This multi-family apartment building in Croatia was planned and constructed to meet the requirements for a Class A energy performance with less than 15 kWh/m².year for heating. It is comprised of 28 apartments distributed between three floors. The walls have been insulated with 20 cm thick stone wool, the roof with 30 cm extruded polystyrene (XPS). The windows are triple-glazed. Heating and cooling are provided by an underfloor system connected to a reversible heat pump and a gas boiler. A ventilation system with a high recuperation factor ensures good indoor air quality. The domestic hot water (DHW) is generated by solar thermal collectors used in combination with the gas boiler. The total final energy includes heating, hot water, cooling, ventilation and lighting and amounts to 66 kWh/m².year, which is 78% lower than the national building energy performance requirements. Twenty two percent (22%) of the final energy is provided by the solar thermal collectors. The most impressive result of the project is that the building was constructed without having any superior cost difference when compared to that of a regular building which fulfils national requirements. The total costs amounted to 912 €/m².
Costs of land, design, management and construction amounted to 11,485,000.00 HRK (~ 1,500,000.00 €) for 1,644.00 m² (28 apartments). There were no additional costs for the A⁺ energy class type of building compared to a standard quality building.
1,539 m² net usable floor area (28 apartments, basement, ground floor and three floors with a ground area of 612 m²) which can be recalculated to 912 €/m².
The structural walls are made of reinforced concrete, 20 cm thick, or of brick masonry block, 25 cm thick. The building envelope is thermally insulated with stone wool of a 20 cm thickness for concrete walls and 15 cm for brick walls. The roof is flat and is made out of 20 cm thick concrete and is thermally insulated with 30 cm XPS. The Polyvinyl chloride (PVC) windows are made with triple low e-coated glazing filled with argon, mounted according to RAL installation. (RAL is a German quality assurance association of windows and front door producers, which publish guidelines for correct window installations).
Building envelope U-values:
- Wall: 0.19 W/m².K (concrete wall) – 0.22 W/m².K (brick wall); allowed Umax = 0.45 W/m².K
- Window: 0.99 W/m².K; allowed Umax = 1.80 W/m².K
- Roof/ceiling to the attic: 0.10 W/m².K; allowed Umax = 0.30 W/m².K
- Cellar ceiling: 0.21 W/m².K; allowed Umax = 0.50 W/m².K
- Ground slab: 0.13 W/m².K; allowed Umax = 0.50 W/m².K
Building service systems
Heating and cooling are provided by an underfloor system using the same pipes for both heating and cooling. Heating is generated by a compact heat pump with a coefficient of performance (COP) = 2.8 (90%) or by boilers using natural gas (10%). Each apartment has its own energy meters. The ventilation system runs constantly to supply 0.5 air changes per hour for the entire volume of the apartment. The waste air heat is taken through a high performance energy recuperation system. Hot water is primarily generated by solar thermal collectors, and, if necessary, complemented by gas boilers.
Renewable energy systems
Solar energy for centralised DHW preparation: solar thermal collectors on the roof of the building, connected to the DHW storage tank with a volume of 4,000 liters. The system is designed to primarily use solar energy for hot water generation, with gas boilers as support.
Building Energy Performance
Final energy use:
HRN EN ISO 13790/PHPP 2009
Monitored in year:
(~ 10% gas boiler,
90% el. heat pump)
(50% solar energy)
Electrical appliances (household electricity)
Primary energy use:
Primary energy factor: 3
Primary energy factor: 1.1
Renewable energy contribution ratio:
22% (solar thermal energy) of the total final energy
Improvement compared to national requirements:
Maximum heating energy demand allowed for new buildings
- ManagEnergy award winner, “The bold new face of Koprivnica” (European Commission, EACI, Sustainable energy week 24.-28. June 2013)
- Recognition for best practice in local government in the energy efficiency category (IN PLUS, Association of Croatian cities)