Mechanical Infiltration Ventilation
As you know, my house is a humidity trap! The major issue was the rising damp in the soil, which seeped up through capillarity in the walls and floor. Fortunately, with the insulation we installed in the flooring, it seems to be much better now.
Additionally, as with most homes, we faced a lot of condensation during the winter due to indoor air being saturated with moisture from normal activities like bathing and cooking.
Because construction standards in Portugal are generally poor, with inadequate insulation and significant thermal bridges, there are drastic temperature differences between the inside and outside, causing humidity in the air to condense near the ceilings, windows, and many walls!
We make improvements by changing to more airtight windows and adding thermal insulation to the house, and suddenly we have even more humidity indoors! This happens because we neglect a crucial element in controlling humidity: air ventilation.
By making the house more airtight, the saturated air has no way to escape and ends up accumulating in cold spots and on objects made of natural materials or prone to mold.
After trying everything and seeking countless solutions, I discovered MVHR (Mechanical Ventilation with Heat Recovery), which involves a device that inflates outdoor air into the house through a system of ducts. In our case, it’s installed in the attic, but it can also be installed in false ceilings, for example.
The incoming air is transported through ducts and is blown through three air outlets in the ceiling. Two of these outlets are located in the center of the house (corridor), and one is in the corner of the living room, strategically placed for the system to be efficient and fulfill its purpose: bringing in fresh outdoor air, filtering pollutants, and blowing it into the interior to clean and push out the saturated air through small grilles installed in window boxes or frames. This positive pressure allows for the evacuation of indoor pollutants, humidity, and CO2.
On colder days, the device preheats the incoming air to avoid cooling the indoor temperature or to maintain the defined comfort temperature. On warmer days, it performs night-time hyperventilation to cool the house. The system has a sensor that controls this automatically, so you don’t need to worry. In terms of maintenance, you need to replace the filter when the system indicates that it’s full (I would say about twice a year, but it depends on the location and external conditions).
To work effectively and reach all rooms, it’s important to keep interior doors open to ensure proper ventilation. This is where we had an isolated case of mold on the frame and dried flowers I showed you. They were in the office, a room we don’t use much, and we often closed the door to avoid heating it or wasting heat for that area. This resulted in an accumulation of humidity due to a lack of ventilation in natural materials.
This was the proof that this was undoubtedly one of the best investments we made because we significantly reduced the humidity in our home, and the air feels less heavy, drier, and healthier.
In addition to MVHR, there are other solutions like Mechanical Ventilation with Centralized Exhaust (VMC), which, in my opinion, is better for new construction as it requires more space for duct installation and more outlets, which can be challenging to implement in a renovation, especially if you’re living in the property.
VMC uses ducts to extract saturated air from wet areas like the kitchen and bathrooms and to blow in clean air into other areas of the house, such as the living room, corridors, and bedrooms. This involves having an inlet/outlet in each room and, if planned from the start, can be very efficient. In most cases, this system has a heat exchanger that transfers heat between the outgoing and incoming air, eliminating the need to heat incoming air using an electric resistance, as in MVHR. It’s a more expensive system but also more energy-efficient.
It’s increasingly important to have good indoor air quality in our homes and in all kinds of buildings. Therefore, I would say that this type of system should be considered when renovating or building a house, if you have the opportunity to do so. For example, in a Passive House, having this equipment is essential, unlike air conditioning equipment, which is optional.