MVHR Mechanical Ventilation & Indoor Air Quality Complete Guide
In an airtight Passive House envelope (n50 ≤ 0.60 h⁻¹], controlled Mechanical Ventilation with Heat Recovery (MVHR] is the respiratory core of the building. In SerVilla cold-formed steel homes, MVHR ensures continuous dust- and pollen-free indoor air circulation while recovering up to 92% of sensible indoor thermal energy without opening a window.
1. MVHR Working Principles & 92% Sensible Thermal Efficiency
The MVHR air handling unit extracts humid, stale air from wet zones (kitchens, bathrooms, utility] and supplies tempered fresh air to habitable spaces (living rooms, bedrooms].
- Counter-Flow Recuperator: In the counter-flow polymeric heat exchanger, outgoing warm air transfers heat across thousands of microscopic plates to the incoming cold airstream without moisture or odor cross-contamination.
- Real-World Energy Yield: With outside ambient at 0°C and indoors at 21°C, supply air enters rooms at approximately 19.3°C without any auxiliary heating element.
- Specific Fan Power (SFP]: State-of-the-art electronically commutated (EC] backward-curved fans operate at less than 0.25 Wh/m³.
2. Moisture Balance & Enthalpy Core Exchangers
In cold winter climates, high ventilation rates can lower indoor relative humidity below comfortable levels (<30\%].
- Latent Energy Transfer: SerVilla recommends enthalpy exchangers featuring semi-permeable polymeric membranes that allow water molecules to migrate from the exhaust stream back into the supply air (65\%–75\% latent efficiency].
- Optimum Indoor Humidity: Maintains indoor relative humidity within the ideal 40% to 60% comfort envelope, preventing dry skin, respiratory discomfort, and timber shrinkage.
3. Airborne Particle & Pollen Filtration (ISO ePM1 / F7 & HEPA]
- High-Grade Air Filtration: Air intakes are equipped with ISO ePM1 70% (F7 grade] or medical-grade HEPA filters, capturing 90\%+ of PM2.5 particulates, smog, traffic soot, and allergens.
- Hypoallergenic Sanctuary: Windows can remain sealed during spring pollen peaks, making passive steel homes exceptionally beneficial for asthma and allergy sufferers.
- Controlled Indoor Carbon Dioxide: In bedrooms with closed doors, CO2 levels remain steadily below 800 ppm, eliminating morning headaches and stale air fatigue.
4. Acoustic Attenuation & In-Duct Silencer Engineering (<25 dB(A]]
An engineered ventilation system must be completely silent.
- In-Line Attenuators: Rigid absorption silencers installed directly on the supply and extract headers suppress fan motor noise at all octave bands.
- Ambient Sound Levels: Supply diffusers in bedrooms operate at sound pressure levels ≤ 25 dB(A] (inaudible against ambient nocturnal background noise].
- Crosstalk Mitigation: Semi-rigid radial PE-HD antibacterial ducting runs in a dedicated star distribution topology from central manifolds, eliminating sound transmission between adjoining rooms.
5. Summer Automatic Bypass & Post-Heater Coils
- 100% Modulating Summer Bypass: When summer nighttime temperatures drop below the indoor setpoint, the bypass damper opens completely to flush the home with cool nocturnal air.
- Hydronic Post-Treatment Integration: Duct-mounted water heating/cooling coils hooked into air-source heat pump circuits deliver 1.5 to 3.0 kW of peak seasonal temper without bulky radiators.
Editorial Disclosure & Engineering Note:
Analysis presented in this guide reflects Eurocode structural benchmarks, Passive House Institute physics, and over two decades of SerVilla international cold-formed steel manufacturing experience. Custom statutory site verification is conducted for every individual plot.
