ᐅ Ground Heat Exchanger Connected to Mechanical Ventilation with Heat Recovery in New Construction

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

However, I often read about hygiene issues with air-to-earth heat exchangers, such as condensation and dirt buildup in the ducts.
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 in midsummer, cooling is then simply done through the underfloor heating system?

Best regards

Hello,

We installed about 40 meters (130 feet) of KG2000 pipe with a diameter of 200 mm (8 inches) as an air-to-ground heat exchanger in our garden. The pipe has a smooth interior and is laid with a slight slope toward the house so that condensation can collect and drain away.

The first F7 filter is, of course, positioned at the outdoor air intake, ahead of the ground heat exchanger. Otherwise, it would quickly become clogged.

You can definitely notice a significant effect. Don’t expect real cooling, but during the peak of summer, instead of bringing in air at +35°C (95°F), you get air at about +22°C (72°F), which at least prevents the house from heating up further. Some moisture also condenses out of the air when it cools from 35 to 22 degrees.

In winter, you can do without a preheating coil or similar devices. Even at very low temperatures of -15°C (5°F), the air reaching the house is still above freezing.

So far, it’s working really well for us.

Best regards,
Andreas

For hygienic reasons, I personally would not install something like that. The advantage is very small since a central mechanical ventilation system with heat recovery always has a heat exchanger that recovers heat in winter and, correspondingly, “cools” in summer. This means that hardly any heat enters the house through the ventilation system even in summer. The humidity also condenses in the heat exchanger accordingly.

So, you can barely reclaim any heat through a pipe in the ground, and you might even risk bringing mold and other issues into the house.

Cooling via underfloor heating works very well for us!

Hello,

RotorMotor schrieb:

which recovers heat in winter and likewise "recovers cold" in summer.

“Recovering cold” only works to a limited extent because a heat exchanger can never fully balance out the temperature differences.

In summer, let’s say the indoor air is 24°C (75°F) and the outside air is over 30°C (86°F). The heat exchanger can then "cool" the incoming air to maybe 25–26°C (77–79°F), but there is still a net heat gain inside. If you can use your underfloor heating system for cooling, however, this will no longer be a crucial issue.

But what happens if in winter you intake air at –10°C (14°F)? Doesn’t the heat exchanger freeze? I didn’t want to install a pre-heating coil back then.

Best regards,

Andreas

andimann schrieb:

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

In summer, the indoor air is, say, 24 degrees Celsius (75°F), while the outdoor air is over 30 degrees Celsius (86°F). The heat exchanger might then "cool" the supply air to around 25-26 degrees Celsius (77-79°F), but there is still a positive heat gain inside the house.

I checked this for myself last summer. Your figures roughly match. But with 24 degrees Celsius (75°F) inside and 25 degrees Celsius (77°F) supply air, we are talking about a delta T of just one degree Celsius (2°F)!

At 150m³/h (88 cfm), that corresponds to a heating capacity of 50 W. 50 watts spread throughout the whole house. A person present generates significantly more heat than that.
With a delta T of two degrees Celsius (4°F), it would be 100 W.
By comparison, the cooling capacity of the underfloor heating system at that moment was over 3500 W.
So even if the ground heat exchanger could eliminate that one degree Celsius delta T, the effect would be imperceptible.

andimann schrieb:

But what happens in winter when you intake air at -10 degrees Celsius (14°F)? Doesn’t the heat exchanger freeze up?

I have a preheating coil for that. It works without any problems.

andimann schrieb:

I didn’t want to install a preheating coil back then.

Why not?

Thank you for your constructive and respectful exchange of arguments. This is not something you can take for granted in this forum.