ᐅ Mechanical Ventilation with Heat Recovery during a Major Fire / Mechanical Ventilation with Heat Recovery on a Summer Night

Hello,

We are planning to install a central mechanical ventilation system with heat recovery in our new build. I have a few questions regarding this:

1. Sometimes in traffic reports, it is advised to keep windows and doors closed due to a large fire in the district. How does a mechanical ventilation system behave in such a situation? Can it be switched off and sealed completely against outside air? Is the incoming air monitored or tested in any way? Could someone (e.g., an intruder) deliberately introduce harmful gases or anesthetic gases into the house through the supply air?

2. During summer nights when it is cooler outside but the house is still warm from the day, I would prefer not to warm the fresh air through the heat exchanger. Is it possible to bypass the heat exchanger for the exhaust air in such cases?

I look forward to your answers and hope I have not caused anyone concern with the idea of external poisoning.

Best regards,
Fokko

If your neighbor is burning plastic in their chimney, you should also turn off your heating system.
Toxic gas is now more of an exception.

watislav schrieb:
So someone (for example, a burglar) could deliberately let toxic gases or anesthetic gases into the house through the fresh air intake.

Forget the impressions that American TV might give you. The reality is different—unless you are under the surveillance of state security, where the perpetrators are a bit more patient waiting for their target 😉

Regarding point 1: A bit paranoid? It’s possible, but it actually happened to me once.

Regarding point 2: The system should have a heat recovery bypass, and possibly also a ground heat exchanger.

Hello.

Here are my experiences:

1.) In our system, the supply air can be turned off. However, this is only possible if the chimney control within the system’s controller is disabled. That means if you have a fireplace, this would not be advisable and could even be dangerous.

2.) Yes, possible with a bypass circuit.

Normally, ventilation systems of this size do not include a damper. Of course, such dampers exist but they come at an additional cost.
For larger units, they are installed because these usually include heating and cooling coils operated with water or a glycol-water mixture.
In case of a heating shutdown during low outside temperatures, the water in the coils could freeze and cause damage. (Even when the fans are off, some air circulation still occurs.)

The extent to which the bypass function supports night cooling in summer depends on the device’s settings.
Since I work in development for a manufacturer of such systems, I am planning the following for my own installation:
Controlled residential ventilation with an enthalpy heat exchanger and bypass (obviously)
Electric preheating coil to prevent freezing
Water-based post-heating coil designed for the supply temperature of the underfloor heating
Additionally, the heat pump can also operate as a cooling system and would then cool via the post-heating coil.
Overall, this would be a custom-built solution, which would be quite expensive for a typical customer.