Heat transfer methods, systems and compositions

1. A refrigerant comprising at least about 99.5% by weight of a blend of four compounds, said blend consisting of:

from about 46% by weight to less than 48% by weight difluoromethane (HFC-32), from about 11% by weight to about 12% by weight pentafluoroethane (HFC-125),

from about 34% by weight to about 36% by weight trifluoroiodomethane (CF3I) and

from about 5% by weight to about 7% by weight 2,3,3,3-tetrafluoropropene (HF0-1234yf),

wherein the percentages are based on the total weight of the four compounds in the blend and

wherein said refrigerant composition has: (a) a (HFC32+HFO1234yf):(CF3I+HFC125) ratio of from greater than about 1:1 to less than 1.2:1; and (b) an evaporator glide of less than 2° C.

2. The refrigerant of claim 1 wherein said blend consists of:

47% by weight difluoromethane (HFC-32),

12% by weight pentafluoroethane (HFC-125),

35% by weight trifluoroiodomethane (CF3I) and

6% by weight 2,3,3,3-tetrafluoropropene (HF0-1234yf),

wherein the percentages are based on the total weight of the four compounds in the blend.

3. The refrigerant of claim 1 wherein the refrigerant consists of said blend.

4. The refrigerant of claim 1 wherein the weight ratio of (HFC-32+HFO-1234yf):(CF3I+HFC-125) is from greater than about 1.1:1 to about 1.18:1.

5. The refrigerant of claim 1 wherein the weight ratio of HFC-32:HFC-125 from greater than 3.5:1 to about 4:1.

6. A heat transfer composition comprising the refrigerant of claim 1 .

7. The heat transfer composition of claim 6 further comprising a stabilizer comprising a phosphorous compound.

8. The heat transfer composition of claim 7 wherein the stabilizer composition comprises a diene based compound.

9. The heat transfer composition of claim 7 wherein the stabilizer composition comprises farnesene.

10. A heat transfer composition comprising a refrigerant as claimed in claim 1 and a stabilizer composition, wherein the stabilizer composition consists of BHT in an amount of from about 0.001% by weight to about 5% by weight.

11. A heat transfer composition comprising a refrigerant as claimed in claim 1 and a stabilizer composition, wherein the stabilizer composition comprises BHT.

12. The heat transfer composition of claim 11 further comprising a lubricant selected from the group consisting of polyol esters (POEs), polyalkylene glycols (PAGs), PAG oils, silicone oils, mineral oil, alkylbenzenes (ABs), polyvinyl ethers (PVE) and poly(alpha-olefin) (PAO).

13. The heat transfer composition of claim 12 wherein the lubricant is a polyol ester (POE).

14. The heat transfer composition of claim 1 wherein said refrigerant has a Global Warming Potential (GWP) of not greater than 750 and an evaporator glide of less than 1.5° C.

15. A method of cooling comprising including in an air conditioning system the heat transfer composition of claim 13 .

16. The method as claimed in claim 15 wherein the air conditioning system is a mobile air conditioning system.

17. The method as claimed in claim 16 wherein the air conditioning system is a residential air-conditioning system having an evaporator temperature in the range of about 0 to about 10° C.

18. The method as claimed in claim 16 wherein the air conditioning system is a low temperature refrigeration system having an evaporator temperature in the range of about −40 to about −12° C.

19. A method of replacing an existing refrigerant contained in a heat transfer system comprising removing at least a portion of said existing refrigerant from said system, said existing refrigerant being R-410A and replacing at least a portion of said existing refrigerant by introducing into said system a refrigerant according to claim 1 .

20. The heat transfer system of claim 19 wherein the heat transfer system is a low temperature refrigeration system having an evaporator temperature in the range of about −40 to about −12° C. and wherein said refrigerant has an evaporator glide of less than 1.5° C.