Source: https://guthlabs.ai/docs/instruments/hvac-heating-cooling-load-estimator-envelope-method/implementation/

instrument implementation / implementation-contract

# HVAC Heating/Cooling Load Estimator (Envelope Method) implementation

A source-bound implementation contract for HVAC Heating/Cooling Load Estimator (Envelope Method); deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t7-127

**Effect**: Computation or source lookup only

## Input and validation requirements

The extreme infiltration input produces a mathematical result of 1.08e310 Btu/h, which overflows ordinary IEEE-754 floating-point arithmetic to a non-finite value. The convention probe also exposes a sign ambiguity: reversing the definition of ΔT changes the reported result from +8960 to -8960 Btu/h even though the physical condition is heating.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "system": "US heating",
    "surfaces": [
      {
        "name": "wall",
        "area_ft2": 800,
        "U_Btu_h_ft2_F": 0.07692307692307693
      },
      {
        "name": "window",
        "area_ft2": 100,
        "U_Btu_h_ft2_F": 0.5
      },
      {
        "name": "roof",
        "area_ft2": 800,
        "U_Btu_h_ft2_F": 0.05263157894736842
      }
    ],
    "indoor_temperature_F": 70,
    "outdoor_temperature_F": 20,
    "infiltration_CFM": 100
  },
  "expected_outputs": {
    "temperature_difference_F": 50,
    "conduction_Btu_h": 7682.186234818,
    "infiltration_Btu_h": 5400,
    "total_heating_load_Btu_h": 13082.186234818,
    "total_cooling_load_Btu_h": 0
  },
  "reference_data": {
    "wall_nominal_R_value_h_ft2_F_per_Btu": 13,
    "wall_U_Btu_h_ft2_F": "1/13 = 0.07692307692307693",
    "wall_source_convention": "Widely tabulated standard nominal insulation value, R-13",
    "roof_nominal_R_value_h_ft2_F_per_Btu": 19,
    "roof_U_Btu_h_ft2_F": "1/19 = 0.05263157894736842",
    "roof_source_convention": "Widely tabulated standard nominal insulation value, R-19",
    "window_U_Btu_h_ft2_F": 0.5,
    "window_source_convention": "Widely tabulated standard value for a representative modern double-glazed window",
    "US_infiltration_factor_Btu_h_per_CFM_F": 1.08,
    "infiltration_factor_source_convention": "Widely tabulated HVAC standard-air conversion value"
  },
  "working": "ΔT = 70 − 20 = 50°F. Wall = (1/13)·800·50 = 3076.923076923 Btu/h. Window = 0.50·100·50 = 2500 Btu/h. Roof = (1/19)·800·50 = 2105.263157895 Btu/h. Conduction = 3076.923076923 + 2500 + 2105.263157895 = 7682.186234818 Btu/h. Infiltration = 1.08·100·50 = 5400 Btu/h. Total heating = 7682.186234818 + 5400 = 13082.186234818 Btu/h. Since outdoor temperature is lower, cooling load = 0."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/hvac-heating-cooling-load-estimator-envelope-method/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/hvac-heating-cooling-load-estimator-envelope-method/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/hvac-heating-cooling-load-estimator-envelope-method/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-tranche7/tranche7-results.json`