Researchers at the University of the Basque Country (EHU) have explored how a combination of photovoltaic energy and heat pumps could be used to carry out the energy retrofitting of social rental housing. The Basque Government’s Zero Plan was used as the basis, and the technologies that the European Union is keen to promote were assessed. The buildings in Araba-Álava were generally found to offer the greatest potential for implementing the system.

Buildings account for 40% of total energy consumption. Under current European legislation relating to construction, retrofitting work based on renewable energies needs to be carried out to achieve energy and climate goals. The public rental housing stock in the Basque Autonomous Community has more than 7,600 homes. The landlord profile varies and changes, and specifying the energy needs of this type of housing poses a major challenge since the profile of use is very different compared with private housing. So it is often difficult to specify and carry out the energy retrofitting of buildings. That is why it is important to specify the most viable actions. Right now, the order for retrofitting buildings is prioritized according to their age and architectural features.

For energy retrofitting, the ENEDI research group of the University of the Basque Country (EHU) explored the possibility of implementing hybrid systems in social rental buildings in the Basque Autonomous Community. So in an innovative study, the potential of hybrid systems comprising photovoltaic technology and heat pumps in 128 public rental buildings in the Basque Country was explored and priorities established for retrofitting the buildings. That makes it easier to select the most suitable buildings for installing these technologies.

In these hybrid systems, “electricity produced by rooftop photovoltaic panels is used to power heat pumps. By using the heat from the air, and by means of a thermodynamic refrigeration cycle, heat pumps transfer heat to the radiators,” explained the ENEDI researcher Mikel Garro. The aim is to centralize the thermal demand of public rental buildings and distribute it from the heat pump to the whole building. In Garro’s opinion, aerothermal heat pumps are ideal for this.

The most suitable buildings are located in Araba-Álava

To rank the buildings, they took into account their useful rooftop surface for obtaining solar energy, and the heating and electricity consumption of each building with great precision. Furthermore, to select the heat pumps, the structure of the building, its thermal needs and its location were taken into consideration. The Zero Plan drawn up by the Basque Government was used to obtain extensive data on the buildings, and assistance was provided by staff at the Building Quality Control Laboratory. This research not only gives a detailed view of each building, but also provides an overview of the three provinces in the Basque Autonomous Community.

Garro is upbeat about the results: “In Araba-Álava, the buildings tend to be lower, they are not that high. The capacity for obtaining solar energy on their rooftops is higher due to higher radiation values, which results in higher photovoltaic production. What is more, since most buildings are lower, the total thermal demand also tends to be lower. So the hybridisation we have studied is highly suited to social rental housing of this type from the perspective of energy retrofitting”. Research has shown that buildings with the largest usable floor area do not always need to be the first to be retrofitted, as the use of housing is an important factor when setting priorities.

In this research, “we assessed the heating system of buildings, but not the system to produce domestic hot water,” said Garro. “Despite bearing in mind the most significant data in this work, we are now creating a model to factor in more variables.” The indicators for ranking retrofitting show which type of building is suited to this hybridization and “this methodology can also be used elsewhere”. The indicators use hourly values of solar radiation and energy demand, which provides this methodology with seasonal and hourly precision.

Additional information

This research is part of the PhD thesis by the engineer Mikel Garro-Aguilar under the supervision of Ana Picallo-Pérez, lecturer at the EHU, and Luis María López-González, lecturer at the University of La Rioja. The ENEDI group belongs to the EHU’s Department of Energy Engineering.