Academia.eduAcademia.edu

Figure 12 – uploaded by Damir Požgaj

See full PDFdownloadDownload figure
Table 11. The results of simulations of systems A, B and C for buildings with present building envelope and present installed radiator (PB-PR). With the present building envelope and presently installed radiator (PB-PR) pipeline, heat losses are reduced by 13% in system B and 55% in system C compared to system A. Systems B and C have lower operating costs than system A for all three energy price scenarios. For energy price scenario 1 (ES1), cost reduction in system B is 59% and 56%in system C. For energy price scenario 2 (ES2), cost reduction in system B is 47% and 43% in system C. For energy price scenario 3 (ES3), cost reduction in system B is 54% and 60% system C.

Table 11 The results of simulations of systems A, B and C for buildings with present building envelope and present installed radiator (PB-PR). With the present building envelope and presently installed radiator (PB-PR) pipeline, heat losses are reduced by 13% in system B and 55% in system C compared to system A. Systems B and C have lower operating costs than system A for all three energy price scenarios. For energy price scenario 1 (ES1), cost reduction in system B is 59% and 56%in system C. For energy price scenario 2 (ES2), cost reduction in system B is 47% and 43% in system C. For energy price scenario 3 (ES3), cost reduction in system B is 54% and 60% system C.

Related Figures (31)

Figure 1. The ground plan of the Kozala DH system.
Figure 1. The ground plan of the Kozala DH system.
Figure 2. Buildings in the Kozala DH system.
Figure 2. Buildings in the Kozala DH system.
Figure 3. Schematic of the existing heating plant. The heating plant provides a centralized supply of thermal energy. In the initial phase of its operation, fuel oil was used. The system is designed as a hot water system with a temperature regime of 130/70 °C with temperature glide adjusted according to ambient temperature. In 2001, it was reconstructed to allow the use of mixed gas (LPG-air) and natural gas, which is used today. Three boilers are in operation and provide a total output of 9240 kW. Today, all three boilers operate with a variable supply temperature that occasionally, in the coldest weather, reaches 105 °C. The schematic of the existing heating plant is shown in Figure 3.
Figure 3. Schematic of the existing heating plant. The heating plant provides a centralized supply of thermal energy. In the initial phase of its operation, fuel oil was used. The system is designed as a hot water system with a temperature regime of 130/70 °C with temperature glide adjusted according to ambient temperature. In 2001, it was reconstructed to allow the use of mixed gas (LPG-air) and natural gas, which is used today. Three boilers are in operation and provide a total output of 9240 kW. Today, all three boilers operate with a variable supply temperature that occasionally, in the coldest weather, reaches 105 °C. The schematic of the existing heating plant is shown in Figure 3.
Table 1. Distributed thermal energy to pipe network and delivered thermal energy to substations (measured during 2018 and 2019). The heating period begins when the outdoor air temperature falls below 12 °C at 9 P.M. for three consecutive days. The heating period ends when the outside temperature rises above 12 °C at 9 P.M. for three consecutive days. The beginning and the end of this period differ from year to year, but on average the heating period begins around October 15 and ends around May 15, so this is the period used in simulations. There are two types of substations: combined substations for the building and DHW heating (K1, K2, K3, K4, K9, and K10) and su provided by hea bstations for t exchangers. he building heating (K5, K6, and K8). An indirect system is n 2019, building K7 was excluded from the district heating system on consumers’ demand as they were not satisfied with the prices of energy supply and has not been included in radiators. The pi pe system in t of the building and vertical pi supply temperat ure is control ~ this study. The apartments in the buildings are heated by he buildings consists of horizontal pipes on the ground floor pes to the radiators on the upper floors of the building. The ed depending on the outdoor air temperature. ae io a -~e = « ck aw ange r pa:
Table 1. Distributed thermal energy to pipe network and delivered thermal energy to substations (measured during 2018 and 2019). The heating period begins when the outdoor air temperature falls below 12 °C at 9 P.M. for three consecutive days. The heating period ends when the outside temperature rises above 12 °C at 9 P.M. for three consecutive days. The beginning and the end of this period differ from year to year, but on average the heating period begins around October 15 and ends around May 15, so this is the period used in simulations. There are two types of substations: combined substations for the building and DHW heating (K1, K2, K3, K4, K9, and K10) and su provided by hea bstations for t exchangers. he building heating (K5, K6, and K8). An indirect system is n 2019, building K7 was excluded from the district heating system on consumers’ demand as they were not satisfied with the prices of energy supply and has not been included in radiators. The pi pe system in t of the building and vertical pi supply temperat ure is control ~ this study. The apartments in the buildings are heated by he buildings consists of horizontal pipes on the ground floor pes to the radiators on the upper floors of the building. The ed depending on the outdoor air temperature. ae io a -~e = « ck aw ange r pa:
Table 2. The main features of the Kozala district heating system.
Table 2. The main features of the Kozala district heating system.
Table 2. Cont.
Table 2. Cont.
Figure 5. Geometry and thermal zones for building K5, K6 and K8 defined in the Sketchup software.
Figure 5. Geometry and thermal zones for building K5, K6 and K8 defined in the Sketchup software.
After the design and validation of the thermal models, a case of reduced thermal energy consumption in the DH system is considered. In this case, the building envelope of all buildings connected to the DH system was refurbished. Energy refurbishment means the implementation of the physical characteristics of the building envelope (improved thermal insulation) according to the current national regulation [38] which is in accordance with the EU directives. This state of the building is in the further text referred to as RB (energy renovated building).
After the design and validation of the thermal models, a case of reduced thermal energy consumption in the DH system is considered. In this case, the building envelope of all buildings connected to the DH system was refurbished. Energy refurbishment means the implementation of the physical characteristics of the building envelope (improved thermal insulation) according to the current national regulation [38] which is in accordance with the EU directives. This state of the building is in the further text referred to as RB (energy renovated building).
Figure 7. Basic functional scheme of DHW substations: (a) DHW heating for two zones; (b) DHW heating for one zone. tanks, heat exchangers, pumps, piping, and control equipment. Buildings K1, K2 and K3, due to their height of 63 m, have the heating of DHW in two zones to prevent high pressures in installation. Buildings K4, K8 and K9 are lower than 60 m and have DHW heating in one zone. The basic functional scheme of the DHW substation is shown in Figure 7. Based on the monitoring data, the daily DHW consumption profile was created. It corresponds to the actual habits of the users and the specific DHW consumption in residential buildings, defined in [36].
Figure 7. Basic functional scheme of DHW substations: (a) DHW heating for two zones; (b) DHW heating for one zone. tanks, heat exchangers, pumps, piping, and control equipment. Buildings K1, K2 and K3, due to their height of 63 m, have the heating of DHW in two zones to prevent high pressures in installation. Buildings K4, K8 and K9 are lower than 60 m and have DHW heating in one zone. The basic functional scheme of the DHW substation is shown in Figure 7. Based on the monitoring data, the daily DHW consumption profile was created. It corresponds to the actual habits of the users and the specific DHW consumption in residential buildings, defined in [36].
The comparison between the design projects and the actual state of the thermal system n the buildings shows that major changes have occurred. Over the years, and especially uring the crises in the heating sector, which were accompanied by unfavorable heating nergy prices, users often removed radiators by themselves and even sometimes with he consent of the heating supplier. The removal of radiators resulted in single-speed yumps being oversized, heating networks not being hydraulically balanced due to a lack yf balancing valves, and the remaining radiators overheating rooms due to a lack of hermostatic radiator valves (TRV). All of this led to unnecessary energy consumption and hermal discomfort. As mentioned above, building K7 was completely excluded from the <ozala heating system, which caused similar problems for the entire heating system.
The comparison between the design projects and the actual state of the thermal system n the buildings shows that major changes have occurred. Over the years, and especially uring the crises in the heating sector, which were accompanied by unfavorable heating nergy prices, users often removed radiators by themselves and even sometimes with he consent of the heating supplier. The removal of radiators resulted in single-speed yumps being oversized, heating networks not being hydraulically balanced due to a lack yf balancing valves, and the remaining radiators overheating rooms due to a lack of hermostatic radiator valves (TRV). All of this led to unnecessary energy consumption and hermal discomfort. As mentioned above, building K7 was completely excluded from the <ozala heating system, which caused similar problems for the entire heating system.
Figure 9. System A, system B, and system C models for dynamic simulation.
Figure 9. System A, system B, and system C models for dynamic simulation.
Figure 10. The cross-section of the pre-insulated twin pipe system. A dynamic simulation model of the DH system with a distribution network and boiler room with gas boilers was created. It will be referred to as system A in the following. It was used to calibrate the base model of DH system. Type 751 was used for the boiler. The total installed heating capacity is 9240 kW. Simulation of DH pipe network is based on Trnsys Type 951 model for buried twin pipe system and comprises thermal energy losses in the DH system pipe network. The DH pipe network were determined and compared with the data calculated with the Logstor calculator [42]. Logstor is a manufacturer of pre-insulated twin pipe systems installed during the 2018 DH distribution rebuild. The cross-section of the pre-insulated twin pipe system is shown in Figure 10.
Figure 10. The cross-section of the pre-insulated twin pipe system. A dynamic simulation model of the DH system with a distribution network and boiler room with gas boilers was created. It will be referred to as system A in the following. It was used to calibrate the base model of DH system. Type 751 was used for the boiler. The total installed heating capacity is 9240 kW. Simulation of DH pipe network is based on Trnsys Type 951 model for buried twin pipe system and comprises thermal energy losses in the DH system pipe network. The DH pipe network were determined and compared with the data calculated with the Logstor calculator [42]. Logstor is a manufacturer of pre-insulated twin pipe systems installed during the 2018 DH distribution rebuild. The cross-section of the pre-insulated twin pipe system is shown in Figure 10.
Table 3. Technical data of the DH network.
Table 3. Technical data of the DH network.
Table 4. Comparison of measured and simulated fuel energy of natural gas for heat production in boilers. System B—R717 heat pump
Table 4. Comparison of measured and simulated fuel energy of natural gas for heat production in boilers. System B—R717 heat pump
Table 5. Investment costs for system A, B and C costs for the present state of buildings (PB). The investment costs for systems A, B and C for the state with completely renovated buildings are shown in Table 6.
Table 5. Investment costs for system A, B and C costs for the present state of buildings (PB). The investment costs for systems A, B and C for the state with completely renovated buildings are shown in Table 6.
Table 6. Investment costs for systems A, B and C for the state with completely renovated buildings (RB). Electricity and gas prices are set for three scenarios. According 1 (ES1), prices are from 2021 in Croatia. According to energy price to energy price scenario scenario 2 (ES2), prices have increased due to the ongoing energy crisis in the EU. The gas price on the Central European Gas Hub (CEGH) gas market on 02 October 2022 was The electricity price on the power market (EEX-PXE) was 489.44 E 62.89 EUR/MWh [46]. UR/MWh in the fourth quarter of 2022 [47]. According to energy price scenario 3 (ES3), gas and electricity prices increase by 50% compared to scenario 2. A concession fee for t operation of heat pump systems is the same for all three energy prices are shown in Table 7. he use of water for the price scenarios. These
Table 6. Investment costs for systems A, B and C for the state with completely renovated buildings (RB). Electricity and gas prices are set for three scenarios. According 1 (ES1), prices are from 2021 in Croatia. According to energy price to energy price scenario scenario 2 (ES2), prices have increased due to the ongoing energy crisis in the EU. The gas price on the Central European Gas Hub (CEGH) gas market on 02 October 2022 was The electricity price on the power market (EEX-PXE) was 489.44 E 62.89 EUR/MWh [46]. UR/MWh in the fourth quarter of 2022 [47]. According to energy price scenario 3 (ES3), gas and electricity prices increase by 50% compared to scenario 2. A concession fee for t operation of heat pump systems is the same for all three energy prices are shown in Table 7. he use of water for the price scenarios. These
Table 7. Electricity, gas, and water use fee prices for three energy price scenarios. The annual maintenance cost for heat energy production systems is estimated at 5% of the investment value, while for PV systems it is estimated at 2.5% of the investment value. The annual maintenance cost of existing system A is calculated from the record acquired from the heat supplier (EUR 99,542).
Table 7. Electricity, gas, and water use fee prices for three energy price scenarios. The annual maintenance cost for heat energy production systems is estimated at 5% of the investment value, while for PV systems it is estimated at 2.5% of the investment value. The annual maintenance cost of existing system A is calculated from the record acquired from the heat supplier (EUR 99,542).
Table 8. Primary energy factors and CO emission factors. 2.2.9. Scope of the Research
Table 8. Primary energy factors and CO emission factors. 2.2.9. Scope of the Research
The results of the year-round simulations of heat consumption for buildings and DHW heating in the substations according to the current characteristics of the buildings anc for the case when all the buildings are renovated are shown in Figure 13, summarized for months.
The results of the year-round simulations of heat consumption for buildings and DHW heating in the substations according to the current characteristics of the buildings anc for the case when all the buildings are renovated are shown in Figure 13, summarized for months.
* PB—the present state of buildings envelopes; RB—energy renovated buildings ** PR—present state of installed radiators; OR—originally installed radiators. Table 9. The designed loads for heating of buildings and minimum required water temperature in radiators for four scenarios.
* PB—the present state of buildings envelopes; RB—energy renovated buildings ** PR—present state of installed radiators; OR—originally installed radiators. Table 9. The designed loads for heating of buildings and minimum required water temperature in radiators for four scenarios.
* PB—the present state of buildings envelopes; RB—energy renovated buildings, ** PR—present state of installe radiators; OR—originally installed radiators. Table 10. The supply temperature in the DH network for different cases of the state of the building envelope and state of the radiators in buildings at an outside air temperature of —8 °C and 12 °C. Table 10. The supply temperature in the DH network for different cases of the state of the building
* PB—the present state of buildings envelopes; RB—energy renovated buildings, ** PR—present state of installe radiators; OR—originally installed radiators. Table 10. The supply temperature in the DH network for different cases of the state of the building envelope and state of the radiators in buildings at an outside air temperature of —8 °C and 12 °C. Table 10. The supply temperature in the DH network for different cases of the state of the building
Figure 14. The annual supply temperature in the DH network of system B and C operating in PB-PR and RB-PR scenarios obtained by dynamic simulation. Se ES Is, BEE IESE IES NEES SEER SN EH SENSIS TSE “System A with hot water boiler i is operated with a temperature glide between 90 and 80 °C, depending on the ambient temperature, which is controlled in the distribution center. System B consists of two central heat pumps with R717 refrigerant that provide all he heating and hot water needs of the building. During the heating season, the supply emperature in the pipe network changes depending on the outside air temperature, but never drops below 65 °C. At the end of the heating season, the supply temperature in the DH network is a constant 65 °C to heat up DHW. System C consists of two central heat pumps with R717 refrigerant for building heating and R744 heat pumps for DHW heating in substations. During the heating season, the supply temperature in the pipe network changes depending on the outside air temperature. At the end of the heating season, he supply temperature in the DH network is maintained at 25 °C which is a suitable temperature for the heat source for R744 heat pumps for DHW heating. The annual change in supply temperature in the DH network for systems B and C operating in PB-PR and RB-PR scenarios, obtained by dynamic simulation, is shown in Figure 14.
Figure 14. The annual supply temperature in the DH network of system B and C operating in PB-PR and RB-PR scenarios obtained by dynamic simulation. Se ES Is, BEE IESE IES NEES SEER SN EH SENSIS TSE “System A with hot water boiler i is operated with a temperature glide between 90 and 80 °C, depending on the ambient temperature, which is controlled in the distribution center. System B consists of two central heat pumps with R717 refrigerant that provide all he heating and hot water needs of the building. During the heating season, the supply emperature in the pipe network changes depending on the outside air temperature, but never drops below 65 °C. At the end of the heating season, the supply temperature in the DH network is a constant 65 °C to heat up DHW. System C consists of two central heat pumps with R717 refrigerant for building heating and R744 heat pumps for DHW heating in substations. During the heating season, the supply temperature in the pipe network changes depending on the outside air temperature. At the end of the heating season, he supply temperature in the DH network is maintained at 25 °C which is a suitable temperature for the heat source for R744 heat pumps for DHW heating. The annual change in supply temperature in the DH network for systems B and C operating in PB-PR and RB-PR scenarios, obtained by dynamic simulation, is shown in Figure 14.
Table 12. The results of simulations of systems A, B and C with renovated building envelope and present installed radiator (RB-PR). With the renovated building envelope and presently installed radiator (RB-PR) it is possible to reduce the supply water temperature and maintain thermal comfort in the buildings. Therefore, pipeline heat losses of system A given in Table 12 are lower than hose shown in Table 11. Pipeline heat losses are reduced by 8% in system B and 52% in system C compared to system A. As expected, all three systems have lower operating costs than those in the scenario with the present state of the buildings (PB-PR). Systems B and C have lower operating costs than system A for all three energy price scenarios. For energy price scenario 1 (ES1), cost reduction in system B is 58% and 53% in system C. For energy price scenario 2 (ES2), cost reduction in system B is 51% and 55% in system C. For energy price scenario 3 (ES3), cost reduction in system B is 53% and 58% in system C.
Table 12. The results of simulations of systems A, B and C with renovated building envelope and present installed radiator (RB-PR). With the renovated building envelope and presently installed radiator (RB-PR) it is possible to reduce the supply water temperature and maintain thermal comfort in the buildings. Therefore, pipeline heat losses of system A given in Table 12 are lower than hose shown in Table 11. Pipeline heat losses are reduced by 8% in system B and 52% in system C compared to system A. As expected, all three systems have lower operating costs than those in the scenario with the present state of the buildings (PB-PR). Systems B and C have lower operating costs than system A for all three energy price scenarios. For energy price scenario 1 (ES1), cost reduction in system B is 58% and 53% in system C. For energy price scenario 2 (ES2), cost reduction in system B is 51% and 55% in system C. For energy price scenario 3 (ES3), cost reduction in system B is 53% and 58% in system C.
Figure 15. Monthly thermal energy for heating produced by system B, electricity to run the heat pump, and SCOP for the present state (PB-PR) and renovated state (RB-PR) of buildings.
Figure 15. Monthly thermal energy for heating produced by system B, electricity to run the heat pump, and SCOP for the present state (PB-PR) and renovated state (RB-PR) of buildings.
Figure 16. COP of the R717 heat pump depending on load and output temperature. There is a drop in SCOP present during the summer period for system B, which can be addressed to the operation of the central heat pump at partial load. COP of the R717 heat pump changes depending on the operating load and the output temperature of the heat pump, as shown in Figure 16.
Figure 16. COP of the R717 heat pump depending on load and output temperature. There is a drop in SCOP present during the summer period for system B, which can be addressed to the operation of the central heat pump at partial load. COP of the R717 heat pump changes depending on the operating load and the output temperature of the heat pump, as shown in Figure 16.
Figure 17. Monthly heat produced by system C with central R717 heat pump, electricity to run the heat pump, and SCOP for the present state (PB-PR) and renovated state (RB-PR) of buildings. HP heat production is reduced by 31%, while electricity consumption for heat pump operation is reduced by 30% on an annual basis in the case of renovated buildings (RB-PR) compared to the present state of buildings (PB-PR).
Figure 17. Monthly heat produced by system C with central R717 heat pump, electricity to run the heat pump, and SCOP for the present state (PB-PR) and renovated state (RB-PR) of buildings. HP heat production is reduced by 31%, while electricity consumption for heat pump operation is reduced by 30% on an annual basis in the case of renovated buildings (RB-PR) compared to the present state of buildings (PB-PR).
Figure 18. Indicator of primary energy and CO? emission for present state (PB) and renovated state (RB) of buildings.
Figure 18. Indicator of primary energy and CO? emission for present state (PB) and renovated state (RB) of buildings.
Figure 19. The global costs of systems A, B and C for present state of building envelope (PB-PR) and three energy prices scenarios: (a) ES1, (b) ES2, and (c) ES3. The global costs of systems A, B and C for the present state of the building envelope (PB-PR) and three scenarios of energy prices (ES1, ES2, ES3) are shown in Figure 19. 3.5. Cost Performance Results
Figure 19. The global costs of systems A, B and C for present state of building envelope (PB-PR) and three energy prices scenarios: (a) ES1, (b) ES2, and (c) ES3. The global costs of systems A, B and C for the present state of the building envelope (PB-PR) and three scenarios of energy prices (ES1, ES2, ES3) are shown in Figure 19. 3.5. Cost Performance Results
Figure 20. The global costs of systems A, B and C for renovated state of buildings envelope (RB-PR) and three energy prices scenarios: (a) ES1, (b) ES2, and (c) ES3. The global costs of systems A, Band C for the renovated state of the building envelope and three scenarios of energy prices are shown in Figure 20.
Figure 20. The global costs of systems A, B and C for renovated state of buildings envelope (RB-PR) and three energy prices scenarios: (a) ES1, (b) ES2, and (c) ES3. The global costs of systems A, Band C for the renovated state of the building envelope and three scenarios of energy prices are shown in Figure 20.
Related topics:
EngineeringEnvironmental ScienceRenewable EnergyHeat pump
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved