def new_mean_temperature(area, height_external, temperature_external, heat):
    """
    Calculates a new mean temperature for the volume.
    :param area: in m^2
    :param height_external: in m
    :param temperature_external: in K
    :param heat: in J
    :return: temperature in K
    """

    volume_air = area * height_external
    specific_heat_capacity = 1005  # J/kgK
    density_air = 1.29 * 273 / temperature_external  # kg/m^3
    energy_air = volume_air * specific_heat_capacity * density_air * temperature_external  # J

    return (energy_air + heat)/(volume_air * density_air * specific_heat_capacity)