1. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Object-oriented Modeling of Heat and Humidity Budgets Of Biosphere 2 Using Bond Graphs François E. Cellier ETH Zürich Àngela Nebot Universitat Politècnica de Catalunya Jürgen Greifeneder Universität Kaiserslautern

2. Start Presentation EnviroInfo 2005: Brno September 9, 2005 What is Biosphere 2 Biosphere 2 is an environmental research facility, located in the desert of Southern Arizona, that allows performing experiments in a materially closed ecological system under controlled experimental conditions. Biosphere 2 was built around 1990 with private funding and has functioned for almost 15 years already for various ecological experiments.

3. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Why Biosphere 2 In Biosphere 1 (the Earth ecosystem), it is difficult to perform experiments, because of limited access to control variables. In Biosphere 1, it is easy to observe phenomena and report them, but it is difficult to interpret these observations in an objective fashion. In Biosphere 1, we are able to correlate data, but correlations per se do not establish cause and effect relationships.

4. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Construction Biosphere 2 was built as a frame construction from a mesh of metal bars. The metal bars are filled with glass panels that are well insulated. During its closed operation, Biosphere 2 was slightly over- pressurized to prevent outside air from entering the structure. The air loss per unit volume was about 10% of that of the space shuttle!

5. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Construction II The pyramidal structure hosts the jungle biome. The less tall structure to the left contains the pond, the marshes, the savannah, and at the lowest level, the desert. Though not visible on the photograph, there exists yet one more biome: the agricultural biome.

6. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Construction III The two “lungs” are responsible for pressure equilibration within Biosphere 2. Each lung contains a heavy concrete ceiling that is flexibly suspended and insulated with a rubber membrane. If the temperature within Biosphere 2 rises, the inside pressure rises as well. Consequently, the ceiling rises until the inside and outside pressure values are again identical. The weight of the ceiling is responsible for providing a slight over-pressurization of Biosphere 2.

7. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Biomes The (salt water) pond of Biosphere 2 hosts a fairly complex maritime ecosystem. Visible behind the pond are the marsh lands planted with mangroves. Artificial waves are being generated to keep the mangroves healthy. Above the cliffs to the right, there is the high savannah.

8. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Biomes II This is the savannah. Each biome uses its own soil composition sometimes imported, such as in the case of the rain forest. Biosphere 2 has 1800 sensors to monitor the behavior of the system. Measurement values are recorded on average once every 15 Minutes.

9. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Biosphere 2: Biomes III The agricultural biome can be subdivided into three separate units. The second lung is on the left in the background.

10. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Living in Biosphere 2 The Biosphere 2 library is located at the top level of a high tower with a spiral staircase. The view from the library windows over the Sonora desert is spectacular.

11. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Rain Maker From the commando unit, it is possible to control the climate of each biome individually. For example, it is possible to program rain over the savannah to take place at 3 p.m. during 10 minutes.

12. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Climate Control The climate control unit (located below ground) is highly impressive. Biosphere 2 is one of the most complex engineering systems ever built by mankind.

13. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Climate Control II Beside from the temperature, also the humidity needs to be controlled. To this end, the air must be constantly dehumidified. The extracted water flows to the lowest point of the structure, located in one of the two lungs, where the water is being collected in a small lake; from there, it is pumped back up to where it is needed.

14. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Conceptual Model

15. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Bond-Graph Model TemperatureHumidity Evaporation Condensation For evaporation, energy is needed. This energy is taken from the thermal domain. In the process, so-called latent heat is being generated. In the process of condensation, the latent heat is converted back to sensible heat. The effects of evaporation and condensation cannot be neglected in the modeling of Biosphere 2.

16. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Dymola Model The overall Dymola model is shown to the left. At least, the picture shown is the top-level icon window of the model.

17. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Dymola Model II Night Sky Temperature Ambient Temperature Temperature of Cover Air Temperature Soil Temperature Vegetation Temperature Water Temperature Air Humidity

18. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Dymola Model III Convection Evaporation and Condensation Night Sky Radiation Solar Radiation Solar Convection

19. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Convection R th = R · T  G th = G / T T e1e1 e2e2 T = e 1 + e 2

20. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Radiation R th = R / T 2  G th = G · T 2 e1e1 e1e1 T = e 1

21. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Evaporation of the Pond Programmed as equations Teten’s law } Sensible heat in = latent heat out

22. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Condensation in the Atmosphere Programmed as equations If the temperature falls below the dew point, fog is created.

23. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Ambient Temperature The ambient temperature is computed here by interpolation from a huge temperature data file. Data were available for the location of Tucson only. Correction factors were used to estimate the effects of the higher altitude of Oracle.

24. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Night Sky Temperature

25. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Solar Input and Wind Velocity

26. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Absorption, Reflection, Transmission Since the glass panels are pointing in all directions, it would be too hard to compute the physics of absorption, reflection, and transmission accurately, as we did in the last example. Instead, we simply divide the incoming radiation proportionally.

27. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Distribution of Absorbed Radiation The absorbed radiation is railroaded to the different recipients within the overall Biosphere II structure.

28. Start Presentation EnviroInfo 2005: Brno September 9, 2005 The Dymola Biosphere Package We are now ready to compile and simulate the Biosphere model. Not bad! (The compilation is still fairly slow, because Dymola isn’t geared yet to deal with such large measurement data files.)

29. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results I The program works with weather data that record temperature, radiation, humidity, wind velocity, and cloud cover for an entire year. Without climate control, the inside temperature follows essentially outside temperature patterns. There is some additional heat accumulation inside the structure because of reduced convection and higher humidity values.

30. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results II Since water has a larger heat capacity than air, the daily variations in the pond temperature are smaller than in the air temperature. However, the overall (long- term) temperature patterns still follow those of the ambient temperature.

31. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results III The humidity is much higher during the summer months, since the saturation pressure is higher at higher temperature. Consequently, there is less condensation (fog) during the summer months. Indeed, it can be frequently observed that during spring or fall evening hours, after sun set, fog starts to build over the high savannah, which then migrates to the rain forest, which eventually gets totally fogged in.

32. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results IV Daily temperature variations in the summer months. The air temperature inside Biosphere 2 would vary by approximately 10 o C over the duration of one day, if there were no climate control.

33. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results V Temperature variations during the winter months. Also in the winter, daily temperature variations are approximately 10 o C. The humidity variations follow the temperature variations almost exactly. This observation shall be explained at once.

34. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results VI The relative humidity is computed as the quotient of the true humidity and the humidity at saturation pressure. The atmosphere is almost always saturated. Only in the late morning hours, when the temperature rises rapidly, will the fog dissolve so that the sun may shine quickly. However, the relative humidity never decreases to a value below 94%. Only the climate control (not included in this model) makes life inside Biosphere II possible.

35. Start Presentation EnviroInfo 2005: Brno September 9, 2005 Simulation Results VII In a closed system, such as Biosphere 2, evaporation necessarily leads to an increase in humidity. However, the humid air has no mechanism to ever dry up again except by means of cooling. Consequently, the system operates almost entirely in the vicinity of 100% relative humidity. The climate control is accounting for this. The air extracted from the dome is first cooled down to let the water fall out, and only thereafter, it is reheated to the desired temperature value. However, the climate control was not simulated here. Modeling of the climate control of Biosphere 2 is still in the works.

36. Start Presentation EnviroInfo 2005: Brno September 9, 2005 References I Brück, D., H. Elmqvist, H. Olsson, and S.E. Mattsson (2002), “Dymola for Multi-Engineering Modeling and Simulation,” Proc. 2 nd International Modelica Conference, pp. 55:1-8.Dymola for Multi-Engineering Modeling and SimulationProc. 2 nd International Modelica Conference Cellier, F.E. (1991), Continuous System Modeling, Springer-Verlag, New York.Continuous System Modeling Cellier, F.E. and J. Greifeneder (2003), “Object-oriented Modeling of Convective Flows Using the Dymola Thermo-Bond-Graph Library,” Proc. ICBGM’03, 6 th Intl. Conference on Bond Graph Modeling and Simulation, Orlando, Florida, pp. 198-204.Object-oriented Modeling of Convective Flows Using the Dymola Thermo-Bond-Graph Library

37. Start Presentation EnviroInfo 2005: Brno September 9, 2005 References II Cellier, F.E. and R.T. McBride (2003), “Object-oriented Modeling of Complex Physical Systems Using the Dymola bond-graph library,” Proc. ICBGM’03, Intl. Conference on Bond Graph Modeling and Simulation, Orlando, Florida, pp.157-162.Object-oriented Modeling of Complex Physical Systems Using the Dymola bond-graph library Cellier, F.E. and A. Nebot (2005), “The Modelica Bond Graph Library,” Proc. 4 th Modelica Conference, Hamburg, Germany, Vol. 1, pp. 57-65.The Modelica Bond Graph Library Greifeneder, J. (2001), Modellierung thermodynamischer Phänomene mittels Bondgraphen, MS Thesis, Institut für Systemdynamik und Regelungstechnik, Universität Stuttgart, Germany.Modellierung thermodynamischer Phänomene mittels Bondgraphen

38. Start Presentation EnviroInfo 2005: Brno September 9, 2005 References III Greifeneder, J. and F.E. Cellier (2001), “Modeling Convective Flows Using Bond Graphs,” Proc. ICBGM’01, 5 th Intl. Conference on Bond Graph Modeling and Simulation, Phoenix, Arizona, pp. 276-284.Modeling Convective Flows Using Bond Graphs Greifeneder, J. and F.E. Cellier (2001), “Modeling Multi- phase Systems Using Bond Graphs,” Proc. ICBGM’01, 5 th Intl. Conference on Bond Graph Modeling and Simulation, Phoenix, Arizona, pp. 285-291.Modeling Multi- phase Systems Using Bond Graphs Greifeneder, J. and F.E. Cellier (2001), “Modeling Multi- element Systems Using Bond Graphs,” Proc. ESS’01, 13 th European Simulation Symposium, Marseille, France, pp. 758-766.Modeling Multi- element Systems Using Bond Graphs

39. Start Presentation EnviroInfo 2005: Brno September 9, 2005 References IV Nebot, A., F.E. Cellier, and F. Mugica (1999), “Simulation of Heat and Humidity Budgets of Biosphere 2 Without Air Conditioning,” Ecological Engineering, 13, pp. 333-356.Simulation of Heat and Humidity Budgets of Biosphere 2 Without Air Conditioning Cellier, F.E. (2005), The Dymola Bond Graph Library, Version 1.1.The Dymola Bond Graph Library Cellier, F.E. (1997), Tucson Weather Data for Matlab.Tucson Weather Data for Matlab