R449A enthalpy mismatch between REFPROP and Danfoss/ASERCOM tools when using T & Q as inputs

[hichem-code]

When calculating the enthalpy of R449A using Temperature (T) and Quality (Q) as input properties, REFPROP returns a value that differs from the Danfoss refrigerant calculator and other tools using ASERCOM / ASEREP reference equations.

Using this Python code:

MASS_BASE_SI = RP.GETENUMdll(0, "MASS BASE SI").iEnum
RP.SETFLUIDSdll("R449A")

result = RP.REFPROPdll(
    "R449A",
    "FTQ",            # Input: Temperature & Quality
    "H",              # Output: Enthalpy
    MASS_BASE_SI,
    1,
    0,
    311.15,           # T = 311.15 K (≈ 38°C)
    0,                # Q = 0 (saturated liquid)
    [1.0]
)

print(result.hOut)    # → 261.27 kJ/kg

Expected result from Danfoss and other ASERCOM-based tools:

H = 257.5 kJ/kg

REFPROP returns:

H = 261.27 kJ/kg

A difference of ~3.7 kJ/kg, which is significant for refrigeration calculations.

Screenshot from Danfoss tool:

Expected Behavior

REFPROP should return thermodynamic properties consistent with industry-standard refrigerant databases for R449A (Danfoss, ASERCOM).

Actual Behavior

REFPROP returns higher enthalpy values than other calculation tools for blends like R449A.

REFPROP Configuration

REFPROP Version: 10

ctREFPROP Version: 10.5

Operating System: Linux (Docker)

Fluid: R449A (blend)

Main Question :

How can I make REFPROP return the same enthalpy value as the Danfoss calculator (or other ASERCOM-compliant refrigerant tools) when using T and Q as inputs for R449A?

[hichem-code]

What’s strange is that when using REFPROP.exe directly (the Windows interface), I get the same result as Coolselector / Danfoss, around 257.5 kJ/kg for R449A at T = 311.15 K and Q = 0.

[Matthew-Boyd]

In the GUI, the default behavior is to apply the reference state to the the currently defined mixture. See:
Options -> Reference State -> Apply reference state to

In Python, the default behavior is to apply the reference state to each pure component, even when a mixture is specified (which is maybe confusing). To also apply the reference state to the currently defined mixture in Python, call:
RP.FLAGSdll("Mixture reference", 2)

(which calls SETREFdll with a ixflag value of 2). You can reset this back to the default Python behavior by calling:
RP.FLAGSdll("Mixture reference", 0)

[marciahuber]

For some of the binary pairs in your mixture we have updated the binary interaction parameters. If you want to try that, please send an email to REFPROP@NIST.GOV.