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)

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US Residential Energy Use* Other 57% Heating and Cooling 43% *US Energy Information Administration 1

US Residential Energy Use* Other 57% Heating and Cooling 30% Homes are ~30% vacant Vacant 13% Smart Thermostat: 28% Savings --Sensys 2010 *US Energy Information Administration 1

US Residential Energy Use* Other 57% Heating and Cooling 15% Unused Rooms 15% Vacant 13% Homes are ~50% used when occupied Our goal: Occupancy-driven zoning *US Energy Information Administration 1

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

RoomZoner • Retrofit centralized HVAC for room-level zoning

69 °F 69 °F 69 °F 72 °F 72 °F 69 °F 69 °F

• • Low cost DIY installation Ensure safety of HVAC system 3

• • • • Zoning Overview Challenges Approach Evaluation Outline 4

DIY Zoning Retrofit 5

69 °F

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64 °F 64 °F 72 °F 71 °F 70 °F 63 °F 65 °F 72 °F 71 °F 70 °F 69 °F 72 °F 71 °F 70 °F 69 °F 68 °F

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• • • • Zoning Overview

Challenges

Approach Evaluation Outline 7

Zoning With a Central HVAC System

Central HVAC

• One sensor • One heater/cooler

RoomZoner

• N sensors • One heater/cooler • N + 1 control signals

Zoned HVAC

• N sensors • N heaters/coolers •

Can a central HVAC system safely be used for zoning?

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Can it be implemented with COTS components?

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Backpressure 9

Backpressure 9

Backpressure 9

Short Cycling

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76 °F 78 °F

Temperature Estimation

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What temperature to use for control decisions?

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76 °F 78 °F

Temperature Estimation Occupied rooms?

74 °F 65 °F

Low system stability

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77 °F 78 °F

Temperature Estimation House average?

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Average = 72°F

70 °F 71 °F

Slow reaction

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77 °F

Occupancy Assessment

78 °F 67 °F 66 °F 65 °F 72 °F 72 °F 70 °F 69 °F

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• • • • Zoning Overview Challenges

Approach

Evaluation Outline 13

Tackling the Challenges •

Challenge

Equipment Safety • Temperature Estimation • Occupancy Assessment •

Approach

Dump Zones • Conservative Averaging • Occupancy Characterization 14

77 °F 78 °F

Dump Zone Selection

74 °F 65 °F

Which additional rooms should you condition?

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77 °F 78 °F

Dump Zone Selection

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77 °F 78 °F

Dump Zone Selection

74 °F 65 °F

How many rooms should be in the dump zone?

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Building a Airflow Model Exponential Measurements 16

Building a Conservative Airflow Model 2N Measurements 17

Conservative Airflow 18

Estimating Total Airflow + + + + + + > T 19

Conservative Temperature Averaging

78 °F 74 °F

Heating: Max Cooling: Min

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Trade-off comfort for stability

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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

Occupancy Characterization • Exhaustive search over frequencies – Minimize total occupancy time

Maximum False Negatives Maximum State Transitions

Stable Transitional 30 4 4 30

Maximum 25 th Percentile Duration (mins)

30 3 Sensor frequencies 22

Outline • • • • Sensor Design Topological Constraints Search

Evaluation

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Experimental Approach • • • • Deployed RoomZoner in a 7-room house 13 registers 12 temperature sensors 42 days (21 RoomZoner / 21 whole house) RoomZoner Whole house Sun Mon Tue Wed Thu Fri Sat … 24

Response to Temperature 25

Energy Savings ~14% less energy 26

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

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

Feedback or Questions?

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Backup Slides 30

Implementation 31

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