Demonstration Center 1
Croatia
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:
- Thermal collectors’ system for capturing heat
- Smart District Heating Substations configuration to enable a proper exchange of heat
- Heat storage (hot water tank)
- 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
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.
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.
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.
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:
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:
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.
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.
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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