07/12/2019
UK: A British company with a history of developing innovative “drop-in” refrigerants is set to introduce a zero-ODP, lower GWP, non-flammable replacement for R410A in existing air conditioning systems.
Designated R470A by ASHRAE, the R410A “drop-in” is one of two new patented, A1, non-flammable and non-toxic refrigerants to be introduced by Cheshire-based Refrigerant Solutions Ltd (RSL) in the new year. The other, its sister refrigerant R470B, offers similar benefits for the replacement of R404A and R507 in existing systems.
Problem
In the face of worldwide moves to phase-down HFC refrigerants, the refrigerant producers and system developers have come up with a number of interim and long-term, low and lower GWP solutions for most existing and new refrigeration applications.
Stationary air conditioning, however, and its use of R410A has proved more of a problem. R32 is becoming increasingly accepted in new systems, but its A2L flammability rating makes it currently unacceptable for larger VRF systems. Honeywell’s promised replacement R466A, although a non-flammable A1 alternative, will at least require the replacement of the condensing unit. So, until now there has been no acceptable lower GWP “drop-in” for existing systems. According to RSL, R470A might be the solution.
To be marketed by RSL as RS-53, R470A is a complicated blend of six recognised components. It combines HFOs with current HFCs and, unusually, the “natural” refrigerant CO2.
In addition to the relatively small amount of CO2, it blends the R410A components, R32 (17%) and R125 (19%), with R134a (7%), HFO1234ze(E) (44%) and a small amount of the less common HFC R227ea (3%).
These components give R470A a GWP of 909, higher than R32’s GWP of 675 and R466A’s 733, but significantly lower than the 2088 of R410A.
According to RSL, R470A has a similar thermodynamic performance to R410A with matching energy efficiency and cooling capacity. It is also said to be compatible with the materials commonly found in R410A equipment and its use in existing split systems would involve no changes to the hardware. It is also compatible with POE lubricants typically used in current R410A systems, avoiding the need for an oil change when retrofitting.
On the subject of glide, RSL technical manager Nick Poole admitted that engineers commonly viewed the glides of zeotropic refrigerants as a problem.
“While accepting that the difference between the dew and bubble points represents a comparative measure for the glides of different zeotropes, this value over-estimates the real evaporator glide, because flashing of the refrigerant in the expansion valve or cap tube reduces the glide.”
According to RSL, the misapprehension arises because a key effect has previously been ignored. This is that the refrigerant coil loops within the heat exchanger causing the refrigerant to flow in opposite directions in adjacent loops. As a result, the glide tends to be self-cancelling.
At an ambient temperature of 25ºC and air exit temperature achieved from the evaporator of around 12ºC, RS-53 has an intrinsic glide of 8K. According to RSL, this can be halved depending on the design of coil in the evaporator and has no detrimental effect on cooling the air compared to R410A. At an ambient temperature of 25ºC, the air exit temperature achieved from the evaporator of around 12ºC is similar to R410A, the company maintains.
