The legacy of a modern symbol

The GESA building, designed by Josep Ferragut Pou in 1963 and constructed between 1967 and 1977, was the headquarters of the historic local electricity company, later integrated into ENDESA/ENEL. Originally intended for administrative use, it is a prominent example of the rationalist style of its era, innovative for its central core design that consolidates services and frees up large, open-plan floors. This solution has since become common in modern office buildings.

Its cubic volume and four glass façades made it an icon of Palma’s skyline. Recognized as an example of the Modern Movement in Mallorca, it was declared a property of cultural interest in 2007. In recent years, however, it has remained unused, awaiting a new project to reintegrate it into urban life.

The rehabilitation challenge: rethinking the envelope and HVAC systems

Within the framework of the  ARV innovation project—which promotes the creation of circular communities and the accelerated renovation of buildings across Europe—AIGUASOL and IREC, in collaboration with the City Council of Palma, undertook the challenge of rehabilitating the GESA building. The goal was to adapt it to future needs and transform it into a positive building, producing more energy than it consumes.

The ambitious objectives were as follows:

• Heating demand below 15 kWh/m² per year.
• Cooling demand below 15 kWh/m² per year.
• Total primary energy below 70 kWh/m² per year, including heating, cooling, humidity control, ventilation, and lighting.

To achieve these goals, the project focused on:
a) rehabilitating the heritage façade,
b) proposing new HVAC systems, and
c) integrating photovoltaic energy production into the façade (BIPV), enabling the building to become an energy producer.

Reducing thermal demand focused primarily on the façade, a critical factor in the building’s thermal performance. Using thermal simulation tools (TRNSYS18), the building was modeled as originally designed, and heating and cooling demands (both sensible and latent) were calculated. While heating demands were below 5 kWh/m² per year, cooling demands exceeded 30 kWh/m² per year.

The heritage status of the building limits façade interventions, requiring the preservation of the original aesthetic and precluding the use of external solar shading. In a fully glazed building, covering 100% of the floor-to-floor height, this presented a significant challenge.

Four alternative façade configurations were analyzed:
a) Replacement of existing glass with photovoltaic glass.
b) Double glazing with exterior photovoltaic panels.
c) Ventilated façade (between slabs) with double glazing and exterior photovoltaic panels.
d) Continuous ventilated façade with double glazing and exterior photovoltaic panels.

Thermal modeling showed that the most effective strategy for reducing thermal demand was the adoption of a double ventilated façade, ultimately selecting a ventilated façade system between slabs.

Following this decision, a parametric optimization was performed, evaluating key parameters such as glass thermal transmittance, solar factor, air cavity thickness, and ventilation method (natural or forced). 

The results recommended:
a) reducing the thermal transmittance of opaque areas by 10%,
b) using glass with a thermal transmittance of 1.10 W/m²K and a solar factor of 0.24, and
c) employing forced ventilation through the ventilated façade cavity.

These strategies reduced the building’s final energy consumption for HVAC (heating, sensible and latent cooling) by 37% compared to the initial design scenario, achieving approximately 7.5 kWh/m² per year.

Optimization of the HVAC System
Two major challenges were addressed:

1. Determining the suitability and hybridization ratio of renewable sources, optimizing a geothermal-aerothermal system for cost, energy efficiency, and environmental impact.
2. Designing interior distribution and emission elements within very constrained spaces.

Parametric analysis led to an optimal hybrid configuration:

• Heating capacity: 873 kW aerothermal + 125 kW geothermal
• Cooling capacity: 777 kW aerothermal + 109 kW geothermal

Geothermal energy serves as the primary system, with aerothermal heat pumps as supplementary units. Four emission system alternatives were considered, with the final solution using ceiling-mounted fan coils with integrated wall-mounted reinforcement, balancing cost, architectural fit, noise, maintenance, and performance.

Smart energy: a model for the future

With the building optimized for demand and energy use, the next step was to achieve positive energy status, generating more energy than it consumes. In addition to conventional rooftop photovoltaic modules, an innovative solution was implemented: integrating photovoltaic panels into the façade, turning the outer layer of the double ventilated skin into an energy generator.

This strategy preserves the building’s original appearance, covers 100% of the energy required for HVAC, provides 43% of total electricity consumption, and results in a 47% reduction in CO₂ emissions compared to a baseline scenario with only aerothermal systems and no photovoltaics.

This optimization, carried out within an innovation project and with deep respect for the building’s essence, has attracted the interest of the City Council of Palma, which is considering leading the restoration of this true architectural landmark of the city.