This response is dependent on the software used.
NatHERS Deemed to Satisfy approach is suitable for all Class 1 buildings.
A class 1b building is a one of the Class 1 building types. A class 1 b hostel cannot exceed 300m2 and is envisaged to be a residence for a number of occupants (12 max) with a number of bedrooms plus shared lounge and kitchen. Accordingly it will have a similar thermal performance profile to a large house. If a Class 1b building design indicates multiple kitchenettes then a NatHERS will not be suitable to substantiate compliance.
HERS is for Classes 1a, 2 & 4. If you want to use the HERS software then it will need to be used as a Performance Solution. If there are other kitchenettes, as in a Class 1 dwelling, then they become Day Time zones.