ᐅ How can you tell when the mechanical ventilation system is working properly?

One00 schrieb:
In an air-to-air heat exchanger, the heat transfer can theoretically only occur up to the point where the supply and exhaust air temperatures are nearly the same, right? That would be the case at 5 degrees Celsius with the parameters mentioned above.

Is the supply air temperature measured at the outlet (which, at such low outside temperatures, is naturally significantly higher due to further heat absorption inside the building envelope than directly behind the heat exchanger) or directly behind the heat exchanger?

Hello.

Here is an excerpt from a manufacturer’s product description. The mechanical ventilation system should be certified for passive houses (which I believe most are):

"...To obtain the Passive House certificate, a demanding testing procedure must be passed. The ventilation unit must be able to achieve a minimum supply air temperature of 16.5°C (61.7°F) without additional heating, even with an outdoor air temperature of -10°C (14°F). This is important because passive houses do not require additional heating surfaces on external components. Therefore, the supply air temperature must be limited from below to avoid uncomfortable drafts of cold air. Additionally, the total electrical power consumption of the ventilation unit in the operating modes intended for passive houses must not exceed 0.45 W/(m³/h) (watts per cubic meter per hour) of supplied air volume flow. ..."

Best regards

Hello,
how do they manage if additional devices (e.g., heating element) as described in the text are not allowed? It can’t work properly just by air bypass between supply and exhaust air...
Although it is called a heat exchanger, it’s not like the temperatures of the supply and exhaust air are simply "exchanged," and the supply air after the heat exchanger nearly reaches the exhaust air temperature.
Without electrical or similar reheating, this is a mystery to me.

@ Cascada

What you describe is, in my opinion, the only acceptable "heating system" for passive houses. If installed in conventional house construction, you can expect a high electricity bill at the end of the year.

Therefore, it is only partially comparable with the controlled residential ventilation with heat recovery discussed in this thread.

Regards, Bauexperte


Bauexperte, posting while on the go

Bauexperte schrieb:
@ Cascada

In my opinion, what you describe is the only acceptable "heating system" for passive houses. If installed in conventional house construction, you can expect a very high electricity bill.

Therefore, it is only partly comparable with the controlled ventilation system with heat recovery discussed in this thread.

Regards, Bauexperte


Bauexperte, on the go

Hi,

For 2013 (January 1 – December 31), I paid well under €500 for my ground-source heat pump (about 2200 kWh). Not a passive house, but KfW 70 standard – and in a very cold region. The supply air temperature of the controlled ventilation system was never in the single-digit Celsius range during winter. At –20°C (–4°F), of course, I don’t know exactly, since the supply air is strongly reduced then (no electric preheater).

Best regards

Cascada schrieb:
Hi,
...The supply air temperature of the controlled residential ventilation system never fell into the single-digit degree range during winter...
Regards

Hello Cascada,
Directly behind the heat recovery unit or at the outlet in the living area? Those are two very different things.
Regards,
100

One00 schrieb:
Hello Cascada,
directly behind the HRV unit or at the outlet point in the living area? Those are two very different things.
Regards,
100

If you look at the layout and the airflow rates of the supply and exhaust ducts, it should be clear that there is no significant temperature difference inside the ducts between the heat recovery ventilation (HRV) unit and the air outlet. Nevertheless, the fresh air at the room outlet has temperatures noticeably above the ‘average temperature’ between indoor and outdoor air—simply because a heat exchanger is not just a simple conductive heat membrane where the air in both ducts flows in the same direction.

Many systems call this component a ‘counterflow heat exchanger’ for a reason—the air volumes flow in opposite directions. The inlet duct of the supply air enters the heat exchanger at the end where the exhaust air outlet exits. This means the exhaust air, which has already been cooled down until this point, can still warm up the even colder incoming supply air. The warmed supply air then exits the heat exchanger at the end where the still somewhat warmer exhaust air enters. This results in the supply air being warmed along the length of the heat exchanger by progressively warmer exhaust air.

Regards,
I.