def calc_theta_int_inc(theta_int_ini, delta_theta_int_inc):
    """
    Eq. (1) in [prEN 15316-2:2014]

    :param theta_int_ini: temperature [C]
    :type theta_int_ini: double
    
    :param delta_theta_int_inc: temperature [C]
    :type delta_theta_int_inc: double
    
    :return: sum of temperatures [C]
    :rtype: double
    """

    return theta_int_ini + delta_theta_int_inc