winter? Doesn't the heat exchanger freeze up on you?

For that I have a preheater. Works without problems.

I didn't want to install a preheater back then.

Why is that?

Thank you very much for your constructive and respectful exchange of arguments. This is not a matter of course here in the forum.