Source: https://guthlabs.ai/docs/instruments/hvac-sensible-latent-load-calculator/mechanism/

instrument mechanism / verified-clean

# HVAC Sensible/Latent Load Calculator mechanism

The inspectable method record for HVAC Sensible/Latent Load Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## 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

[01**Overview**](<https://guthlabs.ai/docs/instruments/hvac-sensible-latent-load-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/hvac-sensible-latent-load-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/hvac-sensible-latent-load-calculator/qualification/>)

## 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`