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Occupancy and hvac energy

Relationship between building occupancy and HVAC system loads for energy efficiency.

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Occupancy and hvac energy

  1. 1. How Does Building Occupancy Influence Energy Efficiency of HVC Systems Zheng Yang Zheng Yang PhD Candidate Viterbi Fellow Innovation in Integrated Informatics Lab ( Department of Civil and Environmental Engineering University of Southern California
  2. 2. Commercial Building Energy Consumption Commercial Buildings Figure. Building Energy Consumption (IEA 2014; DOE 2014) Figure. U.S. Energy Consumption in 2013 (IEA 2014; DOE 2014) 80% Figure. Commercial Building Energy (DOE 2013, 2014) HVAC: Heating, Ventilation and Air Conditioning Image Source: Regulvar Control
  3. 3. HVAC Energy Efficiency Inefficiency: 90% of HVAC systems are inefficient (EIA 2012, Carbon Trust 2012, UNEP 2013) Energy required on the demand side; Energy consumed on the supply side; Building Physical Characteristics Effects have decreased (Guerra-Santin 2010) Governments have introduced regulations and policies New Technology and Systems Infeasible and unpredictable (USGBC 2010) Existing buildings have already installed HVAC systems Demand driven Control React to actual demands (CIBSE 2012) Based on real space loads to keep desired conditions Occupants Control Policies Actual Demands Difference:
  4. 4. Figure. The importance of occupant in HVAC energy consumption Occupancy and HVAC Occupant activity, control preferences and personal information
  5. 5. Heating/Cooling, Terminal and Setpoint Terminals Setpoint Demands Medium Heating / Cooling Supply side Loads Control unit and interface Temperature range (deadband) Thermostat Primary parameter Until 2011, 90% of actively conditioned buildings Thermostat Setpoint (ASHRAE 2012, Johnson Control 2012) SETPOINT HVAC Response Thermal Environment Occupant
  6. 6. Problem Analysis • Stochastic in nature and has variety; • Random variations and variant transitions; • Heterogeneous and even distinct; Why? Systematic research for analyzing the influences of occupancy on HVAC energy efficiency - Occupancy Transitions - Occupancy Variations - Occupancy Heterogeneity How? • Not fully run HVAC system in vacant zones; • Allow temperature to float within a certain range (Setback); • Substantial energy savings have been reported;
  7. 7. Test Bed Building Test bed building in University of Southern California Ambient Sensing based Cross-Space Occupancy Modeling (Zheng et al. 2013, 2014) Initial Energy Modeling Sensitivity Analysis Parametric Comparison Parameter Estimation Base Modeling Discrepancy Analysis Discrepancy Minimization Calibrated Energy Model Non-observable Parameter Recognition and Range Ranking (Level 1) Ranking (Macro Level 2) Estimable Parameter Adjustable Parameter Multi-objective Programming Regression-fitting Estimable Evidence Observable Evidence Significant Parameters Distribution Analysis Random Samples Parameter Range and Condition Semi-calibrated Model Actual Energy Data Input Energy Discrepancy Explanation Actual Energy Data Input Calibration Evaluation Default and Autosized Insignificant Parameters ... Multi-level building energy model calibration (Zheng et al. 2014)
  8. 8. Occupancy Transitions Occupied period – Setpoint; Unoccupied period – Setback; Setpoint Float Setback Reconditioning Effective EffectiveIneffective Occupied Unoccupied Occupied Time Figure. Deviation between occupancy and effective loads Occupied/Unoccupied Transitions ≠ Effective/Ineffective Loads Transitions A portion of the loads during unoccupied periods = Effective loads
  9. 9. Simulation Results • The darker the color is, the more energy reduction and less conditioning miss are achieved. • energy efficiency is expressed as a weighted sum of the two gray maps (50% for each) • Occupancy transitions have significant influences on the HVAC energy efficiency (4% to 21%) Occupancy Transitions and HVAC Energy Efficiency 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 Setpoint/SetbackSchedule(Min) Setpoint/Setback Distance (K) Energy Reduction (%) 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 Setpoint/SetbackSchedule(Min) Setpoint/Setback Distance (K) Conditioning Miss (%)
  10. 10. Stochastic Occupancy Variations ~ effective heating/cooling loads Degree of Occupancy Variation Deterministic Stochastic Long-term Occupancy Habitual patterns Represents typical effective loads Real-time Occupancy Occupancy status for specific time Represents instant effective loads Occupancy Variations Euclidean distance between the actual daily occupancy versus the occupancy profile
  11. 11. Deviation of daily real-time occupancy From occupancy profile Calculate the Daily average variation degree Simulation Results Daily energy reduction and conditioning miss Occupancy based control (15 minutes and 78F) Occupancy Variations and HVAC Energy Efficiency • A Negative linear relationship between the occupancy variation and HVAC energy efficiency. • HVAC energy efficiency for each specific day is significantly influenced by the variation of occupancy for that day (from 3% to 24%)
  12. 12. Presence Probability Time Presence Probability Time Presence Probability Time Presence Probability Time Occupancy Heterogeneous occupancy Effective Loads Heterogeneous load distribution Occupancy Heterogeneity Long-term Occupancy (Occupancy Profile) Load Redistribution Hierarchical and Conditional Occupant Reassignment (Zheng et al. 2014, 2015) Predefined constrains (e.g. room size) Capacity constrains (e.g. number of rooms) Geometry constrains (e.g. zone adjacency) For a specific HVAC control policy Possible Energy Efficiency Increments Influence of Occupancy Heterogeneity
  13. 13. Occupancy Simulation Results 100 random occupant reassignment trials Current occupant assignment as benchmark Heating/Cooling energy reduction and conditioning miss Occupancy based control (15 minutes and 78F) Occupancy Heterogeneity and HVAC Energy Efficiency • The relative locations represented the possibilities of influences of occupancy heterogeneity • Occupancy heterogeneity has significant influences on the HVAC energy efficiency (0.2% to 12%)
  14. 14. THANK YOU !