@staticmethod
def _calc_parallel_connection(element_list, omega):
    """Parallel connection of walls according to VDI 6007

        Calculates the parallel connection of wall elements according to VDI
        6007, resulting in R1 and C1 (equation 23, 24).

        Parameters
        ----------
        element_list : list
            List of inner or outer walls
        omega : float
            VDI 6007 frequency

        Returns
        ----------
        r1 : float [K/W]
            VDI 6007 resistance for all inner or outer walls
        c1 : float [K/W]
            VDI 6007 capacity all for inner or outer walls
        """
    for wall_count in range(len(element_list) - 1):
        if wall_count == 0:
            r1 = (element_list[wall_count].r1 * element_list[wall_count].c1 **
                2 + element_list[wall_count + 1].r1 * element_list[
                wall_count + 1].c1 ** 2 + omega ** 2 * element_list[
                wall_count].r1 * element_list[wall_count + 1].r1 * (
                element_list[wall_count].r1 + element_list[wall_count + 1].
                r1) * element_list[wall_count].c1 ** 2 * element_list[
                wall_count + 1].c1 ** 2) / ((element_list[wall_count].c1 +
                element_list[wall_count + 1].c1) ** 2 + omega ** 2 * (
                element_list[wall_count].r1 + element_list[wall_count + 1].
                r1) ** 2 * element_list[wall_count].c1 ** 2 * element_list[
                wall_count + 1].c1 ** 2)
            c1 = ((element_list[wall_count].c1 + element_list[wall_count + 
                1].c1) ** 2 + omega ** 2 * (element_list[wall_count].r1 +
                element_list[wall_count + 1].r1) ** 2 * element_list[
                wall_count].c1 ** 2 * element_list[wall_count + 1].c1 ** 2) / (
                element_list[wall_count].c1 + element_list[wall_count + 1].
                c1 + omega ** 2 * (element_list[wall_count].r1 ** 2 *
                element_list[wall_count].c1 + element_list[wall_count + 1].
                r1 ** 2 * element_list[wall_count + 1].c1) * element_list[
                wall_count].c1 * element_list[wall_count + 1].c1)
        else:
            r1x = r1
            c1x = c1
            r1 = (r1x * c1x ** 2 + element_list[wall_count + 1].r1 * 
                element_list[wall_count + 1].c1 ** 2 + omega ** 2 * r1x *
                element_list[wall_count + 1].r1 * (r1x + element_list[
                wall_count + 1].r1) * c1x ** 2 * element_list[wall_count + 
                1].c1 ** 2) / ((c1x + element_list[wall_count + 1].c1) ** 2 +
                omega ** 2 * (r1x + element_list[wall_count + 1].r1) ** 2 *
                c1x ** 2 * element_list[wall_count + 1].c1 ** 2)
            c1 = ((c1x + element_list[wall_count + 1].c1) ** 2 + omega ** 2 *
                (r1x + element_list[wall_count + 1].r1) ** 2 * c1x ** 2 * 
                element_list[wall_count + 1].c1 ** 2) / (c1x + element_list
                [wall_count + 1].c1 + omega ** 2 * (r1x ** 2 * c1x + 
                element_list[wall_count + 1].r1 ** 2 * element_list[
                wall_count + 1].c1) * c1x * element_list[wall_count + 1].c1)
    return r1, c1
