Answering a Homeowner’s Question on R-410A System Efficiency

How can one refrigerant be more efficient than another?

Air conditioning system manufacturers have always strived to improve their system’s overall efficiency. Think of this efficiency as the ratio of money paid for watts versus the amount of cooling capacity produced. One way manufacturers have achieved this is to use a more efficient refrigerant.

To help explain this, I am going to use ordinary water (actually R-718) to describe this example. Water is the substance in which heat gains or losses are based. One pound of water requires 1 Btu to raise 1 degree F. So for example, if water is flowing through our system and picking up 144 Btu’s /lb, it is providing a certain amount of heat transfer (cooling capacity) at that rate of flow. If we could magically increase that amount of 144 Btu’s /lb to say 200 Btu’s/lb, then we would see an increase of about +40 percent in heat transfer (cooling capacity).

So to put this in perspective, we have increased the amount of total heat transfer (+40 percent) which increases the output capacity (cooling) without increasing the amount of flow (displacement).

Relate this heat transfer scenario back to a few more common refrigerants used in HVAC. Substitute refrigerant R-22 for plain water at (144BTU/lb), and refrigerant R-410A as “magic water “at (200 BTU/lb). Considering the same compressor displacement, we know that an R-410A compressor would provide more cooling capacity based on the refrigerant’s Btu/ lb of mass flow, than the same displacement sized R-22 compressor.

By increasing the amount of heat transfer in R-410A refrigerant, we need to decrease the R-410A compressor displacement to get the same amount of output capacity as a comparable R-22 compressor. But by reducing the amount of displacement (scroll diameter/vane height) in an R-410A scroll compressor, we remove this amount of mechanical load required by the motor.

Removing this amount of mechanical load from the motor reduces the size of the motor required. By using a smaller sized motor, the amps are reduced, which directly affects the watts (power required). Since compressor watts represent the true cost of powering the compressor, we would pay less money ($/watt) for the same amount of system capacity (heat transfer) that a comparable R-22 compressor would provide. This means that using a newer refrigerant like R-410A, can save us money when compared to refrigerants of the past.

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