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Question DetailsAsked on 7/4/2016

what is the best efficient coolant to use for home AC?

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Truly the most efficient - generally therminol or similar high heat capacity heat transfer fluid operating in a geothermal heating/cooling heat pump system with large heat exchanger, which can sometimes attain an energy efficiency rating equivalent to an A/C SEER rating of about 30-40 - versus maximum of a bit over 20 with air-cooled A/C units. But - ground source heat pumps are few and far between. The day will probably come when burial of ground-source or well water-sourced geothermal system will be standard in house construction, but likely dacades away - as is its sister, the ground-contract slab loop heat pump.

The highest efficiency A/C refrigerant fluids are basically ones that are illegal or limited to commercial use because they are ozone-depleting (most fluorocarbon family ones) or dangerous, so cannot be used in home systems. There are a few very exotic gases in rare home air conditioners (mostly foreign sourced), and CO2 is coming into use again, but basically I would not pick a system based on the coolant - buy based on reputation and long-term performance of the manufacturer, SEER rating, installer reputation and expertise, and lastly cost. To compare unit efficiency, the SEER rating (the detailed test one in actual rating declaration, not the rounded-off-to-nearest-whole-number one) for A/C units or the SEER/HSPF factors for heat pumps tell you the efficiency of the units in cooling/heating.

Generally, there are only one or two gases (and associated lubricating oil, which vary by gas and sometimes by manufacturer) which are compatible with a given system and will deliver the rated cooling capacity and efficiency, so in reality you do not really have much of a choice of gases. For instance, if you currently have R-22 Freon (the "old standby"), you cannot use most of the modern non-ozone depleting gases because their operating pressures and/oil lubricating oils are incompatible with your system. Likewise, with new units, they are rated for use with a specific gas (usually R-410a) and only that gas can legally be isntalled in or used in that unit, so when buying a new unit the only way to "choose a gas" is to buy a new system rated for that refrigerant.

I would not worry about what gas is used - for all effects and purposes the variations in installation conditions is usually greater than the efficiency difference caused by different gases. Use what the unit is rated for for optimal performance for that unit, and pay attention to other factors that affect operating efficiency like making sure the outside unit is in an area with free air flow, preferably on the cool side of the house (assuming this is a house cooling, not medically-dictated A/C unit), and in the shade preferably to reduce the amount of cooling that the unit has to do and to let mother nature help with the cooling.

Do NOT fall victim to the TV and web advertising about "new miracle refrigeant which can save you 50% on cooling costs" - these are not real, in many cases are not even approved refrigerant gases at all, may have incompatible or wrong viscosity or no lubricating oil mixed in, and are in many cases an illegal highly flammable gas like propane. Use what the system is rated for.

Answered 4 years ago by LCD

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