Field Tools

Before you use a number from this app

Calculation basis

Psychrometrics

ASHRAE Handbook — Fundamentals, Ch. 1, Hyland & Wexler formulation. Saturation pressure by eq. 5 (over ice, below 32 °F) and eq. 6 (over water, 32–392 °F). Humidity ratio eq. 20/21, wet bulb eq. 33/34, dew point eq. 37/38, enthalpy eq. 30, specific volume eq. 26. Barometric pressure from the standard atmosphere, eq. 3.

Wet bulb reported is the thermodynamic wet bulb, solved iteratively. It differs slightly from a sling psychrometer reading.

Coil and process loads

Computed from actual mass flow — m = cfm / v using the entering specific volume — not the 4.5 and 1.08 standard-air shortcuts. At 80 °F/67 °F entering at sea level the true factors are 4.33 and 1.06, so the textbook shortcuts overstate capacity by about 3.7%. The gap widens with altitude and with entering temperature. The app shows the effective factors so you can see how far from standard air you actually are.

Duct

ASHRAE Handbook — Fundamentals, Ch. 21. Friction factor from the Colebrook-White implicit equation solved by bisection (not an explicit approximation). Absolute roughness values from Ch. 21 Table 1. Velocity pressure Pv = ρ(V/1097)², which reduces to (V/4005)² at 0.075 lb/ft³. Rectangular duct friction uses the circular equivalent diameter De = 1.30(ab)^0.625/(a+b)^0.25 with velocity taken from the actual cross-section.

Air density is computed for dry air at the entered temperature and elevation — the ASHRAE standard-air basis, which returns 0.0749 lb/ft³ at 70 °F and sea level. Humidity moves density only a few tenths of a percent across the normal supply-air range, and assuming a humidity would be an unstated guess, so the app does not. The density actually used is always displayed.

Fitting loss coefficients are typical values only. They are adequate for sizing a run in the field. They are not adequate for a design of record — use the ASHRAE Duct Fitting Database entry for the specific geometry.

Pipe

Darcy-Weisbach with Colebrook friction factor, water properties (density, kinematic viscosity, vapor pressure) interpolated against temperature from standard steam-table values. Hazen-Williams is offered as a cross-check and is only valid for water near 60 °F in the turbulent range — it will mislead you on hot water, glycol, and low-flow branches. Inside diameters are catalog nominal values; confirm against the specified product. Valve and fitting K values are typical; confirm against published Cv for balancing, control, and strainer components.

Fans and pumps

Affinity laws with speed exponents 1/2/3. Impeller trim uses exponents 1/2/3; a geometrically similar fan wheel family uses 3/2/5. Both degrade outside roughly 80–115% of the reference point, and the app says so.

Plumbing — domestic water and sanitary drain

Basis is the 2021 International Plumbing Code, not the older editions the firm's spreadsheets cite. Water supply fixture units from Table E103.3(2); demand from Table E103.3(3); drainage fixture units from Table 709.1; building drain and sewer capacity from Table 710.1(1). Confirm against the edition the AHJ has adopted and its local amendments — plumbing is one of the most heavily amended trades.

Cold + hot exceeds the total on purpose. Table E103.3(2) note (a) sets each branch at three-fourths of the fixture total, because the cold peak and the hot peak do not happen at the same instant. Each column is summed independently and the total column is never computed as cold + hot. This differs from the firm's existing spreadsheet, which computes its total column as qty × (cold + hot) — so app totals will read lower than that sheet for any fixture with both supplies.

Demand takes the next tabulated row at or above the load rather than interpolating, which is the conservative reading and matches the spreadsheet's lookup behaviour; the interpolated figure is computed too so the two can be compared. Loads below the first row of a column use that first row and say so; loads past the last row return nothing rather than extrapolating. The flushometer-valve column is not tabulated below 5 wsfu. Hot water piping always reads the flush-tank column, per that column's own note, because it serves no flushometer valves. Continuous flows — irrigation, cooling make-up — are added in gpm after the conversion, never as fixture units.

Pipe size is the smallest nominal size whose velocity stays within the entered ceiling (default 8 ft/s), using catalog inside diameters; the velocity actually achieved is always shown. This is the field shortcut, not the IPC Appendix E segmented-loss method — it does not look at available pressure, developed length, meter and backflow losses, or elevation. For a service of record, run the pressure budget. The firm's spreadsheet pairs its Hunter's-curve lookup with a fixed Type L copper size column; results here may differ by a size where that table's implied velocity differs from the ceiling you enter.

Sanitary sizes are reported at 1/2, 1/4 and 1/8 in./ft from Table 710.1(1), including note (a): any building drain serving a water closet is at least 3 in. Sizes below 3 in. are not tabulated at 1/8 in./ft at all. The 4 in. minimum building sewer and the "not over two water closets on 3 in." limit that the firm's legacy SBCCI-based sheet carried are not in current IPC Table 710.1(1); the app flags the 4 in. question rather than enforcing it. Fixture-unit counts here size building drains, sewers, and horizontal branches of the building drain — not stacks, which use Table 710.1(2), and not vents.

Fixtures marked "assumed" are not in the cited IPC table. Hose bibbs, ice machines, bar sinks, clinical sinks and low-flow urinals carry values brought over from the firm's spreadsheets under Table E103.3(2) note (a) and Table 709.2, which permit assigning an unlisted fixture by comparison with a listed one of similar flow and frequency, or by its drain/trap size. The commonly quoted 2.5 wsfu hose bibb is a UPC Table 610.3 value, not IPC. Those rows are engineering assumptions and the reviewing engineer confirms them; the app labels every one rather than hiding it.

Electrical — voltage drop

DC conductor resistance from NEC Chapter 9, Table 8 (uncoated and coated copper, aluminum; solid conductors only through 8 AWG, matching field practice under 310.106(A)). Ampacity from NEC Table 310.16 at the selected 60/75/90 °C column, 30 °C ambient, ≤3 current-carrying conductors — no 310.15(B)/(C) correction or adjustment factors are applied; apply those separately if they govern the actual installation. Voltage drop is Vdrop = R/ft × A × ft × multiplier, multiplier 2 for single phase (current travels out on one conductor and back on the other, so the drop sees twice the one-way resistance) or √3 for three phase (the 120° phase relationship between conductors reduces this from 2 to √3) — the standard 2 × K × I × D formula, matching the firm's SuperiorVDCalc workbook. Provide any two of wire size, distance, and amps and the third is solved for; providing all three checks the actual drop for a known run.

Electrical — marina shore power load

Demand factor by total receptacle count per NEC 555.12(B). Connected load: a 50A/125-250V receptacle counts at its full 50A nameplate rating. A 30A/125V single-pole receptacle counts at 15A, half its nameplate rating — a firm convention, confirmed for this app: the 50A receptacles are two-pole 240V loads that draw on both ungrounded conductors of the shared feeder, while a 30A/125V receptacle is single-pole and loads only one of the two conductors, so on a balanced multiwire feeder carrying both load types its contribution to either conductor is taken as half of nameplate. This assumption is specific to a shared 120/240V multiwire feeder mixing both receptacle types — confirm it still applies to the feeder configuration on the project before using the result. A metered installation (individual kWh submeter per slip, NEC 220.120 criteria) gets the 0.9 multiplier per the firm cheat sheet's note 2. General-use 20A/125V duplex receptacles are counted at 180 VA each (Table 220.14(I)) with the Table 220.44 demand factor (first 10 kVA at 100%, remainder at 50%). Pedestal lights are counted at 9 VA each ×1.25 continuous-load factor (210.19(A)/215.2). All electrical amp figures assume a 240V basis for the duplex/pedestal-light adders, matching the source workbook.

Not included by design: AIC/available fault current rating and standard breaker-size selection are not implemented as calculators here — use the reference legends for conductor/conduit selection and confirm fault current and breaker selection against the project's actual utility/transformer data and the panel schedule.

Reference legends (service entrance, portable cable, and branch circuit/feeder tables) are transcribed from the firm's cheat sheet and cross-checked row by row against this app's own Table 310.16 data — see the validation suite, section 25. They are quick-reference only; the project's issued conductor/conduit schedule governs.

Validation

The calculation engine ships with a test suite of 235 assertions checked against published reference values — ASHRAE psychrometric tables, the ASHRAE duct friction chart and equivalent-diameter tables, the Moody diagram, AHRI rating conditions, steam tables, copper tube and Schedule 40 friction tables, NEC Chapter 9 Table 8 and Table 310.16, IPC Tables E103.3(2), E103.3(3), 709.1 and 710.1(1), and NIST unit factors. Pipe results are cross-validated between Darcy-Weisbach and Hazen-Williams, which share no code; electrical reference legends are cross-validated against the app's own ampacity table; and the IPC fixture-unit transcription is cross-checked against Table E103.3(2)'s own three-fourths rule, which is an independent constraint on the numbers rather than a restatement of them.

Run it with node validation.test.mjs. Every assertion names its source. Treat a failing suite as a stop-work condition on this app, and re-run it after any change to engine.js.

Known limitations, stated plainly: no glycol or steam properties; no duct or pipe insulation heat gain; no acoustics; SMACNA pressure-class and gauge selection is not implemented; the psychrometric chart is drawn for the entered elevation only; electrical calculators assume the 2023 NEC article/table numbers cited above and do not check 310.15(B)/(C) correction/adjustment factors, conduit fill, or AIC/breaker sizing; and the plumbing tool sizes building drains and sewers only — no stacks (IPC Table 710.1(2)), no vents, no traps or trap arms, no grease or sand interceptors, no storm drainage, and no Appendix E pressure budget for the water service.

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