Module: PrototypeFan

Included in:
Standard
Defined in:
lib/openstudio-standards/prototypes/common/objects/Prototype.Fan.rb

Overview

Prototype fan calculation methods that are the same regardless of fan type. These methods are available to FanConstantVolume, FanOnOff, FanVariableVolume, and FanZoneExhaust

Fan collapse

Instance Method Details

#prototype_fan_apply_prototype_fan_efficiency(fan) ⇒ Bool

Sets the fan motor efficiency using the Prototype model assumptions for fan impeller efficiency, motor type, and a 10% safety factor on brake horsepower.


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# File 'lib/openstudio-standards/prototypes/common/objects/Prototype.Fan.rb', line 12

def prototype_fan_apply_prototype_fan_efficiency(fan)
  # Get the max flow rate from the fan.
  maximum_flow_rate_m3_per_s = nil
  if fan.maximumFlowRate.is_initialized
    maximum_flow_rate_m3_per_s = fan.maximumFlowRate.get
  elsif fan.autosizedMaximumFlowRate.is_initialized
    maximum_flow_rate_m3_per_s = fan.autosizedMaximumFlowRate.get
  else
    OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.Fan', "For #{fan.name} max flow rate is not hard sized, cannot apply efficiency standard.")
    return false
  end

  # Convert max flow rate to cfm
  maximum_flow_rate_cfm = OpenStudio.convert(maximum_flow_rate_m3_per_s, 'm^3/s', 'cfm').get

  # Get the pressure rise from the fan
  pressure_rise_pa = fan.pressureRise
  pressure_rise_in_h2o = OpenStudio.convert(pressure_rise_pa, 'Pa', 'inH_{2}O').get

  # Get the default impeller efficiency
  fan_impeller_eff = fan_baseline_impeller_efficiency(fan)

  # Calculate the Brake Horsepower
  brake_hp = (pressure_rise_in_h2o * maximum_flow_rate_cfm) / (fan_impeller_eff * 6356)
  allowed_hp = brake_hp * 1.1 # Per PNNL document #TODO add reference
  if allowed_hp > 0.1
    allowed_hp = allowed_hp.round(2) + 0.0001
  elsif allowed_hp < 0.01
    allowed_hp = 0.01
  end

  # Minimum motor size for efficiency lookup
  # is 1 HP unless the motor serves an exhaust fan,
  # a powered VAV terminal, or a fan coil unit.
  unless fan_small_fan?(fan)
    if allowed_hp < 1.0
      allowed_hp = 1.01
    end
  end

  # Find the motor efficiency
  motor_eff, nominal_hp = fan_standard_minimum_motor_efficiency_and_size(fan, allowed_hp)

  # Calculate the total fan efficiency
  total_fan_eff = fan_impeller_eff * motor_eff

  # Set the total fan efficiency and the motor efficiency
  if fan.to_FanZoneExhaust.is_initialized
    fan.setFanEfficiency(total_fan_eff)
  else
    fan.setFanEfficiency(total_fan_eff)
    fan.setMotorEfficiency(motor_eff)
  end

  OpenStudio.logFree(OpenStudio::Info, 'openstudio.standards.Fan', "For #{fan.name}: allowed_hp = #{allowed_hp.round(2)}HP; motor eff = #{(motor_eff * 100).round(2)}%; total fan eff = #{(total_fan_eff * 100).round}% based on #{maximum_flow_rate_cfm.round} cfm.")

  return true
end