2. RoomZoner: Occupancy-based Room-Level Zoning of a Centralized HVAC System Tamim Sookoor and Kamin Whitehouse April 11, 2013 4 th International Conference on Cyber-Physical Systems (ICCPS)

3. 2

4. US Residential Energy Use* 1 *US Energy Information Administration

5. US Residential Energy Use* 1 Homes are ~30% vacant Smart Thermostat: 28% Savings --Sensys 2010 *US Energy Information Administration

6. US Residential Energy Use* 1 Homes are ~50% used when occupied Our goal: Occupancy-driven zoning *US Energy Information Administration

7. Related Work 2 HVAC Co-design ICCPS 2013 POEM IPSN 2013 PreHeat UbiComp 2011

8. 72 °F 69 °F RoomZoner Retrofit centralized HVAC for room-level zoning Low cost DIY installation Ensure safety of HVAC system 3 72 °F 69 °F

9. Outline Zoning Overview Challenges Approach Evaluation 4

10. DIY Zoning Retrofit 5

11. 6 69 °F

12. 6 72 °F 71 °F 70 °F 69 °F 71 °F 70 °F 69 °F 68 °F 72 °F 71 °F 70 °F 64 °F 63 °F 65 °F 72 °F

13. Outline Zoning Overview Challenges Approach Evaluation 7

14. Zoning With a Central HVAC System 8 Central HVAC One sensor One heater/cooler Zoned HVAC N sensors N heaters/coolers RoomZoner N sensors One heater/cooler N + 1 control signals Can a central HVAC system safely be used for zoning? Can it be implemented with COTS components?

15. Backpressure 9

16. 9

17. 9

18. Short Cycling 10 69 °F 72 °F 71 °F 70 °F 73 °F

19. Temperature Estimation 11 65 °F 69 °F 70 °F 76 °F 74 °F 78 °F What temperature to use for control decisions?

20. Temperature Estimation 11 65 °F 69 °F 70 °F 76 °F 74 °F 78 °F Occupied rooms? Low system stability

21. Temperature Estimation 11 65 °F 69 °F 70 °F 71 °F 77 °F 74 °F 78 °F House average? Average = 72°F Slow reaction

22. Occupancy Assessment 12 72 °F 69 °F 70 °F 72 °F 77 °F 65 °F 78 °F 67 °F 66 °F

23. Outline Zoning Overview Challenges Approach Evaluation 13

24. Tackling the Challenges Challenge Equipment Safety Temperature Estimation Occupancy Assessment Approach Dump Zones Conservative Averaging Occupancy Characterization 14

25. Dump Zone Selection 15 65 °F 69 °F 70 °F 71 °F 77 °F 74 °F 78 °F Which additional rooms should you condition?

26. Dump Zone Selection 15 65 °F 69 °F 70 °F 71 °F 77 °F 74 °F 78 °F

27. Dump Zone Selection 15 65 °F 69 °F 70 °F 71 °F 77 °F 74 °F 78 °F How many rooms should be in the dump zone?

28. Building a Airflow Model 16 Exponential Measurements

29. Building a Conservative Airflow Model 17 2N Measurements

30. Conservative Airflow 18

31. Estimating Total Airflow 19 + + + + + + > T

32. Conservative Temperature Averaging 20 65 °F 69 °F 70 °F 72 °F 77 °F 74 °F 78 °F Heating: Max Cooling: Min Trade-off comfort for stability

33. Occupancy Characterization Analyze Historical Occupancy Data – Find sensor firing frequencies that identify Stable occupancy – Start of long-term usage – End of long-term usage Transitional occupancy – Start of temporary usage – End of temporary usage 21

34. Occupancy Characterization Exhaustive search over frequencies – Minimize total occupancy time 22 Maximum False Negatives Maximum State Transitions Maximum 25 th Percentile Duration (mins) Stable304 Transitional4303 Sensor frequencies

35. Outline Sensor Design Topological Constraints Search Evaluation 23

36. Experimental Approach Deployed RoomZoner in a 7-room house 13 registers 12 temperature sensors 42 days (21 RoomZoner / 21 whole house) 24 Sun MonTueWedThuFriSat … RoomZoner Whole house

37. Response to Temperature 25

38. Energy Savings 26 ~14% less energy

39. Limitations and Future Work Current system built using an ad-hoc approach – Use a control-theoretic approach such as MPC Current evaluation limited in scope – Evaluate system in multiple houses – Extend evaluation period 27

40. Conclusions Centralized HVACs can be retrofitted for zoning – Low-cost DIY installation – Saves energy Requires incorporation of prediction – Predict room-level occupancy (POEM?) – Predict room temperature changes (Matchstick?) One step towards residential room-level zoning of centralized HVAC systems 28

41. 29 Feedback or Questions?

42. 30 Backup Slides

43. Implementation 31

44. Challenges to Central HVAC Zoning Equipment safety – Backpressure – Short-cycling Temperature estimation – N sensors  1 Heater/Cooler Occupancy assessment – Passageway rooms – Short-term room usage – Multi-room usage 32