What EN 16798 Covers
EN 16798 is the European series Energy performance of buildings — Ventilation for buildings, replacing the former EN 15251 framework. Part 1 defines the indoor environmental input parameters — thermal comfort, indoor air quality, and ventilation rates — used to design and assess building energy performance across the EU.
Comfort Categories
The standard divides occupied spaces into four categories that directly set how much outdoor air is required:
| Category | Application | Expectation |
|---|---|---|
| I | High occupant expectation (e.g. prestige offices) | Best quality |
| II | Normal expectation (default) | Common practice |
| III | Acceptable, low expectation | Minimum comfort |
| IV | Values outside I–III | Threshold only |
Ventilation Rate Logic
EN 16798-1 calculates required outdoor air as the greater of a per-person rate (based on occupancy density and category) and a per-floor-area rate (to dilute building emissions). Because higher categories demand more outdoor air, they also raise the heating and cooling load — which is exactly where heat recovery earns its place.
Link to Heat Recovery
- More outdoor air = larger ventilation load = stronger payback for energy recovery.
- The standard's energy calculation modules accept the sensible and latent effectiveness of the recovery device as inputs.
- In nearly zero-energy building (nZEB) targets, recovery is often essential to keep ventilation energy within the envelope.
Indoor Air Quality and CO₂
The standard references CO₂-based demand-controlled ventilation: when CO₂ stays low, outdoor-air flow can be reduced, but the recovery device keeps working across the modulated range. This makes enthalpy wheels and plates attractive for variable-volume systems serving Category II spaces.
Practical Design Steps
- Choose the comfort category with the client.
- Compute the outdoor-air rate from occupancy and area.
- Size the air-handling unit and select a heat recovery device with certified effectiveness.
- Run the EN 16798 energy assessment with recovery included to confirm the building meets its performance target.
Why It Matters
EN 16798 turns "fresh air" from a vague intent into a calculable, auditable input. For any heat recovery specifier in Europe, it is the starting point that decides both how much air must move and how much energy must be recovered to stay compliant.
Worked Example: Setting the Outdoor-Air Rate
A 200 m² open office has a design occupancy of 20 people (density 0.1 person/m²) and uses Category II. EN 16798-1 might allow about 4 L/s per person plus 0.3 L/s per m² of floor area for this type. The required outdoor air is then:
- Per person: 20 × 4 = 80 L/s
- Per area: 200 × 0.3 = 60 L/s
- Total: 140 L/s of outdoor air into the space
That 140 L/s must be conditioned year-round — which is why a Category II office of this size is a textbook heat-recovery candidate, and why raising the category (more OA) makes recovery even more valuable.
Frequently Asked Questions
Which category should I choose? Category II is the normal default; Category I is for high-expectation spaces and costs more to ventilate.
Does more outdoor air mean more energy? Yes, and that is precisely the load heat recovery offsets.
How does it link to nZEB? The ventilation energy calculated under EN 16798 feeds the building's energy performance assessment for nearly zero-energy targets.
Can ventilation be reduced? Demand-controlled ventilation using CO₂ can lower flow when the space is empty, but recovery still helps across the modulation range.
Practical Guidance for Specifiers
Start the ventilation design by agreeing the comfort category with the client, because it sets the outdoor-air rate and therefore the recovery duty. Document the occupancy density and floor area used, since these drive the per-person and per-area terms. When the calculated outdoor air is large, model the building both with and without recovery under EN 16798 to show the energy saving in hard numbers — this also supports any nZEB or incentive submission. Coordinate with the AHU supplier so the selected recovery device's certified effectiveness is entered at the right flow, and confirm the unit's leakage class will not erode it. Finally, consider demand-controlled ventilation for variable-occupancy spaces; recovery still helps across the turn-down range, so the system saves energy even when the room is partly empty.