Module: Fan

Included in:
OpenStudio::Model::FanConstantVolume, OpenStudio::Model::FanOnOff, OpenStudio::Model::FanVariableVolume, OpenStudio::Model::FanZoneExhaust
Defined in:
lib/openstudio-standards/standards/Standards.Fan.rb

Overview

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

Instance Method Summary collapse

Instance Method Details

#adjust_pressure_rise_to_meet_fan_power(target_fan_power) ⇒ Bool

Adjust the fan pressure rise to hit the target fan power (W). Keep the fan impeller and motor efficiencies static.

Parameters:

  • target_fan_power (Double) —

    the target fan power in W

Returns:

  • (Bool) —

    true if successful, false if not



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 95

def adjust_pressure_rise_to_meet_fan_power(target_fan_power)

  # Get design supply air flow rate (whether autosized or hard-sized)

  dsn_air_flow_m3_per_s = 0
  if self.autosizedMaximumFlowRate.is_initialized
    dsn_air_flow_m3_per_s = self.autosizedMaximumFlowRate.get
  else
    dsn_air_flow_m3_per_s = self.maximumFlowRate.get
  end  

  # Get the current fan power

  current_fan_power_w = self.fanPower

  # Get the current pressure rise (Pa)

  pressure_rise_pa = self.pressureRise
  
  # Get the total fan efficiency

  fan_total_eff = self.fanEfficiency

  # Calculate the new fan pressure rise (Pa)

  new_pressure_rise_pa = target_fan_power * fan_total_eff / dsn_air_flow_m3_per_s
  new_pressure_rise_in_h2o = OpenStudio.convert(new_pressure_rise_pa, 'Pa','inH_{2}O').get
  
  # Set the new pressure rise

  self.setPressureRise(new_pressure_rise_pa)
  
  # Calculate the new power

  new_power_w = self.fanPower
  
  OpenStudio::logFree(OpenStudio::Info, "openstudio.standards.Fan", "For #{self.name}: pressure rise = #{new_pressure_rise_in_h2o.round(1)} in w.c., power = #{new_power_w.round} W // #{self.motorHorsepower.round(2)}HP.")
  
  return true

end

#baselineImpellerEfficiency(template) ⇒ Double

TODO:

Add fan type to data model and modify this method

Determines the baseline fan impeller efficiency based on the specified fan type.

Returns:

  • (Double) —

    impeller efficiency (0.0 to 1.0)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 252

def baselineImpellerEfficiency(template)

  # Assume that the fan efficiency is 65% for normal fans

  # and 55% for small fans (like exhaust fans).

  # TODO add fan type to fan data model

  # and infer impeller efficiency from that?

  # or do we always assume a certain type of

  # fan impeller for the baseline system?

  # TODO check COMNET and T24 ACM and PNNL 90.1 doc

  fan_impeller_eff = 0.65

  if self.is_small_fan
    fan_impeller_eff = 0.55
  end

  return fan_impeller_eff

end

#brakeHorsepower ⇒ Double

Determines the brake horsepower of the fan based on fan power and fan motor efficiency.

Returns:

  • (Double) —

    brake horsepower @units horsepower (hp)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 165

def brakeHorsepower()

  # Get the fan motor efficiency

  existing_motor_eff = 0.7
  if self.to_FanZoneExhaust.empty?
    existing_motor_eff = self.motorEfficiency
  end

  # Get the fan power (W)

  fan_power_w = self.fanPower
  
  # Calculate the brake horsepower (bhp)

  fan_bhp = fan_power_w * existing_motor_eff / 746
  
  return fan_bhp

end

#changeImpellerEfficiency(impeller_eff) ⇒ Object

Changes the fan impeller efficiency and also the fan total efficiency at the same time, preserving the motor efficiency.

Parameters:

  • impeller_eff (Double) —

    impeller efficiency (0.0 to 1.0)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 231

def changeImpellerEfficiency(impeller_eff)
  
  # Get the existing motor efficiency

  existing_motor_eff = 0.7
  if self.to_FanZoneExhaust.empty?
    existing_motor_eff = self.motorEfficiency
  end

  # Calculate the new total efficiency

  new_total_eff = existing_motor_eff * impeller_eff
  
  # Set the revised motor and total fan efficiencies

  self.setFanEfficiency(new_total_eff)

end

#changeMotorEfficiency(motor_eff) ⇒ Object

Changes the fan motor efficiency and also the fan total efficiency at the same time, preserving the impeller efficiency.

Parameters:

  • motor_eff (Double) —

    motor efficiency (0.0 to 1.0)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 204

def changeMotorEfficiency(motor_eff)
  
  # Calculate the existing impeller efficiency

  existing_motor_eff = 0.7
  if self.to_FanZoneExhaust.empty?
    existing_motor_eff = self.motorEfficiency
  end
  existing_total_eff = self.fanEfficiency
  existing_impeller_eff = existing_total_eff / existing_motor_eff
  
  # Calculate the new total efficiency

  new_total_eff = motor_eff * existing_impeller_eff
  
  # Set the revised motor and total fan efficiencies

  if self.to_FanZoneExhaust.is_initialized
    self.setFanEfficiency(new_total_eff)
  else
    self.setFanEfficiency(new_total_eff)
    self.setMotorEfficiency(motor_eff)
  end

end

#fanPower ⇒ Double

Determines the fan power (W) based on flow rate, pressure rise, and total fan efficiency(impeller eff * motor eff)

Returns:

  • (Double) —

    fan power @units Watts (W)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 135

def fanPower()
  
  # Get design supply air flow rate (whether autosized or hard-sized)

  dsn_air_flow_m3_per_s = 0
  if self.autosizedMaximumFlowRate.is_initialized
    dsn_air_flow_m3_per_s = self.autosizedMaximumFlowRate.get
  else
    dsn_air_flow_m3_per_s = self.maximumFlowRate.get
  end

  # Get the total fan efficiency,

  # which in E+ includes both motor and

  # impeller efficiency.

  fan_total_eff = self.fanEfficiency
  
  # Get the pressure rise (Pa)

  pressure_rise_pa = self.pressureRise
  
  # Calculate the fan power (W)

  fan_power_w = pressure_rise_pa * dsn_air_flow_m3_per_s / fan_total_eff
  
  return fan_power_w

end

#is_small_fan ⇒ Bool

Zone exhaust fans, fan coil unit fans, and powered VAV terminal fans all count as small fans and get different impeller efficiencies and motor efficiencies than other fans

Returns:

  • (Bool) —

    returns true if it is a small fan, false if not



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 316

def is_small_fan()

  is_small = false

  # Exhaust fan

  if self.to_FanZoneExhaust.is_initialized
    is_small = true
  # Fan coil unit

  elsif self.containingZoneHVACComponent.is_initialized
    zone_hvac = self.containingZoneHVACComponent.get
    if zone_hvac.to_ZoneHVACFourPipeFanCoil.is_initialized
      is_small = true
    end
  # Powered VAV terminal

  elsif self.containingHVACComponent.is_initialized
    zone_hvac = self.containingHVACComponent.get
    if zone_hvac.to_AirTerminalSingleDuctParallelPIUReheat.is_initialized || zone_hvac.to_AirTerminalSingleDuctSeriesPIUReheat.is_initialized
      is_small = true
    end
  end  

  return is_small

end

#motorHorsepower ⇒ Double

Determines the horsepower of the fan motor, including motor efficiency and fan impeller efficiency.

Returns:

  • (Double) —

    horsepower



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 188

def motorHorsepower()

  # Get the fan power

  fan_power_w = self.fanPower
  
  # Convert to HP

  fan_hp = fan_power_w / 745.7 # 745.7 W/HP

  
  return fan_hp

end

#rated_w_per_cfm ⇒ Double

Find the actual rated fan power per flow (W/CFM) by querying the sql file

Returns:

  • (Double) —

    rated power consumption per flow @units Watts per CFM (W*min/ft^3)



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 346

def rated_w_per_cfm()

  # Get design power (whether autosized or hard-sized)

  rated_power_w = self.model.getAutosizedValueFromEquipmentSummary(self, 'Fans', 'Rated Electric Power', 'W')
  if rated_power_w.is_initialized
    rated_power_w = rated_power_w.get
  else
    rated_power_w = self.fanPower
    OpenStudio::logFree(OpenStudio::Warn, "openstudio.standards.Pump", "For #{self.name}, could not find rated fan power from Equipment Summary. Will calculate it based on current pressure rise and total fan efficiency")
  end

  if self.autosizedMaximumFlowRate.is_initialized
    max_m3_per_s = self.autosizedMaximumFlowRate.get
  elsif self.maximumFlowRate.is_initialized
    max_m3_per_s = self.ratedFlowRate.get
  else
    OpenStudio::logFree(OpenStudio::Error, "openstudio.standards.Pump", "For #{self.name}, could not find fan Maximum Flow Rate, cannot determine w per cfm correctly.")
    return false
  end

  rated_w_per_m3s = rated_power_w / max_m3_per_s

  rated_w_per_gpm = OpenStudio::convert(rated_w_per_m3s, 'W*s/m^3', 'W*min/ft^3').get

  return rated_w_per_gpm


end

#set_standard_minimum_motor_efficiency(template, allowed_bhp) ⇒ Object 



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 71

def set_standard_minimum_motor_efficiency(template, allowed_bhp)
  
  # Find the motor efficiency

  motor_eff, nominal_hp = standard_minimum_motor_efficiency_and_size(template, allowed_bhp)

  # Change the motor efficiency

  # but preserve the existing fan impeller

  # efficiency.

  self.changeMotorEfficiency(motor_eff)
  
  # Calculate the total motor HP

  motor_hp = self.motorHorsepower
  
  OpenStudio::logFree(OpenStudio::Info, 'openstudio.standards.Fan', "For #{self.name}: motor nameplate = #{nominal_hp}HP, motor eff = #{(motor_eff*100).round(2)}%.")
  
  return true    

end

#setStandardEfficiency(template) ⇒ Bool

Sets the fan motor efficiency based on the standard. Assumes 65% fan efficiency and 4-pole, enclosed motor.

Returns:

  • (Bool) —

    true if successful, false if not



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 10

def setStandardEfficiency(template)
  
  # Get the max flow rate from the fan.

  maximum_flow_rate_m3_per_s = nil
  if self.maximumFlowRate.is_initialized
    maximum_flow_rate_m3_per_s = self.maximumFlowRate.get
  elsif self.autosizedMaximumFlowRate.is_initialized
    maximum_flow_rate_m3_per_s = self.autosizedMaximumFlowRate.get
  else
    OpenStudio::logFree(OpenStudio::Warn, 'openstudio.standards.Fan', "For #{self.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 = self.pressureRise
  pressure_rise_in_h2o = OpenStudio.convert(pressure_rise_pa, 'Pa','inH_{2}O').get
  
  # Get the default impeller efficiency

  fan_impeller_eff = self.baselineImpellerEfficiency(template)
  
  # 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 self.is_small_fan
    if allowed_hp < 1.0
      allowed_hp = 1.01
    end
  end
  
  # Find the motor efficiency

  motor_eff, nominal_hp = standard_minimum_motor_efficiency(template, 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 self.to_FanZoneExhaust.is_initialized
    self.setFanEfficiency(total_fan_eff)
  else
    self.setFanEfficiency(total_fan_eff)
    self.setMotorEfficiency(motor_eff)
  end
  
  OpenStudio::logFree(OpenStudio::Info, 'openstudio.standards.Fan', "For #{self.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

#standard_minimum_motor_efficiency_and_size(template, motor_bhp) ⇒ Double

Determines the minimum fan motor efficiency for a given motor bhp. This should be the total brake horsepower with any desired safety factor already included. This method

Parameters:

  • motor_bhp (Double) —

    motor brake horsepower (hp)

Returns:

  • (Double) —

    minimum motor efficiency (0.0 to 1.0), nominal HP



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# File 'lib/openstudio-standards/standards/Standards.Fan.rb', line 277

def standard_minimum_motor_efficiency_and_size(template, motor_bhp)

  fan_motor_eff = 0.85
  nominal_hp = motor_bhp

  # Lookup the minimum motor efficiency

  motors = $os_standards["motors"]
  
  # Assuming all fan motors are 4-pole ODP

  search_criteria = {
    "template" => template,
    "number_of_poles" => 4.0,
    "type" => "Enclosed",
  }
  
  motor_properties = self.model.find_object(motors, search_criteria, motor_bhp)
  if motor_properties.nil?
    OpenStudio::logFree(OpenStudio::Error, "openstudio.standards.Fan", "For #{self.name}, could not find motor properties using search criteria: #{search_criteria}, motor_bhp = #{motor_bhp} hp.")
    return [fan_motor_eff, nominal_hp]
  end
 
  fan_motor_eff = motor_properties["nominal_full_load_efficiency"]  
  nominal_hp = motor_properties["maximum_capacity"].to_f.round(1)
  # Round to nearest whole HP for niceness

  if nominal_hp >= 2
    nominal_hp = nominal_hp.round
  end

  # TODO Add exception for small 


  return [fan_motor_eff, nominal_hp]

end