1. Pure Thermodynamic NRE (Benchmark)

58.2 BTU/lb

This is the locked chart value calculated strictly as:

NRE = H₂ − H₁
at 40°F evaporator (dew) / 110°F condenser (bubble)

No superheat, no subcooling, no field variables. Pure enthalpy difference from the refrigerant tables (Hg at evaporator minus Hf at condenser).

2. Field NRE (Recommended – Real World)

62–70 BTU/lb (typical measured range)

This includes your actual measured superheat and subcooling:

Field NRE = (Hg_sat + SH × 0.25) − (Hf_liquid − SC × 0.48)

Use this number for diagnostics, charge calculations, and capacity estimates.

How to Read the Chart

• H1 = Enthalpy of liquid refrigerant after the metering device (post-flash)
• H2 = Enthalpy of vapor leaving the evaporator (at measured superheat)
• NRE = H2 − H1 → This is the actual refrigerating effect per pound of refrigerant circulating.

Our Numbers for R-404A

Type	Value	When to Use
Pure Thermodynamic NRE	58.2 BTU/lb	Benchmark / manufacturer comparison (no SH/SC)
Field NRE (Recommended)	62–70 BTU/lb	Real-world diagnostics with measured SH & SC
Sizing Reference NRE	~59–65 BTU/lb	Conservative value to avoid oversizing equipment

Why the Numbers Are Different

The pure value (58.2 BTU/lb) assumes ideal saturated conditions with zero superheat and zero subcooling. In the real world we always have some superheat (adds energy to the suction vapor, increasing H2) and subcooling (removes energy from the liquid, decreasing H1). This usually increases the effective refrigerating effect per pound — which is why Field NRE is typically higher than the pure benchmark on R-404A systems.

How to Use This Page / Find Your Own H1 & H2

1. Measure liquid line temperature and pressure right after the metering device → look up Hf (this is your H1 base).
2. Measure suction line temperature and pressure at the evaporator outlet → look up Hg and add superheat effect (this is your H2).
3. NRE = H2 − H1
4. Compare your Field NRE to the pure benchmark (58.2) and the recommended range (62–70).

Tip: On the main R-404A diagnostic tool (r404a.htm), the “Field NRE” value already includes your measured superheat and subcooling using the same method.

Note: The pure thermodynamic value (58.2 BTU/lb) comes directly from standard R-404A property tables. Field values typically fall in the 62–70 BTU/lb range depending on your exact superheat and subcooling. R-404A is a common low-temperature refrigerant but has a high GWP.