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Adaptive Optimal Design of Active Thermally 
Insulated (ATI) Windows Using Surrogate Modeling 
Junqiang Zhang, Achille Mes...
2 
Outline 
• Motivation 
• Active Window Technology Overview 
• ATI Window Design 
• Modeling 
• Adaptive Optimization 
•...
3 
Motivation 
53% energy consumed by HVAC 
systems in residential buildings 
44% energy consumed by HVAC 
systems in comm...
4 
Types of Active Windows 
Heat extraction double skin facades 
Absorb the sun’s 
heat outside 
Switchable window coating...
5 
Thermoelectric (TE) Units 
• TE Units can be very small and operate with no moving 
parts, making them ideal to fit ins...
6 
ATI Window Design 
Window Front View Cross Section of Side View 
6 
Side Channel 
Clear glass 
Side Channel 
Fans 
Heat...
7 
ATI Window Design 
• Thermometer, anemometer, and solar radiation sensor 
are used to detect weather conditions. 
• The...
8 
Modeling 
• Motivation 
• Active Window Technology Overview 
• ATI Window Design 
• Modeling 
• TE models 
• CFD Model ...
9 
TE Units Analysis 
• The cold side absorbs heat based on the number of TE units, Nte, the 
electrical current, Ite, the...
Computational Fluid Dynamics (CFD) Model 
• A CFD model is meshed by Gambit 
• A steady-state heat transfer process is 
si...
Solar Insolation 
• Accounting for the thermal 
heat flux, Qconv , from FLUENT, 
and the solar heat, Qsolar , the 
total h...
Heat Sink Analysis 
• Pin spacing is defined by 
the equation below. 
• Pin diameter is 2.5 mm 
Stanescu, G., Fowler, A. J...
Fan Model 
13 
Top Left Top Right 
Bottom Left Bottom Right 
Left Most 
Center Right 
Center Left 
Right Most
Fan Model 
14 
The Pressure Gradients of Fans 
Δpavg : average pressure gradient produced by fans 
k : the slope of the pr...
Control Systems 
TE Units 
15 
Outside Temperature 
Wind Speed 
Solar Radiation 
Thermometer 
Anemometer 
Light Sensor 
Th...
Weather Conditions 
16 
Indoor weather conditions: 
• Indoor temperature: 75 ℉ (297 K) 
• Indoor heat transfer coefficient...
17 
Adaptive Optimization Problems 
Heating Cooling
Approximation of CFD Model 
• Local surrogate models are built during the 
optimization to reduce computational time. 
• T...
Weather Conditions and Optimization Results 
19 
No. 1 2 3 4…… 28 29 30 
Outside T (K) 284.0 296.5 271.5 277.8…… 298.8 273...
Optimization Convergence History 
20 
Convergence History of f(x) under Weather Condition 2 
70.0 
60.0 
50.0 
40.0 
30.0 ...
Surrogate Models of Optimal Operations 
21 
Quadratic Response Surface Method 
Optimal
Surrogate Models of Optimal Operations 
• The three functions are stored in the memories of the thermostats 
• With the in...
Comparison with Passive Windows 
3-Pane 
23 
• Calculate the amounts of heat 
transferred through passive 3- 
pane window ...
Comparison of Heat Flux 
24 
Heating conditions (higher is better) 
Convective Heat (W) 
Weather Condition Number 
+: Out ...
25 
Comparison of Heat Flux 
Cooling Conditions (lower is better) 
Convective Heat (W) 
Weather Condition Number 
+: Out -...
Comparison of Energy Efficiency 
26 
Coefficient Of Performance (COP) is a measurement of energy efficiency. 
The COP of a...
Comparison of Energy Efficiency 
27 
45 
40 
35 
30 
25 
20 
15 
10 
5 
3 
0 
COP of ATI Window 
COP of HVAC 
1 2 3 4 5 6 ...
28 
Concluding Remarks 
• Adaptive optimization is performed to optimize the 
performance of the ATI window under differen...
29 
Thank you
Questions 
30
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ATI_SDM_2010_Jun

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This paper explores the adaptive optimal design of Active Thermally Insulated (ATI) windows to significantly improve energy efficiency. The ATI window design uses ther- mostats to actively control thermoelectric (TE) units and fans to regulate the overall ther- modynamic properties of the windows. The windows are used to maintain a comfortable indoor temperature. Since weather conditions vary with different geographical locations and with time, the thermodynamic properties of the windows should adapt accordingly. The electric power supplied to the TE units and the fans are dynamically controlled so as to provide an optimal operation under varying weather conditions. Optimization of the ATI window design is a multiobjective problem. The problem minimizes both the heat trans- ferred through the window and electric power consumption. The heat transfer through the ATI windows is analyzed using FLUENT; and the optimization is performed using MAT- LAB. Since the computational expense of optimization for numerous weather conditions is excessive, the power supplies are optimized under a reasonably small number of weather conditions. Based on the optimal results obtained for these conditions, a surrogate model is developed to represent the optimal results in a wide range of weather conditions. The surrogate model is used to evaluate optimal power supplies with respect to different val- ues of outside temperature, wind speed, and intensity of solar radiation. Thermometers, anemometers, and solar radiation sensors are used to sense these weather conditions. With the inputs from the sensors, the thermostats determine the operating conditions and cal- culate the corresponding optimal power supplies using the surrogate model. Since the ATI windows are operated with optimal power supplies, high energy efficiency is achieved.

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ATI_SDM_2010_Jun

  1. 1. Adaptive Optimal Design of Active Thermally Insulated (ATI) Windows Using Surrogate Modeling Junqiang Zhang, Achille Messac, Souma Chowdhury, and Jie Zhang Rensselaer Polytechnic Institute Department of Mechanical, Aerospace, and Nuclear Engineering Multidisciplinary Design and Optimization Laboratory 6th AIAA Multidisciplinary Design Optimization Specialist Conference April 2010, Orlando, FL
  2. 2. 2 Outline • Motivation • Active Window Technology Overview • ATI Window Design • Modeling • Adaptive Optimization • Surrogate Model of Optimal Operations • Results and Comparisons • Concluding Remarks
  3. 3. 3 Motivation 53% energy consumed by HVAC systems in residential buildings 44% energy consumed by HVAC systems in commercial buildings • Windows occupy only 10% to 15% of the wall area • Windows can contribute 25% to 30% of the heat gain Department of Energy, “Buildings Energy Data Book”, 2005, http://buildingsdatabook.eere.energy.gov/ Energy Information Administration, “Commercial Buildings Energy Consumption Survey”, 2003, http://www.eia.doe.gov/emeu/cbecs/
  4. 4. 4 Types of Active Windows Heat extraction double skin facades Absorb the sun’s heat outside Switchable window coatings Change optical properties to limit solar heat gain Active control of shading systems Block incident sunlight to limit solar heat gain Thermoelectric Windows Outside Inside
  5. 5. 5 Thermoelectric (TE) Units • TE Units can be very small and operate with no moving parts, making them ideal to fit inside building envelopes or in the small space of the window frames. • A TE unit will form hot and cold sides when subjected to electric current. Melcor Center Hole Series Thermoelectric Cooler Hot Side Cold Side Heat Flow
  6. 6. 6 ATI Window Design Window Front View Cross Section of Side View 6 Side Channel Clear glass Side Channel Fans Heating air flow in Winter 1 m .5 m TE Units & Fin Dividing Wall 6 mm Air Clear Glass Tinted pane 24 mm Out In 12 mm Inner Pane Middle Pane Outer Pane
  7. 7. 7 ATI Window Design • Thermometer, anemometer, and solar radiation sensor are used to detect weather conditions. • Thermostat receive signals from the sensors and adjust the electric power supplies of TE units and fans according to different weather conditions. • Actively regulate the overall thermodynamic properties of the air in the gap between the inner pane and the middle pane to benefit the building occupants.
  8. 8. 8 Modeling • Motivation • Active Window Technology Overview • ATI Window Design • Modeling • TE models • CFD Model • Outside Heat sinks • Thermostats and weather condition sensors • Optimization • Surrogate Model of Optimal Operation • Comparison of Energy Efficiency • Concluding Remarks
  9. 9. 9 TE Units Analysis • The cold side absorbs heat based on the number of TE units, Nte, the electrical current, Ite, the cold side temperature, Tc, and the temperature difference, DTte • The hot side releases the heat absorbed from cold side and the heat converted from the electric power Peltier effect: induce heat flow in the direction of electric current Joules effect: heat generated because of electrical resistance Conduction: heat transfer because of temperature gradient
  10. 10. Computational Fluid Dynamics (CFD) Model • A CFD model is meshed by Gambit • A steady-state heat transfer process is simulated in FLUENT • The outer pane, the middle pane, and the air gap between them, are modeled as an equivalent thermal resistance. • Solar heating of the panes is modeled as volumetric heat generation. • The air flow and associated heat flux in the ATI window are evaluated • Qconv: the heat flux through the inner pane 10
  11. 11. Solar Insolation • Accounting for the thermal heat flux, Qconv , from FLUENT, and the solar heat, Qsolar , the total heat gain is QATI Cross Section Reflected SR Absorbed SA Solar radiation Esky 11 • The incident solar radiation is reflected from the outer pane, absorbed by the panes, or transmitted into the room
  12. 12. Heat Sink Analysis • Pin spacing is defined by the equation below. • Pin diameter is 2.5 mm Stanescu, G., Fowler, A. J., and Bejan, A., “The optimal spacing of cylinders in free-stream cross-flow forced convection,” International Journal of Heat and Mass Transfer, Vol. 39, No. 2, 1996, pp. 311–317 12 A p S d W TE Units H L
  13. 13. Fan Model 13 Top Left Top Right Bottom Left Bottom Right Left Most Center Right Center Left Right Most
  14. 14. Fan Model 14 The Pressure Gradients of Fans Δpavg : average pressure gradient produced by fans k : the slope of the pressure gradients • A linear pressure gradient profile is assumed. • The total electric power consumption of all fans is less than 6% of that of the TE units. It is not minimized.
  15. 15. Control Systems TE Units 15 Outside Temperature Wind Speed Solar Radiation Thermometer Anemometer Light Sensor Thermostat Processor Memory TE Units Power Controller Fan Power Controller Fans • Thermometer, anemometer, and light sensor are used to sense outside temperatures, wind speeds, and intensity of solar radiation. • Thermostat is used to control electric power supplied to TE units and fans.
  16. 16. Weather Conditions 16 Indoor weather conditions: • Indoor temperature: 75 ℉ (297 K) • Indoor heat transfer coefficient: 3.6 W/m2 Outside weather conditions: • Outside temperature: 7 to 97 ℉ (259 to 309 K) • Wind speed: 0 to 21.5 m/s • Solar radiation: 0 to 1000 W/m2 • Number of weather conditions: 10 x 3 (the small set population size) • Combinations: Sobol’s Quasirandom sequence generator algorithm Heating condition: Outside T < Inside T (usually in winter) Cooling condition: Outside T > Inside T (usually in summer) “Comparative Climatic Data for the United States through 2008,” Tech. rep., http://www.noaa.gov. Colaco, M. J., Dulikravich, G. S., and Sahoo, D., “A response surface method-based hybrid optimizer”, Inverse Probl Sci Eng, Vol. 6, No. 16, 2008, pp. 717– 7S4o1bol, I. M., “Uniformly Distributed Sequences with an Additional Uniform Property,” USSR Computational Mathematics and Mathematical Physics, Vol. 16, 1976, pp. 236–242.
  17. 17. 17 Adaptive Optimization Problems Heating Cooling
  18. 18. Approximation of CFD Model • Local surrogate models are built during the optimization to reduce computational time. • Trust region method is used to manage the approximation • Surrogate model was created using extended radial basis functions (ERBF) 18
  19. 19. Weather Conditions and Optimization Results 19 No. 1 2 3 4…… 28 29 30 Outside T (K) 284.0 296.5 271.5 277.8…… 298.8 273.8 280.1 Outside T (℉) 51.5 74.0 29.0 40.3…… 78.2 33.2 44.5 Wind speed (m/s) 10.75 5.38 16.13 8.06…… 0.34 11.09 3.02 Solar radiation (W/m2) 500 750 250 625…… 359 859 234 Vte (V) 1.14 0.97 3.28 1.34…… 1.37 1.86 1.84 Δpavg (Pa) 0.96 0.95 1.77 1.00…… 1.75 1.89 2.00 k 0.07 0.07 0.02 0.08…… 0.01 0.01 0.02 Red: heating conditions (Outside T < Inside T) Blue: cooling conditions (Outside T > Inside T)
  20. 20. Optimization Convergence History 20 Convergence History of f(x) under Weather Condition 2 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 Number of Function Evaluations
  21. 21. Surrogate Models of Optimal Operations 21 Quadratic Response Surface Method Optimal
  22. 22. Surrogate Models of Optimal Operations • The three functions are stored in the memories of the thermostats • With the inputs from the sensors, the thermostat evaluates Vte , Δpavg, and k. • Within the defined ranges of weather conditions, the operation of ATI 22 windows is optimal. Outside Temperature Wind Speed Solar Radiation Surrogate Model (Thermostat) Inputs Vte Δpavg k TE Units Power Controller Fan Power Controller Power of TE Units Power of Fans Outputs
  23. 23. Comparison with Passive Windows 3-Pane 23 • Calculate the amounts of heat transferred through passive 3- pane window in the same weather conditions by WINDOW software. • WINDOW is a software developed by Lawrence Berkeley National Laboratory to analyze window thermal and optical performance. Clear Glass Air Gap Bronze Glass
  24. 24. Comparison of Heat Flux 24 Heating conditions (higher is better) Convective Heat (W) Weather Condition Number +: Out -> In − : In -> Out
  25. 25. 25 Comparison of Heat Flux Cooling Conditions (lower is better) Convective Heat (W) Weather Condition Number +: Out -> In − : In -> Out
  26. 26. Comparison of Energy Efficiency 26 Coefficient Of Performance (COP) is a measurement of energy efficiency. The COP of a standard HVAC system is about 3. The COP of an ATI window, COPATI, is defined as how much heat flux is reduced, compared with a passive window with the same structure, divided by the electric power used.
  27. 27. Comparison of Energy Efficiency 27 45 40 35 30 25 20 15 10 5 3 0 COP of ATI Window COP of HVAC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Weather Condition Number Heating conditions: COP of the ATI windows is generally higher.
  28. 28. 28 Concluding Remarks • Adaptive optimization is performed to optimize the performance of the ATI window under different weather conditions. • Provide active control of the ATI window to adapt to different weather conditions using surrogate modeling. • High energy efficiency is generally achieved under heating conditions.
  29. 29. 29 Thank you
  30. 30. Questions 30

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