def calc_internal_hours(entries):
    """
    Calculates internal utilizable hours from an array of entry dictionaries
    """
    internal_hours = 0.0
    for entry in entries:
        if entry['project_name'][:22] == "TTS Acq / Internal Acq" and not entry['billable']:
            internal_hours = internal_hours + float(entry['hours_spent'])
    return internal_hours