Calibration in OptiMiser Commercial

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    Gamaliel Lodge
    Keymaster

    The calibration page allows the auditor to compare weather normalized utility bills to modeled utility usage.
    Model calibration is very important to ensure accuracy of energy savings estimation. Modelled annual total
    electricity and gas use within ±10% of the utility bill is considered an acceptable calibration. Follow these steps
    to make best use of this tool

    1. Enter completes 12 month set of records for all energy sources in the Utility Bills section:
      • Use exact meter read dates when available
      • Enter annual totals for delivery fuels, unless the tank is topped off reliably and frequently
    2. Use the Electric and Therm Scale Factor controls for partial audits where only a portion of the
      energy consuming systems are modeled:

      • The Scale Factor controls apply a multiplier to the weather normalized utility bills used in the calibration.
      • This is appropriate when the utility consumption in the bills represents more systems or zones
        than you have modeled
      •  For example:
        • If you have modeled only 4 representative units of a 20 unit building, you might apply
          a scale factor of 0.20 to the whole building bills.
        • If you have modeled only the heating systems for a fuel that also supplies DHW
          systems, you might estimate the fraction of the annual total the is attributable to
          heat.
      • Adjustments to the Scale Factors should be made based on your assessment of the scope of
        the model as compared with the systems/zones covered by the bills
      • Adjustments should not be based on a comparison of the model results to the utility totals.  
    3. Adjust the model assumptions to calibrate the model to the appropriately scaled bills:
      • Any model input that has a significant factor of uncertainty should be considered
        during calibration.  Following are some of the most important:
      • Space heating and/or cooling temperature setpoint during occupied and/or
        unoccupied period
      • Minimum Cold/Hot Air Flow Ratio (for Variable Air Volume Boxes)
      • System Operation Schedule
      • Minimum outside air ratio during occupied and/or unoccupied period
      • Supply Air Temperature Setpoint
      • System Efficiency
      • System Oversize Factor 
        • This is especially important because OptiMiser reverse engineers the design
          load and building UA from the system capacities. It’s common mechanical
          equipment capacity does not line up well with space loads due to lack of
          proper design load calculation, design cautions, building/space function
          changes overtime, weatherization improvements and etc. System oversize
          factor therefore becomes an important calibration factor. However, one
          should exhaust adjustment of all other factors listed above before turning to
          this factor. Please be aware that cautions should be used when making large
          adjustment to this factor, especially when there is no evidence for the
          discrepancy.
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