- Email: [email protected]
Evaluation on Performance of a Phase Change Material Based Cold Storage House
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 105 (2017) 3947 – 3952
The 8th International Conference on Applied Energy – ICAE2016
Evaluation on performance of a phase change material based cold storage house Changjiang Wanga, Zitao Hea, Hailong Lib, Ronald Wennersterna, Qie Suna* a
Institute of Thermal Science and Technology, Shandong University, Jingshi Road No.17923, Jinan and 250061, China b School of Business, Society and Technology, Mälardalen University, Sweden
Abstract Technology of phase change materials used in cold storage house has great potential in energy storage and cost saving under the background of peak and valley price of electricity. A kind of cold storage house based on water/ice as phase change material was set up and studied. Performance of this cold storage house was experimentally tested and numerical simulated. The results showed that water/ice is a promising material for its high latent heat density. Cold storage house with water/ice PCM shifts electricity load to off-peak load and then increase operating cost due to peak load power pricing. In addition, water/ice PCM increases the insulation effect and then reduces the cold energy needed. The payback period of water/ice PCM in a laboratory scale is about 4.1 years in this study. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility the scientific committee the 8th International Conference on Applied Energy. Selection and/or peer-reviewofunder responsibility of of CUE
Keywords: energy storage; cold storage house; phase change material; peak load power pricing; economic analysis
1. Introduction Cold storage houses are widely used in agricultural and food industries, e.g. people can store fruits and vegetable in summer and sell them in winter. However, cold storage houses consume large amount of electricity and exacerbate the peak load of the electricity grid [1]. A solution is to shift the cooling load from peak periods to valley periods and this will also help to reduce the owner’s electricity cost under a peak-valley price mechanism. A popular method to shift the cooling load is by adding a phase change material (PCM) based insulation layer to the wall of cold storage houses. During the process of phase change, the temperature remains constant and a large amount of energy can be stored or released [2].
Qie Sun. Tel.:+86-531-88399000-2306 E-mail address: [email protected].
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.820
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
Studies have investigated the application of PCMs to thermal/cold energy storage in recent years. Leducq [3] compared a PCM packing to a polystyrene packing and found that to obtain the same insulation effect the PCM packing could be thinner and thus smaller in size. Oró[4] examined the application of PCM material to storage of ice cream and found it could help to keep the quality of ice cream stable. In addition, Zhu[5] developed a three-layer sandwich-type wall with the outer layers of PCM wallboards and he proved that the PCM layer helps to reduce the electricity demand of the building for heating and cooling and to shift the load of cooling in summer. For high-temperature cold storage houses, i.e. operating temperature between 0℃and 10℃, the optional PCM materials include: water/ice, eutectic salt and organic materials [6-8]. Compared with other options, water/ice has the advantages of high energy density, low cost, small volume changes during phase change process, non-toxic and non-corrosive. However, few studies have investigated the application of water/ice PCMs to cold storage houses. Therefore, the paper aims to study the effects of ice/water PCM insulation on the performance of cold storage houses. To this aim, the paper firstly established a numerical model to determine the thermodynamic characteristics of the cold storage house. The paper then validated the model by an experiment. The paper further applied the validated model to study the effect of the PCM-based insulation on the thermodynamic performance of the cold storage house. In addition, the economic performance of the PCM-based cold storage house was evaluated. 2. Methodology 2.1 Model and experiment to determine the thermodynamic characteristics of the cold storage house An ordinary cold storage house is constructed with insulated walls, as can be seen in Fig. 1. The walls of the cold storage house usually have a sandwich structure, e.g. a layer of polyurethane covered by two layers of metal or concrete. The thickness of the polyurethane layer in the wall is 100mm. Since the walls of the cold storage house are usually identical, the study employed a governing equation of heat conduction in the wall of the cold storage house: ߲ݐሺݔǡ ߬ሻ ߲ ߲ݐሺݔǡ ߬ሻ ߩܿ ൌ ቆ݇ ቇሺͳሻ ߲߬ ߲ݔ ߲ݔ For the thermodynamic simulation, the study made the following assumptions: (1) no heat source inside the wall; (2) natural convection occurs between the outside wall and environmental air; (3) heat flux exists on the surface of inner wall generated by cargos in the cold storage house.
Fig 1 Cold storage house in experiment
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In order to validate the model, an experiment was performed based on a small size high temperature cold storage house with a physical dimension of 2000mm×1200mm×1400mm and the thickness of the insulated wall of 100mm.The model of the compressor is Panasonic 2P17S225ANQ and the power is 2780W, the energy efficiency ratio is 3.2. The experiment was operated from 10:15 am to 10:41 am on 18 April, 2016, and the start-up phase was not considered. A total of 48 temperature measuring probes were fixed in the cold storage house and in the wall of the house to measure the temperature of different parts of the cold storage house. The ambient temperature during the experiment was 25℃ and the natural convection coefficient between the wall of the cold storage house and the environment was 5W/(m2∙℃) and the internal heat flux is 0.7W/m2. 2.2 Examination of the PCM-based cold storage house This study proposed to install a water/ice PCM layer on the inner side of the insulated wall to store energy and thus to shift the load of electricity consumption (Fig. 2). For the water/ice-PCM layer, the apparent heat capacity of water/ice can be described as: ܥ௦ ܶ ൏ ܶ െ ߂ܶሺ݁ݏ݄݈ܽ݀݅ݏሻ
ܥ ൌ ൞ଶ௱்
ೞ ା ଶ
ܶ െ ߂ܶ ܶ ܶ ߂ܶሺ݄݁݃݊ܽܿ݁ݏ݄ܽሻ
(2)
ܥ ܶ ܶ ߂ܶሺ݈݅݁ݏ݄ܽ݀݅ݑݍሻ where Cp is the product of the capacity of ρ and c equal to the real capacity of ice water mixture, L is the latent heat of ice, subscript s and l represents for solid phase and liquid phase respectively. Tf is freezing point and ∆T is 1℃.
Fig 2 Cold storage house model with PCM
The PCM layer should be able to store enough cold energy for the demand during peak time. In the present study, the heat from the stored fruits or vegetable is not considered. Therefore, the electricity needed to support the cold storage house is decided by the fusion process of ice, i.e. ܧൌ ݔܵߩܮ (3) which E is electricity consumed during peak period and can be measured by a coulombmeter, L is the latent heat that ice absorbed in phase change process, ρ is the density of ice, S is the inner superficial area of wall of cold storage house and x0 is the thickness of water/ice PCM layer. As a result, the thickness of the water/ice layer, x0, is 9.4mm. In order to make sure the latent energy in ice is enough for busy and peak period, a 10mm thickness was adopted in this study. 2.3 Application of the validated model to the PCM-based storage house Due to the application of the PCM layer, the thermal resistance in the wall (PCM plus polyurethane) would change. As a result, the load of electricity consumption will be shifted and the total amount of electricity consumption will be reduced.
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
The water/ice-PCM layer increases the thermal resistance and the heat flux from environment to cold storage house through the wall diminish as a result. Overall heat transfer coefficient k0 is an expression as follows: ଵ ௫ ௫ ൌ ುಾ (4) బ
ఒ
ఒುಾ
which λin is heat conductivity coefficient of insulation wall, λPCM is heat conductivity coefficient of PCM, xin and xPCM is the thickness of insulation wall and ice/water layer respectively. The heat flux reduction ΔQ and total energy saving EQ due to heat resistance increment can be calculated as: οܳ ൌ ܵሺ݇ െ ݇ ሻሺݐ௨௧ െ ݐ ሻ (5) which kin is heat transfer coefficient of insulation wall and tD is the time quantum in a day. ܧொ ൌ οܳ ൈ ݐ
(6)
The money saved a day M1 due to the saving in electricity consumption can be calculated by ܯଵ ൌ ͲǤͶ ൈ ܧொ
(7)
Application of PCM to cold storage house can help to shift the loads of electricity consumption and thus save electricity costs under the peak-valley pricing mechanism. The study took the peak-valley tariff in China as an example, i.e. 0.477 RMB/kWh for the off-peak period (11:00~13:00 and 22:00~8:00, day+1); 0.858 RMB/kWh for the busy period (8:00~11:00, 13:00~19:00 and 21:00~22:00); and 1.239 RMB/kWh for the peak period (19:00~21:00). By shifting the loads, the PCM-based cold storage house can help to save electricity cost a day, M2, which is calculated as: ܯଶ ൌ ሺͳǤʹ͵ͻ െ ͲǤͶሻ ൈ ݁ ൈ ݐଵ ሺͲǤͺͷͺ െ ͲǤͶሻ ൈ ݁ ൈ ݐଶ
(8)
which e is the running power of cold storage house, t1 and t2 are peak period and busy period respectively. In this study, e is 0.282kW, t1 is 2h and t2 is 10h. The payback period Y is calculated by: ܻ ൌ ሺெ
భ ାெమ ሻൈଷହ
(9)
which V is the investment cost, i.e. 2300 RMB for the PCM layer suitable for the experimental cold storage house. 3. Results and discussion 3.1 Simulation and validation Fig 3 shows the temperature variation of inner wall surface in simulation and experiment. The temperature measured in the experiment was agreed with that obtained from the simulation. The measured temperature remained about 0.7℃ higher than in simulation in average, it was due to the measuring error of thermocouples. It implies that it is acceptable to employ the model to simulate the heat transfer in the wall of the cold storage house. Therefore, the model is further applied to predict the temperature of wall of cold storage house. 3.2 Simulation results on model with PCM layer (1) The thermodynamic characteristics of the PCM-based storage house. Fig 4 shows temperature variation of model with water/ice-PCM layer during busy period and peak
Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
Fig 3 Temperature curve comparison in simulation and experiment
period. As can be seen in the graph, x=100~110mm represents the region of water/ice as PCM. The temperature did not exceed 5℃ at the moment between 8:00 to 22:00. The temperature inside the cold storage house meets the temperature requirement for food conservation. (2) Results about load shifts The water/ice PCM layer was frozen totally during off-peak time, so the PCM layer was all ice at the beginning of the simulation. About one-sixth ice melted during peak period and five-sixth melted during busy period to maintain a cooling condition. (3) Energy saving due to the application of PCM layer In this study, k0, i.e. the overall heat transfer coefficient, is 0.35W/(m2·℃) and ∆Q, the reduction in heat flux, is 0.25W. Therefore, the additional energy saving due to the increase in heat transfer resistance is 21.6kJ and corresponding electricity saving is 6×10-3 kWh. (4) Total savings of cost and the payback period The total cost savings consist two parts, i.e. one part due to the increase in heat transfer resistance and the other due to load shift. The increased heat transfer resistance can help to save 4.2×10-3 RMB/day and load shifts can contribute to 1.5 RMB/day of cost saving. Payback period in this study is 4.1 years. 4. Conclusions In China, the policy of peak and valley electric charges is undoubtedly going to popularize in the whole country. We should take this advantage of peak shifting to avoid economic, environmental pressure. In this aspect, ice/water-PCM plays an important role in cold energy storage. In this study, performance of a cold storage house with ice/water as PCM is studied experimentally and numerically. The main results of the study include: (1) water/ice is a promising material for cold thermal energy storage in high temperature cold storage house for its high latent heat density, high density, non-toxic and no corrosion. (2) the water/ice layer can absorb the cold thermal energy in off-peak period and release it to run the cold storage house in busy and peak period as an economic operation solution. (3) ice/water layer can increase heat transfer resistance of wall and then reduce the energy needed. (4) the payback period of ice/water PCM is about 4.1 years.
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Fig 4 Temperature through wallboard in contrast simulation
Acknowledgements This work was supported in part by Project ZR2014EEM025 supported by Natural Science Foundation of Shandong Province, China; and the 973 Program 2013CB228305, China. References [1] Qureshi WA, Nair N-KC, Farid MM. Impact of energy storage in buildings on electricity demand side management. Energy Conversion and Management. 2011; 52(5):2110-20. Doi: http://dx.doi.org/10.1016/j.enconman.2010.12.008. [2] Zhou D, Shire GSF, Tian Y. Parametric analysis of influencing factors in Phase Change Material Wallboard (PCMW). Applied Energy. 2014; 119:33-42. Doi: http://dx.doi.org/10.1016/j.apenergy.2013.12.059. [3] Leducq D, Ndoye FT, Alvarez G. Phase change material for the thermal protection of ice cream during storage and transportation. International Journal of Refrigeration. 2015; 52:133-9. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2014.08.012. [4] Oró E, de Gracia A, Cabeza LF. Active phase change material package for thermal protection of ice cream containers. International Journal of Refrigeration. 2013; 36(1):102-9. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2012.09.011. [5] Zhu N, Liu P, Hu P, Liu F, Jiang Z. Modeling and simulation on the performance of a novel double shape-stabilized phase change materials wallboard. Energy and Buildings. 2015; 107:181-90. Doi: http://dx.doi.org/10.1016/j.enbuild.2015.07.051. [6] Veerakumar C, Sreekumar A. Phase change material based cold thermal energy storage: Materials, techniques and applications – A review. International Journal of Refrigeration. 2016; 67:271-89. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2015.12.005. [7] Thambidurai M, Panchabikesan K, N KM, Ramalingam V. Review on phase change material based free cooling of buildings— The way toward sustainability. Journal of Energy Storage. 2015; 4:74-88. Doi: http://dx.doi.org/10.1016/j.est.2015.09.003. [8] Akeiber H, Nejat P, Majid MZA, Wahid MA, Jomehzadeh F, Zeynali Famileh I, Calautit JK, Hughes BR, Zaki SA. A review on phase change material (PCM) for sustainable passive cooling in building envelopes. Renewable and Sustainable Energy Reviews. 2016; 60:1470-97. Doi: http://dx.doi.org/10.1016/j.rser.2016.03.036.
Biography Changjiang Wang is a PhD candidate in Shandong University. He is studying at the Institute of Thermal Science and Technology, Shandong University. His research focuses include sustainable energy system and industrial ecology.
ScienceDirect Energy Procedia 105 (2017) 3947 – 3952
The 8th International Conference on Applied Energy – ICAE2016
Evaluation on performance of a phase change material based cold storage house Changjiang Wanga, Zitao Hea, Hailong Lib, Ronald Wennersterna, Qie Suna* a
Institute of Thermal Science and Technology, Shandong University, Jingshi Road No.17923, Jinan and 250061, China b School of Business, Society and Technology, Mälardalen University, Sweden
Abstract Technology of phase change materials used in cold storage house has great potential in energy storage and cost saving under the background of peak and valley price of electricity. A kind of cold storage house based on water/ice as phase change material was set up and studied. Performance of this cold storage house was experimentally tested and numerical simulated. The results showed that water/ice is a promising material for its high latent heat density. Cold storage house with water/ice PCM shifts electricity load to off-peak load and then increase operating cost due to peak load power pricing. In addition, water/ice PCM increases the insulation effect and then reduces the cold energy needed. The payback period of water/ice PCM in a laboratory scale is about 4.1 years in this study. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility the scientific committee the 8th International Conference on Applied Energy. Selection and/or peer-reviewofunder responsibility of of CUE
Keywords: energy storage; cold storage house; phase change material; peak load power pricing; economic analysis
1. Introduction Cold storage houses are widely used in agricultural and food industries, e.g. people can store fruits and vegetable in summer and sell them in winter. However, cold storage houses consume large amount of electricity and exacerbate the peak load of the electricity grid [1]. A solution is to shift the cooling load from peak periods to valley periods and this will also help to reduce the owner’s electricity cost under a peak-valley price mechanism. A popular method to shift the cooling load is by adding a phase change material (PCM) based insulation layer to the wall of cold storage houses. During the process of phase change, the temperature remains constant and a large amount of energy can be stored or released [2].
Qie Sun. Tel.:+86-531-88399000-2306 E-mail address: [email protected].
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.820
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
Studies have investigated the application of PCMs to thermal/cold energy storage in recent years. Leducq [3] compared a PCM packing to a polystyrene packing and found that to obtain the same insulation effect the PCM packing could be thinner and thus smaller in size. Oró[4] examined the application of PCM material to storage of ice cream and found it could help to keep the quality of ice cream stable. In addition, Zhu[5] developed a three-layer sandwich-type wall with the outer layers of PCM wallboards and he proved that the PCM layer helps to reduce the electricity demand of the building for heating and cooling and to shift the load of cooling in summer. For high-temperature cold storage houses, i.e. operating temperature between 0℃and 10℃, the optional PCM materials include: water/ice, eutectic salt and organic materials [6-8]. Compared with other options, water/ice has the advantages of high energy density, low cost, small volume changes during phase change process, non-toxic and non-corrosive. However, few studies have investigated the application of water/ice PCMs to cold storage houses. Therefore, the paper aims to study the effects of ice/water PCM insulation on the performance of cold storage houses. To this aim, the paper firstly established a numerical model to determine the thermodynamic characteristics of the cold storage house. The paper then validated the model by an experiment. The paper further applied the validated model to study the effect of the PCM-based insulation on the thermodynamic performance of the cold storage house. In addition, the economic performance of the PCM-based cold storage house was evaluated. 2. Methodology 2.1 Model and experiment to determine the thermodynamic characteristics of the cold storage house An ordinary cold storage house is constructed with insulated walls, as can be seen in Fig. 1. The walls of the cold storage house usually have a sandwich structure, e.g. a layer of polyurethane covered by two layers of metal or concrete. The thickness of the polyurethane layer in the wall is 100mm. Since the walls of the cold storage house are usually identical, the study employed a governing equation of heat conduction in the wall of the cold storage house: ߲ݐሺݔǡ ߬ሻ ߲ ߲ݐሺݔǡ ߬ሻ ߩܿ ൌ ቆ݇ ቇሺͳሻ ߲߬ ߲ݔ ߲ݔ For the thermodynamic simulation, the study made the following assumptions: (1) no heat source inside the wall; (2) natural convection occurs between the outside wall and environmental air; (3) heat flux exists on the surface of inner wall generated by cargos in the cold storage house.
Fig 1 Cold storage house in experiment
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
In order to validate the model, an experiment was performed based on a small size high temperature cold storage house with a physical dimension of 2000mm×1200mm×1400mm and the thickness of the insulated wall of 100mm.The model of the compressor is Panasonic 2P17S225ANQ and the power is 2780W, the energy efficiency ratio is 3.2. The experiment was operated from 10:15 am to 10:41 am on 18 April, 2016, and the start-up phase was not considered. A total of 48 temperature measuring probes were fixed in the cold storage house and in the wall of the house to measure the temperature of different parts of the cold storage house. The ambient temperature during the experiment was 25℃ and the natural convection coefficient between the wall of the cold storage house and the environment was 5W/(m2∙℃) and the internal heat flux is 0.7W/m2. 2.2 Examination of the PCM-based cold storage house This study proposed to install a water/ice PCM layer on the inner side of the insulated wall to store energy and thus to shift the load of electricity consumption (Fig. 2). For the water/ice-PCM layer, the apparent heat capacity of water/ice can be described as: ܥ௦ ܶ ൏ ܶ െ ߂ܶሺ݁ݏ݄݈ܽ݀݅ݏሻ
ܥ ൌ ൞ଶ௱்
ೞ ା ଶ
ܶ െ ߂ܶ ܶ ܶ ߂ܶሺ݄݁݃݊ܽܿ݁ݏ݄ܽሻ
(2)
ܥ ܶ ܶ ߂ܶሺ݈݅݁ݏ݄ܽ݀݅ݑݍሻ where Cp is the product of the capacity of ρ and c equal to the real capacity of ice water mixture, L is the latent heat of ice, subscript s and l represents for solid phase and liquid phase respectively. Tf is freezing point and ∆T is 1℃.
Fig 2 Cold storage house model with PCM
The PCM layer should be able to store enough cold energy for the demand during peak time. In the present study, the heat from the stored fruits or vegetable is not considered. Therefore, the electricity needed to support the cold storage house is decided by the fusion process of ice, i.e. ܧൌ ݔܵߩܮ (3) which E is electricity consumed during peak period and can be measured by a coulombmeter, L is the latent heat that ice absorbed in phase change process, ρ is the density of ice, S is the inner superficial area of wall of cold storage house and x0 is the thickness of water/ice PCM layer. As a result, the thickness of the water/ice layer, x0, is 9.4mm. In order to make sure the latent energy in ice is enough for busy and peak period, a 10mm thickness was adopted in this study. 2.3 Application of the validated model to the PCM-based storage house Due to the application of the PCM layer, the thermal resistance in the wall (PCM plus polyurethane) would change. As a result, the load of electricity consumption will be shifted and the total amount of electricity consumption will be reduced.
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
The water/ice-PCM layer increases the thermal resistance and the heat flux from environment to cold storage house through the wall diminish as a result. Overall heat transfer coefficient k0 is an expression as follows: ଵ ௫ ௫ ൌ ುಾ (4) బ
ఒ
ఒುಾ
which λin is heat conductivity coefficient of insulation wall, λPCM is heat conductivity coefficient of PCM, xin and xPCM is the thickness of insulation wall and ice/water layer respectively. The heat flux reduction ΔQ and total energy saving EQ due to heat resistance increment can be calculated as: οܳ ൌ ܵሺ݇ െ ݇ ሻሺݐ௨௧ െ ݐ ሻ (5) which kin is heat transfer coefficient of insulation wall and tD is the time quantum in a day. ܧொ ൌ οܳ ൈ ݐ
(6)
The money saved a day M1 due to the saving in electricity consumption can be calculated by ܯଵ ൌ ͲǤͶ ൈ ܧொ
(7)
Application of PCM to cold storage house can help to shift the loads of electricity consumption and thus save electricity costs under the peak-valley pricing mechanism. The study took the peak-valley tariff in China as an example, i.e. 0.477 RMB/kWh for the off-peak period (11:00~13:00 and 22:00~8:00, day+1); 0.858 RMB/kWh for the busy period (8:00~11:00, 13:00~19:00 and 21:00~22:00); and 1.239 RMB/kWh for the peak period (19:00~21:00). By shifting the loads, the PCM-based cold storage house can help to save electricity cost a day, M2, which is calculated as: ܯଶ ൌ ሺͳǤʹ͵ͻ െ ͲǤͶሻ ൈ ݁ ൈ ݐଵ ሺͲǤͺͷͺ െ ͲǤͶሻ ൈ ݁ ൈ ݐଶ
(8)
which e is the running power of cold storage house, t1 and t2 are peak period and busy period respectively. In this study, e is 0.282kW, t1 is 2h and t2 is 10h. The payback period Y is calculated by: ܻ ൌ ሺெ
భ ାெమ ሻൈଷହ
(9)
which V is the investment cost, i.e. 2300 RMB for the PCM layer suitable for the experimental cold storage house. 3. Results and discussion 3.1 Simulation and validation Fig 3 shows the temperature variation of inner wall surface in simulation and experiment. The temperature measured in the experiment was agreed with that obtained from the simulation. The measured temperature remained about 0.7℃ higher than in simulation in average, it was due to the measuring error of thermocouples. It implies that it is acceptable to employ the model to simulate the heat transfer in the wall of the cold storage house. Therefore, the model is further applied to predict the temperature of wall of cold storage house. 3.2 Simulation results on model with PCM layer (1) The thermodynamic characteristics of the PCM-based storage house. Fig 4 shows temperature variation of model with water/ice-PCM layer during busy period and peak
Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
Fig 3 Temperature curve comparison in simulation and experiment
period. As can be seen in the graph, x=100~110mm represents the region of water/ice as PCM. The temperature did not exceed 5℃ at the moment between 8:00 to 22:00. The temperature inside the cold storage house meets the temperature requirement for food conservation. (2) Results about load shifts The water/ice PCM layer was frozen totally during off-peak time, so the PCM layer was all ice at the beginning of the simulation. About one-sixth ice melted during peak period and five-sixth melted during busy period to maintain a cooling condition. (3) Energy saving due to the application of PCM layer In this study, k0, i.e. the overall heat transfer coefficient, is 0.35W/(m2·℃) and ∆Q, the reduction in heat flux, is 0.25W. Therefore, the additional energy saving due to the increase in heat transfer resistance is 21.6kJ and corresponding electricity saving is 6×10-3 kWh. (4) Total savings of cost and the payback period The total cost savings consist two parts, i.e. one part due to the increase in heat transfer resistance and the other due to load shift. The increased heat transfer resistance can help to save 4.2×10-3 RMB/day and load shifts can contribute to 1.5 RMB/day of cost saving. Payback period in this study is 4.1 years. 4. Conclusions In China, the policy of peak and valley electric charges is undoubtedly going to popularize in the whole country. We should take this advantage of peak shifting to avoid economic, environmental pressure. In this aspect, ice/water-PCM plays an important role in cold energy storage. In this study, performance of a cold storage house with ice/water as PCM is studied experimentally and numerically. The main results of the study include: (1) water/ice is a promising material for cold thermal energy storage in high temperature cold storage house for its high latent heat density, high density, non-toxic and no corrosion. (2) the water/ice layer can absorb the cold thermal energy in off-peak period and release it to run the cold storage house in busy and peak period as an economic operation solution. (3) ice/water layer can increase heat transfer resistance of wall and then reduce the energy needed. (4) the payback period of ice/water PCM is about 4.1 years.
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Changjiang Wang et al. / Energy Procedia 105 (2017) 3947 – 3952
Fig 4 Temperature through wallboard in contrast simulation
Acknowledgements This work was supported in part by Project ZR2014EEM025 supported by Natural Science Foundation of Shandong Province, China; and the 973 Program 2013CB228305, China. References [1] Qureshi WA, Nair N-KC, Farid MM. Impact of energy storage in buildings on electricity demand side management. Energy Conversion and Management. 2011; 52(5):2110-20. Doi: http://dx.doi.org/10.1016/j.enconman.2010.12.008. [2] Zhou D, Shire GSF, Tian Y. Parametric analysis of influencing factors in Phase Change Material Wallboard (PCMW). Applied Energy. 2014; 119:33-42. Doi: http://dx.doi.org/10.1016/j.apenergy.2013.12.059. [3] Leducq D, Ndoye FT, Alvarez G. Phase change material for the thermal protection of ice cream during storage and transportation. International Journal of Refrigeration. 2015; 52:133-9. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2014.08.012. [4] Oró E, de Gracia A, Cabeza LF. Active phase change material package for thermal protection of ice cream containers. International Journal of Refrigeration. 2013; 36(1):102-9. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2012.09.011. [5] Zhu N, Liu P, Hu P, Liu F, Jiang Z. Modeling and simulation on the performance of a novel double shape-stabilized phase change materials wallboard. Energy and Buildings. 2015; 107:181-90. Doi: http://dx.doi.org/10.1016/j.enbuild.2015.07.051. [6] Veerakumar C, Sreekumar A. Phase change material based cold thermal energy storage: Materials, techniques and applications – A review. International Journal of Refrigeration. 2016; 67:271-89. Doi: http://dx.doi.org/10.1016/j.ijrefrig.2015.12.005. [7] Thambidurai M, Panchabikesan K, N KM, Ramalingam V. Review on phase change material based free cooling of buildings— The way toward sustainability. Journal of Energy Storage. 2015; 4:74-88. Doi: http://dx.doi.org/10.1016/j.est.2015.09.003. [8] Akeiber H, Nejat P, Majid MZA, Wahid MA, Jomehzadeh F, Zeynali Famileh I, Calautit JK, Hughes BR, Zaki SA. A review on phase change material (PCM) for sustainable passive cooling in building envelopes. Renewable and Sustainable Energy Reviews. 2016; 60:1470-97. Doi: http://dx.doi.org/10.1016/j.rser.2016.03.036.
Biography Changjiang Wang is a PhD candidate in Shandong University. He is studying at the Institute of Thermal Science and Technology, Shandong University. His research focuses include sustainable energy system and industrial ecology.