Common issues and anomalies

Here’s a list of common anomalies that may arise in energy models, particularly during QC and validation phases. Each anomaly may indicate issues with model inputs, assumptions, or software configurations.

Common issues and anomalies

Unmet Load Hours

Description: Excessive hours where the model cannot maintain temperature setpoints.

Possible Causes: Undersized HVAC equipment, incorrect thermostat schedules, improper zoning, or extreme weather file assumptions.

High Fan Energy Use During Off-Hours

Description: Fans operate at high loads during unoccupied times or overnight.

Possible Causes: Incorrect fan schedules, lack of demand control ventilation, or unintentional overrides in control settings.

Inconsistent Heating and Cooling Peaks

Description: Cooling or heating loads peaking unexpectedly during mild weather or unoccupied periods.

Possible Causes: Incorrect thermostat setpoints, schedule errors, or unrealistic internal load assumptions.

Excessive Lighting or Equipment Loads

Description: Lighting and equipment energy consumption significantly exceeds typical or design values.

Possible Causes: Overestimated lighting power density, equipment density, or schedule errors that assume continuous operation.

HVAC Cycling or Short Cycling

Description: Frequent on/off cycling of HVAC equipment, leading to inefficiency.

Possible Causes: Oversized HVAC systems, tight control deadbands, or inadequate thermal mass in the building model.

Unusual Seasonal Energy Use Patterns

Description: Energy use does not align with seasonal trends (e.g., high heating loads in summer or high cooling loads in winter).

Possible Causes: Incorrect weather file, unrealistic occupancy patterns, or reversed heating/cooling equipment configurations.

Disproportionate Ventilation Loads

Description: Excessive energy use attributed to ventilation even during times of low occupancy.

Possible Causes: High ventilation rates, incorrect outdoor air schedules, or lack of demand-controlled ventilation settings.

Low or Zero Energy Use for Certain Systems

Description: Specific systems (e.g., heating or cooling) showing zero or abnormally low energy consumption.

Possible Causes: Missing or incorrect equipment definitions, faulty schedules, or incomplete input data.

Unrealistic Internal Temperatures or Humidity Levels

Description: Temperatures or humidity levels that are consistently too high or too low, outside comfort ranges.

Possible Causes: Incorrect setpoints, improper HVAC sizing, or lack of dehumidification/humidification controls in humid or dry climates.

Peak Demand Occurs at Unexpected Times

Description: Peak energy demand shows up at unusual times, such as early morning or late evening.

Possible Causes: Incorrect scheduling of loads, unanticipated start-up loads, or equipment ramp-up issues.

Overestimated or Underestimated Renewable Energy Production

Description: Modeled renewable generation (e.g., PV or wind) is significantly higher or lower than expected.

Possible Causes: Incorrect solar irradiance or wind speed data, improper system orientation, or system efficiency inputs that don’t match specifications.

High Infiltration or Envelope Loads

Description: Excessive heating or cooling loads attributable to infiltration.

Possible Causes: Overestimated infiltration rates, missing or low insulation values, or poor envelope construction assumptions.

Inconsistent Load Distribution Among Zones

Description: Interior zones have similar loads as perimeter zones, or vice versa, which is atypical.

Possible Causes: Incorrect zoning configurations, uniform internal load assumptions, or misassigned internal gains.

Extreme Equipment Efficiency (COP or EER) Values

Description: COP (Coefficient of Performance) or EER (Energy Efficiency Ratio) values fall outside typical ranges.

Possible Causes: Misconfigured equipment parameters, faulty library data, or input errors in efficiency values.

Unreasonable Schedules for Occupancy, Lighting, or Equipment

Description: Energy use remains constant regardless of time of day or occupancy pattern.

Possible Causes: Incorrect or generic schedules that do not align with actual building usage patterns.