1. Pure Thermodynamic NRE (Benchmark)

74.5 BTU/lb

This is the locked chart value calculated strictly as:

NRE = H₂ − H₁
at typical conditions (~35°F evaporator / ~105°F condenser)

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)

58–68 BTU/lb (typical measured range)

In the field we always have some superheat and subcooling. The diagnostic tool uses this simple, stable method:

Thermodynamic NRE = (Hg_sat + SH × 0.24) − Hf_liquid
Field NRE = Thermodynamic NRE × 0.965
Sizing Reference NRE = Field NRE × 0.92

The main diagnostic tool (r134a.htm) computes this live using the actual table data from data/r134a.json and applies the deratings.

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-134a

Type	Value	When to Use
Pure Thermodynamic NRE	74.5 BTU/lb	Benchmark / manufacturer comparison (no SH/SC)
Field NRE (Recommended)	58–68 BTU/lb	Real-world diagnostics with measured SH & SC
Sizing Reference NRE	~55–64 BTU/lb	Conservative value to avoid oversizing equipment

Why Field NRE Differs from Pure

The pure value (74.5 BTU/lb) is the published manufacturer benchmark at standard conditions (40°F evaporator / 110°F condenser) with zero superheat and zero subcooling.

The code first calculates the full Thermodynamic NRE at your actual pressures and temperatures using the table enthalpies (from data/r134a.json) plus a superheat correction of ×0.24 (vapor Cp for R-134a). It then applies a 0.965 field derating factor for realistic field conditions (line losses, oil, etc.) to produce the "Field NRE" value shown in the tool. Sizing Reference NRE applies an additional ×0.92 factor on top of Field NRE for conservative equipment selection.

R-134a is azeotropic (no glide — bubble point = dew point).

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; subcooling further lowers it using ≈0.22 liquid Cp in the tool).
2. Measure suction line temperature and pressure at the evaporator outlet → look up Hg and add superheat effect using the R-134a Cp ≈0.24 (this is your H2).
3. Thermodynamic NRE = H2 − H1
4. Field NRE = Thermodynamic NRE × 0.965 (what the tool primarily displays)
5. Compare your Field NRE to the pure benchmark (74.5) and the recommended range (58–68). Sizing uses the extra ×0.92 factor.

Tip: On the main R-134a diagnostic tool (r134a.htm), the “Field NRE” value already includes your measured superheat and subcooling. It first computes the full Thermodynamic NRE from the table + 0.24 Cp, then applies the 0.965 derating (and 0.92 for Sizing).

Note: The pure value (74.5 BTU/lb) is the standard thermodynamic benchmark at 40°F/110°F saturated conditions. The tool computes Thermodynamic NRE at your actual conditions (using 0.24 Cp for superheat and 0.22 for subcool liquid correction in the flash calc), then derates by 0.965 for the displayed Field NRE. Values will vary with your measured superheat and subcooling. R-134a is a common HFC refrigerant being phased down due to its GWP of 1,430.