Predictive Maintenance For HVAC Arnab Biswas Data Scientist, EcoEnergy, Carrier Global Corporation @arnabbiswas1 

HVAC (Heating, Ventilation, Air Conditioning) Controls temperature, humidity & air quality for indoor environment 

HVAC Equipment Accounts for 40% of energy usage in commercial buildings (US) Reduction in energy, cost & greenhouse gas emission can be achieved via proper design, installation & maintenance Heavily dependent on Annual Maintenance 

Types of Maintenance Type Part Replacement Part’s Life Utilization Downtime Reactive On Failure Complete Unplanned Proactive Periodic, Before Failure Pre-determined Scheduled Predictive Just Before Failure Almost complete Scheduled 

Predictive Maintenance Predict reason for failure Predict days to failure Predict a failure in future Predicting equipment’s failure over a future time period, based on its historical behavior 

PdM Architecture 

Data Science For PdM Understanding Business Problem Defining ML Problem Understand Data Prepare Data Build & Evaluate Model Deploy Model Maintain Model 

Business Problem into ML Problem • Predict if HVAC is going to fail within next 2 weeks Binary Classification • Predict amount of time before next failure Regression • Predict if HVAC is going to fail in next 3w, 2w, 1w Multi-class Classification • Predict if HVAC is going to fail within next 2 weeks for a particular reason Multi-class Classification 

Regression vs Classification? • Prefer Classification over Regression if business allows • Regression is equivalent to Classification with infinite number of classes • Single Stage Model • Multistage Model • Stage 1: Predict assets going to fail in next 2 weeks • Stage 2: Predict reason for failure for assets from Stage 1 

Data Temporal Health Return Air Temperature Supply Air Temperature Run Time Set Point Temperature Power Consumption Zone Temperature Weather Outside Air Temperature Relative Humidity Pressure Maintenance Failure History Repair History Root Cause Parts Replaced Others Building Occupancy Static Equipment Metadata Climate Zone Geographic Location Building Metadata Maintenance Agency Data Collection 

Prepare Data Structure data from various sources into tabular format 

• Standard: Forward Filling, Interpolation • Domain Specific: Fill missing value of vibration on 1 PM, Tuesday • with last Tuesday 1 PM’s value • with Tuesday 1 PM’s value averaged over last 1 month • Strategy should be validated using cross-validation Missing Value Handling (TS Data) • Maintenance Data needs attention Duplicate Handling • TS Data: Data with higher deviation from normal may indicate degradation • Maintenance data: May indicate human error Outlier Handling Data Preprocessing 

Feature Engineering (TS Data) • Rolling/Tumbling Aggregate • Need of Aggregation • Data Collection & Prediction frequency may not match • Data over individual time unit is noisy • Needs to be smoothened by aggregating over time windows • Lag Window • “How far in future the model has to predict” influences “how far in past the model has to look back” • Window Size should be validated using cross-validation Aggregation Average Maximum Minimum Median Standard Deviation Variance Count Sum Cumulative Sum Derivate 2nd Derivate Count of outliers 

Feature Engineering • Date • Day • Week • Weekday/Weekend • Month • Quarter • Year • … • Maintenance Data • Days since last failure • Days since last failure because of specific reason • Days since specific part replacement • Days since last maintenance • Static Data • Age of the equipment • Building Type 

• Cross Validation • Split Data in Time Dependent Manner • On Test Data • Split by Time • Separate Train & Test data by the window size • Split by Equipment • Better performance with new equipment • Metrics • Imbalanced Data • High Cost of False Positive Measure Model Performance 

Algorithms Phase I • Simpler Model • Simpler Features Phase II • Complex Features Phase III • Complex Models Multi-class Classification Regression RNN, LSTM RNN, LSTM DNN DNN GBM Random Forest SVM Hidden Markov Chain … GBM RF Regression … 

Model Serving & Monitoring • Serving : Batch Scoring • Monitoring • Compare predictions with Ground Truth (Maintenance Data from Future) • Degradation of model’s performance • Change in the incoming data • Bug in Data Pipeline • Drift in data 

References • Azure AI guide for predictive maintenance solutions • A process for implementing industrial predictive maintenance • A Survey of Predictive Maintenance: Systems, Purposes and Approaches • Rules of ML 

https://speakerdeck.com/arnabbiswas1/predictive-maintenance-in-hvac-industry @arnabbiswas1