Sensible & Latent Heat / Psychrometric Calculator mechanism

Model scope

NEEDS_REVIEW because the product description names ASHRAE/NIST methods but does not select an exact saturation-pressure correlation, wet-bulb algorithm, convergence tolerance, pressure/elevation precedence rule, or fully defined unit basis. The listed vectors are deterministic reference checks under the explicit assumptions stated above; the implementation should expose those assumptions in its UI and output labels.

• Q_sensible=1.08·CFM·ΔT is standard only for IP units: CFM, dry-air density/specific heat incorporated in 1.08, and ΔT in °F; this unit domain is not stated explicitly.
• Q_latent=0.68·CFM·ΔgrW is standard only when ΔgrW is grains of moisture per lb of dry air and CFM is actual volumetric airflow under the assumptions embedded in 0.68. The specification does not define whether grW means grains/lb dry air or another humidity unit.
• The alternative mass-based enthalpy method is mentioned but no formula, air mass-flow basis, or unit system is supplied.
• “Psychrometric relations (ASHRAE)” is not a reproducible algorithm: the saturation-vapor-pressure correlation, valid temperature range, pressure correction, and wet-bulb equation are unspecified.
• Wet-bulb temperature requires a defined psychrometric model, such as solving h(Tdb,w)=h(Twb,ws(Twb)) or using an ASHRAE psychrometric equation; no exact method or convergence tolerance is specified.
• Dew-point calculation is not explicitly defined, including the inverse saturation-pressure correlation and behavior when RH=0 or RH=100%.

Units and conventions

• Test vectors use temperature in °C, pressure in kPa absolute, humidity ratio in kg water/kg dry air, and enthalpy in kJ/kg dry air.
• For load calculations, the 1.08 and 0.68 coefficients use CFM, ΔT in °F, and ΔgrW in grains/lb dry air; these are deliberately separate IP inputs from the SI psychrometric inputs.
• The test calculations use pws=0.61078·exp(17.2694·T/(T+237.29)) kPa for the stated temperature range, pv=RH·pws, w=0.621945·pv/(P-pv), and h=1.006·T+w·(2501+1.86·T) kJ/kg dry air.
• Wet-bulb values use bisection on h(Tdb,w)-[1.006·Twb+ws(Twb)·(2501+1.86·Twb)]=0, with the same saturation-pressure equation, stopping at absolute temperature interval below 1e-6 °C.
• The reported psychrometric values are rounded outputs from the stated correlation; production output must identify the selected correlation and pressure convention.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "dry_bulb_C": 25,
    "relative_humidity": 0.5,
    "pressure_kPa_abs": 101.325,
    "airflow_CFM": 500,
    "delta_T_F": 10,
    "delta_grW_per_lb_dry_air": 20
  },
  "expected_outputs": {
    "humidity_ratio_kg_per_kg_dry_air": 0.009873,
    "enthalpy_kJ_per_kg_dry_air": 50.3,
    "dew_point_C": 13.87,
    "wet_bulb_C": 17.821,
    "Q_sensible_Btu_per_h": 5400,
    "Q_latent_Btu_per_h": 6800,
    "Q_total_Btu_per_h": 12200
  },
  "working": "pws(25)=0.61078·exp(17.2694·25/(25+237.29))≈3.167 kPa. pv=0.5·3.167=1.5835 kPa. w=0.621945·1.5835/(101.325−1.5835)=0.009873 kg/kg. h=1.006·25+0.009873·(2501+1.86·25)=25.150+0.009873·2547.5≈50.30 kJ/kg. Dew point solves pws(Tdp)=1.5835, giving Tdp≈13.87 °C. Wet-bulb bisection: initial bracket [0,25] °C; iteration 1 midpoint 12.5 °C gives saturated enthalpy below the target, so retain [12.5,25]; iteration 2 midpoint 18.75 °C gives saturated enthalpy above the target, so retain [12.5,18.75]. Continuing until interval <1e-6 °C gives Twb=17.8210 °C. Qs=1.08·500·10=5400 Btu/h. Ql=0.68·500·20=6800 Btu/h. Qt=5400+6800=12200 Btu/h."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

At 100 °C, 100% RH, and 101.325 kPa, pv equals total pressure, so the psychrometric humidity-ratio denominator P-pv is exactly zero. The instrument must reject the state rather than return a numeric humidity ratio or enthalpy.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json
• BOUNDARY_HAZARD_CATALOG.json