To render to disk, simply change the Display Device to a file type, such as openexr. Press the Render to Disk button.
For rendering to deep exr, type in deepexr in the Display Device or you can pick it from the pulldown list next to Display Device. RenderMan for Houdini will automatically output "Ci,a" and its required DisplayChannels. Note that we can render deepexr for both primary and secondary outputs (AOVs).