How Is MEP Designed for a Passive House?

I size the ERV or HRV to deliver the required fresh air per person plus the floor-area component, then lay out the ductwork for quiet, effective distribution. Low face velocities keep the system silent — a ventilation system the occupants can hear is a ventilation system they will switch off, which defeats the entire concept. Supply air goes to living rooms and bedrooms, exhaust comes from kitchens, baths, and laundry, and I balance the system so every room gets its share rather than the closest rooms getting all of it. Heat recovery effectiveness is the number that makes or breaks the energy model, so I select units on tested performance rather than brochure claims and I design the installation to preserve it: insulated ducts, sealed joints, and no long uninsulated runs through cold spaces. In cold climates I include frost protection for the heat exchanger; in humid climates I manage condensate with proper drainage. Commissioning includes measured airflow at every grille — I do not accept a ventilation design on faith.

The heating load calculation for a Passive House often surprises owners: a whole house needing less heat than a hair dryer is normal. I meet that load with equipment that modulates down gracefully — small cold-climate heat pumps, ventilation post-heaters, or compact ductless units — and I verify minimum turndown against the load so the equipment is not cycling. Cooling gets a real design in any climate with a summer: I check the overheating criteria, design shading and night-flush ventilation first, then add mechanical cooling only for what passive measures cannot handle. Dehumidification deserves special attention in humid regions. A superinsulated envelope keeps sensible loads tiny, which means a standard air conditioner sized for the sensible load may never run long enough to dehumidify — the classic cold-and-clammy failure. I design the latent side explicitly: either a heat pump with good part-load latent performance or a dedicated dehumidifier integrated with the ventilation system. Indoor humidity targets are part of the design criteria, not an accident of equipment selection.

Passive House MEP succeeds on precision — small loads, tight envelopes, and no room for the slop that conventional construction absorbs. • Size the ERV/HRV to occupancy and area; lay out low-velocity, quiet ductwork with measured airflow at every grille • Right-size heating to the calculated peak — small modulating equipment, never conventional rules of thumb • Design domestic hot water as a major end use: efficient generation, short insulated runs, realistic draw profiles • Give summer comfort and dehumidification their own calculations, especially in hot-humid climates • Detail and minimize every air-barrier penetration; keep all ductwork inside the thermal envelope • Commission the ventilation, verify the blower-door result, and leave the owner a filter-maintenance plan they will follow