Demonstration Center 1

Croatia

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The demo center in the Zagreb County was planned for launching during the project duration but ended up being delayed due to numerous barriers encountered in the project development phase. The Regional Energy Agency of Northwest Croatia (REGEA) and the Zagreb County were collaborating in establishment of a pilot project – a demonstration center WP I1 where an innovative approach in heating sector should have been introduced. The primary goal of this pilot project is to reduce greenhouse gas emissions and heating costs by introducing renewable energy sources and heat storage, as well as to test the advanced application of city storage and sector coupling within the existing public building owned by Zagreb County.  

This demo center aimed to be the first heat prosumer in Croatia, making it possible for a public building (respectively a public high school) to capture thermal energy for its own consumption by using solar thermal collector systems and to feed surplus heat into the local District Heating System (DHS).

In other words, this pilot addresses a smart heating solution which combines a solar thermal installation on a public building (or ground installation) and district heating system through the local district heating network. Integration of smart heating substation allows bidirectional exchange of solar thermal energy between district heating distribution network and solar system which will be carefully explored.

Regarding the location of the demonstration center, the project envisages a public building owned by the Zagreb County, which is in one of the cities where DHS is active – Zaprešić, Samobor or Velika Gorica. As a part of collaboration between project partners (REGEA and the Zagreb County) and inclusion of feedback from Associated Strategic Partner (HEP Toplinarstvo – national district heating company), stakeholders evaluated current and future strategic development plans and opted out for the High School Ban Josip Jelačić, Zaprešić.

The technologies that should have been included: 

  1. Thermal collectors’ system for capturing heat
  2. Smart District Heating Substations configuration to enable a proper exchange of heat  
  3. Heat storage (hot water tank) 
  4. sensing and monitoring equipment, advanced regulation, and central control systems

 

Selection of public building for connection to DHS

07-09/2020

Detailed feasibility and enigneering study of demo center

09/2020-01/2021

Change of demo center and over coming barriers

01-09/2021

Adjustment of feasibility studies and decision making process

09-12/2021

Expansion of DHS grid

12/2021 - 08/2022

Public procurement for puchase of necessary equipment and preparation of work

08 - 10/2022

installation of equipment and connection to DHS system

10/2022 - 02/2023

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Advanced technical scheme of demo center’s boiler room as it was initially planned. It consists of solar thermal collectors system, three sets of heat exchangers, heat storage and central control system.

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The demo center should have used flat vacuum solar thermal collectors which are a patent of a Swiss Company TVP Solar. These solar thermal collectors have the possibility to heat up the water for both space heating and domestic hot water preparation which makes them an ideal system for an innovative apporach as the public school requires high temperatures which are also the operational temperatures of local district heating system. That is why the bidirectional exchange of heat between the demo center and local district heating system is possible.

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Based on the needs for thermal energy and domestic hot water that have so far been met by two hot water boilers whose dismantling is planned: Viessmann Vitoplex 100 with a capacity of 2 x 575 kW, the Danfoss compact heat transfer substation with a capacity of 1047 kW and temperature regime: primary 90 / 70°C, secondary 60 / 80°C. The heating station uses energy supplied from the district heating system of the city of Zaprešić operated by HEP-Toplinarstvo (boiler room Mokrička 61) and consists of primary and secondary part installed on a supporting frame with accompanying electrical installations. Maintaining the pressure in the heating installation in a certain area is solved by the existing expansion system, manufactured by PIREKO, with a tank capacity of 750 L. 

On the primary part of the compact heating station, a heat meter and a differential pressure regulator are installed in the return line. The differential pressure regulator adjusts the flow and return pressure in advance: this indirectly defines in advance the maximum permissible flow of the primary circuit through the compact station of the building. The flow value itself is defined by the lease of the heat output from the heat distributor. In addition to the above equipment, the primary circuit also contains a heating control valve and the associated electric motor drive, as well as shut-off valves and manometers and thermometers for measuring the pressure and temperature of the primary heating circuit of a compact heating station. The secondary circuit of the compact heat substation consists of the following newly designed equipment: 

  • Circulation pump with frequency control
  • Dirt trap
  • Non-return valve
  • Heating flow temperature sensor
  • Thermometers and manometers (drawing number 03)
  • Shut-off valve on the heating return line.

The thermal compact station in question will supply the heating and hot water heating system of the facility in the period when there will be no heat energy from the solar collector system available or the production from the same will be insufficient for current needs.

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In the premises of the thermal substation, it is planned to place a heat exchanger with a capacity of 309 kW, temperature regime: primary 95/65°C, secondary 60/80°C, intended for the transfer of excess of heat energy produced by the solar collector system to district heating system of Zaprešić, consisting of primary and secondary part installed on the supporting frame with accompanying electrical installations. The purpose of this installation is the transfer of thermal energy generated in the solar collector system at a time when there is no need for thermal energy for the school and at the same time there is the production of thermal energy from solar energy. 

Compensation for the elongation of the glycol / water mixture in the primary part of the collector system is provided with an expansion vessel with a volume of 2000 litres, together with a pre-expansion vessel with a volume of 700 litres. The pre-expansion vessel is by nature a heat reservoir that does not allow temperature increases above the allowable values ​​to occur in the expansion vessel, which could damage the membrane of the expansion vessel. Maintaining the pressure in the secondary heating installation in a certain area is solved by a common existing expansion system, manufactured by PIREKO, with a tank capacity of 750 l.  

Therefore, this part of installation consists of a plate heat exchanger with a capacity of 309 kW, shut-off valves, dirt trap, temperature sensors, circulation pump, thermometer, manometer, and flow meter. These installations are connected to the district heating system through the same lines, and the control valves connected to the common control system determine when energy is received from the district heating system and when it is delivered in the system. Summary of technical specifications for heat exchanger:

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The idea of this demonstration center states that in addition to energy from the DH system (as the main source of heat energy), solar collectors are used to generate heat energy for school needs while there is a need for heat energy, and when it does not exist, the generated energy is sent to the DH system. 

In the given conditions, it was established that it is not possible to install solar collectors on the south side of the sloping roof of the school (roof slope 45 °, area 95×9.25-9 * 9.25 / 2 = 837 m2), and it is possible on the western part of the sloping roof of the sports hall. roof pitch 11 °, area 19×45 = 855 m2). More info is given in first part of this document.  

The existing heating system is the central supply of thermal energy to the entire school and sports hall. The solar station, together with two newly designed transceiver compact heat stations (explained above), is installed in the heat substation. The maximum expected thermal power from the solar system is 349 kW. 

The absorbed solar energy is fed via a solar medium to the heating station where in a plate exchanger this energy is transferred to the water which is led to the newly designed heat energy tank. If there is a need for thermal energy in the school or hall, the thermal energy is directed from the specified tank to the distributor, and if there is no thermal need, the energy is sent to the DH system. Summary of technical specifications for heat exchanger:

 

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The installation of a 4 m3 thermal energy (water) tank is also planned in the thermal substation. This tank has the function of creating a reserve of a certain amount of thermal energy so that the automatic control system of the complete thermal substation system can regulate all smart substations according to predefined settings and current requirements for heating and domestic hot water and available thermal energy from the solar collector system. The heat energy tank is manufactured by PIREKO and is technically designed as a hydraulic diverter. All three smart compact heat substations/exchangers and consumers (radiators) on the heating installation (5 circuits in total) are connected to it. Each of these circuits in certain conditions independently produces/takes heat from it, which in ideal conditions should be approximately constant (60-80°C). Heat storage is used to increase share of RES (Used in periods when there is more production from solar field than necessary heat consumption (in school).

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A total of three heat meters are planned to be installed in the smart heat substation system:  

  • On the primary part of the smart heat substation to measure heat taken from the distribution system 
  • In the boiler room Mokrička 61, before the connection to the part to produce thermal energy from the solar collector system (the thermal energy produced in the solar collector field and delivered to the distribution system of HEP-Toplinarstvo is measured)
  • Secondary part of smart heat substation to measure amount of heat sent to heat storage

Furthermore, thermometer will be integrated in heat storage to gather information about current temperatures in building’s heating system (all parts).  

Each heat meter is equipped with an M-bus module for remote reading of energy consumption. The heat meters are connected to one unit by an internal M-bus wire system, and in the central unit, data on the consumption of all heat meters of the mentioned heat circuits are collected and stored. The central unit with the possibility of reading all individual heat meters of the mentioned heat circuits is in the heat station. The described measurement system will be able to accurately monitor the produced thermal energy from the solar collector system and how much of that energy is delivered to the school building for heating and hot water consumption and how much is delivered to the DH system of HEP-Toplinarstvo. The thermal energy taken over by the school building from the DH system will also be measured, and it will be possible to calculate the settlement of its consumption between the school owner and the thermal energy distributor. 

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In the boiler room of the district heating system HEP-Toplinarstvo, for the purposes of this project, the following equipment is installed: 

  1. ON / OFF three-way valves to the supply and return line of the hot water connection between the boiler room and the high school. The valves have the task of using the existing hot water connection for the production and sale of thermal energy. Given the above, the valves will have two modes of operation:
  • CASE 1: there is a need to transfer heat energy from the DH system to the high school. In this case, both three-way valves will be 100% open and the supply and return lines of the Mokrička boiler room will be directly connected to the compact heat station of the high school.
  • CASE 2: there is an excess of heat energy in the heat tank in the High School, and that excess is handed over to the DH system. In this case, both three-way valves will be 100% closed and water will be taken from the return manifold in the hot water boiler room Mokrička 61, raise its temperature level according to the availability of energy in the heat tank in the heating station and connect and send to the supply line of the base condensing boiler in the hot water boiler room Mokrička 61.
  1. Three-way control valve on the inlet (return) line of the base condensing boiler in the hot water boiler room Mokrička 61. The specified control valve will be intended for mixing the required amount of heated water from the solar collector system to the inlet line of the base condensing boiler in the Mokrička boiler room. will depend on the amount of heat available in the heat storage tank. 

When a certain temperature difference occurs between the temperature sensor located on the collector and in the lower part of the newly designed tank, the pump of the primary part of the solar system is started. The pump of the secondary part of the solar system is started when a certain temperature difference is reached between the temperature sensor of the heat exchanger of the solar station and the temperature sensor located in the lower part of the tank. The pump speed and pump shutdown depend on the temperature differences between these sensors. The transfer station pumps start when the tank temperature drops below a certain value. 

If there is no heat consumption in the school and hall, ie if there is no flow between the newly designed tank and the manifold and if there is a certain temperature between the tank and the sensor on return to the DH system, and if automatic control recognizes that the tank is filled with heat from the solar system, only then are the pumps of the production station started and the heat energy is transferred to the DH system. As shown in Figure 1, control three-way “on off” valves are installed on the supply and return lines, the purpose of which is to redirect the energy flows generated on the collectors and changed on the exchanger of the production compact station to the boiler room “Mokrička 61”. The output of the production compact station is led to the boiler room “Mokrička 61” and is connected to the return branch of the heating on the busbar for the base condensing boiler Viessmann Vitovrossal 300 with a nominal power of 1250 kW. The return of the production station is connected to the return line to the boiler room “Mokrička 61”.

 

 

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Implementation process focused on definition of heat prosumer concept in cooperation with stakeholders which required numerous roundtable meetings and engagement with external expert services. First part of cooperation throughout the project was dedicated to the selection of public building according to availability of district heating system and willingness of public building to connect to HEP Toplinarstvo due to price competitiveness of natural gas.  

Developed model could have been achieved in one of three ways based on current condition in selected public buildings 

Option 1: Building not connected to the HEP district heating system: 

  • The building is connected to the district heating system.
  • HEP Toplinarstvo installs solar collectors on the building.
  • Zagreb County is installing a smart substation, a sensor and control system and a heat tank on the building.
  • Solar collectors supply the building with thermal energy, excess energy is transferred to the network, the deficit is taken from the network, the heat tank serves to maximize the heat taken from the solar collectors.

Option 2: Building already connected to the HEP Toplinarstvo system: 

  • HEP Toplinarstvo installs solar collectors on the building.
  • Zagreb County is installing a smart substation, a sensor and control system and a heat tank on the building.
  • Solar collectors supply the building with thermal energy, excess energy is transferred to the network, the deficit is taken from the network, the heat tank serves to maximize the heat taken from the solar collectors.

Option 3: Building that is already connected to the HEP Toplinarstvo system but supplies domestic hot water locally with its own boilers: 

  • The building switches from individual domestic hot water preparation to HEP Toplinarstvo (DHS).
  • HEP Toplinarstvo installs solar collectors on the building.
  • Zagreb County is installing a smart substation, a sensor and control system and a heat tank on the building.
  • Solar collectors supply the building with thermal energy, excess energy is transferred to the network, the deficit is taken from the network, the heat tank serves to maximize the heat taken from the solar collectors.

Technical high school in Zaprešić was selected as location of demonstration center following option 1 to maximize the impact of solar energy since both space heating and domestic hot water are produced by using old natural gas boilers. Throughout the development of necessary project documentation (engineering studies, static load of rooftop construction, solar thermal collectors system) and relevant contracts according to Croatian legislation1, modification of the concept was introduced where solar thermal collectors system is moved to nearby green field due to problems in static of roofs.  

One of the main advocates for selection of this building was its location near main boiler room of district heating in the city of Zaprešić and synergy with strategic development of district heating in the city

The purpose of a specific set of substation components would be to regulate the bidirectional (two-way) exchange of heat between the public (heat prosumer) building and DHS. Using developed management and control programmes, the smart substation through its set of heat exchangers would use captured solar energy on collectors directly for the building’s space heating (and domestic hot water), store it in thermal heat storage (water tank) or send it to local DHS as excess heat through regulated valves, pumps, and other equipment. This decision would come based on continuously monitored parameters and central control system. Conversely, during low production periods, the school receives thermal energy from the DHS once its own reserves have been exhausted. This allows for compensating for any shortages during times of bad weather or peak usage. This smart heating solution, to its full extent, has been facilitated through close collaboration between included local energy company, city and county, energy agency and international manufacturers of equipment.

Goal of this concept is to achieve lower Levelised Cost of Heat (LCOH) for public buildings by applying solar thermal systems and  to set a proof-of-concept for replication, and consequently to secure a low cost heating energy for a public building (fixed price for 3-5 years) in alignment with the current legislation in the sector.

The building would combine solar thermal energy and energy from district heating system to meet its heating demand. However, since solar thermal collectors (installed at the expense of ASP HEP Toplinarstvo and not financed through the CSSC Lab project directly) would not be optimized for school’s heating needs, but larger, interactivity between the school and district heating system has to be introduced as follows:  

  • Solar thermal collectors would be installed on rooftop of selected high school to produce renewable energy based on geographical location and output of the system. 
  • A smart heating substation will be built, which will connect the public building to the district heating network via a heat exchangers (equipped with monitoring and control equipment)
  • All produced energy would be consumed directly in school in case that heat demand needs to be met (according to projections based on gathered data)
  • In case of excess of solar energy, smart substation would be used to regulate the system and enable delivery of solar energy to DH system which would act as a big heat storage and deliver this solar energy to another customer (this is independent decision of HEP Toplinarstvo as owner of solar thermal collectors)
  • In case of lack of solar heat, smart substation would communicate with main boiler room of DH system – heat would be delivered from DH system to the school. 
  • Heat storage within the school is integrated to evaluate technical and economic feasibility of enabling the possibility to store solar energy directly in school instead of sending total value to DH system.
  • The monitoring and control equipment controls when and how much heat energy needs to be exchanged with the DH network and stored in the heat storage tank.

By applying this concept, the school would manage to lower its reliance on fossil fuels for heating, switching from gas to solar thermal energy. It would therefore directly reduce its carbon footprint.  In its initial concept, including storage facilities in the system would allow the usage of additional heat during low production times. This helps avoid wastage and maximises the amount of green energy it consumes. Also, the bidirectional exchange would feed excess heat into the DHS and uses it as larger heat storage which can distribute this renewable heat to other users, making the entire DHS greener.

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During negotiation period and planning phase, project partners REGEA and the Zagreb County, as well as HEP Toplinarstvo agreed to alternate the initial plan due to several reasons.

As presented, solar thermal collectors are planned for installation of rooftop. During creation of engineering study (contracted by the Zagreb County to consultancy office Element Energetika, Zagreb) and in excessive communication with manufacturers and designers of solar thermal collectors, problems with rooftop installations appeared as these systems are quite heavy and would present significant load on current stability. This would not be the problem to perform but require higher investment costs which would have to be covered by HEP Toplinarstvo.

On the other hand, the Zagreb County recently concluded a public procurement for delivery of gas in all of their buildings. Since a joint public procurement has been performed, a significant decrease in natural gas prices took place which definitively endangered the feasibility of demonstration center and put a stoppage on further development of the demo center until the new contract is not finalized (until Q1 2023).  

Due to rooftop installation problems, the project consortium decided to move the the solar system to the ground which completely changed the concept and resulted in the simplification of the solution where the solar thermal system and related heat exchangers, as well as heat storage, have been excluded, leaving only the connection to DHS in the boiler room. This change means that the concept of the demonstration center is moderated as follows.

In previous concept, solar thermal collectors would directly send solar heat to school, while in this concept, solar thermal collectors are directly connected to district heating network which would be used for delivering heat to school for meeting heat demand. Heat storage within the school would still be installed and would be filled in periods when solar system is producing the heat. In case like this, monitoring and regulation equipment would play the main part of this demonstration center – determining shares of solar energy, heat demand and interaction with heat storage. 

However, since the solar thermal system is moved to the ground, the local district heating system took the advantage of the situation and opted out for the large-scale utilization of this technology due to the fact that they managed to agree with the city of Zaprešić on renting a large green field near high school. As a result, a larger system (3 000 m2) is planned to be developed by the local district heating company.

By doing that, the concept changed again where heat storage has been excluded from the boiler room, completely simplifying the boiler room where one heat exchanger would be installed for a connection to the district heating system. It would be used to take the energy from the distribution network to internal consumers within the demo center.

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Current operational and maintenance costs for the demo center are around 24 000 €, mostly accounted for the natural gas as energy source for the current heating system.

In total around 110.000 € was planned for investment which include creation of project documentation (for both the demo center and district heating company), purchase and installation of necessary equipment for demo center boiler room and  for building a connecting pipeline from demo center to local district heating. Part of this investment price should have been covered by the district heating company, while all equipment and construction work were a subject of CSSC Lab demonstration center.  

​Due to introduced changes (moving solar thermal system to the ground), certain changes in financial aspects took change. Firstly, the total amount needed for the boiler room of the demo center were reduced to around 75,000 € since several parts of the demo center were excluded from the boiler room and shifted to the green field. By doing that, the district heating company accepted to finance these parts by their own funds.

Furthermore, since the demo center (after changes) aimed to install a large scale solar thermal field (3 000 m2), CAPEX for the equipment and expansion of heat distribution network were estimated at around 2 300 000 €.

Information for solar thermal system:

  • CAPEX: 2 300 000 € ​(including400 m of pipeline)​
  • OPEX: cca 10 000 €/year​
  • Calculatedproduction of RE heat: 2 000 000 kWh​
  • Specificproduction: 660 kWh/kWp​
  • %RE heatin DH boiler room: 23% yearly​
  • %RE heatin DH boiler room: 104% of summer load​
  • ​ Yearlyheat demand: 682 000 kWh​

Information for demo center

  • Currentgas price: 0,035 €/kWh (until 10/2022)​
  • 0,05 €/kWhif investment in new boiler is considered 
  • New gasprice: 0,06 €/kWh until end of 2023 – governmental decision​
  • New (predicted) gasprice: 0,25 €/kWh​

After integration of solar thermal system​

  • RE heatdelivered from the field: 535 000 kWh/year​
    • 27% of totalfield production​
    • 87% of total heatdemand ​
  • Fixedprice of energy for 3-5 years: 0,46 €/kWh​
  • CO2savings in demo center: 1 200 t/year​

Due to delays and movement of the investment in 2022, prices of necessary equipment and work will significantly increase after the project lifetime due to current situation on energy market. This presents a possible threat to implementation of equipment in the future.

However, a basic calculation in terms of total costs for a demo center are performed where the graph below gives an overview of comparison of costs between business-as-usual scenario (red) and scenario of connecting to the district heating. Observed period is 10 years. For the purposes of calculations, a steady increase of natural gas price was taken into account due to the current status on the energy market. It can be clearly see that the long-term (financial) benefits of this concept were more than double at the end of period.

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Most successful elements 

  • Finalization and acceptance of plan (at this moment) to integrate large scale solar thermal collectors’ field on green field for the purposes of local district heating system (and selected public building). 
  • Identification of main problems in current legislation regarding heat purchase agreements for local district heating systems (according to HERA). 
  • Usage of solar energy for space heating at high temperatures (more than 80 degrees). 
  • Clear pathway for decarbonisation of selected public building’s heating system – more than 70% 
  • Collaboration with Zagreb County and HEP Toplinarstvo – public procurement documentation, “Design&Build” tender documentation

Lessons learned 

  • Issues with static load of rooftop (weight of solar collectors’ system is a very big factor) – beneficial for future analysis
  • Main problems identified in terms of replication of this model such as current legislation puts limits on energy bills structure and prices – calculation of pricses  
  • Decision-making process in district heating sector and willingness of public authorities to commit investments
  • Development of heat purchase agreement as a basis for future heat prosumer model 
  • Time needed for organization of cooperation between local, regional and national public authorities

Difficulties encountered 

  • Legal problems regarding heat purchase 
  • Roof available static load 
  • Decision-making process (acceptance of the city of Zaprešić to participate)
  • Obtaining usage permission for green field (by HEP Toplinarstvo) from the city of Zaprešić
  • Inertia of public procurement processes within national DH company

Potential for knowledge transfer 

  • Great collaboration with relevant stakeholders (apart from DH company)
  • Knowhow on planning of solar thermal collectors’ field and awareness about benefits of renewable energy 
  • Heat prosumer model for public buildings (cooperation with local district heatings) – setting minimum requirements on share of RES and preparation of basic documentation
  • Dissemination of knowhow to other district heating operators (outside of Zagreb County) throughout the Croatian Chamber of Economy (and its association of district heating operators)
  • The selected public building is technical high school which participates in national project Regional Centers of Competitiveness where focus is put on capacity building on renewable energy, energy efficiency and decarbonization in general. 

Future perspectives 

There are several aspects of demonstration center which are available besides of renewable energy in heating systems. Since the rooftop is available (solar thermal collectors are moved to green field), REGEA and Zagreb County will collaborate on expanding decarbonisation of energy consumption by adding PV panels on rooftop through PVMax project (REGEA – EIB). REGEA will provide technical, financial and legal assistance to Zagreb County in terms of engineering study, tender documentation, financing, as well as to add monitored impact of PV system on demonstration center.  

On the other hand, by continuing to develop a large-scale solar thermal field project, HEP Toplinarstvo as local district heating company will decarbonize their system and comply with standards for low-emission heat energy. This will be then used as a main advocacy for future expansion of the grid and connection of public buildings.

The CSSC Lab project laid ground for detailed preparation of documentation and negotiation process for future work in the Zagreb Country where REGEA will continue to promote this concept. In case that the Zagreb County decide to re-active the implementation of it in any of their buildings, all gained knowledge will be used, while all investments will be covered by Zagreb County’s own financial funds.

 

Demo sites

Croatia

Slovenia

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