Office and service complex POSEJDON
nZEB Example

The building has been constructed based on renovation and extension of the former department store constructed in 1928: DeFaKa (Deutches Familien-Kaufhaus). Currently, the facility includes office spaces, a conference centre, two hotels belonging to the Marriott group, and a shopping area (including Lidl). The building is equipped with a ground heat exchanger consisting of 46 vertical boreholes, each 300-metre deep, with designed operational temperatures of 12/8°C in winter and 26/30°C in summer. Heating and cooling is ensured by a decentralised system of 910 water-air (water-loop) heat pumps, which are all interconnected and generate heat and cold where and when needed. The heat pumps coefficient of performance exceeds 4.1. Peak heat demand is backed up by a reserve heat pump, while the cooling system is backed up by evaporator-cooling towers on the roof. Domestic hot water is prepared using district heating substation with hot water storage tanks, with additional preheating using energy from ground heat exchangers. On-site electricity generation is provided by a PV panel system with a total power of approx. 102.6 kWp. Energy efficiency of lighting is improved thanks to LED lamps and motion sensors installed in bathrooms, car parks, and staircases. In addition, treated rainwater is used for toilet flushing, watering green roofs and a green wall. Local BMS is installed as well, which is controlling the energy consumption based on occupancy rates.

Building owner

Porto Sp. z o.o.

Building type
Project type
Year of construction / major renovation

Construction: 1928
Major renovation: 2019

Total floor area
49200 m²
Construction U-value

External Walls

0.184 W/m²K


0.144 W/m²K

Floor on the ground

0.297 W/m²K
Windows Uw Uf Ug G


0.9 W/m²K N/A N/A N/A
nZEB Parameters

Annual demand for final energy for heating and ventilation: 29 kWh/m2/a
CO2 emissions: 5.35 kg CO2 m2/a
Coverage of annual electricity demand by onsite renewable energy generation: 36%

Building part / Posejdon / National requirements for nZEB binding from 01/01/2021
External walls / 0.184 / 0.200
Roof / 0.144 / 0.150
Floor on the ground / 0.297 / 0.300
Windows / 0.900 / 0.900


The building received a BREEAM certificate in the New Construction 2016 category on the level “Excellent”.

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