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Challenge / Goal

Under the GrowSmarter project, GNF(Gas Natural Fenosa) has implemented energy refurbishment of almost 12,500 m2 of tertiary buildings. It is estimated that this solution will reduce combined energy consumption of the refurbished buildings by almost 2GWh/year.

Three buildings with very different uses have been retrofitted, and one of them is a hotel H10 Catedral, which met challenges in requiremnts of  high stadard of thermal comfort in the rooms (hearting and cooling), individual temperature settings for each room, and continuous consumption (lingting and air conditioning) for common areas. The aim is to validate the technical and economic feasibility of executing an energy refurbishment of a tertiary building as part ofan integral refurbishment promoted by the customer, i.e. the owner of the building.


The building energy retrofitting measures are: 

Passive measures:

1. Façade insulation, roof insulation:

  • In winter, external Thermal Insulation Composite Systems (ETICS) reduce heating demand and improve internal comfort.
  • In summer, external insulation reduces the heating of the façade due to solar irradiation while preventing heat dispersion from inside to the exterior. It is also important to use natural ventilation and to avoid direct sunlight using solar protection systems.
  • External insulation reduces cold bridges in comparison to internal insulation.

2. Change of windows:

  • Improves thermal insulation (lower U than the existing windows) and reduces solar transmission to the inside.
  • Overcomes the cold bridge of the window itself by installing a window with a thermal break.
  • Reduces infiltration thanks to a high quality installation and higher air permeability class (UNE EN 12207).
  • Improves acoustic comfort.

Active measures:

1. Replacement of existing boiler:

  • A medium performance of 1 is considered for the use of condensing boiler (nominal performance 1.09), in comparison to a medium performance of 0.85 for the use of conventional boiler.

2. Replacement of existing chiller with high efficiency heating pump:

  • The chillers proposed within this solution have a seasonal energy efficiency ratio of 3.8-4.3.
  • In the case of chillers with heat recovery, an evaluation of the recovered heat in comparison to the heating demand is required during months with simultaneous cooling and heating demand. This is important because heat recovery reduces the performance of cooling generation, and most of the recovered heat needs to be used to compensate for this loss.
  • It is also important to evaluate the performance of partial loads and to analyse the difference in performances when installing one or more chillers.
  • Optimisation of the chiller operation by monitoring its performance allows further reduction of electricity consumption by improving the management of the on/off profile and adapting the load profile.

3. BEMS (Building Energy Management System) installation:

  • Monitoring of energy consumptions (electricity, gas, water..) and possibility to export monitoring reports to Excel
  • Clear display of consumption for each system and zone
  • Help controlling consumption and to take decisions for the optimisation of the working calendar of different systems, in order to improve both the control system and thermal comfort.

Implemented renewable energy solutions:

1.Aerothermal heat pumps for the cooling process with  performance higher than 2.5 (European Directive 2014/11/UE).


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Time period

Implementation time: 6 months to 1 year

    Main benefits

  • Decreasing energy consumption in buildings

  • Reducing energy bills

  • Improving energy usage efficiency

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