HVAC Sensible/Latent Load Calculator mechanism

Model scope

The underlying load formulas are standard under their stated assumptions, but the specification is incomplete and ambiguous about humidity-ratio units, dry-air basis, hfg, delta sign convention, total-load and SHR formulas, and zero-total-load handling. The honest label should explicitly state that the 0.68 latent constant requires grains/lb rather than a generic ΔW unit.

• The metric sensible formula Qs=1.006·ṁ·ΔT is correct for dry-air mass flow in kg/s, temperature difference in K or °C, and output in kW, but the required dry-air basis and sign convention are not stated.
• The metric latent formula Ql=ṁ·hfg·ΔW is correct when hfg is in kJ/kg and ΔW is kg water/kg dry air, producing kW; however, hfg is not specified and varies with temperature.
• The imperial sensible approximation 1.08·CFM·ΔT is valid for standard HVAC assumptions with CFM, temperature difference in °F, and output in BTU/h.
• The imperial latent approximation 0.68·CFM·ΔW is valid when ΔW is in grains of water per pound of dry air, not when ΔW is expressed as lb/lb or kg/kg; the spec does not state this required unit.
• The formulas for total load and sensible heat ratio are omitted. They should be Qt=Qs+Ql and SHR=Qs/Qt.
• The entering-versus-leaving direction for ΔT and ΔW is unspecified. For positive cooling loads, the usual definitions are ΔT=Tin−Tout and ΔW=Win−Wout.

Units and conventions

• Metric calculations use ṁ in kg/s of dry air, ΔT in K or °C, ΔW in kg water/kg dry air, hfg in kJ/kg, and outputs in kW.
• Imperial sensible calculations use CFM, ΔT in °F, and output in BTU/h.
• Imperial latent calculations use ΔW in grains of water per pound of dry air; 1 lb/lb equals 7000 grains/lb.
• The 1.08 and 0.68 constants assume approximately standard sea-level HVAC air conditions; they are not universal across altitude, pressure, or substantially different air density.
• The worked cooling-load examples define ΔT=entering temperature−leaving temperature and ΔW=entering humidity ratio−leaving humidity ratio.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "system": "metric",
    "mass_flow_kg_per_s": 0.5,
    "entering_temperature_C": 30,
    "leaving_temperature_C": 20,
    "entering_humidity_ratio_kg_per_kg_dry_air": 0.018,
    "leaving_humidity_ratio_kg_per_kg_dry_air": 0.01,
    "hfg_kJ_per_kg": 2500
  },
  "expected_outputs": {
    "Qs_kW": 5.03,
    "Ql_kW": 10,
    "Qt_kW": 15.03,
    "SHR": 0.33466467
  },
  "working": "ΔT=30−20=10 K. ΔW=0.018−0.010=0.008 kg/kg. Qs=1.006×0.5×10=5.03 kW. Ql=0.5×2500×0.008=10.00 kW. Qt=5.03+10.00=15.03 kW. SHR=5.03/15.03=0.33466467."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The calculator has an unavoidable undefined-result trap when total load is zero: SHR becomes 0/0 or a nonzero value divided by zero. The specification also leaves the CFM-versus-mass-flow branch selection, humidity-ratio units, and load sign convention insufficiently defined, allowing materially different outputs or sign reversals.

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-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json