Energy Performance Investigation of Bi-Directional Convergence Energy Prosumers for an Energy Sharing Community

energies

Article Energy Performance Investigation of Bi-Directional Convergence Energy Prosumers for an Energy Sharing Community

Min-Hwi Kim * , Dong-Won Lee, Deuk-Won Kim, Young-Sub An and Jae-Ho Yun

Renewable Heat Integration Research Lab., Korea Institute of Energy Research, Gajeong-ro 152, Daejeon 34129, Korea; [email protected] (D.-W.L.); [email protected] (D.-W.K.); [email protected] (Y.-S.A.); [email protected] (J.-H.Y.) * Correspondence: [email protected]; Tel.: +82-42-860-3507

Abstract: Due to the wide-spread use of photovoltaic (PV) systems, interest regarding economic beneﬁt and energy-sharing from surplus electricity has been raised. In this study, decentralized thermal and electric convergence energy prosumers for an energy-sharing community are proposed. For the convergence energy system, a simultaneous heating and cooling heat pump (SHCHP) system integrated with a thermal network is proposed, and the energy performance and operating energy savings of the proposed system were investigated. A smart village located in the Busan Eco Delta Smart City was selected as a case study for the simulation analysis. Experimental data of the heat pump system were used to analyze the SHCHP. The analysis results showed that the proposed system could provide over 53% and 86% of the load cover and supply cover factors, respectively. The proposed system can earn economic beneﬁts, such as energy trading from the surplus electricity of PV systems and thermal energy produced by an SHCHP, more than 30.5 times those of conventional

air-source heat pump systems. These beneﬁts mainly originate that a conventional system can trade the surplus electricity from a PV system but the proposed system can trade produced thermal energy

Citation: Kim, M.-H.; Lee, D.-W.; from SHCHPs and the surplus electricity from PV systems. Kim, D.-W.; An, Y.-S.; Yun, J.-H. Energy Performance Investigation of Keywords: energy sharing community; heat pump; simultaneous cooling and heating; self-sufficiency; Bi-Directional Convergence Energy thermal and electric prosumer Prosumers for an Energy Sharing Community. Energies 2021, 14, 5544. https://doi.org/10.3390/en14175544 1. Introduction Academic Editor: Adrián Mota Extensive efforts have been invested into increasing the applicability of various new Babiloni renewable energy systems for responding to the climate crisis [1]. As part of such efforts, district heating has been utilized in various ways for a long time to resolve the issue of Received: 28 July 2021 urban heat islands and to increase the efﬁciency of heat supplies while reducing particulate Accepted: 1 September 2021 Published: 5 September 2021 matter [2,3]. In recent years, considerable effort has been invested into increasing renewable energy shares in the district cooling and heating, as well as power sectors. Accordingly, the

Publisher’s Note: MDPI stays neutral applicability of fifth generation district heating has been considered to achieve advances with regard to jurisdictional claims in beyond the fourth generation [4,5]. published maps and institutional affil- Decentralized district cooling and heating are gaining increasing interest over con- iations. ventional central supply systems. The concept of power prosumers has been expanded to include prosumers of district cooling and heating thermal networks. To this end, a considerable number of studies have been conducted to develop prosumers based on solar and thermal energy as alternatives to unused heat sources and waste heat [6–12]. Previous studies have focused on selling excess heat from solar thermal systems to thermal networks Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. by linking solar thermal systems with district heating networks [7,8,11,12]. Brange et al. This article is an open access article Reference [6] proposed methods for using a gas boiler and heat pump to implement a distributed under the terms and thermal prosumer in a district heating network. However, one disadvantage of these conditions of the Creative Commons methods is that the excess heat produced by the prosumer is concentrated in summer. Attribution (CC BY) license (https:// Therefore, there is currently a demand for a prosumer who can provide cooling energy. creativecommons.org/licenses/by/ In addition to supplying excess heat from solar thermal systems in the summer season 4.0/). to thermal networks, high prosumer efficiency can be achieved via the applicability of heat

Energies 2021, 14, 5544. https://doi.org/10.3390/en14175544 https://www.mdpi.com/journal/energies Energies 2021, 14, 5544 2 of 17

pump systems that use waste heat or unused heat sources. Changes in daily loads are responded to via short-term thermal energy storage (TES) in a thermal network, which is considerably less expensive than battery energy storage systems (BESSs) used for storing and utilizing electric power, thus improving the applicability of prosumers using thermal network [13,14]. If air conditioning and water heating are simultaneously operated by a building in summer by separating cooling and heat energies through district cooling and heating, the applicability of a simultaneous heating and cooling heat pump (SHCHP) system can be considered very high. An SHCHP system is one where heat and cooling energies produced in the condenser and evaporator, respectively, of the heat pump are utilized for the heating, domestic hot water (DHW), and cooling of a building. Shin et al. [15] proposed an operation strategy method to improve the energy efficiency of an SHCHP in a system where a thermal storage tank was applied; they analyzed its applicability using the TRNSYS simulation program. Kang et al. [16] analyzed an operational optimization method for a heat pump when the cooling and heating demands occur simultaneously in one building. Ghoubali et al. [17] analyzed the performance of a heat pump in terms of refrigerants in an SHCHP system through a TRNSYS simulation. These studies only analyzed efficiency increases in SHCHP systems when supplying cooling and heat energies under simultaneous cooling and heating demands in a single building such as a hotel or a hospital. Byrne and Ghoubali [18] analyzed an operation strategy when implementing an SHCHP system based on an air source heat pump and the exergy aspects based on prototype operation. While a general heat pump is operated to produce cooling or heat energies, an SHCHP simultaneously uses both cooling and heat energies in buildings such as hotels or hospitals, where there are simultaneous cooling and heating demands or the balance between the two needs to be secured through a separate TES for cooling and heat energies [15]. Unlike conventional mechanisms, applicability in a single building can be heightened if a district heating and cooling network is formed and the produced cooling and heat energies are supplied to a thermal network in the form of a thermal prosumer. Conventional residential buildings commonly employ energy transferring or trading through peer-to-grid (P2G) and cooling, heating, and hot water served through an air- source heat pump (ASHP); meanwhile, the power generated by photovoltaic (PV) systems is supplied to houses, and excess power is supplied to the grid. A measure to maximize self-consumption is required because the cost of selling power to the grid is less than the cost of purchasing power from the grid. Therefore, BESSs have been employed as the most general method to maximize the usage of power generation in PV. However, a battery is expensive and the surplus energy produced by a PV system is supplied back to the grid, thus inducing problems in voltage stabilization. Thus far, prosumers have been trading via the P2G format between themselves and central energy suppliers. However, a new mode of trading is required for renewable and distributed energy sharing within communities to expand the amount of renewable energy supplied at the community level [19–21]. The employment of low-carbon energy-sharing communities is one such approach to spread and disseminate zero-energy communities. These energy-sharing communities aim to improve energy efficiency and achieve zero energy by sharing the thermal and electric power from the renewables between buildings or communities. In recent years, various studies have been conducted in communities where energy sharing is possible to design measures to share or trade surplus power produced by a PV system installed in a single building with the neighborhood, to produce heat through a power-to-heat (P2H) mechanism where excess power is converted to heat [22], or to store heat produced by the building itself [23–25]. In a previous study [19], a centralized energy-sharing system for communities was proposed and investigated. Individual PV systems were installed on the roofs of each house, and shared electric energy was produced through a shared PV system installed in a common area. Furthermore, a BESS was located Energies 2021, 14, x FOR PEER REVIEW 3 of 17

heat produced by the building itself [23–25]. In a previous study [19], a centralized energy- sharing system for communities was proposed and investigated. Individual PV systems were installed on the roofs of each house, and shared electric energy was produced through a shared PV system installed in a common area. Furthermore, a BESS was located Energies 2021, 14, 5544 near the community center and stored the surplus electricity produced by the3 of PV 17 system. The cooling, heating, and hot water load of the houses were served by the centralized mechanical system with heat pumps. The sources of heat pumps included ground and nearriver the water community source centers. and stored the surplus electricity produced by the PV system. The cooling,However, heating, in this and study, hot water a decentralized load of the houses thermal were network served bywith the convergence centralized energy mechanicalprosumers system is proposed with heat in a pumps. specific The single sources-family of heathouse pumps for tr includedading and ground sharing and electricity riverand waterthermal sources. energy. Seven houses in the case study village were configured with an in- dependentlyHowever, formed in this study, distributed a decentralized thermal thermalnetwork network in a residential with convergence complex energywith 56 single- prosumers is proposed in a speciﬁc single-family house for trading and sharing electricity family houses where a district cooling and heating network was formed; two houses were and thermal energy. Seven houses in the case study village were conﬁgured with an independentlyset as thermal formed prosumers distributed within thermal the network distributed in a residential thermal network. complex with The 56 applicability single- of familysimultaneously houses where producing a district cooling and and heating heat energies network with was formed;the SHCHP two houseswas analyzed were using seta thermal as thermal prosumer. prosumers The within energy the performance distributed thermal and operation network. cost The were applicability comparatively of an- simultaneouslyalyzed against producing a conventional cooling andmethod heat energiesthat employs with the an SHCHP ASHP. was The analyzed heat pump using was ana- alyzed thermal based prosumer. on the actual The energy operation performance results of and a water operation-to-water cost were heat comparativelypump (WWHP) in the analyzedeco-friendly against energy a conventional town Jincheon method [1]. that This employs case study an ASHP. smart Thevillage heat is pump located was in the wa- analyzedterfront basedarea of on the the Busan actual operationEco Delta results City,of which a water-to-water is a national heat smart pump city (WWHP) pilot project in and the eco-friendly energy town Jincheon [1]. This case study smart village is located in the contains various technologies in terms of innovation renewable energy and ecosystems. waterfront area of the Busan Eco Delta City, which is a national smart city pilot project and contains various technologies in terms of innovation renewable energy and ecosystems. 2. Convergence Energy Prosumer System in an Energy-Sharing Community 2.2.1. Convergence Operating Schematic Energy Prosumer of Proposed System Bi-Directional in an Energy-Sharing Thermal Prosumer Community 2.1. Operating Schematic of Proposed Bi-Directional Thermal Prosumer The authors of this study analyzed a P2H mechanism where surplus power was con- vertedThe to authors heat, and of this an study energy analyzed reduction a P2H effect mechanism was observed where surplus when powerthe produced was con- heat was verted to heat, and an energy reduction effect was observed when the produced heat was supplied to a district cooling and heating network. An SHCHP, which can simultaneously supplied to a district cooling and heating network. An SHCHP, which can simultaneously produceproduce cooling cooling and and heat heat energies, energies, was applied was applied to implement to implement P2H, and P2H, the applicability and the applicability of sharingof sharing or trading or trading the produced the produced cooling cooling and heating and energies heating to energies a distributed to a coolingdistributed and cooling heatingand heating network network was analyzed was analyzed (Figure1 ).(Figure 1).

FigureFigure 1. 1.Schematic Schematic of hybridof hybrid energy energy system system integrated inte withgrated a convergence with a convergence energy prosumer energy system prosumer sys- fortem an for energy-sharing an energy-sharing community. community.

Out of 56 houses, 7 single-family houses were conﬁgured with a distributed thermal network. Two of the seven single-family houses were conﬁgured to facilitate the sharing and trading of heat energy and power in a P2P format. These houses are called convergence energy prosumers, and the system in which bidirectional energy trade is possible is called

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Out of 56 houses, 7 single-family houses were configured with a distributed thermal network. Two of the seven single-family houses were configured to facilitate the sharing Energies 2021, 14, 5544 and trading of heat energy and power in a P2P format. These houses are called conver-4 of 17 gence energy prosumers, and the system in which bidirectional energy trade is possible is called a convergence energy system. This energy system comprises a WWHP that simul- taneouslya convergence produces energy cooling system. and This heat energy energies, system a substation comprises afor WWHP supplying that simultaneouslythe produced coolingproduces and cooling heat energies and heat into energies, a block a substation cooling and for heating supplying network, the produced and a distributed cooling and thermalheat energies network into to a separately block cooling manage and heatingthe energy network, for implementing and a distributed the thermal thermal prosumer network withinto separately a district manage cooling the and energy heating for network. implementing the thermal prosumer within a district coolingIn the and convergence heating network. energy prosumer systems installed at the two houses in this study,In the the power convergence generated energy by a building prosumer-integrated systems photovoltaic installed at ( theBIPV two) system houses was in first this consumedstudy, the powerby the generatedhouses. The by system a building-integrated was designed photovoltaicso that basic(BIPV) cooling, system heating, was and first DHWconsumed loads bycan the be houses.utilized Theat prosumer system was houses designed through so thata central basic heat cooling, supply. heating, Surplus and powerDHW is loads significantly can be utilized produced at prosumerin the summer houses season through when a centralthe cooling heat demand supply. is Surplus high. Apower 3 RT SHCHP is significantly was installed produced in both in the houses summer where season surplus when power the cooling was used demand for P2P is high. trade A or3 RTsold SHCHP to the grid was when installed it exceed in bothed houses the power where consumption surplus power of the was heat used pump. for P2P trade or soldIn to this the study, grid when the power it exceeded remaining the power after the consumption operation of of the the SHCHIP heat pump. was sold to the grid. TheIn this heat study, generated the power through remaining the operati afteron the of operation the SHCHP of the was SHCHIP first consumed was sold in to the the building,grid. The and heat then generated the excess through heat was the operationsupplied or of sold the SHCHPto a distributed was first thermal consumed network. in the Tbuilding,he excess andheat then remaining the excess after heat consum wasption supplied at the or seven sold to houses a distributed was supplied thermal or network. sold to theThe centralized excess heat thermal remaining network, after consumption which supplie atd the the seven energy houses to 56 was single supplied-family or houses. sold to Thethe heat centralized produced thermal by the network, SHCHP which and supplied supplied to the the energy network to 56was single-family measured using houses. a calorimeterThe heat produced for each household by the SHCHP and charged and supplied according to the to networkthe set rate. was Fig measuredure 2 shows using the a designcalorimeter schematics for each for household the bidirectio andnal charged heat exchange according using to the a set heat rate. pump Figure in 2the shows district the coolingdesign and schematics heating fornetwork the bidirectional comprising heat 56 single exchange-family using houses, a heat where pump 7 inhouses the district were configuredcooling and with heating block network cooling and comprising heating network 56 single-familys. houses, where 7 houses were configured with block cooling and heating networks.

Smart village Electricity Cooling Heating & DHW

Mechanical room in the community center

Thermal

Electricity grid BIPV Load

GSHP

Electric

PV Load WSHP

TES TES EV (Cooling & (Heating ESS Heating) & DHW)

Thermal network (Cooling)

Thermal network (Heating & DHW)

Distributed network

Electric Thermal BIPV Load Load

Residential houses Electric Thermal Electric Thermal BIPV SHCHP BIPV (Consumers) Load Load Load Load

Residential houses

Residential houses (Five Consumers)

(Two Prosumers)

(a)

Figure 2. Cont.

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MV2-D2 MV2-D4 °C °C Distributed thermal network °C TD3 °C TD1 (7 houses) TD4 TD2

LPM FD2 LPM FD1

CWR

HWR CWS bar PD2 HWS bar PD1 MV2-D1 MV2-D3 DP7-1(A/B) DP7-2(A/B)

MV3-D1 MV3-D3 MV3-D2 MV3-D4 HWR CP19-2(A/B) HWS 12 houses CWR CP19-1(A/B) CWS

HWR Community center HWS TM9 CWR °C TS1 CWS TM8 TM1 PS1 TS2 FS1 TS3 °C FQ1 TQ1 PQ1 °C MV-P1 °C TES (Cooling/Heating) bar °C LPM °C HX 19-1 LPM °C bar

TQ2 TM7 TM6 HX- MV-HB1 TT1 °C MV-HB4 °C °C °C Cool PM4 PM3 PM2 bar FQ2 TQ3 PQ2 bar bar TT2 °C PS2 bar HX 37-1 LPM °C bar FM1 WSP1/2 TT3 °C TS4 TQ4 LPM HX- °C Cool °C 37 houses TT4 °C PS3 MV-HP4 MV-HP2 FM2 WSP3/4 PM1 TM2 TS6 bar LPM bar °C °C MVBY-1 MV-HP3 MV-HP1 TT5 °C WP19-1/2 WP37-1/2 TS5 TM3 MV-HB2 MV-HB3 MVC-HB3 °C TM5 TM4 °C °C °C WSP5/6 FM3 LPM MVBY-A

TL1 FL1 TP1 PP1 TP2 50 RT °C LPM TES (Heating/DHW) 50 RT 30 RT 30 RT 30 RT °C MVH-P2 bar MVBY-B °C WSHP WSHP GSHP WSHP GSHP WP19-3/4 (19-1) (37-2) (37-1) (37-1) (19-1) WP37-3/4 TN1 °C PP2 FQ3 TQ5 PQ3 bar HX 19-2 LPM °C bar TN2 °C TR? TR? TR4 TR? TR5 WSP7/8 TP3 HX- TQ6 °C °C °C °C °C °C °C TN3 °C Heat PP3 FQ4 TQ7 PQ4 TL4 bar HX 37-2 LPM °C bar °C TN4 °C TL2 PL1 FP1 TQ8 Source side °C HX- Source side bar LPM °C 37 houses header (return) header (supply) TN5 °C Heat 20 RT 30 RT MVH-P1 TP7 TP6 TP5 TP4 TR1 GSHP GSHP TR2 TL3 °C °C MVBY-2 °C °C °C (19-2) (37-2) °C FR1 °C LPM PR1 bar TR3 TR6 °C °C (b)

FigureFigure 2. 2. DetailDetailss of of the the hybrid hybrid energy energy system system integrated integrated with with the the convergence convergence energy energy prosumer prosumer systems systems:: (a (a) )Schematic Schematic of of proposedproposed system system;; (b (b) )c connectiononnection of of the the centralized centralized district district thermal thermal network network with with the the distributed distributed thermal thermal network. network.

AnAn energy energy sharing sharing coordinator coordinator (ESC) (ESC) determine determinedd whether whether the the surplus surplus energy energy pro- pro- ducedduced by by the the PV PV system system within within the the community community was was stored stored in in the the ESS ESS or or if if a aheat heat pump pump waswas operated operated to to produce produce or or store store the the energy energy;; further furthermore,more, the the ESC ESC determine determinedd the the energy energy andand payment payment balance. balance. The The ESC ESC was was positioned positioned in the in low the- low-voltagevoltage substation substation between between the mainthe maingrid and grid the and community, the community, and it and monitor it monitoreded the real the-time real-time power power output, output, usage, usage, and thermaland thermal energy energy consumption consumption through through a smart a meter. smart meter.The charging The charging and discharging and discharging of the batteryof the batteryand thermal and thermalstorage storagewere also were monitored also monitored to minimize to minimize the power the energy power energybeing suppliedbeing supplied to or from to orthe from grid. the Accordingly, grid. Accordingly, the cost of the power cost ofconsumption power consumption of the commu- of the nitycommunity was minimized, was minimized, and the andsaved the cost saved was cost distributed was distributed to each to building each building through through a P2P a pricingP2P pricing mechanism. mechanism. 2.2. Overview of Case Study Community: Smart Village 2.2. Overview of Case Study Community: Smart Village The case study community was a smart village located in the Busan Eco Delta Smart The case study community was a smart village located in the Busan Eco Delta Smart City. The village comprises 56 single-family houses and community centers (Figure3)[ 19]. CityThe. The village village has comprises a site area 56 of single 7202 m-family2, a building houses area and ofcommunity 2200 m2, andcenter a totals (Figure ﬂoor 3) area [19] of. 2 2 The3620 village m2. Detailed has a site physical area of 7202 information m , a building is shown area in of Table 22001. m In, theand residential a total floor houses, area of a 2 3620total m of. 88Detailed kWp of physical the BIPV information system was is installed shown in on Table the roofs 1. In of the 19 residential houses, and houses, 10.8 and a total34.9 of kWp 88 kWp of the of PV the systems BIPV system were installed was installed in garages on the and roof corridors,s of 19 houses respectively., and 10.8 and 34.9 kWp of the PV systems were installed in garages and corridors, respectively.

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FigureFigure 3. 3.Overview Overview of of the the smart smart village. village.

TableTable 1. 1.Physical Physical information information of of buildings buildings in in the the smart smart village. village.

ResidentialResidential Houses Houses Community Community Facility TotalTotal 72027202 Area Area BuildingBuilding 16361636 266 266 (m(m2)2) TotalTotal floor ﬂoor 23742374 1192 1192 StorStoriesies 2 22 2 LightweightLightweight steelsteel structures struc- ReinforcedReinforced concrete concrete struc- MaterialsMaterials turescombined combined with with reinforced rein- structures concrete structures tures forced concrete structures Inﬁltration (1/h@50 pa) 0.3 1.5 Infiltration (1/h@50 pa) 0.3 1.5 Direct 0.147 0.147 ExternalExternal Direct 0.147 0.147 wall Indirect - 0.195 wall Indirect - 0.195 Roof 0.103 0.107 U-valueU-value Roof 0.103 0.107 (W/(m2·K) Direct 0.138 0.140 (W/(m2∙K) Floor Direct 0.138 0.140 Floor Indirect 0.175 0.214 Indirect 0.175 0.214 Window 0.997, 0.963 0.997 Window 0.997, 0.963 0.997 SHGC Window 0.35 0.4 SHGC Window 0.35 0.4

3. Simulation 3. Simulation To analyze the energy and thermal performance of the proposed SHCHP system, To analyze the energy and thermal performance of the proposed SHCHP system, the the cooling, heating, and hot water demand of the houses were analyzed with detailed cooling, heating, and hot water demand of the houses were analyzed with detailed simu- simulations. Additionally, the SHCHP system was investigated based on experimental HP lations. Additionally, the SHCHP system was investigated based on experimental HP op- operation data. eration data. We analyzed the seven houses included in the distributed thermal network. These We analyzed the seven houses included in the distributed thermal network. These houses were named H1–H7, and only H1 and H2 were speciﬁed as convergence energy houses were named H1–H7, and only H1 and H2 were specified as convergence energy prosumers. Houses H1–H7 had 3.42 kWp of the BIPV system installed. prosumers.For the simulation,Houses H1– TRNSYSH7 had 3.42 18 (Madison,kWp of the WI, BIPV USA) system was installed. selected to model the PV system,For and the EnergyPlus simulation, (U.S. TRNSYS Department 18 (Madison, of Energy, WI, USA) was usedselected to analyze to model the the cool- PV ingsystem, and heatingand EnergyPlus demands (U.S. (Figure Department4). Meteonorm of Energy, 7.3 (Fabrikstrasse,USA) was used Switzerland) to analyze the with cool- theing TMY2 and heating data format demands was (Figure used to 4) generate. Meteonorm the meteorological7.3 (Fabrikstrasse, data Switzerland) for the simulation. with the

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TMY2 data format was used to generate the meteorological data for the simulation. Ac- cordingAccording to the to theTMY2 TMY2 weather weather data, data, the the annual annual averageoutdoor outdoor temperature temperature was was 14.6 14.6◦C °C andand the the annual annual h horizontalorizontal solar solar radiation waswas 1345 1345 kWh/m kWh/m2.2.

FigureFigure 4. 4. SimulationSimulation overview.

3.1.3.1. Thermal Thermal and and Electric Electric Demand Demand Estimation EnergyPlus (U.S. Department of Energy, USA) was used to analyze the cooling and EnergyPlus (U.S. Department of Energy, USA) was used to analyze the cooling◦ and heatingheating loads loads ofof the the houses houses.. The The indoor indoor setpoint setpoint temperature temperature was was set set to to 20 20 and and 26 26 °CC dur- during the heating and cooling seasons, respectively. The lighting load was 9.15 W/m2. ing the heating and cooling seasons, respectively. The lighting load was 9.15 W/m2. Through the simulation, the annual heating and cooling loads for the 56 households were Through the simulation, the annual heating and cooling loads for the 56 households were calculated at 196 and 120 MWh/year, respectively. These could be converted to heating calculatedand cooling at 196 loads and per 120 unit MWh/year, area as 31 and respectively. 19 kWh/m These2 year, could respectively. be converted The maximum to heating 2 andheating cooling and loads cooling per loads unit werearea 25as and31 and 25 W/m 19 kWh/m2, respectively.year, respectively. The hot water The load maximum used heatingin this and research cooling was loads chosen were based 25 onand previous 25 W/m measurement2, respectively. data. The This hot loadwater model load wasused in thisanalyzed research based wason chosen the measurement based on previous data of a measurement single-family house data. [This26,27 load]. The model annual was hot an- alyzedwater based load was on calculatedthe measurement as 2839 kWh. data of a single-family house [26,27]. The annual hot water load was calculated as 2839 kWh. 3.2. Convergence Energy Prosumer System Operation 3.2. ConvergenceFigure2b showsEnergy the Prosumer details System of a piping Operation diagram in which a central energy supply system is connected to a distributed thermal network system. The operation shown in Figure 2b shows the details of a piping diagram in which a central energy supply Figure4 is required to link a central energy supply system with a distributed thermal systemnetwork. is connected Figure4 shows to a distributed the bidirectional thermal heat network supply operationsystem. The mode operation where energy shown in Figurecan be 4 suppliedis required to orto fromlink a central centralized energy thermal supply network system (Figure with5 a)a distributed and an isolated thermal network.operation Figure mode 4 of shows the distributed the bidirectional thermal networkheat supply (Figure operation5b) can be mode configured where between energy can bethe supplied distributed to or thermal from a networkcentralized and thermal the centralized network district (Figure thermal 5a) and network. an isolated To configure operation modesuch of a network,the distributed two three-way thermal valves network (i.e., (Figure MV3-D1–MV3-D4) 5b) can be forconfigured each network between to divide the dis- tributedthe two thermal networks, network circulation and pumpsthe centralized (i.e., DP7-1 district and DP7-2) thermal for network. each cooling To andconfigure heating such a network,network for two a single three operation-way valves of the (i.e., distributed MV3-D1 thermal–MV3- network,D4) for each and twonetwork two-way to divide valves the two(i.e., networks, MV2-D1–MV2-D4) circulation forpumps inducing (i.e., DP7 water-1 toand flow DP7 toward-2) for theeach circulation cooling and pump heating were net- workrequired. for a Assingle shown operation in Figure of4 ,the the distributed two networks thermal could be network, linked through and two the two operation-way valves of each valve and pump. (i.e., MV2-D1–MV2-D4) for inducing water to flow toward the circulation pump were required. As shown in Figure 4, the two networks could be linked through the operation of each valve and pump.

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(a)

(b)

FigureFigure 5. Diagram ofof thethe thermal thermal network network system system operation: operation (a:) ( Bi-directionala) Bi-directional heat heat supply supply with with a a centralizedcentralized system;system; ((bb)) heat heat supply supply from from convergence convergence energy energy prosumers. prosumers.

Figure6 6 shows shows the the method method for for linking linking a convergence a convergence energy energy prosumer prosumer to a distributed to a distrib- utedthermal thermal network. network. As shown As shown in Figure in 6Figurea, two heat6a, two exchangers, heat exchangers, two two-way two valves,two-way and valves, a andcirculation a circulation pump pump were required were required to link the to link system. the system. Figure6b–d Figure shows 6b– thed show operations the meth-operation methodsods of the of central the central energy energy supply, supply, self-sufﬁciency, self-sufficiency, and energy and sellingenergy modes, selling respectively.modes, respec- The proposed system was designed to improve stability by separating a heat exchanger tively. The proposed system was designed to improve stability by separating a heat ex- used to supply energy from a centralized thermal network and a heat exchanger used to changer used to supply energy from a centralized thermal network and a heat exchanger sell energy. used to sell energy.

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FigureFigure 6. 6. OperationOperation details details of of a a convergence convergence energy prosumer systemsystem withwitha a distributeddistributed thermal thermal network onnetwork the condenser on the condenser side: (a) side:basic ( aconfiguration;) basic configuration; (b) central (b) central energy energy supply supply mode; mode; (c) self (c)-consumption self- mode;consumption (d) heat mode; prosumer (d) heat mode prosumer. mode. To boost renewable energy power sources such as PV systems or wind turbines, subsidiesTo boost such renewable as renewable energy energy power certificates sources (RECs) such and as feed-in PV systems tariffs (FITs) or wind have turbine been s, sub- sidiesserved. such This as has renewable caused the energy initial costcertificate of renewables (REC energys) and sourcesfeed-into tariff be highers (FITs than) have been servedconventional. This has power caused plant t sources.he initial However, cost of renewable increasing theenergy use ofsources PV and to wind be h turbineigher than con- ventionalpower and power decreasing plant the sources. use of conventional However, inexpensiveincreasing power the use plants of PV (e.g., and coal wind and turbine powernuclear) and due decreasing to environmental the use problems of conventional have led to inexpensive the surplus electricity power plant feed-ins ( pricese.g., coal and nuclearthrough) renewabledue to environmental energy and the problems prices of RECs have and led FITs to the to become surplus lower. electricity In China feed and-in prices throughEurope, therenewable feed-in price energy has alreadyand the decreased prices of toREC ones thirdand FIT of thes to purchased become lower. price [20 In,28 China]. and The authors of this research assumed that the purchased price of electricity was Europe,200 Won/kWh the feed and-in the price surplus has already PV power decreased feed-in price to one was third 82.7Won/kWh. of the purchase This feed-ind price [20,28]. priceT washe authors the five-year of this (2016–2020) research assumed average electricity that the systempurchase marginald price price of electr (SMP)icity in was 200 Won/kWhSouth Korea. and The the thermal surplus energy PV power price wasfeed assumed-in price towas be 82.7 89.62 Won/kWh Won/kWh,. This which feed is -in price wasthe currentthe five thermal-year energy(2016–2020) price ofaverage the Korea electricity District Heating system Corporation marginal price (Seongnam-si, (SMP) in South Korea.South Korea). The thermal energy price was assumed to be 89.62 Won/kWh, which is the current thermal energy price of the Korea District Heating Corporation (Seongnam-si, South Ko- 3.3. Heat Pump System Performance rea). The SHCHP used in this study was analyzed based on the actual measurement of a 50 RT WWHP installed in the eco-friendly energy town of Jincheon [1]. The heat pump 3.3. Heat Pump System Performance used an R134a refrigerant. As shown in Figure7, actual data of the heat pump were measured,The SHCHP and the used operation in this data study from was 8 to 12analyzed March 2018 based were on used. the actual The temperature, measurement of a 50flow RT rate, WWHP and electrical installed energy in the were eco measured-friendly every energy 30 s totown monitor of Jincheon the performance [1]. The of theheat pump ◦ usedheat pump.an R134a When refrigerant. the inlet temperature As shown ofin the Figure condenser 7, actual and data the evaporator of the heat were pump 50.8 wereC meas- ◦ ured,and 11.0 andC, the respectively, operation the data outlet from temperatures 8 to 12 March at the condenser2018 were and used. the evaporatorThe temperature, were flow 8.3 and 54.3 ◦C, respectively. The power consumption was 50.7 kWh, while the production rate, and electrical energy were measured every 30 s to monitor the performance of the energy of the condenser was 164.0 kWh. The coefficient of performance (COP) of the heat heatpump pump. during When the measurement the inlet temperature period was 3.2, of athe value condenser we used and to conduct the evaporator our analysis. were In 50.8 °C andthis study,11.0 °C, we respectively used a 3 RT capacity, the outlet of WWHP, temperature and thes simulation at the condenser was performed and the under evaporator werethe assumptions 8.3 and 54.3 that °C, the respectively. WWHP operated The power part load consumption operation and was operating 50.7 kWh, energy while was the pro- ductionmainly provided energy of by the the condenser PV system. was 164.0 kWh. The coefficient of performance (COP) of the heat pump during the measurement period was 3.2, a value we used to conduct our analysis. In this study, we used a 3 RT capacity of WWHP, and the simulation was performed under the assumptions that the WWHP operated part load operation and operating energy was mainly provided by the PV system. The analysis was performed by assuming that the chilled water and hot water energy were produced using an ASHP during cooling to compare the proposed system with a conventional heat pump system. The COP of the ASHP was assumed to 3.0.

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60 5

] -

50 4.5 C]

° 40 4

30 3.5

20 3 Temperature [ Temperature

10 2.5 Coefficient of Performacne [ Performacne of Coefficient

0 2

2018-03-08 19:40 2018-03-08 12:10 2018-03-09 02:00 2018-03-10 03:00 2018-03-11 2018-03-08 13:35 2018-03-08 14:00 2018-03-08 18:50 2018-03-08 19:15 2018-03-08 20:05 2018-03-08 20:30 2018-03-08 20:55 2018-03-08 21:20 2018-03-08 23:30 2018-03-08 23:55 2018-03-08 00:20 2018-03-09 00:45 2018-03-09 01:10 2018-03-09 01:35 2018-03-09 02:00 2018-03-09 11:45 2018-03-09 12:35 2018-03-09 13:00 2018-03-09 13:55 2018-03-09 14:20 2018-03-09 17:40 2018-03-09 18:05 2018-03-09 20:40 2018-03-09 23:30 2018-03-09 23:55 2018-03-09 00:20 2018-03-10 00:45 2018-03-10 01:10 2018-03-10 01:35 2018-03-10 02:25 2018-03-10 02:50 2018-03-10 15:45 2018-03-10 16:10 2018-03-10 23:40 2018-03-10 00:05 2018-03-11 00:30 2018-03-11 00:55 2018-03-11 01:20 2018-03-11 01:45 2018-03-11 02:10 2018-03-11 02:35 2018-03-11 03:25 2018-03-11 03:50 2018-03-11 03:50 2018-03-12 T_evap,in T_evap,out T_cond,in T_cond,out COP

FigureFigure 7. 7.OperationOperation temperature temperature and and COP COP profile profile of of heat heat pump pump system system.. The analysis was performed by assuming that the chilled water and hot water energy 3.4. Photovoltaic System were produced using an ASHP during cooling to compare the proposed system with a conventionalTo analyze heat BIPV pump power system. generation The COP, TRNSYS of the 18 ASHP with wasthe TYPE assumed 566 tomodule 3.0. was used. The installed PV panel had a size of 1994 × 1000 mm2, a reference capacity of 380 W, and a reference3.4. Photovoltaic efficiency System of 19.1%. Using the TMY2 weather data, it was found that the annual PV generationTo analyze rates BIPV was power 1281.6 generation, kWh/kWp. TRNSYS 18 with the TYPE 566 module was used. The installed PV panel had a size of 1994 × 1000 mm2, a reference capacity of 380 W, and a 3.5.reference Self-Consumption efficiency and of 19.1%. Self-Sufficiency Using the Analysis TMY2 weather data, it was found that the annual PVThe generation self-consumption rates was 1281.6 and self kWh/kWp.-sufficiency rates of community and houses can be es- timated using load cover factor (LCF) and supply cover factor (SCF) indices. LCF and SCF were3.5. used Self-Consumption to analyze the and self Self-Sufficiency-consumption Analysis rate of the BIPV system integrated with the SHCHPThe in self-consumption the houses and communit and self-sufficiencyies of this studyrates of. LCF community represents and self houses-sufficiency, can be whichestimated is defined using as load the cover fraction factor of (LCF)the entire and power supply load cover supplied factor (SCF) by the indices. BIPV LCFand andPV powerSCF were: used to analyze the self-consumption rate of the BIPV system integrated with the SHCHP in the houses and communities of this study. LCF represents self-sufficiency, which

is deﬁned as the fraction of the entire power[( load supplied ) by the] dt BIPV and PV power:

LCF h i (1) R t2 ( BIPV + PV ) load t min ( P i,t P i,t ,Pi,t)dtdt LCF = 1 (1) R t2 (Pload + PSHCHP)dt SCF represents self-consumption, whicht1 i,t is definedi,t as the fraction of the sharing of the PVSCF and representsBIPV generation self-consumption, power supplied which to the is deﬁned load. High as the self fraction-consumption of the sharing and self of- sufficiencythe PV and values BIPV mean generation that the power electricity supplied load to theis mostly load. High covered self-consumption by BIPV and PV and sys- self- temssufﬁciency. values mean that the electricity load is mostly covered by BIPV and PV systems.

[( ) ] dt R t2 h i min (PBIPV + PPV),Pload dt SCF t1 i,t i,t i,t (2) SCF = (2) R t2 BIPV PV (( P + P )dt)dt t1 i,t i,t wherewhere 푃P퐵퐼푃푉BIPV isis the the power generation of BIPV (kWh),(kWh), P푃PV푃푉is is the the power power generation generation of of PV PV in load SHCHP inparking parking lots lots (kWh), (kWh),P 푃푙표푎푑is theis the power power consumption consumption of of houses house (kWh),s (kWh), and andP 푃푆퐻퐶퐻푃is theis thepower power consumption consumption of of SHCHPs SHCHP (kWh).s (kWh).

4.4. Simulation Simulation Results Results 4.1. Thermal Performance of SHCHP Integrated with PV 4.1. Thermal Performance of SHCHP Integrated with PV Figure8 illustrates the results of the analysis of the electric energy balance when the proposedFigure SHCHP8 illustrates and the conventional results of the ASHP analysis were of used; the here,electric the energy BIPV systembalance output when andthe proposedpower loads SHCHP of H1 and were conventional identical. The ASHP simulations were used were; here, conducted the BIPV from system July to output September, and powerbut to loads more of precisely H1 were demonstrateidentical. The thesimulations energy performance were conducted of the from system, July to the September, graph in but to more precisely demonstrate the energy performance of the system, the graph in Figure

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8 only shows the hourly operation results for July. As shown in Figure 8a, the power gener- atedFigure by8 theonly BIPV shows system the hourly was responsible operation resultsfor the for consumption July. As shown of the in ASHP Figure 8operationa, the power and thegenerated power byloads the of BIPV the systembuilding, was whereas responsible the surplus for the consumptionpower was mostly of the ASHPsent to operationthe grid. Theand amount the power of power loads ofgenerated the building, by the whereas BIPV system the surplus during power the month was mostly of July sentwas to796.3 the kWh,grid. Thewhere amount 502.9 kWh of power (63.2% generated) of the total by the power BIPV generated system during by the theBIPV month system of was July sent was to796.3 the kWh,grid as where surplus 502.9 power kWh after (63.2%) power of the was total consumed power generated in the operation by the BIPVof thesystem ASHP and was thesent plug to the loads grid within as surplus the powerhouses. after Moreover, power was34.6% consumed of the power in the loads operation need ofed the to ASHPbe re- ceiveand thed from plug the loads grid within, when no the power houses. was Moreover, generated 34.6% by the of BIPV the power system loads. In contrast, needed when to be surplusreceived power from thefrom grid, the whenBIPV nosystem power was was used generated to simultaneously by the BIPV produce system. co Inoling contrast, and heatwhen energies surplus through power fromthe operation the BIPV of system the SHCHP, was used 99.7 to kWh simultaneously of power from produce generated cooling by theand BIPV heat energiessystem were through sent the to operationthe grid as of surplus the SHCHP, (Figure 99.7 8b) kWh; thus, of powerapproximately from generated 12.5% ofby power the BIPV production system were was sent sent to to the the grid grid. as In surplus addition, (Figure the8 amountb); thus, of approximately insufficient power 12.5% loadsof power received production from the was grid sent during to the the grid. time In when addition, no power the amount was generated of insufﬁcient by the power BIPV systemloads received was 96.2 from kWh, the which grid duringindicates the that time operation when no was power possible was generatedwhen receiving by the 12.1% BIPV ofsystem power was from 96.2 the kWh, grid. which indicates that operation was possible when receiving 12.1% of power from the grid.

(a)

(b)

Figure 8. ElectricityElectricity balance balance of of the the H1 H1 house house during during July July:: (a)( aConventional) Conventional houses houses with with the theBIPV BIPV system system and andASHP ASHP;; (b) p(broposed) proposed convergence convergence energy energy prosumer prosumer with with the theBIPV BIPV system system and and SHCHP. SHCHP.

4.2.4.2. Energy Energy Performance Performance of of the the Community Community FigureFigure 9 shows the the amount amount of of cooling cooling and and heat heat energies energies produced produced in inthe the H1 H1and and H2 houses,H2 houses, as well as as well the as thermal the thermal energy energy balance balance within a within distributed a distributed thermal network. thermal Figure network. 9a showsFigure 9thata shows the amounts that the of amountscooling and of coolingheating energ and heatingy produced energy during produced the month during of July the frommonth the of SHCHP July from in the SHCHPH1 house in comprised the H1 house 2.5 and comprised 11.3 times 2.5 andthe cooling 11.3 times and the hot cooling water

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anddemand hots water, respectively. demands, When respectively. the monthly When production the monthly amount production was calculated, amount we was found calculated,that 40.1% we found of the thatcooling 40.1% energy of the produced cooling energyby the SHCHP produced was by consumed the SHCHP in wasthe H1 consumed house, inwhile the H191.4% house, was whileconsumed 91.4% in was the consumed distributed in thermal the distributed network thermal such that network the remaining such that the8.6% remaining needed to 8.6% be supplied needed to to be the supplied centralized to the thermal centralized network. thermal Further network.more, Furthermore,8.8% of the 8.8%heat energy of the heatproduced energy by producedthe SHCHP by could the SHCHP be used couldto supply be used hot water to supply to the hot H1 waterhouse to, the61.9% H1 of house, heat energy 61.9% ofwas heat consumed energy wasin a consumeddistributed inthermal a distributed network, thermal and the network, remaining and the38.1% remaining of heat energy 38.1% ofwas heat used energy in the was centralized used in the thermal centralized network. thermal Cooling network. energy Cooling was energyproduced was by produced the SHCHP by when the SHCHP power was when generated power wasby the generated BIPV system by the. Therefore, BIPV system. ex- Therefore,cess heat in excess the distributed heat in the thermal distributed network thermal had networkto be supplied had to back be supplied to the centralized back to the centralizedthermal network. thermal network.

(a)

(b)

FigureFigure 9. 9.Thermal Thermal loadload andand generatedgenerated thermal energy in in the H1 H1 and and H2 H2 houses houses within within the the distributed distributed thermal thermal networks networks:: (a(a)) Single Single house house (H1) (H1) operationoperation proﬁle;profile; ((bb)) distributeddistributed thermalthermal network with 7 houses.

4.3. Self-ConsumptionSelf-Consumption and and Operation Operation Cost Cost of of SHCHP SHCHP Compared Compared with with ASHP ASHP Figure 1010 shows shows a a comparison comparison of of the the LCF LCF and and SCF SCF when when using using the conventional the conventional ASHP andASHP SHCHP and SHCHP for the for H1 the house. H1 house. The results The results indicate indicate that that the LCFthe LCF and an SCFd SCF were were 50.4% 50.4% and 61.0%,and 61.0%, respectively, respectively, during during the cooling the cooling season season when when the conventionalthe conventional ASHP ASHP was was operated. op- Inerated. contrast, In contrast, the LCF the and LCF SCF and were SCF 53.3% were and 53.3% 86.0%, and respectively, 86.0%, respectively, during the during cooling the seasoncool- whening season the proposed when the SHCHPproposed was SHCHP operated. was operated. The surplus The surplus power ofpower the BIPV of the system BIPV sys- was minimizedtem was minimized by actively by usingactively the using produced the produced power through power thethrough operation the operation of the SHCHP. of the SHCHP.

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(a)

(b)

FigureFigure 10. 10. SCFSCF and and LCF LCF profiles profiles of of the the proposed proposed systems systems:: (a ()a )Conventional Conventional ASHP ASHP operation operation;; (b (b) )p proposedroposed convergence convergence energyenergy prosumer prosumer operation. operation. Figure 11 shows a comparison of the profits obtained from the operation of the Figure 11 shows a comparison of the profits obtained from the operation of the con- conventional ASHP and the proposed SHCHP for the month of July. For the surplus ventional ASHP and the proposed SHCHP for the month of July. For the surplus power power of the BIPV system, the SHCHP used 99.7 kWh while the conventional ASHP of the BIPV system, the SHCHP used 99.7 kWh while the conventional ASHP used 502.9 used 502.9 kWh; therefore, the surplus power of the SHCHP was only 19.8%. However, kWh; therefore, the surplus power of the SHCHP was only 19.8%. However, the cooling the cooling and heating energies produced by the SHCHP were 1151.1 and 1699.2 kWh, and heating energies produced by the SHCHP were 1151.1 and 1699.2 kWh, respectively, respectively, and a higher operating profit than that of the ASHP could be obtained because and a higher operating profit than that of the ASHP could be obtained because most of most of the produced power was sold. the produced power was sold. Consequently, while a total of 17,826 Won profit was earned when the conventional Consequently, while a total of 17,826 Won profit was earned when the conventional ASHP system was used for the cooling period of three months, a total of 544,859 Won profit ASHP system was used for the cooling period of three months, a total of 544,859 Won (approximately 30.5 times higher than that achieved by the ASHP system) was earned profit (approximately 30.5 times higher than that achieved by the ASHP system) was when the proposed SHCHP system was operated. earned when the proposed SHCHP system was operated.

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Figure 11. Cost benefit of the proposed system operation. Figure 11. Cost benefit benefit of the proposed system operation.operation. 4.4. Annual Operation Result 4.4. Annual AnnualIn the previousOperation Operation analyses, Result Result the results of the SHCHP operation in the summer season, the effectsInIn the the on previous LCF and analyses, SCF, and the the operationresults results o off the profit SHCHP were examined. operation in inHowever, the summer summer the season, season,annual theoperationthe effects effects ofon each LCF system and SCF, also andand needs operationoperation to be examined. profitprofit werewere Figure examined.examined. 12 shows However, a comparison the annual of the operationLCF, SCF, ofand each operating system also profit needs of the to anbe nual examined. operation Figure of the 12 showstwo systems. a comparison As shown of the in LCF,Figure SCF, 12a, and the operatingproposed profitprofitsystem of ha thed high annualannual LCF operationoperation and SCF ofvalues the two in the systems. summer As season shown but in Figurelower value 12a, the s than proposed that of system the conventional ha hadd high LCF ASHP and in SCF the valuesother periods.in the summer The conventional season but lowerASHPlower value valueswas operateds than than that according of the conventional to cooling and ASHP heating in the demands other periods.periods.; as such, The the conventionalLCF and SCF ASHPwere affected was was operated operated because according according the system to to cooling coolingwas alsoand and heatingoperated heating demands during demands; ; theas such, as day. such, the In LCF thecontrast, LCFand SCFandthe wereSHCHPSCF wereaffected only affected obtainbecause becauseed energythe the system systemfrom was the was alsocentralized also operated operated thermal during during network the the day. day. during In In contrast, contrast, the winter the SHCHPand interim only only period obtain obtaineds edbecause energy it couldfrom the only centralized be operated thermal during network periods whenduring both the cooling winter and interim heating period periodswere required.s because Thus,it could the only power be operated was only during consumed period periods fors when plug loadsboth coolingduring andwinter heating and summer we werere required. , so the coverageThus, the of power surplus was power only became consumed low. for Accordingly, plug loads duringthe an- winternual LCF and and summer,summer SCF of,so so the the the conventional coverage coverage of of surplus AS surplusHP were power power 42.9% became became and low. 55.4% low. Accordingly, Accordingly,, respectively the .t annual heThose an- nualofLCF the andLCF proposed SCFand ofSCF system the of conventional the were conventional 45.1% ASHP and AS were55.1%,HP 42.9%were respectively 42.9% and 55.4%, and. T he55.4% respectively. annual, respectively cover Those factor. T ofhose val- the ofuesproposed the of proposedthe systemtwo systems system were 45.1%were were similar and45.1% 55.1%, .and respectively.55.1%, respectively The annual. The coverannual factor cover values factor of val- the uestwo of systems the two were systems similar. were similar.

(a) (a) Figure 12. Cont.

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(b)

FigureFigure 12. 12. MonthlyMonthly operation operation results results of of each each system system:: ( (aa)) LCF LCF and and SCF SCF of of systems systems;; ( (b)) o operatingperating cost of systems.

FigureFigure 12b12b shows shows the the annual annual operation operation cost cost per per month month,, where where it can it can be seen be seen that thatthe conventionalthe conventional ASHP ASHP had a had higher a higher operating operating profit than profit the than SHCHP the SHCHP in all months, in all months,exclud- ingexcluding the summer the summer season. season. The conventional The conventional ASHP ASHP hadhad an an annual annual profit profit of of 3290 3290 Won, Won, whereaswhereas the the SHCHP SHCHP ha hadd an an annual annual profit profit of of 385,645 Won Won because of its high operating profitprofit in summer. Thus, Thus, the the proposed proposed SHCHP SHCHP had a a higher overall operating profit profit from thethe annual annual perspective. perspective. 5. Conclusions 5. Conclusions In this research, a convergence energy prosumer concept was proposed to increase the In this research, a convergence energy prosumer concept was proposed to increase renewable energy sharing rate and self-consumption of a community via the operation of the renewable energy sharing rate and self-consumption of a community via the operation an SHCHP system that established a separate distributed thermal network with a district of an SHCHP system that established a separate distributed thermal network with a dis- thermal network. The operation results were compared with those of a conventional trict thermal network. The operation results were compared with those of a conventional ASHP. The operation of the proposed system was analyzed from July to September, when ASHP. The operation of the proposed system was analyzed from July to September, when both cooling and heating energies were required for building cooling and supplying hot both cooling and heating energies were required for building cooling and supplying hot water, respectively. Through a detailed simulation, it was found that more than 60% of waterthe power, respectively produced. Through by the BIPV a detailed system simulation, was sold toit thewas gridfound when that ASHP more wasthan applied60% of thein thepower system. produced However, by the the BIPV proposed system system was sold only to the sent grid 12.5% when of theASHP power was toapplied the grid. in theFurthermore, system. However the conventional, the proposed ASHP system operation only sent recorded 12.5% 50.4% of the and power 61.0% to the LCF grid. and Fur- SCF thervalues,more respectively,, the conventional and the ASHP proposed operation system recorded recorded 50.4% 53.3% and and61.0% 86.0% LCF LCFand andSCF SCFval- uesvalues,, respectively respectively., and Moreover, the proposed the proposedsystem recorded system obtained53.3% and 30.5 86.0% times LCF more and operating SCF val- uesprofit, respectively. than the conventional Moreover, system the proposed from July system to September. obtained This 30.5 means times that more the operating proposed profitsystem than could the conventional provide both system cooling from and July heating to September. energy to This a thermal means that network, the proposed as well systemas leading could to aprovide relatively both higher cooling thermal and heating energy energy price than to a thatthermal of the network electricity, as well sold as to leadingthe grid. to a relatively higher thermal energy price than that of the electricity sold to the grid. Due to the limitations of proof-of-concept simulations, the reported operating profit doesD notue accuratelyto the limitation reflects theof proof costs- aof thermal-concept network, simulations maintenance,, the reported system operating control, profit and doessettlement. not accurately Hence, thereflect more the realistic costs a calculationthermal network, of costs maintenance, is required in system future work,control, which and settlementcan be achieved. Hence, by the considering more realistic initial calculation and maintenance of costs is costs, required among in future others. work, In addition, which canexpandability be achieved in by acity considering unit needs initial to be and considered, maintenance while cost practicalitys, among shouldothers.be In improvedaddition, expandabilitythrough empirical in a city experiments unit needs regarding to be considered, small-scale while distributed practicality thermal should networks. be improved through empirical experiments regarding small-scale distributed thermal networks.

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Author Contributions: Writing—original draft preparation, M.-H.K.; methodology and software, Y.-S.A.; software and analysis, D.-W.K.; writing—review and editing, D.-W.L.; supervision and project supervisor, J.-H.Y. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Korea Agency for Infrastructure Technology Advance- ment and funded by the Ministry of Land, Infrastructure, and Transport (No. 21PIYR-B153277-03). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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