Reference
Methodology
Last updated May 15, 2026
BuildSolver runs HVAC engineering calculations as deterministic code following the procedures published in ACCA Manual J 8th Edition, ACCA Manual S, ACCA Manual D, ASHRAE 62.1, and the ASHRAE Handbook of Fundamentals. The AI layer orchestrates the conversation and chooses which tool to call - the math itself is not LLM inference. Every result on a BuildSolver PDF cites the section of the standard it came from.
01 · Standards used
What we follow
| Standard | What we use it for |
|---|---|
ACCA Manual J 8th Edition Air Conditioning Contractors of America - Residential Load Calculation, 8th Edition | Block and (forthcoming) room-by-room cooling and heating loads. |
ACCA Manual S ACCA - Residential Equipment Selection | Sensible / latent capacity match-up against AHRI-rated equipment at design conditions. |
ACCA Manual D (simplified) ACCA - Residential Duct Systems | Friction-rate sizing for residential branch runs; equal-friction balancing. |
ASHRAE 62.1 ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality | Ventilation rate calculations (R_p × P + R_a × A) for non-residential spaces. |
ASHRAE Handbook of Fundamentals ASHRAE Handbook - Fundamentals, Chapter 1: Psychrometrics | Saturation vapor pressure (Magnus-Tetens), enthalpy, mixing of moist air streams. |
IECC International Energy Conservation Code (current cycle) | Climate zone defaults: U-values, infiltration rates, design temperatures. |
NFPA 70 (NEC) National Electrical Code | Electrical service sizing context where it intersects HVAC equipment specs. Not the primary scope. |
02 · Per-tool methodology
How each calculation runs
Cooling load
- ACCA Manual J 8th Ed. §6 (sensible)
- ACCA Manual J 8th Ed. §8 (latent)
Sensible gains summed from envelope (UA × CLTD), internal loads (people, lights, appliances), infiltration, duct losses. Latent gains from infiltration moisture, occupant respiration, and ventilation. Design conditions looked up by ZIP/climate zone from ACCA Manual J Table 1A and the IECC climate-zone map.
The code lives in lib/manual-j/load.ts.
Heating load
- ACCA Manual J 8th Ed. §5
Envelope UA × ΔT (indoor design − 99% outdoor design), infiltration via the crack/ach method. No credit taken for solar or internal gains, per Manual J convention.
The code lives in lib/manual-j/heating-load.ts.
Equipment selection
- ACCA Manual S §3
- AHRI 210/240 ratings
Match the calculated sensible heat ratio against AHRI-rated coil performance at 95°F outdoor / 80°F return / 67°F wet-bulb. Check latent capacity against the latent load at design conditions. Golden test fixtures pin output against published Manual S worked examples.
The code lives in lib/manual-s/equipment-selection.ts.
Duct sizing (simplified)
- ACCA Manual D
Friction-rate method for residential branch runs with equal-friction balancing. This is preliminary sizing - not a full pressure-drop / TEL calculation. For permit-grade duct designs, use a full Manual D package.
The code lives in lib/manual-d/duct-size.ts.
Psychrometric state
- ASHRAE Handbook of Fundamentals Ch. 1
Saturation vapor pressure via the Magnus-Tetens approximation. Wet-bulb, dew point, enthalpy, and humidity ratio derived from dry-bulb + one secondary variable. Mixing of two moist-air streams via mass-weighted enthalpy and humidity ratio.
The code lives in lib/psychrometrics/state.ts.
03 · Transparency commitments
What you can verify
- Every row in a BuildSolver PDF includes the section reference from the standard it came from.
- Inputs are logged in the audit trail at the bottom of each generated report - climate zone, U-values, design conditions, and any overrides the user supplied.
- Calculations execute as deterministic code, not LLM inference. The AI chooses which tool to call and how to phrase the explanation; the numbers themselves come from the formula modules listed above.
- The test suite includes golden fixtures that pin output against published Manual J/S worked examples - regressions show up before any change ships.
04 · Scope and limits
Where to use BuildSolver - and where not to
Use BuildSolver for the sales phase
Preliminary sizing, client quotes, retrofit estimates, equipment shortlists, ballpark psychrometric checks, and branch-run duct sizing. The target is the call where you need a defensible number in 90 seconds, not a stamped permit submittal.
Use a licensed engineer for the permit phase
AHJs in most US jurisdictions require an ACCA-approved package (Wrightsoft, Cool Calc, Kwik Model) with a licensed mechanical engineer's seal. BuildSolver output is preliminary and clearly stamped as such - it is not a substitute for a PE review and final design.
The tools cover HVAC only
BuildSolver is intentionally scoped to HVAC. Electrical, structural, plumbing, and fluid mechanics are not on the roadmap. The chat will refuse off-scope questions rather than guess across disciplines we have not validated.
05 · Disclaimer