FanEnergyIndex.h

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#pragma once
 
#include <cmath>
class FanEnergyIndex {
  public:
    FanEnergyIndex(const double flowRate, const double inletPressure, const double outletPressure,
                   const double airDensity, const double motorPower)
        : flowRate(flowRate), inletPressure(inletPressure), outletPressure(outletPressure), airDensity(airDensity),
          motorPower(motorPower) {}
 
    double calculateEnergyIndex() {
        const double pressure         = outletPressure - inletPressure;
        const double referencePower   = (flowRate + 250) * (pressure + 0.4 * (airDensity / 0.075)) / (6343 * 0.66);
        const double kWreferencePower = referencePower * 0.7457;
        const double efficiency1      = 0.96 * std::pow(referencePower / (referencePower + 2.2), 0.05);
        double       efficiency2      = 0.962;
        if (kWreferencePower < 185) {
            efficiency2 = -0.003812 * std::pow(std::log10(kWreferencePower), 4) +
                          0.025834 * std::pow(std::log10(kWreferencePower), 3) +
                          -0.072577 * std::pow(std::log10(kWreferencePower), 2) +
                          0.125559 * std::log10(kWreferencePower) + 0.850274;
        }
 
        return (kWreferencePower * (1 / efficiency1) * (1 / efficiency2)) / motorPower;
    }
 
  private:
    const double flowRate, inletPressure, outletPressure, airDensity, motorPower;
};