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Application of earth-air heat exchanger cooling technology in an office building in Jinan city
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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Energy Procedia 158 Energy Procedia 00(2019) (2017)6105–6111 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Application of earth-air heat exchanger cooling technology in an Application heat exchanger cooling Theof 15thearth-air International Symposium on District Heatingtechnology and Cooling in an office building in Jinan city office building in Jinan city Assessing the feasibility of using the heat demand-outdoor Hao Wengangaa, Lu yifengaa, Lai Yanhuaa,b *, Lyu Mingxinbb a,b Haofunction Wengang for , Lu a yifeng , Lai Yanhua *, Lyu Mingxin temperature long-term district heat demand forecast School of Energy and Power Engineering, Shandong University, Jinan 250061, Shandong, China a a
b
Suzhou Shandong University, 215028, Jiangsu, China School of Energy andInstitute, Power Engineering, ShandongSuzhou University, Jinan 250061, Shandong, China a,b,c a a b c b Suzhou Institute, Shandong University, Suzhou 215028, Jiangsu, China
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc
a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Systèmes et Environnement - IMTventilation, Atlantique, 4application rue Alfred Kastler, 44300 Nantes, France In this paper, Département based on the study Énergétiques of the effect of indoor natural of earth-air heat exchanger cooling In this paper, on was the study of the effect indoor ventilation, application of earth-air exchanger cooling technology in based an office investigated. Takingofan officenatural building in Jinan City as an example, thisheat research analyzed the technology office was between investigated. Taking office building Jinan City and as an example, this thermal researchenvironments. analyzed the performanceinofaninteractions earth-air heatanexchanger coolingintechnology building indoor performance ofenvironment interactions was between earth-air exchanger cooling andfluid building indoorthethermal Indoor thermal analyzed with heat numerical simulation of technology computational dynamics, Airpakenvironments. software was Abstract Indoor environment was analyzed with numerical simulation computational fluid theofAirpak software applied thermal for numerical calculation to gain the indoor temperature field,ofvelocity field and thedynamics, distribution the PMV index.was In applied numerical calculation to gain indoor temperature field, velocity field and distribution of theorganization PMV index.isIna addition,for energy utilization efficiency wasthe also analyzed in this paper; results showed thatthereasonable airflow District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the addition, utilization efficiency also analyzed in this the paper; results showed that reasonable airflow organization is a significantenergy content in airflow design was of office rooms under small temperature difference of earth-air heat exchanger greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat significant This content airflow design of office roomsof under theheat small temperature difference conditions. willinprovide basic reference for design earth-air exchanger cooling system. of earth-air heat exchanger sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, conditions. This will provide basic reference for design of earth-air heat exchanger cooling system. prolonging the investment return period. Copyright © 2018 Elsevier Ltd. All rights reserved. main of this paper isby to Elsevier assess the feasibility of using the heat demand – outdoor temperature function for heat demand ©The 2019 Thescope Authors. Published Ltd. Copyright © 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied This is an open under thelocated CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) forecast. The access districtarticle of Alvalade, in Lisbonlicense (Portugal), was used as a caseth study. The district is consisted of 665 Conference on Applied Selection and peer-review underofresponsibility of the scientific committee theInternational 10 International Energy (ICAE2018). Peer-review under responsibility the scientific of ICAE2018 – Theof10th Conference on Applied buildings that vary in both construction periodcommittee and typology. Three weather scenarios (low, medium, high) and threeEnergy. district Energy (ICAE2018). renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Keywords: Earth-air heat exchanger; Numerical simulation; Thermal comfort; Energy utilization efficiency compared with results from a dynamic heat demand model, previously developed and validated by the authors. Keywords: Earth-air heat exchanger; Numerical simulation; Thermal comfort; Energy utilization efficiency The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1. Introduction scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1. Introduction The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Earth-air heatnumber exchanger is an hours energy methodtheofheating preheating or (depending cooling ofon supply air to a building, which decrease in the of heating of efficient 22-139h during season the combination of weather and Earth-air heat exchanger is anOn energy efficient method of preheating or cooling of supply to a capacity building,ofwhich has receivedscenarios increasing attention during the last several years [1]. The geothermal energy has adecade huge heat renovation considered). the other hand, function intercept increased for 7.8-12.7% per air (depending on the has received increasing during could theoflast [1]. energy has hugeiscapacity of heat storage and heat release, the temperature stratum higher than thegeothermal outdoor air in for winter, and lower than the coupled scenarios). The attention values suggested beseveral used istoyears modify theThe function parameters the ascenarios considered, and storage release, thedemand temperature of stratum is higher than the outdoor air in winter, and is lower than the improveand the heat accuracy of heat estimations.
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86-133-0640-6388.
address:author. [email protected] * E-mail Corresponding Tel.: +86-133-0640-6388. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. th Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10 International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 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 ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.503
6106 2
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
outdoor air in summer, therefore, it is betters effects of energy-saving to cooling or heating by earth-air heat exchanger [2-4]. In order to take advantage of earth-air heat exchanger, it is very important to understand the dynamic heat transfer effect between the tunnel and the air. A number of studies have attempted to address this problem [5-7], Liu et al. [8] studied a numerical model developed to describe the simultaneous heat transfer between air and the tunnel surface, taking into account the condensation phenomena inside the tunnel. The developed model is validated against field measurements which showed good agreement between the simulated results and measurement data. The model is then applied to an underground tunnel operating for a ten-year-period. However, little information has been done on the performance of the interactions between earth-air heat exchanger and building indoor thermal environments. The purpose of this paper was to reveal building indoor thermal environments under the action of EAHE system, and take an office room in Jinan city as research subjects; EAHE system was designed for it under taking into account construction cost and effect of system conditions, meanwhile, in order to compare with the effect of nature ventilation, the indoor thermal environment of the office room were also simulated under nature ventilation conditions. In addition, indoor thermal environment of the office room were simulated with numerical simulation which was carried out by Airpak software, and were analyzed through different evaluation index, 2. Climatic Analysis and System Design 2.1. Climatic Analysis Jinan city (N36.65°，E117°), which is capital city of Shandong province, belongs to the cold climate zone of the building climate district. Main typical meteorological parameter of Jinan city: the dry bulb temperature of outdoor in summer is 34.8 ℃, the wet bulb temperature of outdoor in summer is 27.0 ℃, the average annual temperature of soil surface is 15.7 ℃, and the amplitude of the surface temperature is ±17 ℃. Building design strategies were analyzed with Climate consultant software, which was shown in Fig.1. Nature ventilation cooling and fan-forced ventilation cooling respectively account for 10.4%, 9.8% in building design strategy, it illustrated that ventilation cooling technology has a great role in the building design process in Jinan city, at the same time, earth-air heat exchanger cooling technology could not only meet the quantity of fresh air for indoor persons, but also could play the role of cooling in the summer. Therefore, it is of great significance to analyze the application of the earth-air heat exchanger cooling technology in the office building in Jinan city.
Fig. 1. Schematic of design strategies in Jinan city
2.2. EAHE System Design The concept of the EAHE is that of several pipes buried in the ground, one end of the EAHE system acts as the entrance for outdoor ambient air, while the other end of the EAHE system releases air to the interior of a building.
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
6107 3
Ambient air is drawn into the pipe inlet by axial flow fan, the air travelling through the pipe exchanging heat with the surrounding underground environment. In order to determine the design parameters of EAHE systems, it was necessary to carry out a comparison of economic and technical, in which the depth and length of tunnel was very important factors. The depth and length of tunnel have great influence on the air outlet temperature and the cooling capacity. System design parameter selection: the temperature of indoor design and calculation is 28℃, the temperature of outdoor ventilation calculation is 30.9℃, the design wind speed of pipe cross section is 5m/s, the layout of tunnel adopted S type. After EAHE system design calculation, the pipe diameter was 1.2m, the length of the tube was 28m and ventilation volume was 678m³/s conditions, pipe depth in the 6m was the best, and then temperature of outlet of pipe can be controlled at about 26 ℃. The EAHE system design for the building room was shown in Fig.2.
Fig. 2. Schematic of EAHE system design for the building room
3. Description of Numerical Modeling 3.1. Physical Models Three dimensional physical model of the research object was shown in Fig.3, the size of the room is 5m×5m×3m, the size of the air inlet and the air outlet was the same as 1m×0.6m, the design layout of the simulated room by simplifying the physical model was shown in Fig.3.
Fig. 3. Schematic of physical model of simulation object
3.2. Mathematical model In order to simplify the indoor environment simulation, the following assumptions were applied:
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
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(1)The indoor air flow is incompressible and regular Newtonian fluid, and the steady state of turbulent flow is consistent with the Boussinesq hypothesis; (2)Without considering the solar radiation and radiation heat transfer on the surface of the room, and the room is closed without considering the leakage effect. So this paper chooses the standard model of the incompressible gas, the basic control equation is as follows [10]: Continuity equation：
( ui ) 0 xi
(1)
Momentum equation：
p ui u j 3 u ( ui u j ) ) i ij gi Fi ( xi xi x j x j xi 2 xi
(2)
Energy equation：
( ui h) xi xi
t h ( ) Sh pr t xi
(3)
Where
t C
k2
(4)
Transport equations for the realizable K model：
t k ui ui u j ( k) ( kui ) ( ) ( ) t k x j t xi x j x j x j xi
t C1 ui ui u j 2 ( ) ( ui ) ( ) C2 ( ) x j t xi xi k x j x j xi k C1 And
(5)
(6)
1.44, C2 1.92, C 0.09, k 1.0, 1.3
3.3. Boundary Conditions The boundary conditions for numerical simulation were listed in Table 1. Under different position of the air-inlet conditions, the indoor environment was analyzed. Air-inlet is located in the north wall of the upper, middle and lower position, which was listed in Table.2.
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
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Table 1. Boundary conditions for numerical simulation Model types Room External windows Interior windows Person Computer Lamp Air-inlet Air-outlet door
Quantity 1 2 1 2 2 4 1 1 1
Dimension[m] 5×5×3 1.5×2.1 0.8×0.8 0.4×0.25×1.75 0.4×0.4×0.3 1.2×0.3×0.3 1×0.6 1×0.6 1.2×2.5
Boundary type Constant temperature Constant temperature Constant temperature Constant heat flux Constant heat flux Constant heat flux free outflow Constant temperature
Defined value 35[℃] 32[℃] 30[℃] 104.67[W] 120[W] 40[W] V=2.5[m/s], T=26[℃] 32[℃]
Table 2. Position of air-inlet Position Upper Middle Lower
Distance of air inlet to the indoor floor[m] 0.5 1 1.5
Serial number a b c
4. Results and discussion 4.1. Analysis of nature ventilation effect The simulation conditions are divided into three types, which are summer, winter and transitional season. In order to fully explain the influence of natural ventilation in three different conditions, the results of indoor temperature field and wind field are analyzed in this paper. Meanwhile, PMV/PPD evaluation system was introduced as the evaluation index of indoor thermal environment satisfaction degree. Simulated room height Y=1.0m plane was cut out as simulation result analysis. This is because the room height is the average human perception region. The distribution of temperature field under nature ventilation conditions was shown in Fig.4. The indoor temperature during the summer can be reduced by nature ventilation, which results in enhancing the indoor thermal comfort. In contrast, the people cold sense can be aggravated under winter and transitional season conditions, which will cause discomfort sense.
Fig. 4. The distribution of temperature field under nature ventilation conditions
The distribution of wind field under nature ventilation conditions was shown in Fig.5. The indoor air flow rate of working area under different conditions is almost the same, and then the indoor thermal comfort cannot be judged by indoor air flow rate. The PMV value near the work area during the summer condition is about -0.51, this shows that the thermal comfort of people in a slightly cooler state. Meanwhile it can be seen that nature ventilation during summer condition is better than the other two kinds of operating state. In addition, the degree of indoor thermal comfort dissatisfaction under summer conditions is 12.04%, which is lower than the other two kinds of operating state. Thus, it again can be proved that natural ventilation during the summer condition can enhance indoor thermal comfort.
Hao Wengang et al. Procedia / Energy Procedia (2019) 6105–6111 Author name / Energy 00 (2018)158 000–000
66110
Fig. 5. The distribution of wind field under nature ventilation condition
4.2. EAHE system cooling effect In order to further study the effect of EAHE system, different air-outlet positions was designed for the office room (see Table 2). Distribution of temperature, flow rate, PMV was obtained through Simulated room height Y=1.0m plane. Under three different air outlet positions conditions, the curve of working area temperature change with the position of air-inlet was shown in Fig.6 (a), With the upward shift of the position of the air-inlet, temperature of simulated room height Y=1.0m plane gradually increased, design comfortable temperature for indoor temperature was 28℃, It was not difficult to find that position of a and b met it. In addition, the rest of indoor working area which was far away from the air inlet, wasn’t influenced by earth-air heat exchanger cooling technology, this design met the requirements of energy conservation. In addition, the curve of working area air velocity change with the position of air-inlet was shown in Fig.6 (b), the simulated results of velocity was Va>Vb>Vc, design comfortable velocity for indoor was < 3m/s, thus, combined with indoor temperature factors, position of a and b was relatively good, which was more beneficial to human health.
(a)
(b)
Fig. 6. Curve of working area temperature (a) and air velocity (b) change with the position of air-inlet
4.3. Energy Utilization Efficiency Analysis In order to analyze the energy utilization efficiency of air distribution mode, energy utilization coefficient is generally expressed as:
Hao Wengang et al. / Energy Procedia 158000–000 (2019) 6105–6111 Author name / Energy Procedia 00 (2018)
te ti tn ti
61117
(7)
Energy utilization efficiency was calculated by indoor environment simulation results, the result of energy utilization coefficient was
b＞a＞c , the energy utilization efficiency of b position is higher than others.
4. Conclusion In this paper, the thermal environment of the office room was simulated by using CFD technology, the simulation of building thermal environment under nature ventilation and EAHE system conditions led to the following findings: (1) Through the simulation of different air-inlet position, position of b and earth-air heat exchanger cooling technology was the best combination, because it could meet the indoor thermal comfort and enhance energy utilization efficiency. (2) In addition, in the case of very small temperature difference of earth-air heat exchanger cooling system, reasonable airflow organization is a significant content in airflow design of office rooms. It is important to achieve the purpose of energy-saving. Therefore, it is effective energy-saving measures that combination of natural cold source and high efficiency ventilation technology. (3) The deficiency of this paper lies in the lack of experimental verification, which needs to be further improved. In the process of earth-air heat exchanger cooling system design, under meet the basic cooling requirements conditions, designer need to strictly control the costs of construction and operating.. Acknowledgements It is gratefully acknowledged that this project is supported by the National Natural Science Foundation of China (No.51476093) and Shandong Province Science and Technology Development Program (2013GGX10403) and The Fundamental Research Funds of Shandong University (2014YQ007). References [1] S.K. Soni, M. Pandey, V.N. Bartaria, Ground coupled heat exchangers: A review and applications, Rene. and Sustain. Energy Rev, 47 (2015) 83-92. [2] H. Li, Y. Yu, F. Niu, M. Shafik, B. Chen, Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney, Rene. Energy, 62 (2014) 468-477. [3] L.L. Tan, J.A. Love, A Literature Review on Heating of Ventilation Air with Large Diameter Earth Tubes in Cold Climates, Energies, 6 (2013) 3734-3743. [4] T.S. Bisoniya, A. Kumar, P. Baredar, Experimental and analytical studies of earth-air heat exchanger (EAHE) systems in India: A review, Rene. and Sustain. Energy Rev, 19 (2013) 238-246. [5] R.d.S. Brum, J. Vaz, L.A.O. Rocha, E.D. dos Santos, L.A. Isoldi, A new computational modeling to predict the behavior of Earth-Air Heat Exchangers, Energy Build., 64 (2013) 395-402. [6] G. Gan, Simulation of dynamic interactions of the earth–air heat exchanger with soil and atmosphere for preheating of ventilation air, Appl. Energy, 158 (2015) 118-132. [7] M. Khabbaz, B. Benhamou, K. Limam, P. Hollmuller, H. Hamdi, A. Bennouna, Experimental and numerical study of an earth-to-air heat exchanger for air cooling in a residential building in hot semi-arid climate, Energy Build., 125 (2016) 109-121. [8] X. Liu, Y. Xiao, K. Inthavong, J. Tu, A fast and simple numerical model for a deeply buried underground tunnel in heating and cooling applications, Appl. Therm. Eng., 62 (2014) 545-552.
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 158 Energy Procedia 00(2019) (2017)6105–6111 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Application of earth-air heat exchanger cooling technology in an Application heat exchanger cooling Theof 15thearth-air International Symposium on District Heatingtechnology and Cooling in an office building in Jinan city office building in Jinan city Assessing the feasibility of using the heat demand-outdoor Hao Wengangaa, Lu yifengaa, Lai Yanhuaa,b *, Lyu Mingxinbb a,b Haofunction Wengang for , Lu a yifeng , Lai Yanhua *, Lyu Mingxin temperature long-term district heat demand forecast School of Energy and Power Engineering, Shandong University, Jinan 250061, Shandong, China a a
b
Suzhou Shandong University, 215028, Jiangsu, China School of Energy andInstitute, Power Engineering, ShandongSuzhou University, Jinan 250061, Shandong, China a,b,c a a b c b Suzhou Institute, Shandong University, Suzhou 215028, Jiangsu, China
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc
a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Systèmes et Environnement - IMTventilation, Atlantique, 4application rue Alfred Kastler, 44300 Nantes, France In this paper, Département based on the study Énergétiques of the effect of indoor natural of earth-air heat exchanger cooling In this paper, on was the study of the effect indoor ventilation, application of earth-air exchanger cooling technology in based an office investigated. Takingofan officenatural building in Jinan City as an example, thisheat research analyzed the technology office was between investigated. Taking office building Jinan City and as an example, this thermal researchenvironments. analyzed the performanceinofaninteractions earth-air heatanexchanger coolingintechnology building indoor performance ofenvironment interactions was between earth-air exchanger cooling andfluid building indoorthethermal Indoor thermal analyzed with heat numerical simulation of technology computational dynamics, Airpakenvironments. software was Abstract Indoor environment was analyzed with numerical simulation computational fluid theofAirpak software applied thermal for numerical calculation to gain the indoor temperature field,ofvelocity field and thedynamics, distribution the PMV index.was In applied numerical calculation to gain indoor temperature field, velocity field and distribution of theorganization PMV index.isIna addition,for energy utilization efficiency wasthe also analyzed in this paper; results showed thatthereasonable airflow District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the addition, utilization efficiency also analyzed in this the paper; results showed that reasonable airflow organization is a significantenergy content in airflow design was of office rooms under small temperature difference of earth-air heat exchanger greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat significant This content airflow design of office roomsof under theheat small temperature difference conditions. willinprovide basic reference for design earth-air exchanger cooling system. of earth-air heat exchanger sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, conditions. This will provide basic reference for design of earth-air heat exchanger cooling system. prolonging the investment return period. Copyright © 2018 Elsevier Ltd. All rights reserved. main of this paper isby to Elsevier assess the feasibility of using the heat demand – outdoor temperature function for heat demand ©The 2019 Thescope Authors. Published Ltd. Copyright © 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied This is an open under thelocated CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) forecast. The access districtarticle of Alvalade, in Lisbonlicense (Portugal), was used as a caseth study. The district is consisted of 665 Conference on Applied Selection and peer-review underofresponsibility of the scientific committee theInternational 10 International Energy (ICAE2018). Peer-review under responsibility the scientific of ICAE2018 – Theof10th Conference on Applied buildings that vary in both construction periodcommittee and typology. Three weather scenarios (low, medium, high) and threeEnergy. district Energy (ICAE2018). renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Keywords: Earth-air heat exchanger; Numerical simulation; Thermal comfort; Energy utilization efficiency compared with results from a dynamic heat demand model, previously developed and validated by the authors. Keywords: Earth-air heat exchanger; Numerical simulation; Thermal comfort; Energy utilization efficiency The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1. Introduction scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1. Introduction The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Earth-air heatnumber exchanger is an hours energy methodtheofheating preheating or (depending cooling ofon supply air to a building, which decrease in the of heating of efficient 22-139h during season the combination of weather and Earth-air heat exchanger is anOn energy efficient method of preheating or cooling of supply to a capacity building,ofwhich has receivedscenarios increasing attention during the last several years [1]. The geothermal energy has adecade huge heat renovation considered). the other hand, function intercept increased for 7.8-12.7% per air (depending on the has received increasing during could theoflast [1]. energy has hugeiscapacity of heat storage and heat release, the temperature stratum higher than thegeothermal outdoor air in for winter, and lower than the coupled scenarios). The attention values suggested beseveral used istoyears modify theThe function parameters the ascenarios considered, and storage release, thedemand temperature of stratum is higher than the outdoor air in winter, and is lower than the improveand the heat accuracy of heat estimations.
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86-133-0640-6388.
address:author. [email protected] * E-mail Corresponding Tel.: +86-133-0640-6388. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. th Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10 International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 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 ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.503
6106 2
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
outdoor air in summer, therefore, it is betters effects of energy-saving to cooling or heating by earth-air heat exchanger [2-4]. In order to take advantage of earth-air heat exchanger, it is very important to understand the dynamic heat transfer effect between the tunnel and the air. A number of studies have attempted to address this problem [5-7], Liu et al. [8] studied a numerical model developed to describe the simultaneous heat transfer between air and the tunnel surface, taking into account the condensation phenomena inside the tunnel. The developed model is validated against field measurements which showed good agreement between the simulated results and measurement data. The model is then applied to an underground tunnel operating for a ten-year-period. However, little information has been done on the performance of the interactions between earth-air heat exchanger and building indoor thermal environments. The purpose of this paper was to reveal building indoor thermal environments under the action of EAHE system, and take an office room in Jinan city as research subjects; EAHE system was designed for it under taking into account construction cost and effect of system conditions, meanwhile, in order to compare with the effect of nature ventilation, the indoor thermal environment of the office room were also simulated under nature ventilation conditions. In addition, indoor thermal environment of the office room were simulated with numerical simulation which was carried out by Airpak software, and were analyzed through different evaluation index, 2. Climatic Analysis and System Design 2.1. Climatic Analysis Jinan city (N36.65°，E117°), which is capital city of Shandong province, belongs to the cold climate zone of the building climate district. Main typical meteorological parameter of Jinan city: the dry bulb temperature of outdoor in summer is 34.8 ℃, the wet bulb temperature of outdoor in summer is 27.0 ℃, the average annual temperature of soil surface is 15.7 ℃, and the amplitude of the surface temperature is ±17 ℃. Building design strategies were analyzed with Climate consultant software, which was shown in Fig.1. Nature ventilation cooling and fan-forced ventilation cooling respectively account for 10.4%, 9.8% in building design strategy, it illustrated that ventilation cooling technology has a great role in the building design process in Jinan city, at the same time, earth-air heat exchanger cooling technology could not only meet the quantity of fresh air for indoor persons, but also could play the role of cooling in the summer. Therefore, it is of great significance to analyze the application of the earth-air heat exchanger cooling technology in the office building in Jinan city.
Fig. 1. Schematic of design strategies in Jinan city
2.2. EAHE System Design The concept of the EAHE is that of several pipes buried in the ground, one end of the EAHE system acts as the entrance for outdoor ambient air, while the other end of the EAHE system releases air to the interior of a building.
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
6107 3
Ambient air is drawn into the pipe inlet by axial flow fan, the air travelling through the pipe exchanging heat with the surrounding underground environment. In order to determine the design parameters of EAHE systems, it was necessary to carry out a comparison of economic and technical, in which the depth and length of tunnel was very important factors. The depth and length of tunnel have great influence on the air outlet temperature and the cooling capacity. System design parameter selection: the temperature of indoor design and calculation is 28℃, the temperature of outdoor ventilation calculation is 30.9℃, the design wind speed of pipe cross section is 5m/s, the layout of tunnel adopted S type. After EAHE system design calculation, the pipe diameter was 1.2m, the length of the tube was 28m and ventilation volume was 678m³/s conditions, pipe depth in the 6m was the best, and then temperature of outlet of pipe can be controlled at about 26 ℃. The EAHE system design for the building room was shown in Fig.2.
Fig. 2. Schematic of EAHE system design for the building room
3. Description of Numerical Modeling 3.1. Physical Models Three dimensional physical model of the research object was shown in Fig.3, the size of the room is 5m×5m×3m, the size of the air inlet and the air outlet was the same as 1m×0.6m, the design layout of the simulated room by simplifying the physical model was shown in Fig.3.
Fig. 3. Schematic of physical model of simulation object
3.2. Mathematical model In order to simplify the indoor environment simulation, the following assumptions were applied:
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
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(1)The indoor air flow is incompressible and regular Newtonian fluid, and the steady state of turbulent flow is consistent with the Boussinesq hypothesis; (2)Without considering the solar radiation and radiation heat transfer on the surface of the room, and the room is closed without considering the leakage effect. So this paper chooses the standard model of the incompressible gas, the basic control equation is as follows [10]: Continuity equation：
( ui ) 0 xi
(1)
Momentum equation：
p ui u j 3 u ( ui u j ) ) i ij gi Fi ( xi xi x j x j xi 2 xi
(2)
Energy equation：
( ui h) xi xi
t h ( ) Sh pr t xi
(3)
Where
t C
k2
(4)
Transport equations for the realizable K model：
t k ui ui u j ( k) ( kui ) ( ) ( ) t k x j t xi x j x j x j xi
t C1 ui ui u j 2 ( ) ( ui ) ( ) C2 ( ) x j t xi xi k x j x j xi k C1 And
(5)
(6)
1.44, C2 1.92, C 0.09, k 1.0, 1.3
3.3. Boundary Conditions The boundary conditions for numerical simulation were listed in Table 1. Under different position of the air-inlet conditions, the indoor environment was analyzed. Air-inlet is located in the north wall of the upper, middle and lower position, which was listed in Table.2.
Hao Wengang et al. / Energy Procedia 158 (2019) 6105–6111 Author name / Energy Procedia 00 (2018) 000–000
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Table 1. Boundary conditions for numerical simulation Model types Room External windows Interior windows Person Computer Lamp Air-inlet Air-outlet door
Quantity 1 2 1 2 2 4 1 1 1
Dimension[m] 5×5×3 1.5×2.1 0.8×0.8 0.4×0.25×1.75 0.4×0.4×0.3 1.2×0.3×0.3 1×0.6 1×0.6 1.2×2.5
Boundary type Constant temperature Constant temperature Constant temperature Constant heat flux Constant heat flux Constant heat flux free outflow Constant temperature
Defined value 35[℃] 32[℃] 30[℃] 104.67[W] 120[W] 40[W] V=2.5[m/s], T=26[℃] 32[℃]
Table 2. Position of air-inlet Position Upper Middle Lower
Distance of air inlet to the indoor floor[m] 0.5 1 1.5
Serial number a b c
4. Results and discussion 4.1. Analysis of nature ventilation effect The simulation conditions are divided into three types, which are summer, winter and transitional season. In order to fully explain the influence of natural ventilation in three different conditions, the results of indoor temperature field and wind field are analyzed in this paper. Meanwhile, PMV/PPD evaluation system was introduced as the evaluation index of indoor thermal environment satisfaction degree. Simulated room height Y=1.0m plane was cut out as simulation result analysis. This is because the room height is the average human perception region. The distribution of temperature field under nature ventilation conditions was shown in Fig.4. The indoor temperature during the summer can be reduced by nature ventilation, which results in enhancing the indoor thermal comfort. In contrast, the people cold sense can be aggravated under winter and transitional season conditions, which will cause discomfort sense.
Fig. 4. The distribution of temperature field under nature ventilation conditions
The distribution of wind field under nature ventilation conditions was shown in Fig.5. The indoor air flow rate of working area under different conditions is almost the same, and then the indoor thermal comfort cannot be judged by indoor air flow rate. The PMV value near the work area during the summer condition is about -0.51, this shows that the thermal comfort of people in a slightly cooler state. Meanwhile it can be seen that nature ventilation during summer condition is better than the other two kinds of operating state. In addition, the degree of indoor thermal comfort dissatisfaction under summer conditions is 12.04%, which is lower than the other two kinds of operating state. Thus, it again can be proved that natural ventilation during the summer condition can enhance indoor thermal comfort.
Hao Wengang et al. Procedia / Energy Procedia (2019) 6105–6111 Author name / Energy 00 (2018)158 000–000
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Fig. 5. The distribution of wind field under nature ventilation condition
4.2. EAHE system cooling effect In order to further study the effect of EAHE system, different air-outlet positions was designed for the office room (see Table 2). Distribution of temperature, flow rate, PMV was obtained through Simulated room height Y=1.0m plane. Under three different air outlet positions conditions, the curve of working area temperature change with the position of air-inlet was shown in Fig.6 (a), With the upward shift of the position of the air-inlet, temperature of simulated room height Y=1.0m plane gradually increased, design comfortable temperature for indoor temperature was 28℃, It was not difficult to find that position of a and b met it. In addition, the rest of indoor working area which was far away from the air inlet, wasn’t influenced by earth-air heat exchanger cooling technology, this design met the requirements of energy conservation. In addition, the curve of working area air velocity change with the position of air-inlet was shown in Fig.6 (b), the simulated results of velocity was Va>Vb>Vc, design comfortable velocity for indoor was < 3m/s, thus, combined with indoor temperature factors, position of a and b was relatively good, which was more beneficial to human health.
(a)
(b)
Fig. 6. Curve of working area temperature (a) and air velocity (b) change with the position of air-inlet
4.3. Energy Utilization Efficiency Analysis In order to analyze the energy utilization efficiency of air distribution mode, energy utilization coefficient is generally expressed as:
Hao Wengang et al. / Energy Procedia 158000–000 (2019) 6105–6111 Author name / Energy Procedia 00 (2018)
te ti tn ti
61117
(7)
Energy utilization efficiency was calculated by indoor environment simulation results, the result of energy utilization coefficient was
b＞a＞c , the energy utilization efficiency of b position is higher than others.
4. Conclusion In this paper, the thermal environment of the office room was simulated by using CFD technology, the simulation of building thermal environment under nature ventilation and EAHE system conditions led to the following findings: (1) Through the simulation of different air-inlet position, position of b and earth-air heat exchanger cooling technology was the best combination, because it could meet the indoor thermal comfort and enhance energy utilization efficiency. (2) In addition, in the case of very small temperature difference of earth-air heat exchanger cooling system, reasonable airflow organization is a significant content in airflow design of office rooms. It is important to achieve the purpose of energy-saving. Therefore, it is effective energy-saving measures that combination of natural cold source and high efficiency ventilation technology. (3) The deficiency of this paper lies in the lack of experimental verification, which needs to be further improved. In the process of earth-air heat exchanger cooling system design, under meet the basic cooling requirements conditions, designer need to strictly control the costs of construction and operating.. Acknowledgements It is gratefully acknowledged that this project is supported by the National Natural Science Foundation of China (No.51476093) and Shandong Province Science and Technology Development Program (2013GGX10403) and The Fundamental Research Funds of Shandong University (2014YQ007). References [1] S.K. Soni, M. Pandey, V.N. Bartaria, Ground coupled heat exchangers: A review and applications, Rene. and Sustain. Energy Rev, 47 (2015) 83-92. [2] H. Li, Y. Yu, F. Niu, M. Shafik, B. Chen, Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney, Rene. Energy, 62 (2014) 468-477. [3] L.L. Tan, J.A. Love, A Literature Review on Heating of Ventilation Air with Large Diameter Earth Tubes in Cold Climates, Energies, 6 (2013) 3734-3743. [4] T.S. Bisoniya, A. Kumar, P. Baredar, Experimental and analytical studies of earth-air heat exchanger (EAHE) systems in India: A review, Rene. and Sustain. Energy Rev, 19 (2013) 238-246. [5] R.d.S. Brum, J. Vaz, L.A.O. Rocha, E.D. dos Santos, L.A. Isoldi, A new computational modeling to predict the behavior of Earth-Air Heat Exchangers, Energy Build., 64 (2013) 395-402. [6] G. Gan, Simulation of dynamic interactions of the earth–air heat exchanger with soil and atmosphere for preheating of ventilation air, Appl. Energy, 158 (2015) 118-132. [7] M. Khabbaz, B. Benhamou, K. Limam, P. Hollmuller, H. Hamdi, A. Bennouna, Experimental and numerical study of an earth-to-air heat exchanger for air cooling in a residential building in hot semi-arid climate, Energy Build., 125 (2016) 109-121. [8] X. Liu, Y. Xiao, K. Inthavong, J. Tu, A fast and simple numerical model for a deeply buried underground tunnel in heating and cooling applications, Appl. Therm. Eng., 62 (2014) 545-552.