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EspaiZero. A semi-retrofit of an existing building; the first Net Zero-Energy experience in Spain

Wyróżniony Przypadek July 2014
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The new Wattia Headquarters and EspaiZero laboratory has achieved 100% zero-energy balance in the retrofit of the ground floor of an existing building.


The management company’s main objective was to demonstrate that it is possible to achieve a zero-energy consumption balance through the implementation of a series of energy saving measures, renewable energy sources and an automatic control system which correctly manages the entire ground floor.

The EspaiZero project is of particular interest in Spain as the law for the Electrical Sector (Ley 24/2013) has become more restrictive in buildings connected to the grid with a selective auto-consumption rate. This could be considered an exemplary case for designing self-sufficient buildings off the grid.

This particular building was chosen taking into consideration the following aspects:

The physical orientation parameters of the building as well as the feasibility of installing passive and active energy efficiency solutions.

In the rehabilitation project, which primarily affected the ground floor of the building, the idea to exploit the existing construction and its surrounding architectural characteristics was paramount in order to obtain an energetically efficient site while still being integrated into its natural environment. These architectural features were used to their best advantage and in doing so, there was also enough room to install the renewable systems.

The selection and integration of the renewable Systems: chilled beams, floor heating, solar thermal, solar photovolatics, electric accumulation with fuel and water batteries and heat pumps connected to underground loops for heating and cooling.

The office has been provided with well known systems as well as some experimental ones to improve energy efficiency. These systems can significantly reduce the energy demand of EspaiZero, making the goal of self-sufficiency achievable.

This concept of retrofitting only a part of a building can serve as a less expensive solution  for “sustainable  offices” instead of new construction of the whole building.



EspaiZero is located in Olot, in Northeastern Spain (Mediterranean climate, Csa), within a consolidated urban area which is near the municipal district end.  The site has all the basic urban services.  The buildings of the area are predominantly residential and municipal services.

The office is situated on the ground floor of a residential building.

Address:  Carrer de Bòsnia, numbers 6-8,  Olot,  Catalonia, Spain.

Project management:


TELLUS IGNIS: thermal design

Sustainable objectives:

The highest level of Energy Performance Certification: A, according to RD 235/2013 ( has been achieved.

100% energy self-sufficient: Net Zero-Energy consumption balance

Time Schedule:
Existing building construction: 2005

Design: 2011
Refurbishment: 2012
Delivery: April 2013

Total Surface area:

Whole Ground floor: 700 m²

Retrofitted Ground floor: 200 m² Total | 170 m² usable floor area

Preferential Scheme:
New design to reduce the maximum amount of energy demand and produce all energy coming from renewable sources

Construction and Exploitation costs:
Cost/m² : 1.350 €/m²

Whole refurbishment cost: 270.000 €

Cost for Renewable systems installed: 80.000€



Suitable existing building choice
This is a suitable option for retrofitting an existing building as a Net Zero-Energy Building (NZEB) or if there is interest in only obtaining a net zero-energy consumption balance in a part of a building.

Two key factors of this particular building:
-Correct orientation - essentially South facing.
-The structure and architecture of the building needed to allow a high energy demand reduction of the building and to integrate the implementation of renewable systems

Energy consumption on ground floor only:

Total primary energy need:  95,00 kWh PE/m²/year
Total primary energy need for standard building:  215,00 kWh PE/m²/year
Total primary energy consumption: 0 KWh PE/m²/year (the 100% energy demand is covered with the renewable production from the systems: solar thermal, solar photovoltaic and geothermal)

The total energy consumption is not just heating and cooling, but also includes lighting and equipment load.

GHG in use:  24,12 KgCO2/m²/year

At the present time, the real EspaiZero energy consumption is very close to zero. Since the inauguration of the EspaiZero building April, 2013, the monthly energy bill has been less than 2 kWh;  this means less than 1€ in consumed energy.
Envelope performance:
 S/V = 0,39 (1/m)

Façades: 0,31 W/m2K
 0,41 W/m2K ‐ 0,029 W/m2K (with additional isolation of underfloor heating)
Glazings: 2,30 W/m2K; Glass: 0,80 W/m2K. Solar Factor g: 0,42

The building envelope has a continuous layer of at least 8 cm of highly insulating material. This layer provides a good level of insulation as well as the elimination of thermal bridge effects. This isolation was not only applied on all façades and walls but also on the ceiling and floor. The windows have also been designed and built with the most efficient materials available.

Energy Efficient measures
Solar collection
Thermal break frames
Low-emission triple glazing with double air chamber and argon gas inside
Natural light
Work station separation to solar usage
Automated Cross-Ventilation
Recovered stratification

Building Automatization and control with BMS
Heating system: geothermal heat pump, with underfloor heating
Cooling system: geothermal heat pump, with chilled beams
Hot water system: solar thermal collectors
100% renewable system production:
Solar thermal
Solar photovoltaic
Outdoor solar protection
Outdoor free cooling ventilation in the equipment room
Lighting controls using LEDs  
Regulated illumination due to natural light as an external contribution
Geothermal power system with earth warming tubes and 10m solar chimney, radiant floor, radiant ceiling, solar system and accumulation room, window glazing with photovoltaic cells, free cooling and solar protection,
Data Processing Center and Efficient PC servers connected with KNX sensors,

SmartLite (FSL) 24 measurements points of electric consumption
iENetB: Datalogger system KNX with 60 sensors
iES7: Datalogger system PLC Siemens
Davis Weather station

Indexed electric tariff


Original source: C21 platform

Acronym of the case


Lessons learnt

Besides being the new Wattia headquarters, EspaiZero is also a laboratory where it is possible to experiment, collect data and reaffirm/discard thesis or ideas. Being able to use the energy efficiency systems installed - together or independently - allows for the opportunity to get real answers for implementation in other customer´s projects. In order to support these experimental procedures, the system has been provided with multitude of sensors. It is considered to be an important tool for the near future, in which all new buildings will have to be nearly zero consumption.

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