Communicate your buildings performances Subscribe to the newsletter

Pilot Project Of Energy Efficiency Improvements In Buildings - Energy Institute “HRVOJE POZAR” Office Building


The Energy Institute “Hrvoje Pozar” is a non-profit research institution and co-ordinator of 12 National Energy Programmes, with a central role in the development and implementation of the national energy sector reform. It aims to demonstrate and implement a wide range of up-to-date energy efficiency measures in its own building.
Activities planned and performed at the Institute, and particularly those involving the realisation of the National Energy Programmes, promote the utilisation of renewable energy sources and the implementation of the latest energy efficiency measures.

The building housing the Energy Institute was in need of renovation. The building envelope needed to be reconstructed in order to prevent thermal transmission and noise pollution. The building needed reinforcement and the façade needed to be renovated to improve the aesthetics of the building. The pre-fabricated components of the reinforced concrete parapet wall needed to be removed in order to relieve the skeleton, maintain the building’s structural stability and facilitate the fastening of the new façade coating.

The Energy Institute’s building before (above) and after (below) reconstruction.

Funding to renovate the Institute’s premises was gained through the KUENbuilding programme. This is a programme that has received financial support from the Ministry of Environmental Protection and Physical Planning of the Republic of Croatia. The programme aims to improve the energy efficiency of buildings at a national level. Its objectives are to establish mechanisms that would permanently reduce energy demand in the design, construction, utilisation, refurbishment and reconstruction phases for new and existing buildings and settlements.

Energy-aware building construction has several goals:

- To reduce heat losses in a building by improving the thermal insulation of its envelope and ensuring an appropriate surface area to volume ratio of the building;
- To increase heat gains by using solar energy and by ensuring that the building is favourably oriented;
- To use renewable energy sources;
- and to increase the efficiency of installed thermal energy systems.

These goals were incorporated into the renovation of the Energy Institute’s building as much as possible. The building’s new light aluminium façade combines full elements of flat plate, full parapet elements with enamelled glass and new windows with external shutters. A stone plate coating was applied on the ground floor and the basement floor.

Building details

Type of building
Administrative building that is the headquarters of the Energy Institute.



The aim of this project was to renovate the Energy Institute’s premises to improve the building’s energy efficiency, aesthetics and structural stability. The project also aimed to turn the premises into a demonstration building for energy efficiency.

Key points
Reconstruction of the building

_ Reconstruction of the Institute’s premises involved four basic processes:

- Application of additional thermal insulation to the front of the building;
- Replacement of windows and the construction of a new, low-pitched roof;
- Reconstruction of the interior in accordance with the Institute’s needs;
- Installation of a modern heating, ventilation and air-conditioning (HVAC) system;
- Installation of a centralised energy control and management system which enables key energy indicators to be measured and monitored.

_ However, structural analysis of the original skeletal construction’s stability needed to be performed before any construction work could be undertaken. Revision of the 1971 structural calculation revealed that the building did not conform with seismic regulations in view of its real weight and location in the ninth seismic zone. The skeleton was found to be inadequately resistant in terms of both strain and distortion in the direction of the building’s frame.

_ In order to reduce the level of seismic straining, it was decided to reinforce the frame structure with steel, which would relieve the burden of horizontal forces. The frame’s resilience was thus increased to withstand earthquakes of an even greater intensity than those usually occurring in the eighth zone of seismic activity. The remaining weaknesses in relation to vertical stress (beams) were eliminated by tearing down heavy brick partition walls and replacing them with light drywalls in corridors. This provided heightened resistance to vertical load. The weakness of the construction to seismic stress was additionally reduced by the removal of concrete pre-fabricated parapet facing and flat roof layers.

_ The new wall structure consists of:

- The original reinforced concrete parapet wall - 15cm
- Mineral (stone) wool - Tervol 10cm
- Layer of ventilated air - 4cm
- Final layer - glass (0.8cm), aluminium sheet (0.25cm) or stone slab (3cm)


_ The original aluminium window frames, which had high thermal transmission, have been replaced with high-quality aluminium window frames which have a disconnected thermal bridge and insulating glass manufactured by Schûcco (Royal S 70 material group: 1, k factor: 1.1). Rooms are provided with natural cooling and ventilation through the windows. As soon as a window is opened, the heating or cooling is automatically turned off by an embedded micro-switch connected to the centralised energy control and management system.

_ Following reconstruction, the rooms on the four upper floors are now used as offices. In addition, the fourth floor houses a computer centre and a kitchen cafeteria. The multimedia room is located on the ground floor, whereas the basement houses the library and the main HVAC system power and control room.

_ Lighting

_ High-quality direct and indirect lights equipped with daylight sensors (i. e. self-regulating lighting that responds to daylight intensity) is used, which both saves significant amounts of energy and makes the offices more comfortable and pleasant working environments.

_ HVAC System

_ Since the original HVAC system was assessed as incapable of meeting the Institute’s needs, a new system was designed, based on the latest research on thermal energy. The new HVAC system consists of a two-pipe fan-coil heating and cooling system and a complete ventilation system that is connected to the library, the multimedia room, the bank office, and the cafeteria.


_ The original heating substation could have been renovated and supplied with an electric chiller unit to meet the HVAC needs of the building. However, since the building was intended as a pilot project to demonstrate energy efficiency and the use of contemporary technology, the energy units making up the HVAC system were extended considerably beyond the essential requirements.

_ The HVAC system consists of three main energy units:
A heating substation - compact, indirect-type heating substation (with a capacity of 250 kW), connected directly to the city’s district hot-water supply network; includes a heat exchanger, a sanitary hot-water tank (with a capacity of 0.1 m3), and a calorimeter.

_ A heat pump with an ice bank - the chiller, designed as a heat pump (with a capacity of 95/119 kW cooling/ heating), has been designed for charging the ice bank (with a total capacity of 670 kWh) in the night-time saving mode. In addition, the chiller can both produce and transmit cooling energy directly into the system, as well as generate heat (when the temperature of the surroundings is up to -5°C) when operating as a heat pump.


_ A trigeneration system - the cogeneration-based trigeneration system is supplied with a gas engine (with a power capacity of 75 kW and a heating capacity of 160 kW) and a single-stage absorption chiller (with a capacity of 105 kW) powered by heat generated as a waste product within the cogeneration system. The gas engine, on the other hand, is powered by natural gas that has been transported to the location. The system is designed to cover the building’s basic needs for hot and cool air as well as electric power.


Reason for inclusion as Shining Example

The reconstruction of the Institute’s office building encompassed the repair of the building’s membrane with the aim of increasing the energy efficiency of the building. In addition, it involved interior reconstruction and the installation of both a heating, ventilation and air-conditioning system, and a central monitoring and control system. All interventions aimed at raising the efficiency of energy use in the building and the new technologies (whether they were implemented during reconstruction, or after the building was put into operation) are monitored by measuring relevant energy related parameters. The results will be used as guidelines for future energy management at a national level.


View of the multimedia room in use

_ The technologies for the production, transformation and saving of energy that were applied in the Institute’s office building required a greater investment cost compared to conventional technologies. Therefore it will take longer to demonstrate the economic and environmental feasibility of the implemented measures and technologies in relation to similar energy systems. The first measurements of energy performance and the comparison of the building’s consumption before and after reconstruction indicates a significant decrease in the amount of heat energy used since the reconstruction (note: the calculated total amount of heat used includes heat used for the preparation of sanitary hot water in the kitchen and restrooms, which used to be significantly lower before the reconstruction).


View of the cafeteria after reconstruction

_ The recorded annual consumption of heat supplied by the city’s district heating network and consumable hot water amounted to 283 kWh/m2 before the reconstruction, but has since been reduced to 103 kWh/m2. This latter figure includes system-related losses. This is a 64% reduction in the building’s total heat consumption.

_ In addition, prior to the reconstruction, specific thermal power totalled 128 W/m2, but it has since been reduced to 97 W/m2 (i.e. it has decreased by 24%). The analysis indicates that specific consumption of heat energy used for heating (i.e. not including system-related losses), which totaled 235 kWh/m2 before reconstruction, has since been reduced to 81 kWh/m2 (i.e. it has decreased by 65%).


_ The reconstruction of the Energy Institute’s building was conceived as a pilot project for demonstrating the application of new energy efficiency technologies. The level of its technical, technological, operational and managerial complexity remains unmatched in Croatia. In addition, the project has successfully dealt with an accompanying demand for a lecture and seminar centre for educating students, technical staff and experts in the field of energy efficiency.

To know more



Energy Institute “Hrvoje Pozar”, Zagreb, Croatia

Branka Jelaviæ, Ph. D., Head of Department

+3851 6040 588



You are here: > English > Shining Examples > Croatia > Zagreb > Pilot project of energy efficiency improvement inbuildings - energy (...) > English
Your communication campaign
Display in a nutshell
The Campaign
Display adaptation
How to participate
Participation fees
Users Clubs
Communication tools
Examples to follow
Photos and videos
Media coverage
Communication download
Shining Examples
What is the TCA Award?
Shining Examples
TCA Award Ceremony 2011 - Brussels (BE)
Building statistics poster
Exhibition Gallery
Campaign coordination: Energy Cities - 2, chemin de Palente - 25000 Besançon
Peter Schilken - Tél. : +49 7661 98 26 14 - Raphaël Chatelet - Tél. : +33 3 81 65 36 80

RSS Help | Contact | Partners | Credits | Legal
With the support of