Refbase does not appear to offer a special field for the number of volumes which comprise a particular publication. For those who like me, have been looking for a workaround, consider the use of hyphens and forward slashes:

Vol. 1-13: as the hyphen usually denotes a range, this would mean that this publication consists of 13 volumes.
Vol. 5/13: meaning the 5th volume of a total of 13 volumes
Vol. 4-6/13: i.e. volumes 4, 5 and 6 of a total of 13 volumes

I don't know of any workaround for year ranges, except for including each volume individually or noting down the year range in Abstracts field.

(Obviously, the above does not apply to periodicals)