class NECB2017

  # Check if ERV is required on this airloop.
  #
  # @return [Bool] Returns true if required, false if not.
  def air_loop_hvac_energy_recovery_ventilator_required?(air_loop_hvac, climate_zone)

    erv_required = nil

    # ERV Not Applicable for AHUs that have no OA intake.
    oa_system = nil
    controller_oa = nil
    if air_loop_hvac.airLoopHVACOutdoorAirSystem.is_initialized
      oa_system = air_loop_hvac.airLoopHVACOutdoorAirSystem.get
      controller_oa = oa_system.getControllerOutdoorAir
    else
      OpenStudio.logFree(OpenStudio::Info, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name}, ERV not applicable because it has no OA intake.")
      return false
    end

    # Get the AHU design supply air flow rate
    dsn_flow_m3_per_s = nil
    if air_loop_hvac.designSupplyAirFlowRate.is_initialized
      dsn_flow_m3_per_s = air_loop_hvac.designSupplyAirFlowRate.get
    elsif air_loop_hvac.autosizedDesignSupplyAirFlowRate.is_initialized
      dsn_flow_m3_per_s = air_loop_hvac.autosizedDesignSupplyAirFlowRate.get
    else
      OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{air_loop_hvac.name} design supply air flow rate is not available, cannot apply efficiency standard.")
      return false
    end

    # Get the minimum OA flow rate
    min_oa_flow_m3_per_s = nil
    if controller_oa.minimumOutdoorAirFlowRate.is_initialized
      min_oa_flow_m3_per_s = controller_oa.minimumOutdoorAirFlowRate.get
    elsif controller_oa.autosizedMinimumOutdoorAirFlowRate.is_initialized
      min_oa_flow_m3_per_s = controller_oa.autosizedMinimumOutdoorAirFlowRate.get
    else
      OpenStudio.logFree(OpenStudio::Warn, 'openstudio.standards.AirLoopHVAC', "For #{controller_oa.name}: minimum OA flow rate is not available, cannot apply efficiency standard.")
      return false
    end

    hdd = BTAP::Environment::WeatherFile.new(air_loop_hvac.model.weatherFile.get.path.get).hdd18
    flow = min_oa_flow_m3_per_s
    oaf = min_oa_flow_m3_per_s / dsn_flow_m3_per_s
    erv_required = eval(self.get_standards_formula('heat_recovery_requirement_formula'))

    return erv_required
  end

end