[Koha] Reference books & books for loan

In our library, there's a big part of books which a patron can read inside of the library but which are not available for loan. There's another part of the library which contains books for loan. I would like to ask how is it possible to distinguish these categories in Koha. If I simply check the "Not for loan" field for items which are for referene only, the OPAC search summary displays "No copies available" (but they are available, but not for loan). I could also define that for ex. that books are not for loan (in the "Item types and circulation" settings). But in this case I can't distinguish books which are for loan. Would anyone know how to resolve this difficulty? Thanks Ondrej Mleca Casa Balthasar Roma