Biomass cogeneration for a tertiary site in Luxembourg: sizing right at the design stage
Tertiary site >70 kW: how to size a pellet-fired biomass CHP unit at the design stage to cut heating bills and secure heat supply.
Why does biomass CHP make sense above 70 kW?
Above 70 kW, a tertiary site (school, hospital, office, hotel) carries an almost continuous base heat load. A biomass CHP unit turns that heat into useful electricity, with an overall efficiency above 85 %.
The trigger is simple: at least 4 000 base-load heat hours per year. Below that, the investment does not pay back.
How to size it correctly at the design stage?
Three numbers must be locked in before the design stage: useful thermal output, expected electrical output, and the hourly load curve of the site. Without these, the manufacturer cannot guarantee efficiency.
Rule of thumb: size the unit at 50 to 60 % of peak thermal load, and cover the rest with a condensing gas backup or a buffer tank. The buffer tank also unlocks a subsidy bonus.
- Useful output = 50 to 60 % of peak thermal load.
- Base-load heat ≥ 4 000 h/year.
- Buffer tank ≥ 1 hour of full-load operation.
- Electrical efficiency: 12 to 25 % depending on unit size.
Which compliance is required at the permit stage?
EU Regulation 2015/1189 (EcoDesign) sets minimum efficiency and emission thresholds for every biomass boiler placed on the market. EN 303-5 Class 5 is the reference standard for solid-fuel boilers.
On the fuel side, specify ENplus A1 certified pellets in the specification. That guarantees calorific value, moisture below 10 %, and full traceability — three keys to a stable sizing.
What is the net cost after 2026 subsidies?
Klimabonus 2026 supports pellet boilers: up to €8,000 for a single-family home, €6,000 per dwelling in multi-family housing (capped at €40,000), and €6,000 for district heating (capped at €24,000). Add a +15 % bonus with a buffer tank, plus €1,000 flat if the heating plant also integrates solar thermal.
Communal aids vary from one municipality to another and are stackable with the state Klimabonus. Before the design stage, run a simulation on aides.klima-agence.lu to calibrate the budget.
- Up to €8,000 for a single-family home (€4,000 without replacement).
- €6,000 per dwelling in multi-family, capped at €40,000.
- €6,000 for district heating, capped at €24,000.
- +15 % bonus with buffer tank, +€1,000 with solar thermal.
- Communal aids: variable and stackable — check municipality by municipality.
Sources
Need personalised advice?
Our team supports you with selection, sizing and subsidy paperwork.