- Email: [email protected]
STES—Typical Scenarios for Heat Accumulator Cooperation
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 50 (2014) 414 – 420
The International Conference on Technologies and Materials for Renewable Energy, Environment and Sustainability, TMREES14
STES—typical scenarios for heat accumulator cooperation -DURVáDZ0LOHZVNL *:RMFLHFK%XMDOVNL Warsaw University of Technology, Institute of Heat Engineering, 21/25 Nowowiejska Street, Warsaw, 00-665, Poland
Abstract The article presents an analysis of real operational data of a Seasonal Thermal Energy Storage system connected to a local heating grid. 8 years of operation time was analyzed to determine typical scenarios for cooperation with the heating grid and solar collectors7KHUHVHDUFKVKRZVWKDWWKUHHPDLQZRUNLQJPRGHVRIWKHDFFXPXODWRUPD\EHSDUWLFXODUL]HG FKDUJLQJGLVFKDUJLQJ and transient modes, and that the maximum speed of charge/discharge is on average below 0.3ӓC/day. © 2014 2014Published The Authors. Published by Elsevier Ltd. © by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD). (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) Keywords: Seasonal Thermal Energy Storage
1. Introduction Rising fuel prices and electricity consumption are driving the search for new and more efficient ways of heat and power generation. Energy needed for heating and domestic hot water accounts for a third of energy consumed in LQGXVWULDOL]HGFRXQWULHVOLNH3RODQG5HGXFWLRQVLQIRVVLOIXHOFRQVXPSWLRQDQGSROOution emission may be achieved by using solar based technologies. In the case of electricity, solar energy may be used directly (PV panels) or indirectly through the utilization of biofuels [1, 2], for example in fuel cells [3–7] which can achieve very high efficiency due to direct conversion of chemical energy into electrical current. Water heating with solar collectors is currently a competitive solution [9] comparing to other technologies, but it is limited by solar radiation intensity and available only in summer. Unfortunately, heat is mostly needed in winter.
&RUUHVSRQGLQJDXWKRU7HO ID[ E-mail address: PLOHZVNL#LWFSZHGXS
1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi:10.1016/j.egypro.2014.06.050
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
415
Solar energy storage for heating appears justified in cases where the amount of solar energy for heating is higher than 20%. Issues involved in Seasonal Thermal Energy Storage in a ground heat accumulator were discussed in [10], where SDUDPHWHUV OLNH KHDW FDSDFLW\ RI WKH DFFXPXODWRU DQG VRLO KXPLGLW\ ZHUH DQDO\]HG &DOFXODWLRQV FRQFHUQHG transportation of heat and water—the maximum water temperature was assumed to be 90ӓC. Calculations were performed for a system with a capacity of 174 N:thFRPSRVHGRIDZDWHUFRQWDLQHURIYROXPH m3 and 140 vertical, tubular heat exchangers immersed 30 m deep. $KHDWDFFXPXODWRULQWKHIRUPRIURFNZDVSURSRVHGLQ [11]. Using a mathematical model, the heat capacity of the accumulator was estimated, and heat loss of 10—20% per cycle was determined. The accumulator’s size was DVVXPHGWREHIURPWRPGHHSDQGWKHZRUNLQJPHGLXPZDVSURSDQH0RGHOVIRU67(6FDOFXODWLRQVZHUH presented in [12–16]. They were used for simulation of long-term operation of a system equipped with a spherical or semi-spherical heat accumulator, which would be used for both heating and cooling. Results prove that there is no reason to install solar panels on a surface area in excess of 60 m2/ builGLQJLQDFOLPDWHVLPLODUWRWKDWLQ7XUNH\7KH authors made similar calculations for a cylindrical accumulator [17] which marginally increases the solar energy XWLOL]DWLRQIDFWRU2SWLPDOVHOHFWLRQRIHOHPHQWVOLNHFRQGHQVLQJERLOHUFRPSUHVVLRQRUDEVRUSWLRQKHDWSXPSHWF composing a cogeneration system supplying 100 well thermally insulated buildings was presented in [18]. The calculation results were compared with condensing boiler and grid supplied electricity, showing that the greater the investment made, the larger the profits are. The solar power share in covering heat demand was 80% whereas renewable energy sources accounted for 40 % of electrical energy production, which results in lower fossil fuel consumption. In [19] simulation results were given for a solar heating system for 90 buildings with a floorspace of 100 m2 each. It was proven that a 3 000 m2 area of solar panels installed on roofs and a borehole accumulator (60 000 m3) are able to cover 60 % of heat demand. In paper [20] a simulation of a central solar heating system that FRYHUV % of heat demand was presented. In addition to global indicators (e.g. solar energy share in the whole EDODQFH WKH FKDQJHV WDNLQJ SODFH GXULQJ RSHUDWLRQ RI WKH ZKROH V\VWHP ZHUH FRQVLGHUHG 2SHUDWLRQ RI D V\VWHP containing a seasonal heat accumulator is a quite difficult issue in terms of the control strategy due to large uncertainties concerning both the amount of accumulated solar energy and the varying load during the heating season. It seems that algorithms based on artificial intelligence, which proved useful in similar applications OLNH [21, 22], could be widely used in this case as well. Matters regarding improving the characteristics of selected 67(6V\VWHPVPHULWVHSDUDWHDQDO\VHV,QZRUN [23], the heating effectiveness and economic issues of three different NLQGV RI FHQWUDO VRODU KHDWLQJ V\VWHPV IRU 7XUNLVK FRQGLWLRQV ZHUH LQYHVWLJDWHG 7KH RXWFRPH ZDV WKH HVWLPDWHG return of investment in 19 years and, if 100 % of heat demand were covered by solar energy, the period extends to 40 years [24]. The paper [] contains simulation results of a quite large STES in Chinese conditions, comprising a solar panel area of 1 000 m2 connected with an accumulator of volume 90 000 m3— and a relatively low temperature of the ”cold” part of 30°C assumed. A comprehensive review of STES technology may be found in [26]—where various options were discussed, even extraordinary ones. Results of long-term operation simulation RIDKHDWDFFXPXODWRU \HDUV DUHLQWKHDUWLFOH [27]. The results were obtained using the most popular application used for calculation of STES systems (TRNSYS) (inter alia [28, 29]). In addition to this program, other calculation tools are often used [30]. A separate problem is cooperation of a STES system with an existing heating grid supplied by combined heat and power plants [32–34]. The STES system influence their generation capabilities in winter. The main motive for ZULWLQJWKHSDSHUZDVWRWU\WRDQVZHUWKHTXHVWLRQ +RZVHQVLEOHLVLWWREXLOGVXFKLQVWDOODWLRQVIRUWKHSXUSRVHRI supplying heat to existing buildings with poor thermal insulation parameters in Polish conditions? The target would be to achieve about a 60 % share in heating energy demand assuming reasonable costs and dimensions of the whole installation. 7KHUHDUHVHYHUDOWHFKQLFDOVROXWLRQVUHJDUGLQJWKHKHDWDFFXPXODWRUXVHGLQ67(6V\VWHPV x x x x x x
7DQNWKHUPDOHQHUJ\storage—77(6 –80 N:KP3 Pit thermal energy storage—37(6 –80 N:KP3 [36] Borehole thermal energy storage—%7(6 –30 N:KP3 [19, 37, 38] Aquifer thermal energy storage—$7(6 –40 N:KP3 [39, 40] $FFXPXODWRUVZLWKHOHPHQWVVXEMHWWRWKHUPRFKHPLFDOUHDFWLRQV –460 N:KP3 [41–44] Phase Change Material storage—PCM []
416
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
7KHUHJXODUWHPSHUDWXUHUDQJHDWZKLFK67(6V\VWHPZRUNVLVӓC, the effectiveness of heat storage grows VLJQLILFDQWO\ZKHQWKH\DUHZHOOFRQWUROOHGLQRUGHUWRPDLQWDLQVWUDWLILFDWLRQLQVLGHWKHWDQN2QWKHRWKHUKDQGWKH thermocline broadens over longer periods , hence maintaining complete stratification is technically difficult. The SUHVHQWHGOLWHUDWXUHUHYLHZVKRZVWKDWWKHRSWLPDOUDWLRRIWDQNYROXPHWRFROOHFWRUVXUIDFHDUHD 9$ LV (m3/m2) [18]. 2 External conditions influencing operation of the heat accumulator Many elements influence the selection of cooperation modes of the heat accumulator with solar collectors and EXLOGLQJV7KHNH\RQHVDUH x
x
technological structure of the system o are heating boilers present? o is a heat pump present? o LVVWUDWLILFDWLRQSUHVHQWLQWKHWDQN" operation parameters of the grid and charging/discharging of the accumulator
The number of possible cooperation combinations is practically infinite. It is essential to identify the significant features influencing the various action schemes. The first element to be discussed is the power of the accumulator and the cooperating heating grid. The absolute power generated by the solar panels and the accumulator is not significant, but the proportions of the accumulator and the power of solar panels is important. In the case of the accumulator not only its power but also its capacity should be mentioned. In general, it is assumed that the power and capacity would normally have to be correlated. Maximum charging/discharging speed is limited by the maximum flow velocity of water, for which purpose it is possible to design a diffuser. This limitation WUDQVODWHVGLUHFWO\WRWKHVKDSHRIWKHDFFXPXODWRU¶VWDQN,WLVKRZHYHUSRVVLEOHWROLPLWWKHPD[LPXPDFFXPXODWRU charging speed by designing a smaller system diffuser—pumping-flow system. Such limitation on the maximum speed is not desirable because it decreases the functionality of the accumulator. It is then assumed that the accumulator’s charging speed and its capacity will be correlated.
Figure Temperature development in the hot-water seasonal heat store in Friedrichshafen [8]
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
Figure Averaged values of hot and cold temperatures during year If currently existing systems’ accumulator—VRODU FROOHFWRUV DUH FRQVLGHUHG WKH UDWLR RI SRZHU WDNHQ IURP WKH accumulator and the heating power of the collectors varies vastly. In some systems the size of the accumulator enables autonomic operation of the accumulator for several months. In others the possibility of feeding from the heat accumulator accounts only for a little share of the power that has to be supplied to the buildings. Apart from the accumulator charging speed and capacity ratio, a significant role is also played by the excess DPRXQWRILQVWDOOHGSRZHULQFROOHFWRUV([FHVVVL]HPDNHVLWSRVVLEOHWRHDVLO\FKDUJHWKHDFFXPXODWRUDWIXOOSRZHU (at any time). Otherwise, limitations are caused by low production capabilities of the FROOHFWRUV 7KLV NLQG RI limitation may also be present at minimal loads. When the heat demand is more or less equal to the technical minimum of the collector system–it is not possible to discharge the accumulator. In this case it may be necessary to charge/discharge the accumulator in half-year periods (spring/autumn). :KHQH[SORULQJWKHSRVVLELOLW\RIOLQNLQJWKHDFFXPXODWRUZLWKRWKHUV\VWHPHOHPHQWVWKHUHDVRQVIRULQVWDOOLQJ DFFXPXODWRUVVKRXOGEHGHWHUPLQHG x x x x x
compensation of heating source load at YDULDEOHKHDWGHPDQG FRYHULQJRISHDNKHDWGHPDQG LQFUHDVHRIDYDLODELOLW\,QVWHDGRIPDLQWDLQLQJERLOHUVLQKRWUHVHUYHRUWZRZRUNLQJXQLWVDWSDUWLDOORDG RQHZRUNLQJERLOHUDQGDQDFFXPXODWRUHQVXUHVDIHKHDWVXSSO\ ensuring heat supply in emerJHQF\FDVHV PDNLQJRSHUDWLRQRIVRODUFROOHFWRUVSRVVLEOHZKHQKHDWGHPDQGLVORZHUWKDQWKHWHFKQLFDOPLQLPXPRI heating devices.
417
418
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
Figure Charging and discharging speeds of the chosen STES The listed functions are by and large not mutually exclusive. The accumulator may perform different functions in the whole system. In order to specify the most typical situations the most important (basic) functions of an accumulator installed in a system should be selected. It seems that the largest financial benefits from the possibility of heat accumulation stem from maximization of profits from avoided heat production by heating boilers. The use of solar collectors changes the total heat demand of the system—FROOHFWRUV ZRUN FRQWLQXRXVO\ LQ KHDW SURGXFWLRQ mode. Due to this fact, the heat produced by the collectors does not alter the heat supplied to consumers. Profit PD[LPL]DWLRQIURPWKHDYRLGHGIXHOSXUFKDVHIRUWKHERLOHUVPD\ILJXUHLQ x x
higher solar energy share in winter, change to the heat production curve during the day—increased heat production from the accumulator at high fuel prices and minimization of its operation at low prices (currently natural gas prices do not vary daily or seasonally).
3 Typical cooperation scenarios of heat accumulator and grid The following format for temperatures present in the accumulator was selected tbottom/tupper(tupper-tbottom), e.g. PHDQV WKDW LQ WKH XSSHU SDUW RI WKH WDQN WKH WHPSHUDWXUH LV °C, in the bottom 40°C and that the temperature difference is 20°C. $FFXPXODWRUFKDUJLQJWDNHVSODFHZKHQWKHUHLVDVXUSOXVRIKHDWSURGXFHGE\WKHVRODUFROOHFWRUVFRPSDUHGZLWK the demand required by the local heating grid, that the period starts in between March and April and lasts until October. The assumptions are confirmed by calculations performed on the basis of data published in [8] presented in Fig. 2. The beginning of the charging season is in mid-February and starts with temperatures 40/44(4), which means PRUHRUOHVVWKHVDPHWHPSHUDWXUHLQWKHZKROHYROXPHRIWKHWDQN7KHHQGRIWKHFKDUJLQJSURFHVVLVDWWKHHQGRI August. From this time on the upper temperature starts to drop, which most probably is connected with the fact that collectors are not able to cover the losses to the environment. The heat from the accumulator may also be used to cover heat demand on cold nights.
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
The charging and discharging speed of the accumulator for specific months may be determined through analyzing trend-lines—see Fig. 3. The maximum speed at which the accumulator is charged and discharged is ą0.3ӓC/24 h. Based on the presented calculations three main aFFXPXODWRURSHUDWLRQVFHQDULRVPD\EHVSHFLILHG 1.
Charging, for G7»GW!0.1ӓC, period from May to July
2. 3.
Discharging, for G7»GW -0.1ӓC, period from September to December Transient time at which the accumulator is used occasionally (charged during the day and discharged at night)—period from July to September—RUGRHVQRWZRUNDWDOO—period from December to February.
,QDOOWKHVFHQDULRVWKHWRSWHPSHUDWXUHRYHUWDNHVWKHERWWRPRQHE\FDRQHPRQWK Another important issue is the difference of temperatures present in the accumulator, heat pump operation (if present), heating grid parameters and thermocline position. They allow one to estimate the amount of stored energy DYDLODEOHIRUKHDWLQJSXUSRVHVLQWKHWDQN7KHSDUDPHWHUVGRQRWFKDQJHWKHDFFHSWHGVFenarios and are not analyzed DWWKHGLVFXVVLRQVWDJHGXHWRWKHODFNRIDSSURSULDWHGDWD 4 Summary and conclusions The analysis of real operational data of a Seasonal Thermal Energy Storage system connected to a local heating grid. 8 years of operation time was analyzed to determine typical scenarios for cooperation with the heating grid and VRODU FROOHFWRUV 7KH UHVHDUFK VKRZV WKDW WKUHH PDLQ ZRUNLQJ PRGHV RI WKH DFFXPXODWRU PD\ EH SDUWLFXODUL]HG charging, discharging and transient modes, and that the maximum speed of charge/discharge is on average below 0.3°C/day Acknowledgments The project was funded by the National Science Centre by decision number DEC-2012/07/B/ST8/03937. References [1] A. 6REROHZVNL Bartela, A. 6NRUHN-2VLNRZVND 7 ,OXN &RPSDULson of the economic efficiency of chp plants integrated with gazela JHQHUDWRU >SRUyZQDQLH HIHNW\ZQRĞFL HNRQRPLF]QHM XNáDGyZ NRJHQHUDF\MQ\FK ] JHQHUDWRUHP JD]X SURFHVRZHJR JD]HOD@ 5\QHN (QHUJLL 102 –37. [2] W. %XG]LDQRZVNL 6XVWDLQDEOH ELRJDV HQHUJ\ LQ SRODQG 3URVSHFWV DQG FKDOOHQJHV 5HQHZDEOH DQG 6XVWDLQDEOH (QHUJ\ 5HYLHZV (1) (2012) 342–349. [3] G. De Lorenzo, P. Fragiacomo, Electrical and electrical-thermal power plants with molten carbonate fuel cell/gas turbine-integrated systems, International Journal of Energy Research 36 – [4] G. Discepoli, G. Cinti, U. Desideri, D. Penchini, S. 3URLHWWL &DUERQ FDSWXUH ZLWK PROWHQFDUERQDWH IXHO FHOOV ([SHULPHQWDO WHVWVDQG IXHO cell performance assessment, International Journal of Greenhouse Gas Control 9 (2012) 372–384. >@ + Jeong, S. Cho, D. .LP+ Pyun, D. +D& +DQ0 Kang, M. Jeong, S. Lee, A heuristic method of variable selection based on principal FRPSRQHQWDQDO\VLV DQG IDFWRUDQDO\VLV IRU PRQLWRULQJLQ D NZ PFIF SRZHU SODQW ,QWHUQDWLRQDO -RXUQDO RI +\GURJHQ (QHUJ\ 37 (2012) 11394–11400. [6] + Marzooghi, M. Raoofat, M. Dehghani, G. (ODKL '\QDPLF PRGHOLQJ RI VROLG R[LGH IXHO FHOO VWDFN EDVHG RQ ORFDO OLQHDU PRGHO WUHH DOJRULWKP,QWHUQDWLRQDO-RXUQDORI+\GURJHQ(QHUJ\ –4376. [7] P. 3LDQNR-Oprych, Z. -DZRUVNL 1XPHULFDO PRGHOOLQJ RI WKH PLFUR-WXEXODU VROLG R[LGH IXHO FHOO VWDFNV >SU]HJODG PHWRG PRGHORZDQLD QXPHU\F]QHJRPLNURUXURZ\FKVWDáRWOHQNRZ\FKVWRVyZRJQKZSDOLZRZ\FK@3U]HP\VO&KHPLF]Q\ (9) (2012) 1813– [8] T. Schmidt, J. 1XVVELFNHU 0RQLWRULQJ UHVXOWV IURP JHUPDQ FHQWUDO VRODU KHDWLQJ SODQWV ZLWK VHDVRQDO VWRUDJH LQ 6RODU :RUOG &RQJUHVV ,6(6SS–6. [9] F. Chabane, N. Moummi, S. Benramache, Experimental analysis on thermal performance of a solar air collector with longitudinal fins in a UHJLRQRIELVNUDDOJHULD-RXUQDORI3RZHU7HFKQRORJLHV – [10] M. Reuss, M. %HFN- 0OOHU'HVLJQRIDVHDVRQDOWKHUPDOHQHUJ\VWRUDJHLQWKHJURXQG6RODUHQHUJ\ (4) (1997) 247– [11] G. +HOOVWU|P 6 Larson, Seasonal thermal energy storage–WKH K\GURFN FRQFHSW %XOOHWLQ RI (QJLQHHULQJ *HRORJ\ DQG WKH (QYLURQPHQW 60 – [12] M. Inalli, M. Unsal, V. Tanyildizi, A computational model of a domestic solar heating system with underground spherical thermal storage, Energy 22 (12) (1997) 1163–1172. [13] R.
419
420
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
>@ R.@ J. Zhao, Y. Chen, S. Lu, SimuODWLRQVWXG\ RQ RSHUDWLQJ PRGHV RI VHDVRQDO XQGHUJURXQG WKHUPDO HQHUJ\ VWRUDJH LQ 3URFHHGLQJV RI ,6(6 World Congress 2007 (Vol. I–Vol. V), Springer, 2009, pp. 2119–2122. [26] P. Pinel, C. &UXLFNVKDQN, Beausoleil-Morrison, A. Wills, A review of available methods for seasonal storage of solar thermal energy in UHVLGHQWLDODSSOLFDWLRQV5HQHZDEOHDQG6XVWDLQDEOH(QHUJ\5HYLHZV (7) (2011) 3341– [27] M. Sweet, J. 0F/HVNH\ 1XPHULFDO VLPXODWLRQ RI XQGHUJURXQG VHDVRQDO VRODU WKHUPDO HQHUJ\ VWRUDJH sstes) for a single family dwelling using trnsys, Solar Energy. [28] M. de Guadalfajara, M. A. Lozano, L. M. Serra, Evaluation of the potential of large solar heating plants in spain, Energy Procedia 30 (2012) 839–848. [29] M. L. Sweet, J. 70F/HVNH\ Jr, Numerical simulation of underground seasonal solar thermal energy storage (SSTES) for a single family dwelling using TRNSYS, Solar Energy 86 (1) (2012) 289–300. [30] K. dRPDNO , U. dDN r, M. Kaya, K. %DNLUFL7KHUHODWLRQRIFROOHFWRUDQGVWRUDJHWDQNVL]e in solar heating systems, Energy Conversion and Management 63 (2012) 112–117. [31] T. Schmidt, D. Mangold, New steps in seasonal thermal energy storage in germany, Tech. rep., Solites - Steinbeis Research Institute for Solar and Sustainable Thermal Energy Systems (2006). [32] T.-M. Tveit, T. Savola, A. Gebremedhin, C.-J. Fogelholm, Multi-period minlp model for optimising operation and structural changes to &+3SODQWVLQGLVWULFWKHDWLQJQHWZRUNVZLWKORQJ-term thermal storage, Energy Conversion and ManaJHPHQW (3) (2009) 639–647. [33] L. Bartela, J. Kotowicz, Influence of membrane CO2 separation process on the effectiveness of supercritical combined heat and power plant >ZSá\Z SURZDG]HQLD PHPEUDQRZHJR SURFHVX VHSDUDFML &22 QD HIHNW\ZQRĞü QDGNU\W\F]QHM HOHNWURFLHSáRZQL ZĊJORZHM@ 5\QHN (QHUJLL 97 (6) (2011) 12–19. [34] K. Janusz-6]\PDĔVND(FRQRPLFHIILFLHQF\RIDQLJFFV\VWHPLQWHJUHWHGZLWKFFVLQVWDOODWLRQ>HIHNW\ZQRĞüHNRQRPLF]QDXNáDGXJD]RZRSDURZHJR]LQWHJURZDQHJR]H]JD]RZDQLHPZĊJODRUD]]LQVWDODFMDą&&6@5\QHN(QHUJLL –30. >@ D. Mangold, Seasonal storage – a german success story, Sun & Wind Energy 1 (2007) 48– [36] +-F. Zhang, X.-6*H+ Ye, Modeling of a space heating and cooling system with seasonal energy storage, Energy 32 – [37] +-J. Diersch, D. Bauer, W. +HLGHPDQQ : 5KDDN 3 6FKlW]O )LQLWH HOHPHQW PRGHOLQJ RI ERUHKROH KHDW H[FKDQJHU V\VWHPV 3DUW fundamentals, Computers & Geosciences 37 (8) (2011) 1122– [38] +-J. Diersch, D. Bauer, W. +HLGHPDQQ : 5KDDN 3 6FKlW]O )LQLWH HOHPHQW PRGHOLQJ RI ERUHKROH KHDW H[FKDQJHU V\VWHPV 3DUW numerical simulation, Computers & Geosciences 37 (8) (2011) 1136–1147. [39] + 3DNVR\ 2 Andersson, S. $EDFL + Evliya, B. 7XUJXW +HDWLQJ DQG FRROLQJ RI D KRVSLWDO XVLQJ VRODU HQHUJ\ FRXSOHG ZLWK VHDVRQDO thermal energy storage in an aquifer, Renewable Energy 19 (1) (2000) 117–122. [40] J. Kim, Y. Lee, W. S. Yoon, J. S. Jeon, M.-+ .RR < Keehm, Numerical modeling of aquifer thermal energy storage system, Energy – [41] R. Cuypers, N. Maraz, J. (YHUVGLMN & )LQFN ( +HQTXHW + 2YHUVORRW + Y 6SLMNHU $ de Geus, Development of a seasonal thermochemical storage system, Energy Procedia 30 (2012) 207–214. [42] + .HUVNHV% Mette, F. Bertsch, S. $VHQEHFN+ 'UFN&KHPLFDOHQHUJ\VWRUDJHXVLQJUHYHUVLEOHVROLGJDV-reactions (CWS)–results of the research project, Energy Procedia 30 (2012) 294–304. [43] B. 0HWWH + .HUVNHV + 'UFN &RQFHSWV RI ORQJ-term thermochemical energy storage for solar thermal applications–selected examples, Energy Procedia 30 (2012) 321–330. [44] B. Michel, N. Mazet, S. Mauran, D. Stitou, J. ;X 7KHUPRFKHPLFDO SURFHVV IRU VHDVRQDO VWRUDJH RI VRODU HQHUJ\ &KDUDFWHUL]DWLRQ DQG modeling of a high density reactive bed, Energy. >@ J. Fan, S. Furbo, E. Andersen, Z. Chen, B. Perers, M. Dannemand, Thermal behavior of a heat exchanger module for seasonal heat storage, Energy Procedia 30 (2012) 244– [46] T. Pauschinger, Solar district heating with seasonal thermal energy storage in germany, Tech. rep., Steinbeis Research Institute for Solar and Sustainable Thermal Energy Systems (2012).
ScienceDirect Energy Procedia 50 (2014) 414 – 420
The International Conference on Technologies and Materials for Renewable Energy, Environment and Sustainability, TMREES14
STES—typical scenarios for heat accumulator cooperation -DURVáDZ0LOHZVNL *:RMFLHFK%XMDOVNL Warsaw University of Technology, Institute of Heat Engineering, 21/25 Nowowiejska Street, Warsaw, 00-665, Poland
Abstract The article presents an analysis of real operational data of a Seasonal Thermal Energy Storage system connected to a local heating grid. 8 years of operation time was analyzed to determine typical scenarios for cooperation with the heating grid and solar collectors7KHUHVHDUFKVKRZVWKDWWKUHHPDLQZRUNLQJPRGHVRIWKHDFFXPXODWRUPD\EHSDUWLFXODUL]HG FKDUJLQJGLVFKDUJLQJ and transient modes, and that the maximum speed of charge/discharge is on average below 0.3ӓC/day. © 2014 2014Published The Authors. Published by Elsevier Ltd. © by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD). (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) Keywords: Seasonal Thermal Energy Storage
1. Introduction Rising fuel prices and electricity consumption are driving the search for new and more efficient ways of heat and power generation. Energy needed for heating and domestic hot water accounts for a third of energy consumed in LQGXVWULDOL]HGFRXQWULHVOLNH3RODQG5HGXFWLRQVLQIRVVLOIXHOFRQVXPSWLRQDQGSROOution emission may be achieved by using solar based technologies. In the case of electricity, solar energy may be used directly (PV panels) or indirectly through the utilization of biofuels [1, 2], for example in fuel cells [3–7] which can achieve very high efficiency due to direct conversion of chemical energy into electrical current. Water heating with solar collectors is currently a competitive solution [9] comparing to other technologies, but it is limited by solar radiation intensity and available only in summer. Unfortunately, heat is mostly needed in winter.
&RUUHVSRQGLQJDXWKRU7HO ID[ E-mail address: PLOHZVNL#LWFSZHGXS
1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi:10.1016/j.egypro.2014.06.050
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
415
Solar energy storage for heating appears justified in cases where the amount of solar energy for heating is higher than 20%. Issues involved in Seasonal Thermal Energy Storage in a ground heat accumulator were discussed in [10], where SDUDPHWHUV OLNH KHDW FDSDFLW\ RI WKH DFFXPXODWRU DQG VRLO KXPLGLW\ ZHUH DQDO\]HG &DOFXODWLRQV FRQFHUQHG transportation of heat and water—the maximum water temperature was assumed to be 90ӓC. Calculations were performed for a system with a capacity of 174 N:thFRPSRVHGRIDZDWHUFRQWDLQHURIYROXPH m3 and 140 vertical, tubular heat exchangers immersed 30 m deep. $KHDWDFFXPXODWRULQWKHIRUPRIURFNZDVSURSRVHGLQ [11]. Using a mathematical model, the heat capacity of the accumulator was estimated, and heat loss of 10—20% per cycle was determined. The accumulator’s size was DVVXPHGWREHIURPWRPGHHSDQGWKHZRUNLQJPHGLXPZDVSURSDQH0RGHOVIRU67(6FDOFXODWLRQVZHUH presented in [12–16]. They were used for simulation of long-term operation of a system equipped with a spherical or semi-spherical heat accumulator, which would be used for both heating and cooling. Results prove that there is no reason to install solar panels on a surface area in excess of 60 m2/ builGLQJLQDFOLPDWHVLPLODUWRWKDWLQ7XUNH\7KH authors made similar calculations for a cylindrical accumulator [17] which marginally increases the solar energy XWLOL]DWLRQIDFWRU2SWLPDOVHOHFWLRQRIHOHPHQWVOLNHFRQGHQVLQJERLOHUFRPSUHVVLRQRUDEVRUSWLRQKHDWSXPSHWF composing a cogeneration system supplying 100 well thermally insulated buildings was presented in [18]. The calculation results were compared with condensing boiler and grid supplied electricity, showing that the greater the investment made, the larger the profits are. The solar power share in covering heat demand was 80% whereas renewable energy sources accounted for 40 % of electrical energy production, which results in lower fossil fuel consumption. In [19] simulation results were given for a solar heating system for 90 buildings with a floorspace of 100 m2 each. It was proven that a 3 000 m2 area of solar panels installed on roofs and a borehole accumulator (60 000 m3) are able to cover 60 % of heat demand. In paper [20] a simulation of a central solar heating system that FRYHUV % of heat demand was presented. In addition to global indicators (e.g. solar energy share in the whole EDODQFH WKH FKDQJHV WDNLQJ SODFH GXULQJ RSHUDWLRQ RI WKH ZKROH V\VWHP ZHUH FRQVLGHUHG 2SHUDWLRQ RI D V\VWHP containing a seasonal heat accumulator is a quite difficult issue in terms of the control strategy due to large uncertainties concerning both the amount of accumulated solar energy and the varying load during the heating season. It seems that algorithms based on artificial intelligence, which proved useful in similar applications OLNH [21, 22], could be widely used in this case as well. Matters regarding improving the characteristics of selected 67(6V\VWHPVPHULWVHSDUDWHDQDO\VHV,QZRUN [23], the heating effectiveness and economic issues of three different NLQGV RI FHQWUDO VRODU KHDWLQJ V\VWHPV IRU 7XUNLVK FRQGLWLRQV ZHUH LQYHVWLJDWHG 7KH RXWFRPH ZDV WKH HVWLPDWHG return of investment in 19 years and, if 100 % of heat demand were covered by solar energy, the period extends to 40 years [24]. The paper [] contains simulation results of a quite large STES in Chinese conditions, comprising a solar panel area of 1 000 m2 connected with an accumulator of volume 90 000 m3— and a relatively low temperature of the ”cold” part of 30°C assumed. A comprehensive review of STES technology may be found in [26]—where various options were discussed, even extraordinary ones. Results of long-term operation simulation RIDKHDWDFFXPXODWRU \HDUV DUHLQWKHDUWLFOH [27]. The results were obtained using the most popular application used for calculation of STES systems (TRNSYS) (inter alia [28, 29]). In addition to this program, other calculation tools are often used [30]. A separate problem is cooperation of a STES system with an existing heating grid supplied by combined heat and power plants [32–34]. The STES system influence their generation capabilities in winter. The main motive for ZULWLQJWKHSDSHUZDVWRWU\WRDQVZHUWKHTXHVWLRQ +RZVHQVLEOHLVLWWREXLOGVXFKLQVWDOODWLRQVIRUWKHSXUSRVHRI supplying heat to existing buildings with poor thermal insulation parameters in Polish conditions? The target would be to achieve about a 60 % share in heating energy demand assuming reasonable costs and dimensions of the whole installation. 7KHUHDUHVHYHUDOWHFKQLFDOVROXWLRQVUHJDUGLQJWKHKHDWDFFXPXODWRUXVHGLQ67(6V\VWHPV x x x x x x
7DQNWKHUPDOHQHUJ\storage—77(6 –80 N:KP3 Pit thermal energy storage—37(6 –80 N:KP3 [36] Borehole thermal energy storage—%7(6 –30 N:KP3 [19, 37, 38] Aquifer thermal energy storage—$7(6 –40 N:KP3 [39, 40] $FFXPXODWRUVZLWKHOHPHQWVVXEMHWWRWKHUPRFKHPLFDOUHDFWLRQV –460 N:KP3 [41–44] Phase Change Material storage—PCM []
416
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
7KHUHJXODUWHPSHUDWXUHUDQJHDWZKLFK67(6V\VWHPZRUNVLVӓC, the effectiveness of heat storage grows VLJQLILFDQWO\ZKHQWKH\DUHZHOOFRQWUROOHGLQRUGHUWRPDLQWDLQVWUDWLILFDWLRQLQVLGHWKHWDQN2QWKHRWKHUKDQGWKH thermocline broadens over longer periods , hence maintaining complete stratification is technically difficult. The SUHVHQWHGOLWHUDWXUHUHYLHZVKRZVWKDWWKHRSWLPDOUDWLRRIWDQNYROXPHWRFROOHFWRUVXUIDFHDUHD 9$ LV (m3/m2) [18]. 2 External conditions influencing operation of the heat accumulator Many elements influence the selection of cooperation modes of the heat accumulator with solar collectors and EXLOGLQJV7KHNH\RQHVDUH x
x
technological structure of the system o are heating boilers present? o is a heat pump present? o LVVWUDWLILFDWLRQSUHVHQWLQWKHWDQN" operation parameters of the grid and charging/discharging of the accumulator
The number of possible cooperation combinations is practically infinite. It is essential to identify the significant features influencing the various action schemes. The first element to be discussed is the power of the accumulator and the cooperating heating grid. The absolute power generated by the solar panels and the accumulator is not significant, but the proportions of the accumulator and the power of solar panels is important. In the case of the accumulator not only its power but also its capacity should be mentioned. In general, it is assumed that the power and capacity would normally have to be correlated. Maximum charging/discharging speed is limited by the maximum flow velocity of water, for which purpose it is possible to design a diffuser. This limitation WUDQVODWHVGLUHFWO\WRWKHVKDSHRIWKHDFFXPXODWRU¶VWDQN,WLVKRZHYHUSRVVLEOHWROLPLWWKHPD[LPXPDFFXPXODWRU charging speed by designing a smaller system diffuser—pumping-flow system. Such limitation on the maximum speed is not desirable because it decreases the functionality of the accumulator. It is then assumed that the accumulator’s charging speed and its capacity will be correlated.
Figure Temperature development in the hot-water seasonal heat store in Friedrichshafen [8]
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
Figure Averaged values of hot and cold temperatures during year If currently existing systems’ accumulator—VRODU FROOHFWRUV DUH FRQVLGHUHG WKH UDWLR RI SRZHU WDNHQ IURP WKH accumulator and the heating power of the collectors varies vastly. In some systems the size of the accumulator enables autonomic operation of the accumulator for several months. In others the possibility of feeding from the heat accumulator accounts only for a little share of the power that has to be supplied to the buildings. Apart from the accumulator charging speed and capacity ratio, a significant role is also played by the excess DPRXQWRILQVWDOOHGSRZHULQFROOHFWRUV([FHVVVL]HPDNHVLWSRVVLEOHWRHDVLO\FKDUJHWKHDFFXPXODWRUDWIXOOSRZHU (at any time). Otherwise, limitations are caused by low production capabilities of the FROOHFWRUV 7KLV NLQG RI limitation may also be present at minimal loads. When the heat demand is more or less equal to the technical minimum of the collector system–it is not possible to discharge the accumulator. In this case it may be necessary to charge/discharge the accumulator in half-year periods (spring/autumn). :KHQH[SORULQJWKHSRVVLELOLW\RIOLQNLQJWKHDFFXPXODWRUZLWKRWKHUV\VWHPHOHPHQWVWKHUHDVRQVIRULQVWDOOLQJ DFFXPXODWRUVVKRXOGEHGHWHUPLQHG x x x x x
compensation of heating source load at YDULDEOHKHDWGHPDQG FRYHULQJRISHDNKHDWGHPDQG LQFUHDVHRIDYDLODELOLW\,QVWHDGRIPDLQWDLQLQJERLOHUVLQKRWUHVHUYHRUWZRZRUNLQJXQLWVDWSDUWLDOORDG RQHZRUNLQJERLOHUDQGDQDFFXPXODWRUHQVXUHVDIHKHDWVXSSO\ ensuring heat supply in emerJHQF\FDVHV PDNLQJRSHUDWLRQRIVRODUFROOHFWRUVSRVVLEOHZKHQKHDWGHPDQGLVORZHUWKDQWKHWHFKQLFDOPLQLPXPRI heating devices.
417
418
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
Figure Charging and discharging speeds of the chosen STES The listed functions are by and large not mutually exclusive. The accumulator may perform different functions in the whole system. In order to specify the most typical situations the most important (basic) functions of an accumulator installed in a system should be selected. It seems that the largest financial benefits from the possibility of heat accumulation stem from maximization of profits from avoided heat production by heating boilers. The use of solar collectors changes the total heat demand of the system—FROOHFWRUV ZRUN FRQWLQXRXVO\ LQ KHDW SURGXFWLRQ mode. Due to this fact, the heat produced by the collectors does not alter the heat supplied to consumers. Profit PD[LPL]DWLRQIURPWKHDYRLGHGIXHOSXUFKDVHIRUWKHERLOHUVPD\ILJXUHLQ x x
higher solar energy share in winter, change to the heat production curve during the day—increased heat production from the accumulator at high fuel prices and minimization of its operation at low prices (currently natural gas prices do not vary daily or seasonally).
3 Typical cooperation scenarios of heat accumulator and grid The following format for temperatures present in the accumulator was selected tbottom/tupper(tupper-tbottom), e.g. PHDQV WKDW LQ WKH XSSHU SDUW RI WKH WDQN WKH WHPSHUDWXUH LV °C, in the bottom 40°C and that the temperature difference is 20°C. $FFXPXODWRUFKDUJLQJWDNHVSODFHZKHQWKHUHLVDVXUSOXVRIKHDWSURGXFHGE\WKHVRODUFROOHFWRUVFRPSDUHGZLWK the demand required by the local heating grid, that the period starts in between March and April and lasts until October. The assumptions are confirmed by calculations performed on the basis of data published in [8] presented in Fig. 2. The beginning of the charging season is in mid-February and starts with temperatures 40/44(4), which means PRUHRUOHVVWKHVDPHWHPSHUDWXUHLQWKHZKROHYROXPHRIWKHWDQN7KHHQGRIWKHFKDUJLQJSURFHVVLVDWWKHHQGRI August. From this time on the upper temperature starts to drop, which most probably is connected with the fact that collectors are not able to cover the losses to the environment. The heat from the accumulator may also be used to cover heat demand on cold nights.
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
The charging and discharging speed of the accumulator for specific months may be determined through analyzing trend-lines—see Fig. 3. The maximum speed at which the accumulator is charged and discharged is ą0.3ӓC/24 h. Based on the presented calculations three main aFFXPXODWRURSHUDWLRQVFHQDULRVPD\EHVSHFLILHG 1.
Charging, for G7»GW!0.1ӓC, period from May to July
2. 3.
Discharging, for G7»GW -0.1ӓC, period from September to December Transient time at which the accumulator is used occasionally (charged during the day and discharged at night)—period from July to September—RUGRHVQRWZRUNDWDOO—period from December to February.
,QDOOWKHVFHQDULRVWKHWRSWHPSHUDWXUHRYHUWDNHVWKHERWWRPRQHE\FDRQHPRQWK Another important issue is the difference of temperatures present in the accumulator, heat pump operation (if present), heating grid parameters and thermocline position. They allow one to estimate the amount of stored energy DYDLODEOHIRUKHDWLQJSXUSRVHVLQWKHWDQN7KHSDUDPHWHUVGRQRWFKDQJHWKHDFFHSWHGVFenarios and are not analyzed DWWKHGLVFXVVLRQVWDJHGXHWRWKHODFNRIDSSURSULDWHGDWD 4 Summary and conclusions The analysis of real operational data of a Seasonal Thermal Energy Storage system connected to a local heating grid. 8 years of operation time was analyzed to determine typical scenarios for cooperation with the heating grid and VRODU FROOHFWRUV 7KH UHVHDUFK VKRZV WKDW WKUHH PDLQ ZRUNLQJ PRGHV RI WKH DFFXPXODWRU PD\ EH SDUWLFXODUL]HG charging, discharging and transient modes, and that the maximum speed of charge/discharge is on average below 0.3°C/day Acknowledgments The project was funded by the National Science Centre by decision number DEC-2012/07/B/ST8/03937. References [1] A. 6REROHZVNL Bartela, A. 6NRUHN-2VLNRZVND 7 ,OXN &RPSDULson of the economic efficiency of chp plants integrated with gazela JHQHUDWRU >SRUyZQDQLH HIHNW\ZQRĞFL HNRQRPLF]QHM XNáDGyZ NRJHQHUDF\MQ\FK ] JHQHUDWRUHP JD]X SURFHVRZHJR JD]HOD@ 5\QHN (QHUJLL 102 –37. [2] W. %XG]LDQRZVNL 6XVWDLQDEOH ELRJDV HQHUJ\ LQ SRODQG 3URVSHFWV DQG FKDOOHQJHV 5HQHZDEOH DQG 6XVWDLQDEOH (QHUJ\ 5HYLHZV (1) (2012) 342–349. [3] G. De Lorenzo, P. Fragiacomo, Electrical and electrical-thermal power plants with molten carbonate fuel cell/gas turbine-integrated systems, International Journal of Energy Research 36 – [4] G. Discepoli, G. Cinti, U. Desideri, D. Penchini, S. 3URLHWWL &DUERQ FDSWXUH ZLWK PROWHQFDUERQDWH IXHO FHOOV ([SHULPHQWDO WHVWVDQG IXHO cell performance assessment, International Journal of Greenhouse Gas Control 9 (2012) 372–384. >@ + Jeong, S. Cho, D. .LP+ Pyun, D. +D& +DQ0 Kang, M. Jeong, S. Lee, A heuristic method of variable selection based on principal FRPSRQHQWDQDO\VLV DQG IDFWRUDQDO\VLV IRU PRQLWRULQJLQ D NZ PFIF SRZHU SODQW ,QWHUQDWLRQDO -RXUQDO RI +\GURJHQ (QHUJ\ 37 (2012) 11394–11400. [6] + Marzooghi, M. Raoofat, M. Dehghani, G. (ODKL '\QDPLF PRGHOLQJ RI VROLG R[LGH IXHO FHOO VWDFN EDVHG RQ ORFDO OLQHDU PRGHO WUHH DOJRULWKP,QWHUQDWLRQDO-RXUQDORI+\GURJHQ(QHUJ\ –4376. [7] P. 3LDQNR-Oprych, Z. -DZRUVNL 1XPHULFDO PRGHOOLQJ RI WKH PLFUR-WXEXODU VROLG R[LGH IXHO FHOO VWDFNV >SU]HJODG PHWRG PRGHORZDQLD QXPHU\F]QHJRPLNURUXURZ\FKVWDáRWOHQNRZ\FKVWRVyZRJQKZSDOLZRZ\FK@3U]HP\VO&KHPLF]Q\ (9) (2012) 1813– [8] T. Schmidt, J. 1XVVELFNHU 0RQLWRULQJ UHVXOWV IURP JHUPDQ FHQWUDO VRODU KHDWLQJ SODQWV ZLWK VHDVRQDO VWRUDJH LQ 6RODU :RUOG &RQJUHVV ,6(6SS–6. [9] F. Chabane, N. Moummi, S. Benramache, Experimental analysis on thermal performance of a solar air collector with longitudinal fins in a UHJLRQRIELVNUDDOJHULD-RXUQDORI3RZHU7HFKQRORJLHV – [10] M. Reuss, M. %HFN- 0OOHU'HVLJQRIDVHDVRQDOWKHUPDOHQHUJ\VWRUDJHLQWKHJURXQG6RODUHQHUJ\ (4) (1997) 247– [11] G. +HOOVWU|P 6 Larson, Seasonal thermal energy storage–WKH K\GURFN FRQFHSW %XOOHWLQ RI (QJLQHHULQJ *HRORJ\ DQG WKH (QYLURQPHQW 60 – [12] M. Inalli, M. Unsal, V. Tanyildizi, A computational model of a domestic solar heating system with underground spherical thermal storage, Energy 22 (12) (1997) 1163–1172. [13] R.
419
420
Jarosław Milewski and Wojciech Bujalski / Energy Procedia 50 (2014) 414 – 420
>@ R.