Reference
Methodology
Last updated 2026-05-15
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.
Source module: 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.
Source module: 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. Apply the half-excess-latent reallocation rule when sensible capacity is oversized. Golden test fixtures pin output against published Manual S worked examples.
Source module: 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.
Source module: 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.
Source module: 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.
Tool-bound scope: 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