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Air & comfort·applied

Heat-Recovery Ventilation

Why it matters

An airtight, well-insulated building creates a paradox: the tighter the envelope, the more deliberately it must breathe. But every cubic metre of fresh winter air exchanged the old way (a cracked window) carries heat out with it. Heat-recovery ventilation resolves the paradox with an elegant swap: outgoing stale air and incoming fresh air pass through a heat exchanger without mixing. The warmth that took energy to make stays in the building while the staleness leaves. The result is continuous fresh air for a fraction of the heating penalty. This is the technology that lets a near-passive building be both sealed and alive. Without it, envelope quality and air quality are enemies. With it, they are the same project.

Role in 001's holistic picture

HRV is the winter half of the breathing pact with Hybrid & Natural Ventilation. It comes on duty when open windows would bleed the envelope's savings away. In low-energy buildings its ducts can even become heat distribution: at Unity Hub the supply air to every floor is post-heated by a water coil on the same loop that feeds the radiant floors. The HRV itself makes no heat — it only keeps heat from escaping. It is standard equipment on the road to the Passive House Standard, and a daily worker for Indoor Environmental Quality.

How 001 engages with it

House 001 earned this page's formative lesson the empirical way: the living lab runs individual per-room recuperators, and years of use returned a nuanced verdict. In normal occupancy they work well. But when the small house fills with guests, the units react to the air and spin up to plainly audible noise. That scaling behaviour is one reason Unity Hub's design went centralized: a community building lives at exactly the occupancy that pushes per-room units to their loud end. Balance is the other reason: heat recovery only survives while supply and extract flows stay balanced. That is exactly why the Passive House Institute certifies recovery cores only under balanced flow, with mandatory flow-balancing controls, and only above a 75 percent effective-efficiency floor. And small decentralized units on a windy site are the hardest place to hold that balance. House 001's actual leak story both confirms the wind problem and acquits the recuperators: the units themselves resist backflow well. The real leaks came through the kitchen and bathroom exhaust vents, whose imperfectly designed check valves yield when a strong wind hits them head-on.

That lesson flowed directly into Unity Hub, where centralized ventilation is confirmed in the accepted concept and sized with deliberate conservatism. When we evaluated recovery cores for the project, the numbers told the usual story: manufacturers advertise up to 91–96 percent heat recovery, independent measurements typically land at 60–75 percent sensible efficiency, and our design assumes a conservative 80 percent. That is the figure we will defend, not the one on the brochure. Around that assumption sit the other design values: a base air exchange of 900 m³/h (thirty people at 30 m³/h each), and acoustic targets of NR 25 in quiet zones and NR 30 elsewhere so the unit stays quiet enough to leave running. The ducts also carry a double duty: the supply air on every floor is post-heated by a water coil on the same low-temperature (28–31 °C) loop that feeds the radiant floors.

Maturity: applied. Tested through daily life at House 001 (including the failed per-room variant we report as data). Centralized HRV confirmed in the Unity Hub concept.

Further reading