Eight dwellings near San Sebastian on the Bay of Bisay, Pasaia
The EU-funded project HAPPENING’s concept is based on cascade heat pumps in refurbished multi-family buildings in order to allow for ‘tailor-made solutions’.

In the North of Spain, next to San Sebastian lies the small town of Pasaia. In this mild climate zone, a multi-family building was constructed in 2008. It consists of eight dwellings, each of which has an approximate size of 75 square meters.
The (Basque Country) state funded company Alokabide owns this building which was built with renewable energies in mind as it had Solar Thermal components installed but still drew both Domestic Hot Water (DHW) and Space Heating (SH) from individual gas boilers with 100l TES in each dwelling.
By the time of refurbishment, the Solar Thermal parts were out of order. Still, the building is owned by the aforementioned company as part of the public social housing policies of the region.
Before refurbishment the building had an energy consumption of ~32,3 MWh/y (SH 6 DHW) + 12,8 MWh/y (electricity consumption)
Lessons learned
- Versatility, as each single dwelling can decide the configuration that better fits their needs and interests.
Key facts
Building | Heat Pump and Source | ||
Location | Pasaia, Spain | Number of HP | 2 (central) + 8(decentral) |
Construction | 2008 | Installed power | 84kW (2x 18kW + 8x 6kW) |
Refurbishment | yes | Operation mode | monoenergetic |
Heat distribution | radiators | Heat source | ambient air, interal loop |
Heated area | approx. 600 m² | Type of system | Central + decentral |
No. of apartments | 8 | Model | – |
level of insulation | good | ||
Heating sytem | Domestic Hot Water | ||
Heat demand | – kWh / (m²a) | DHW demand | – kWh / (m²a) |
Heating temperature | 55°C | Max. temperature | 70°C nominal capacity, 50°C used as SP |
Additional heating | Gas boiler 390kW | Circulation system | – |
Type | centralized system | ||
Other information | |||
PV installed | yes | COP | – |
Climate Zone | Cfb (Temperate Oceanic Climate) | Refrigerant | R290 |

Description of the technical concept
The two existing boilers were replaced with 2 high-efficiency heat pumps with inverter technology and ecological refrigerant R32 Sheen EVO 2.0 and 2 condensing boilers of 200 kW, which are used as back-up and integration in situations where high temperature water is required. The heat pumps can also be used as a back-up to the chiller in peak cooling demand.
To replace the 2 old chillers, a high-efficiency chiller with Magnum WSAT-XEM inverter technology was installed.
The entire system is managed by Clivet’s INTELLIPLANT Building Management System, which coordinates the entire heating and cooling plant, activating the plant resources according to the requests received from the individual flats and always activating the most efficient resource, has made it possible to operate the heat pumps in conjunction with the boilers, thus providing a perfectly reliable and efficient hybrid system. Intelliplant also makes it possible to maximise the total efficiency of the system by making the units work at their maximum efficiency and allows the customer to monitor thermal, cooling and electrical consumption.
The system allows for constant monitoring and therefore prompt intervention at any time or in the event of faults or failure.
ES003 Project HAPPENING Public Social Housing