Column Vol. 4 “The House Also Breathes ‘Intelligently’ — The Optimal Solution of ‘Demand-Controlled Ventilation’ to Prevent Over-Drying and Heat Loss”

Column Vol. 4
“The House Also Breathes ‘Intelligently’ — The Optimal Solution of ‘Demand-Controlled Ventilation’ to Prevent Over-Drying and Heat Loss”

Ono from Wald

In Volume 2, I discussed “windows (DAKO),” and in Volume 3, “insulation (PAVATEX),” explaining how we enhance the performance of the home’s “shell” itself to prevent condensation and control moisture.

By adopting high-performance windows and breathing walls, the “airtightness (C-value)” of the house becomes extremely high. (Note: PAVATEX is permeable to moisture vapor, but not to air.)

In such an “airtight” home, a “ventilation system” is absolutely essential.

The Dilemma of 24-Hour Ventilation

Current Japanese law mandates the operation of a 24-hour ventilation system to counter sick building syndrome, requiring that the entire volume of air in a house be replaced once every two hours.

However, this mechanism of “continuously ventilating the same amount of air 24/7” presents a major dilemma, especially for a high-performance home like those Wald builds.

That dilemma is “excessive dryness” and “heat loss” during the winter.

For example, let’s say in mid-winter the outside air temperature is 0°C (32°F) and the humidity is 30%.

Even if the comfortable indoor air is 20°C (68°F) and 50% humidity, the ventilation system will mercilessly exhaust that warm air to the outside, while continuously bringing in cold, dry air.

What happens as a result?

The heat provided by the heating system is immediately stolen, and at the same time, the room becomes excessively dry. The phenomenon many of you experience in winter—”my throat gets parched when the A/C is on”—is caused not only by the air conditioner itself, but is also heavily influenced by this “over-ventilation.”

Our Solution: “Demand-Controlled” Ventilation

To solve this problem, we are focusing on a “humidity-sensing demand-controlled ventilation system,” born in France, which ventilates “only the amount needed, only when it’s needed.”

“Demand” means “requirement or necessity.”

This system constantly monitors the state of the indoor air and automatically adjusts (controls) the ventilation volume according to the level of air contaminants (especially humidity).

A Simple, Non-Electric Mechanism

The mechanism is extremely simple and rational.

Whereas conventional 24-hour ventilation runs one large fan for the whole house, demand-controlled ventilation incorporates a “humidity sensor” into the exhaust vent of each room. This sensor uses no electricity. It utilizes the physical principle of a nylon ribbon “stretching” when it absorbs moisture and “shrinking” when it dries.

For example, when a family member takes a bath, cooks in the kitchen, or even just sleeps in a bedroom, the humidity in that specific area rises due to human respiration and activity.

The sensor detects this humidity and automatically “opens” the exhaust vent to discharge the stale air. When the room’s humidity returns to a comfortable level, the vent automatically “closes.”

The Benefits of “Intelligent” Ventilation

The benefits of this “intelligent” ventilation system are immense.

1. Fundamentally Prevents Over-Drying
   When the indoor humidity is within a comfortable range (e.g., 40%-60%), the system throttles the ventilation to a minimum. This eliminates unnecessary ventilation in winter and preserves the room’s “moisture.” This perfectly complements the humidity-buffering performance of PAVATEX (Vol. 3) and the “non-drying” characteristic of the PS radiant heating (Vol. 5).
2. Overwhelming Energy Savings
   This system minimizes the loss of “heat” (air warmed by your heating system) that conventional systems would simply throw away. According to some estimates, it can reduce heating energy consumption by up to 50% compared to standard 24-hour ventilation.
3. Maintains Clean Air at All Times
   It ventilates robustly when the family is present and active (= producing CO2 and moisture) but rests when rooms are unoccupied or activity is low. This balance ensures the home’s air is always kept “just clean enough.”

The House Breathes as a System

In Volume 3, I spoke of how “the walls breathe moisture.” This demand-controlled ventilation can be described as a system where “the entire house breathes intelligently, in sync with human activity.”

The “Breathing Home (Breathability)” is only truly complete when the high-performance “shell” and the “system” that circulates air efficiently and comfortably within it, work together as one.