ᐅ Decentralized ventilation units for larger rooms (older buildings)

Hello everyone,

I have an older building, built in 1976.
Next year, I plan to install triple-glazed windows in several rooms.
The exterior walls have U-values mostly around 0.90, with some individual exterior walls as high as 1.4.

In one room (laundry room), I have been using a Bavarian-style ventilator (ventilation with heat recovery) for about two years, and since then, I have had no moisture problems, even though the window is always closed and sometimes a clothes dryer is running and damp laundry is being dried.

The rooms where the windows will be replaced are quite large.
One room is 66 m² (room volume 178.2 m³ (6291 ft³)).
The other room consists of a main area (living room) with 48 m² (room volume 130.39 m³ (4603 ft³)) and an adjoining kitchen (separated only by a glass door) with about 15 m² (room volume 40.96 m³ (1445 ft³)).

I would like a decentralized ventilation system with heat recovery for both rooms to avoid condensation issues with the new windows and to remove any excess humidity.
This would only replace manual ventilation since I do not want to have to ventilate constantly.

Only my wife and I live in the apartment (2 persons).

I do not want a alternating system but rather a unit with heat recovery and separate fans for supply and exhaust air.

I want to install the units myself (I also installed the Bavarian ventilator).
So, the installation should not be more complicated than the Bavarian ventilator.

The problem is that the house is built on a slope.
I can only exhaust to the front side (valley side), which has fairly large window fronts.
No more than one ventilation unit fits per room, and only if I reduce the size of one window.

In the meantime, I spoke with the company Meltem, and they said that a "heat recovery-II" unit would be sufficient for the living room.
They would recommend an airflow rate of 50 m³/h (about 30 CFM).
For the other room, they actually recommend two units with the same settings.
With the Bavarian ventilator, you generally estimate an air exchange rate of about 0.2 times per hour, so in 5 hours a complete exchange of air occurs.
I can easily achieve this or do it faster with the Meltem device.
The older "heat recovery" model (without II) is about 400.00 Euros cheaper, but the newer device is clearly recommended.
I would go for a version with a humidity sensor and controls.

What do you think?
Two units in one room is a bit difficult.
Maybe additionally window frame ventilators?

Best regards,
Unreal

Hi Unreal,

your approach with triple glazing combined with decentralized ventilation units sounds reasonable, but with your wall U-values, the risk of condensation and mold will likely come more from the wall than from the windows. What you mention about the large window fronts on the valley side raises a fundamental question: how do you plan to achieve balanced air exchange for such large volumes with only one ventilation unit per room? Air distribution throughout the entire room geometry is far from guaranteed in this case; most likely, a kind of "fresh air zone" will develop directly in front of the unit.

What might be left to you besides the traditional alternating units are units with heat recovery, but these quickly reach their limits in large rooms. You should pay close attention to the maximum air flow rate (usually in m³/h) and calculate the actual air change rate (depending on room use). Have you already considered a combination with cross ventilation, for example through trickle vents in the window frame for additional fresh air supply? Or do you plan to keep the air exchange rate so low during continuous operation that the humidity can be reduced evenly throughout the entire room?

Good luck!

Hi, and thanks 🙂

As I already mentioned in the text, I don’t want an alternating device but one with heat recovery.
I’ve also added the cubic meter volumes of the rooms, as well as the suggested (continuous) capacity of the Meltem unit.
Window frame ventilators could be an option, but I believe they only work well if installed on opposite sides of the room?
Unfortunately, that’s not possible because the property is on a slope, and one side is underground.

Best regards,
RealUnreal

RealUnreal schrieb:

I don’t want an alternating device, but a device with heat recovery and separate fans for supply and exhaust air.

You need to separate a lot of half-knowledge here.

1. There are fans that blow air in one direction only. Very "basic" devices.
2. There are decentralized ventilation systems. These can be two types of devices: alternating with heat recovery or with cross-flow heat exchangers.
3. There are central ventilation systems. One device with supply and exhaust air, distributed via ducts to where it is needed.

I am not aware of any devices with heat recovery AND two separate fans. You probably mean decentralized units with cross-flow heat exchangers.

Every online store offers you a free ventilation plan according to your wishes. After that, you can (and must) select the appropriate devices. Units with cross-flow heat exchangers are very rare, as they are significantly more expensive compared to alternating units.

RealUnreal schrieb:

Trickle vents in the window rebate would be an option

, but a pointless one. In that case, you might as well just leave your windows on tilt or drill holes in your walls.

Nauer schrieb:

What might remain for you besides the classic alternating units

, are the classic alternating units WITH heat recovery. Practically no fans without heat recovery are available anymore—only standard exhaust fans (bathroom/WC in older buildings, to remove odors and humidity from showering).

P.S. I have installed and used all of these myself. Currently, I am using decentralized devices with heat recovery from Raumluftshop.

Have you ever seen a decentralized cross-flow heat exchanger like this? The units are huge; I wouldn’t want to spoil the look of my apartment with something like that. Traditional decentralized swing-type ventilators with heat recovery would be ideal for me—you basically only see the grille. Choose a model with a flat grille, and no larger than about 10cm by 10cm (4 inches by 4 inches).
GD

Gerddieter schrieb:

Have you ever seen a decentralized cross-flow heat exchanger like this?

Here’s one measuring about 40 x 60 cm (16 x 24 inches), so the original poster can get a sense of its size.