- Email: [email protected]
Operation Analysis of a Compound Air Conditioning System using Measurement and Simulation
Available online at www.sciencedirect.com
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 1454–1460
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Operation Analysis of a Compound Air Conditioning System using Measurement and Simulation Huixin Fanga,b,c, Wei Wangd, Jiying Liua,b,c,*, Linhua Zhanga,b,c aSchool of Thermal Engineering, Shandong Jianzhu University, Jinan 250101, China Key Laboratory of Renewable Energy Technologies for Buildings, Ministry of Education, Jinan 250101, China cc Shandong Key Laboratory of Renewable Energy Technologies for Buildings, Jinan 250101, China d dLinyi Institute of Architectural Design CO. LTD, Linyi 276000, China a
bb
Abstract It has a great impact on the energy saving of buildings when the system scheme combining the underground pipe with the floor radiant cooling. In this study, the model was established and optimized using TRNSYS under different conditions. The results were analysed, so as to find the threshold value of energy consumption and indoor comfort of control system. Throughout the entire cooling season, the water temperature of buried pipe is between 18-20°C, the return water temperature is between 18-21°C. The peak of the water return temperature of the buried pipe usually occurs 20:00 in the evening, and the valley value appears at 9:00 in the morning, with the same rule of 24 hours. The peak of the water supply temperature is around 18:00 in the evening, and the valley value is at 8:00 in the morning. The contrast can be seen that buried pipe for the return water temperature, indoor temperature simulation value and actual value are basically identical. The reliability of the simulation model is verified by comparing the simulation data with the monitoring data. It provides technical guarantee for the future analysis of different operation strategies directly using TRNSYS software. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords: TRNSYS; compound air conditioning; simulation optimization
Nomenclature
Q
air conditioning load, KW
* Corresponding author. Tel.: +86-150-9873-6935. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.360
2
t S λ cp qs T q
Huixin Fang et al. / Procedia Engineering 205 (2017) 1454–1460 Huixin Fang et al./ Procedia Engineering 00 (2017) 000–000
1455
time, s air conditioning area, m2 thermal conductivity, W/(m·K) specific heat capacity, J/(kg·k) supply water flow, kg/h absolute temperature, K heat flow of per unit volume, W/m2
1.Introduction Ground source heat pump system is the basis for low grade energy conversion, which can be used to recycle and make full use of cold heat stored in soil, groundwater and surface water. The ground source heat pump system mainly includes underground water source heat pump, surface water heat pump and underground pipe heat pump. Direct cooling exchanger technology is most widely used in ground source heat pump system. It directly extracts the amount of cold in the soil through the U-type underground heat exchanger, and the amount of cooling is radiated from the ceiling or floor to the air conditioning room through the indoor terminal unit (usually the radiant plate). The technology of floor radiant cooling coupled ventilation system has been developed, but there are few successful applications in China. The biggest advantage of the system is that the same set of end devices can be realized in winter and summer, namely, the freezing water supply of the underground tube during the summer and the heating of cold water in winter, which saves the investment expense [1]. In the construction, the system scheme combining the underground pipe with the floor radiant cooling can effectively improve the energy efficiency, which has a great impact on the energy saving of buildings. The operating strategy of this system is mainly to use the embedded pipe directly and the floor coupled cooling system to bear the majority of the indoor thermal load. The winter operating strategy is mainly to use the heat pump system, through the energy storage tank continuously to the indoor heating [2]. The concept of floor radiant cooling first appeared in the middle of the 20th century. It is similar to the radiant floor heating system. It releases cold energy by radiation to achieve the goal of cold load and indoor temperature reduction. By the end of last century, Feustel and Stetiu [3] made some studies in floor radiant cooling as the premise, focusing on the heat transfer mechanism between the environment of the building and the human body. The results show that the floor radiant cooling system can satisfy the thermal comfort of the human body by providing a good thermal environment around the human body. At present, the floor radiant cooling system was studied by Niu and Shi [4], in which the rationality, energy saving effect, comfort of indoor environment and structure of radiant floor were discussed, respectively. It is concluded that the floor radiant cooling system can meet the temperature requirement of summer indoor air conditioning, and has a significant advantage in technical and economic performance compared with the conventional cooling system [5]. Therefore, this paper established the model and optimized it under different conditions. Then, the results were analysed, so as to find the threshold of energy consumption and indoor comfort of control system. 2.Model and simulation setup 2.1. Simulation study of air conditioning system based on TRNSYS The TRNSYS energy efficiency simulation system is one of the software that is used in the air-conditioning load and energy consumption simulation, and it presents a large advantage to the complex system of complex air conditioning system. Chiasson and Yavuzturk [6] used the simulation software to run a continuous simulation of solar energy and ground source heat pump system, and analyzed its operation characteristics and economy. By 2008, Hackel [7] put forward an optimization plan for the areas dominated by the cooling and heating load based on TRNSYS software. He did some research on design methods and operation strategies of ground pipe heat exchanger. In China, the utilization of TRNSYS simulation is mostly in the regional research institutes, where TRNSYS has a lot of research cases with ground source heat pumps. The calculation of the buried pipe in the ground source heat
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pump adopts the internationally recognized g-function algorithm, which can accurately calculate the heat transfer of buried pipes in the composite system and the thermal equilibrium of soil. Li [8] built two typical air conditioning systems, cooling tower composite ground source heat pump system and boiler composite ground source heat pump system using TRNSYS, and puts forward two through detailed data analysis system of the corresponding optimal operation strategy. The simulation of various air conditioning systems using TRNSYS can save a large amount of experimental time. By repeated simulation, the real reliability of the simulation is also improved gradually. 2.2. Air-conditioning load calculation The influence factors of cooling load can be divided into the envelope, body heat, equipment and lighting heat, air permeability and moisture migration, and so on. Sometimes, it also needs to consider the state parameters of the pipeline, the outdoor air permeability and heat, air reheat effect. The building load varies from time to time, and the purpose of load calculation is to determine the maximum load of the building, thereby selecting the unit, equipment and water pump that can bear the load. Calculation of building load in TRNSYS requires detailed description of building maintenance structures and indoor personnel equipment and ventilation in TRN Build. The outdoor environment parameters required in the building model are provided by the meteorological parameters in the typical TMY2 format, which is the external file to be read in the type15-2 in Fig.1. The meteorological external document in this experiment is a typical annual meteorological parameter TMY2. It is derived from EnergyPlus [9,10], which includes hourly data of solar radiation, outdoor temperature and humidity change, wind speed and other meteorological parameters. When calculating the load, we need select sensible heating load (QLATD) and latent heating load (QSENS) from building model. Then we need calculate the sum of the two previous values. It is the construction of the total load, and at the same time we can also output first layer load. The heating and cooling load of one layer is 27.93 KW, the latent heating and cooling load is 13.83 KW, and the new air cooling load is 4.10 KW.
Fig. 1. Schematic diagram of simulation of building load.
As shown in Fig. 2, the maximum cold load of the building is 208.69 KW, and the air conditioning area is 3815m2, so the unit area of air conditioning refrigeration is 57.97 W/m2. The heat load is 172.94 KW, the latent heat load is 35.75 KW, and the radiation cooling system can only take the indoor heat load. Therefore, the floor radiation usually only takes part of the heat load, while the residual heat load, the total latent heat load and the fresh air load need to be taken by the displacement ventilation system.
4
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Fig. 2. Total cooling load during cooling season.
2.3. Building model setup When the radiant floor cooling system is combined with the displacement ventilation system, the radiant floor is usually covered by 55% of the air-conditioning load. The remaining 45% of the cooling load is borne by the displacement ventilation system. In the case of the project, the water supply flow of the radiant floor is usually floating in 20000kg/h over the summer. When building model is set up, we establish the Active Layer, as shown in Fig. 3(a). When floor heat transfer characteristics, we establish the Active Layer in the Wall Type "middle tier, as shown in Fig. 3(b). The radiant floor usually includes insulation layer, embedded pipe layer, structural layer leveling layer and ground layer. (a)
(b)
Fig. 3. The radiation floor layer structure in TRN Build. (a) Active Layer (b) Wall Type
3.Results 3.1. Run simulation and data analysis The simulation time starts from June 15. The circulation pump keeps the open mode during the whole cooling season. The maximum water supply flow is 20000kg/h. We can see from the Fig.4, during the cooling season, the supply water temperature of buried pipe ranges is between 18-20°C, and return water temperature varies from 18°C to 21°C. The supply water temperature and the return water temperature difference are between 0.26°C and 1.18°C, respectively.
Huixin Fang et al./ Procedia Engineering 00 (2017) 000–000 Huixin Fang et al. / Procedia Engineering 205 (2017) 1454–1460
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Fig. 4. The backwater temperature curve of the buried pipe.
The water supply temperature of the buried pipe is relatively stable, and the variation of meteorological parameters and room load is very small, which is the greatest advantage of choosing soil source as the cold source. When the ambient temperature was lower or the indoor cooling load significantly decreased, the water temperature change was more obvious, as shown in Fig. 5. (a)
(b)
Fig. 5. Changes of water temperature of buried pipe with outdoor temperature, (a) Variation of return water temperature, (b) variation of outdoor temperature.
As seen from the above Fig.5 (a), after July 13, the temperature of typical day in the next three days had the sharp decline. The daily maximum temperature ranges from 32.4°C to 26.5°C. This kind of phenomenon often appears in the summer, and the return water temperature began to fall in. The maximum temperature is from 20.47°C to 19.92°C. The peak of return water temperature usually appears at around 20:00 in the evening, and the valley occurs at 9:00 in the morning. And it changes in a 24-hour cycle. The peak of the supply water temperature is around 18:00 in the evening, and the valley is at 8:00 in the morning.
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3.2. Statistical analysis of monitoring data The demonstration building air conditioning system adopts advanced electromechanical integration design and uses the Siemens building automation and energy saving equipment monitoring system. The air conditioning refrigeration process combined with automatic control to achieve the real-time monitoring and control of air conditioning system.In each floor of the room, every functional room has temperature humidity, floor temperature sensor as shown in Fig.6.
Fig. 6. Indoor temperature and humidity sensor.
Fig. 7. Indoor temperature monitoring situation.
A large amount of testing points are arranged to monitor temperature in each space. The indoor average temperature variation is monitored by each terminal temperature sensor, as shown in Fig 7. As you can see from Fig. 7 from June 15, to September 15, 2016, the entire cooling season, indoor temperature fluctuation was between 22°C and 27°C. 3.3. The comparison between monitoring and simulation data During the whole cooling season, the water supply temperature of the buried pipe is between 18°C and 20°C, and the return water temperature is between 18°C and 21°C.The minimum temperature difference between the supply and return water is 0.26°C, and the maximum difference is 1.18°C. The actual test shows that the supply water temperature of the ground source wells on the north side is 18.3°C, the temperature of the supply water of the ground source wells in the south is 19.3°C, and the return water temperature of the buried pipes is 20.8°C. The indoor simulation temperature of the first floor is between 20°C and 28°C, and the measured temperature is between
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23°C and 28°C.The simulation of indoor relative humidity in refrigeration season is 45%~90%, and the measured is 50%~80%. The simulated of outdoor mean temperature is 26.06°C, and the measured is 27.58°C. The simulation of power consumption is 15536 kWh, and the measured is 16355 kWh. The data obtained through the simulation data and monitoring platform, the contrast can be seen that buried pipe for the return water temperature, indoor temperature simulation data and actual data are basically identical. The indoor and outdoor temperature in different temperature range is different, but if we don't consider individual data, the simulation is credible. 3.4. The reason for the error The simulation data is not consistent with the measured data, and the main points are summarized as follows. Indoor personnel activity floating objective existence, and in the software to calculate the building load, only takes into consideration the fixed value of the number of people, and personnel heat dissipation is one of the important factors affecting indoor cooling load. When indoor personnel suddenly increase or decrease, the indoor temperature and humidity sensor can measure the change value by time, and pass it to the computer. In the optimization of operation strategy, it should be improved, and the feedback control loop can be set up to adjust the air volume and so on. The main operating equipment has been described in detail in the model, but many details are not specific enough, such as the loss of heat in the pipe and the energy loss at the entrance of the equipment. 4. Conclusions It was found that the temperature is not uniform in the cooling season. The first layer as the example, we can see that the temperature difference of each layer can be effectively reduced by regulating the supply water flow of the ground pipe direct, so that it can be basically controlled within 0.5 degrees. It solves the phenomenon of different heating and cooling due to different load, so that the cooling quantity can be distributed according to demand. By comparing the simulation data with the monitoring data, the practicability of the simulation model is proved. It provides technical support for the analysis of different operation strategies directly using TRNSYS software in the future. Acknowledgements This study was sponsored by Natural Science Foundation of China (NSFC, No.51176104), Natural Science Foundation of Shandong Province (ZR2016EEB08), Science and Technology Plan Project of University in Shandong Province (J16LG07), Science and Technology Development Plan in Shandong Province (2012GGX10416). References [1] F.Q. Zhao. Research on the application of the direct cooling system and water storage air conditioning system, 2014. [2] Y.T. Zhang. Research on operation strategy of floor radiant cooling system for office buildings, 2014. [3] H.E. Feustel, C. Stetiu. Hydronic radiant cooling—preliminary assessment. Energy & Buildings, 22(3) (1995) 193-205. [4] F.J. Niu, K.Y. Shi. The technical and economic analysis of floor radiation cooling. Gas and heat, 10 (1) (2000) 89-90. [5] J.Y. Liu, X.N. Xie, F.H. Qin, S.J. Song, D.L. Lv. A case study of ground source direct cooling system integrated with water storage tank system. Building simulation. 9 (6) (2016) 659-668. [6] A.D. Chiasson, C. Yavuzturk. Assessment of the viability of hybrid geothermal heat pump systems with solar thermal collectors. Ashrae Transactions, 109 (1) (2003) 487-500. [7] S.P. Hackel. Development of design guidelines for hybrid ground-coupled heat pump systems. Madison University of Wisconsin-Madison, 2008. [8] X. Li. The analysis and comparison of different control strategies of hybrid ground-source heat pump systems. Huazhong University of Science and Technology, 2008. [9] S. Zhu. J.F. Chen. A simulation study for a low carbon consumption HVAC project using EnergyPlus. International Journal of Low-Carbon Technologies. (2012) 248-254. [10] P. Hua, Q. Yi, R Fan, Z.Z. Huang. The influence factors of the thermal balance of heat pump of soil source heat pump based on TRNSYS. Building energy efficiency, 03 (1) (2012) 23-29.
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 1454–1460
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
Operation Analysis of a Compound Air Conditioning System using Measurement and Simulation Huixin Fanga,b,c, Wei Wangd, Jiying Liua,b,c,*, Linhua Zhanga,b,c aSchool of Thermal Engineering, Shandong Jianzhu University, Jinan 250101, China Key Laboratory of Renewable Energy Technologies for Buildings, Ministry of Education, Jinan 250101, China cc Shandong Key Laboratory of Renewable Energy Technologies for Buildings, Jinan 250101, China d dLinyi Institute of Architectural Design CO. LTD, Linyi 276000, China a
bb
Abstract It has a great impact on the energy saving of buildings when the system scheme combining the underground pipe with the floor radiant cooling. In this study, the model was established and optimized using TRNSYS under different conditions. The results were analysed, so as to find the threshold value of energy consumption and indoor comfort of control system. Throughout the entire cooling season, the water temperature of buried pipe is between 18-20°C, the return water temperature is between 18-21°C. The peak of the water return temperature of the buried pipe usually occurs 20:00 in the evening, and the valley value appears at 9:00 in the morning, with the same rule of 24 hours. The peak of the water supply temperature is around 18:00 in the evening, and the valley value is at 8:00 in the morning. The contrast can be seen that buried pipe for the return water temperature, indoor temperature simulation value and actual value are basically identical. The reliability of the simulation model is verified by comparing the simulation data with the monitoring data. It provides technical guarantee for the future analysis of different operation strategies directly using TRNSYS software. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords: TRNSYS; compound air conditioning; simulation optimization
Nomenclature
Q
air conditioning load, KW
* Corresponding author. Tel.: +86-150-9873-6935. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.360
2
t S λ cp qs T q
Huixin Fang et al. / Procedia Engineering 205 (2017) 1454–1460 Huixin Fang et al./ Procedia Engineering 00 (2017) 000–000
1455
time, s air conditioning area, m2 thermal conductivity, W/(m·K) specific heat capacity, J/(kg·k) supply water flow, kg/h absolute temperature, K heat flow of per unit volume, W/m2
1.Introduction Ground source heat pump system is the basis for low grade energy conversion, which can be used to recycle and make full use of cold heat stored in soil, groundwater and surface water. The ground source heat pump system mainly includes underground water source heat pump, surface water heat pump and underground pipe heat pump. Direct cooling exchanger technology is most widely used in ground source heat pump system. It directly extracts the amount of cold in the soil through the U-type underground heat exchanger, and the amount of cooling is radiated from the ceiling or floor to the air conditioning room through the indoor terminal unit (usually the radiant plate). The technology of floor radiant cooling coupled ventilation system has been developed, but there are few successful applications in China. The biggest advantage of the system is that the same set of end devices can be realized in winter and summer, namely, the freezing water supply of the underground tube during the summer and the heating of cold water in winter, which saves the investment expense [1]. In the construction, the system scheme combining the underground pipe with the floor radiant cooling can effectively improve the energy efficiency, which has a great impact on the energy saving of buildings. The operating strategy of this system is mainly to use the embedded pipe directly and the floor coupled cooling system to bear the majority of the indoor thermal load. The winter operating strategy is mainly to use the heat pump system, through the energy storage tank continuously to the indoor heating [2]. The concept of floor radiant cooling first appeared in the middle of the 20th century. It is similar to the radiant floor heating system. It releases cold energy by radiation to achieve the goal of cold load and indoor temperature reduction. By the end of last century, Feustel and Stetiu [3] made some studies in floor radiant cooling as the premise, focusing on the heat transfer mechanism between the environment of the building and the human body. The results show that the floor radiant cooling system can satisfy the thermal comfort of the human body by providing a good thermal environment around the human body. At present, the floor radiant cooling system was studied by Niu and Shi [4], in which the rationality, energy saving effect, comfort of indoor environment and structure of radiant floor were discussed, respectively. It is concluded that the floor radiant cooling system can meet the temperature requirement of summer indoor air conditioning, and has a significant advantage in technical and economic performance compared with the conventional cooling system [5]. Therefore, this paper established the model and optimized it under different conditions. Then, the results were analysed, so as to find the threshold of energy consumption and indoor comfort of control system. 2.Model and simulation setup 2.1. Simulation study of air conditioning system based on TRNSYS The TRNSYS energy efficiency simulation system is one of the software that is used in the air-conditioning load and energy consumption simulation, and it presents a large advantage to the complex system of complex air conditioning system. Chiasson and Yavuzturk [6] used the simulation software to run a continuous simulation of solar energy and ground source heat pump system, and analyzed its operation characteristics and economy. By 2008, Hackel [7] put forward an optimization plan for the areas dominated by the cooling and heating load based on TRNSYS software. He did some research on design methods and operation strategies of ground pipe heat exchanger. In China, the utilization of TRNSYS simulation is mostly in the regional research institutes, where TRNSYS has a lot of research cases with ground source heat pumps. The calculation of the buried pipe in the ground source heat
1456
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pump adopts the internationally recognized g-function algorithm, which can accurately calculate the heat transfer of buried pipes in the composite system and the thermal equilibrium of soil. Li [8] built two typical air conditioning systems, cooling tower composite ground source heat pump system and boiler composite ground source heat pump system using TRNSYS, and puts forward two through detailed data analysis system of the corresponding optimal operation strategy. The simulation of various air conditioning systems using TRNSYS can save a large amount of experimental time. By repeated simulation, the real reliability of the simulation is also improved gradually. 2.2. Air-conditioning load calculation The influence factors of cooling load can be divided into the envelope, body heat, equipment and lighting heat, air permeability and moisture migration, and so on. Sometimes, it also needs to consider the state parameters of the pipeline, the outdoor air permeability and heat, air reheat effect. The building load varies from time to time, and the purpose of load calculation is to determine the maximum load of the building, thereby selecting the unit, equipment and water pump that can bear the load. Calculation of building load in TRNSYS requires detailed description of building maintenance structures and indoor personnel equipment and ventilation in TRN Build. The outdoor environment parameters required in the building model are provided by the meteorological parameters in the typical TMY2 format, which is the external file to be read in the type15-2 in Fig.1. The meteorological external document in this experiment is a typical annual meteorological parameter TMY2. It is derived from EnergyPlus [9,10], which includes hourly data of solar radiation, outdoor temperature and humidity change, wind speed and other meteorological parameters. When calculating the load, we need select sensible heating load (QLATD) and latent heating load (QSENS) from building model. Then we need calculate the sum of the two previous values. It is the construction of the total load, and at the same time we can also output first layer load. The heating and cooling load of one layer is 27.93 KW, the latent heating and cooling load is 13.83 KW, and the new air cooling load is 4.10 KW.
Fig. 1. Schematic diagram of simulation of building load.
As shown in Fig. 2, the maximum cold load of the building is 208.69 KW, and the air conditioning area is 3815m2, so the unit area of air conditioning refrigeration is 57.97 W/m2. The heat load is 172.94 KW, the latent heat load is 35.75 KW, and the radiation cooling system can only take the indoor heat load. Therefore, the floor radiation usually only takes part of the heat load, while the residual heat load, the total latent heat load and the fresh air load need to be taken by the displacement ventilation system.
4
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Fig. 2. Total cooling load during cooling season.
2.3. Building model setup When the radiant floor cooling system is combined with the displacement ventilation system, the radiant floor is usually covered by 55% of the air-conditioning load. The remaining 45% of the cooling load is borne by the displacement ventilation system. In the case of the project, the water supply flow of the radiant floor is usually floating in 20000kg/h over the summer. When building model is set up, we establish the Active Layer, as shown in Fig. 3(a). When floor heat transfer characteristics, we establish the Active Layer in the Wall Type "middle tier, as shown in Fig. 3(b). The radiant floor usually includes insulation layer, embedded pipe layer, structural layer leveling layer and ground layer. (a)
(b)
Fig. 3. The radiation floor layer structure in TRN Build. (a) Active Layer (b) Wall Type
3.Results 3.1. Run simulation and data analysis The simulation time starts from June 15. The circulation pump keeps the open mode during the whole cooling season. The maximum water supply flow is 20000kg/h. We can see from the Fig.4, during the cooling season, the supply water temperature of buried pipe ranges is between 18-20°C, and return water temperature varies from 18°C to 21°C. The supply water temperature and the return water temperature difference are between 0.26°C and 1.18°C, respectively.
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5
Fig. 4. The backwater temperature curve of the buried pipe.
The water supply temperature of the buried pipe is relatively stable, and the variation of meteorological parameters and room load is very small, which is the greatest advantage of choosing soil source as the cold source. When the ambient temperature was lower or the indoor cooling load significantly decreased, the water temperature change was more obvious, as shown in Fig. 5. (a)
(b)
Fig. 5. Changes of water temperature of buried pipe with outdoor temperature, (a) Variation of return water temperature, (b) variation of outdoor temperature.
As seen from the above Fig.5 (a), after July 13, the temperature of typical day in the next three days had the sharp decline. The daily maximum temperature ranges from 32.4°C to 26.5°C. This kind of phenomenon often appears in the summer, and the return water temperature began to fall in. The maximum temperature is from 20.47°C to 19.92°C. The peak of return water temperature usually appears at around 20:00 in the evening, and the valley occurs at 9:00 in the morning. And it changes in a 24-hour cycle. The peak of the supply water temperature is around 18:00 in the evening, and the valley is at 8:00 in the morning.
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3.2. Statistical analysis of monitoring data The demonstration building air conditioning system adopts advanced electromechanical integration design and uses the Siemens building automation and energy saving equipment monitoring system. The air conditioning refrigeration process combined with automatic control to achieve the real-time monitoring and control of air conditioning system.In each floor of the room, every functional room has temperature humidity, floor temperature sensor as shown in Fig.6.
Fig. 6. Indoor temperature and humidity sensor.
Fig. 7. Indoor temperature monitoring situation.
A large amount of testing points are arranged to monitor temperature in each space. The indoor average temperature variation is monitored by each terminal temperature sensor, as shown in Fig 7. As you can see from Fig. 7 from June 15, to September 15, 2016, the entire cooling season, indoor temperature fluctuation was between 22°C and 27°C. 3.3. The comparison between monitoring and simulation data During the whole cooling season, the water supply temperature of the buried pipe is between 18°C and 20°C, and the return water temperature is between 18°C and 21°C.The minimum temperature difference between the supply and return water is 0.26°C, and the maximum difference is 1.18°C. The actual test shows that the supply water temperature of the ground source wells on the north side is 18.3°C, the temperature of the supply water of the ground source wells in the south is 19.3°C, and the return water temperature of the buried pipes is 20.8°C. The indoor simulation temperature of the first floor is between 20°C and 28°C, and the measured temperature is between
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23°C and 28°C.The simulation of indoor relative humidity in refrigeration season is 45%~90%, and the measured is 50%~80%. The simulated of outdoor mean temperature is 26.06°C, and the measured is 27.58°C. The simulation of power consumption is 15536 kWh, and the measured is 16355 kWh. The data obtained through the simulation data and monitoring platform, the contrast can be seen that buried pipe for the return water temperature, indoor temperature simulation data and actual data are basically identical. The indoor and outdoor temperature in different temperature range is different, but if we don't consider individual data, the simulation is credible. 3.4. The reason for the error The simulation data is not consistent with the measured data, and the main points are summarized as follows. Indoor personnel activity floating objective existence, and in the software to calculate the building load, only takes into consideration the fixed value of the number of people, and personnel heat dissipation is one of the important factors affecting indoor cooling load. When indoor personnel suddenly increase or decrease, the indoor temperature and humidity sensor can measure the change value by time, and pass it to the computer. In the optimization of operation strategy, it should be improved, and the feedback control loop can be set up to adjust the air volume and so on. The main operating equipment has been described in detail in the model, but many details are not specific enough, such as the loss of heat in the pipe and the energy loss at the entrance of the equipment. 4. Conclusions It was found that the temperature is not uniform in the cooling season. The first layer as the example, we can see that the temperature difference of each layer can be effectively reduced by regulating the supply water flow of the ground pipe direct, so that it can be basically controlled within 0.5 degrees. It solves the phenomenon of different heating and cooling due to different load, so that the cooling quantity can be distributed according to demand. By comparing the simulation data with the monitoring data, the practicability of the simulation model is proved. It provides technical support for the analysis of different operation strategies directly using TRNSYS software in the future. Acknowledgements This study was sponsored by Natural Science Foundation of China (NSFC, No.51176104), Natural Science Foundation of Shandong Province (ZR2016EEB08), Science and Technology Plan Project of University in Shandong Province (J16LG07), Science and Technology Development Plan in Shandong Province (2012GGX10416). References [1] F.Q. Zhao. Research on the application of the direct cooling system and water storage air conditioning system, 2014. [2] Y.T. Zhang. Research on operation strategy of floor radiant cooling system for office buildings, 2014. [3] H.E. Feustel, C. Stetiu. Hydronic radiant cooling—preliminary assessment. Energy & Buildings, 22(3) (1995) 193-205. [4] F.J. Niu, K.Y. Shi. The technical and economic analysis of floor radiation cooling. Gas and heat, 10 (1) (2000) 89-90. [5] J.Y. Liu, X.N. Xie, F.H. Qin, S.J. Song, D.L. Lv. A case study of ground source direct cooling system integrated with water storage tank system. Building simulation. 9 (6) (2016) 659-668. [6] A.D. Chiasson, C. Yavuzturk. Assessment of the viability of hybrid geothermal heat pump systems with solar thermal collectors. Ashrae Transactions, 109 (1) (2003) 487-500. [7] S.P. Hackel. Development of design guidelines for hybrid ground-coupled heat pump systems. Madison University of Wisconsin-Madison, 2008. [8] X. Li. The analysis and comparison of different control strategies of hybrid ground-source heat pump systems. Huazhong University of Science and Technology, 2008. [9] S. Zhu. J.F. Chen. A simulation study for a low carbon consumption HVAC project using EnergyPlus. International Journal of Low-Carbon Technologies. (2012) 248-254. [10] P. Hua, Q. Yi, R Fan, Z.Z. Huang. The influence factors of the thermal balance of heat pump of soil source heat pump based on TRNSYS. Building energy efficiency, 03 (1) (2012) 23-29.