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I am not very familiar with this model but I can give you some insight into what I see in code.

1) How the actual reject heat by the condenser is calculated?

The description above says "The condenser is modeled via the heat rejection performance curve." which led me to this input field in the IDD. So I would think the user would provide a performance curve that is a function of the temperature difference between the refrigerant condensing temperature and ambient.

Refrigeration:Condenser:AirCooled, \memo Air cooled condenser for a refrigeration system (Refrigeration:System). A2 , \field Rated Effective Total Heat Rejection Rate Curve Name \note Rating as per ARI 460 \note Be sure the rating corresponds to the correct refrigerant \type object-list \object-list UnivariateFunctions \note HeatRejection(W)=C1 +C2(Condensing Temp - Entering Air Temp, deg C) \note Will be adjusted for elevation automatically

2) What does E stand for in the correction factor of the rated heat rejected (1 −7.17E − 5 × Elevation)?

The E is for exponential notation "E-5" or 0.0000717. This appears to be an empirical correlation to correct the heat rejection rate for elevation. Maybe ARI 460 will discuss this correlation?

3) what is the WetCoilFactor?

I found this comment in code and believe the WetCoilFactor is a way to translate between the European standard ratings for Nominal and Standard capacity. This excerpt is from the Engineering Reference:

18.2.5.2 European Standard Ratings Five standard rating conditions have been defined in a European rating system. The capacity is reported at the rating condition as either the “Nominal” or “Standard” capacity. The “Nominal” capacity includes both latent and sensible loads and the “Standard” capacity includes sensible loads only. “Wet Coil Factors” are provided with the ratings to translate between the two, along with a chart giving the impact of Air Inlet Temperature on the Wet Coil Factor. The user identifies the rating condition used and whether the capacity input is “Nominal” or “Standard”. These rating factors, along with the air inlet temperature and evaporating temperature are used to calculate the actual cooling capacity.

Comment found in the refrigeration model code. Note that the PARAMETER variables are arrays with for example 1.35 being EuropeanWetCoilFactor[0] and 1.0 being EuropeanWetCoilFactor[4] (which I don't see being used here but is used elsewhere).

case SHRCorrectionType::European: {
    // With European ratings, either start with rated total sensible capacity or rated total capacity
    //    If rated total capacity is used, 'get input'
    //    translated it to rated total sensible capacity using
    //    PARAMETER ::EuropeanWetCoilFactor = (/1.35D0, 1.15D0,  1.05D0,  1.01D0,   1.0D0/)
    //    That sensible capacity rating was then turned to a rated UnitLoadFactor using
    //    the rated temperature difference. That sensible rating was also corrected
    //    for refrigerant and fin material in 'get input' and is given as UnitLoadFactor
    //  The total (sens + latent) capacity is equal to that * DT1 * WetCoilFactor(TcoilIn)
    //    Sensible capacity max already has DT1, just need WetCoilFactor(TcoilIn)
    // PARAMETER ::EuropeanWetCoilFactor = (/1.35D0, 1.15D0,  1.05D0,  1.01D0,   1.0D0/)
    // PARAMETER ::EuropeanAirInletTemp  = (/10.0D0,  0.0D0, -18.0D0, -25.0D0, -34.0D0/)
    // PARAMETER ::EuropeanEvapTemp      = (/ 0.0D0, -8.0D0, -25.0D0, -31.0D0, -40.0D0/)
    // PARAMETER ::EuropeanDT1           = (/10.0D0,  8.0D0,   7.0D0,   7.0D0,   6.0D0/)
    if (CoilInletTemp <= -25.0) {
        SHRCorrection = 1.0;
    } else if (CoilInletTemp > -25.0 && CoilInletTemp <= 0.0) {
        SHRCorrection = (EuropeanWetCoilFactor[1] - EuropeanWetCoilFactor[3]) / (EuropeanAirInletTemp[1] - EuropeanAirInletTemp[3]) *
                            (EuropeanAirInletTemp[1] - CoilInletTemp) +
                        EuropeanWetCoilFactor[3];
    } else if (CoilInletTemp > 0.0 && CoilInletTemp <= 5.0) {
        SHRCorrection = (EuropeanWetCoilFactor[0] - EuropeanWetCoilFactor[1]) / (EuropeanAirInletTemp[0] - EuropeanAirInletTemp[1]) *
                            (EuropeanAirInletTemp[0] - CoilInletTemp) +
                        EuropeanWetCoilFactor[1];
    } else if (CoilInletTemp > 5.0) {
        SHRCorrection = EuropeanWetCoilFactor[0];
    } // calc correction as a function of coil inlet temperature

I am not very familiar with this model but I can give you some insight into what I see in code.

1) How the actual reject heat by the condenser is calculated?

The description above says "The condenser is modeled via the heat rejection performance curve." which led me to this input field in the IDD. So I would think the user would provide a performance curve that is a function of the temperature difference between the refrigerant condensing temperature and ambient.

Refrigeration:Condenser:AirCooled,
         \memo Air cooled condenser for a refrigeration system (Refrigeration:System).
  A2 ,  \field Rated Effective Total Heat Rejection Rate Curve Name
        \note Rating as per ARI 460
        \note Be sure the rating corresponds to the correct refrigerant
        \type object-list
        \object-list UnivariateFunctions
        \note HeatRejection(W)=C1 +C2(Condensing Temp - Entering Air Temp, deg C)
        \note Will be adjusted for elevation automatically
automatically

case SHRCorrectionType::European: {
    // With European ratings, either start with rated total sensible capacity or rated total capacity
    //    If rated total capacity is used, 'get input'
    //    translated it to rated total sensible capacity using
    //    PARAMETER ::EuropeanWetCoilFactor = (/1.35D0, 1.15D0,  1.05D0,  1.01D0,   1.0D0/)
    //    That sensible capacity rating was then turned to a rated UnitLoadFactor using
    //    the rated temperature difference. That sensible rating was also corrected
    //    for refrigerant and fin material in 'get input' and is given as UnitLoadFactor
    //  The total (sens + latent) capacity is equal to that * DT1 * WetCoilFactor(TcoilIn)
    //    Sensible capacity max already has DT1, just need WetCoilFactor(TcoilIn)
    // PARAMETER ::EuropeanWetCoilFactor = (/1.35D0, 1.15D0,  1.05D0,  1.01D0,   1.0D0/)
    // PARAMETER ::EuropeanAirInletTemp  = (/10.0D0,  0.0D0, -18.0D0, -25.0D0, -34.0D0/)
    // PARAMETER ::EuropeanEvapTemp      = (/ 0.0D0, -8.0D0, -25.0D0, -31.0D0, -40.0D0/)
    // PARAMETER ::EuropeanDT1           = (/10.0D0,  8.0D0,   7.0D0,   7.0D0,   6.0D0/)
    if (CoilInletTemp <= -25.0) {
        SHRCorrection = 1.0;
    } else if (CoilInletTemp > -25.0 && CoilInletTemp <= 0.0) {
        SHRCorrection = (EuropeanWetCoilFactor[1] - EuropeanWetCoilFactor[3]) / (EuropeanAirInletTemp[1] - EuropeanAirInletTemp[3]) *
                            (EuropeanAirInletTemp[1] - CoilInletTemp) +
                        EuropeanWetCoilFactor[3];
    } else if (CoilInletTemp > 0.0 && CoilInletTemp <= 5.0) {
        SHRCorrection = (EuropeanWetCoilFactor[0] - EuropeanWetCoilFactor[1]) / (EuropeanAirInletTemp[0] - EuropeanAirInletTemp[1]) *
                            (EuropeanAirInletTemp[0] - CoilInletTemp) +
                        EuropeanWetCoilFactor[1];
    } else if (CoilInletTemp > 5.0) {
        SHRCorrection = EuropeanWetCoilFactor[0];
    } // calc correction as a function of coil inlet temperature