Chillers - that is, encompassing cold and not entirely warm purposes (3,6)

'chillers' is the definition.

'encompassing cold and not entirely warm purposes' is the wordplay.
'encompassing cold' becomes 'ice' (I've seen this before. I am not sure about the 'encompassing' bit.**).
'and' means one lot of letters go next to another.
'not entirely' means to remove the last letter.
'warm' becomes 'hot' ('hot' can be a synonym of 'warm').
'purposes' becomes 'uses' ('use' can be a synonym of 'purpose').
'hot' with its last letter taken off is 'ho'.
'ice'+'ho'+'uses'='ICE HOUSES'

'that is' acts as a link.