Compositions, methods and systems which comprise or utilize a multi-component mixture comprising: (a) from about 10% to about 35% by weight of HFC-32; (b) from about 10% to about 35% by weight of HFC-125; (c) from about 20% to about 50% by weight of HFO-1234ze, HFO-1234yf and combinations of these; (d) from about 15% to about 35% by weight of HFC-134a; and optionally (e) up to about 10% by weight of CF3I and up to about 5% by weight of HFCO-1233ze, with the weight percent being based on the total of the components (a)-(e) in the composition.