Prefer a browser? Use the free psychrometric calculator without login, or follow the altitude worked example.
Run an HVAC calculation without logging in#
Calculation commands execute locally. They do not send project data to VentilatePro, do not require a token, and return the same structured result when called from the CLI or the local MCP server. Add --json for automation, test fixtures, spreadsheets, or agent workflows.
ventilatepro calc catalogventilatepro calc psychrometrics --dry-bulb 25 --relative-humidity 50 --units si --jsonEngineering sign convention
Airside load commands report positive values for cooling or dehumidification and negative values for heating or humidification. Hydronic load follows the sign of delta_t. Use absolute values only when equipment capacity—not heat-flow direction—is the required result.
Calculation catalog#
| Command | Primary output | Calculation basis |
|---|---|---|
calc psychrometrics | Complete moist-air state | PsychroLib 2.5.0, IP or SI |
calc sensible-load | Btu/h and refrigeration tons | Q = 1.08 × CFM × ΔT, coefficient overridable |
calc total-load | Btu/h and refrigeration tons | Q = 4.5 × CFM × Δh, coefficient overridable |
calc air-process | Sensible, latent, total, SHR, mass flow, water removal | PsychroLib endpoint states and entering-air specific volume |
calc hydronic-load | Btu/h and refrigeration tons | Q = 60 × GPM × ρ × cₚ × ΔT |
calc hydronic-flow | Required GPM | Inverse hydronic energy balance |
calc steam | Saturated properties and required lb/h | IAPWS-IF97 water and steam formulation |
calc fan-power | Shaft hp, input hp, input kW | hp = CFM × in. w.g. / (6356 × η) |
calc pump-power | Shaft hp, input hp, input kW | hp = GPM × head × SG / (3960 × η) |
calc duct-size | Area, round diameter, rectangular sides | Continuity at target velocity |
calc lmtd | Terminal differences and LMTD | Parallel-flow or counterflow logarithmic mean |
Psychrometrics#
Supply dry-bulb temperature plus exactly one independent moisture property: relative humidity, wet bulb, dew point, or humidity ratio. When pressure is omitted, VentilatePro evaluates PsychroLib’s standard-atmosphere station pressure at the supplied elevation. Explicit pressure always overrides elevation.
IP example#
ventilatepro calc psychrometrics --dry-bulb 75 --relative-humidity 50Temperature is °F, pressure is psi, elevation is ft, enthalpy is Btu/lb dry air, and specific volume is ft³/lb dry air. Humidity ratio is also returned in grains/lb.
SI example#
ventilatepro calc psychrometrics --dry-bulb 25 --relative-humidity 50 --units si --jsonTemperature is °C, pressure is Pa, elevation is m, enthalpy is J/kg dry air, and specific volume is m³/kg dry air.
Returned properties#
Dry bulb, wet bulb, dew point, relative humidity, humidity ratio, grains per pound in IP, moist-air enthalpy, dry-air-basis specific volume, moist-air density, vapor pressure, degree of saturation, and station pressure. The JSON response also identifies the input pair, unit system, property units, and calculation basis.
Sensible, total, and complete air-process loads#
Sensible load#
ventilatepro calc sensible-load --cfm 5000 --entering-dry-bulb 80 --leaving-dry-bulb 55The default 1.08 coefficient represents standard-density air and typical moist-air specific heat. Override it when project elevation, density, or calculation standards require a different coefficient.
Total load from enthalpy#
ventilatepro calc total-load --cfm 5000 --entering-enthalpy 31.2 --leaving-enthalpy 22.8The default 4.5 lb dry air/h per CFM factor is the conventional standard-air approximation. Use air-process when altitude-adjusted mass flow is important.
Altitude-adjusted air process#
ventilatepro calc air-process --cfm 5000 --entering-dry-bulb 80 --entering-rh 50 --leaving-dry-bulb 55 --leaving-rh 95 --jsonVentilatePro calculates both endpoint states with PsychroLib, converts CFM to dry-air mass flow using entering specific volume, evaluates total load from enthalpy difference, evaluates sensible load with moist-air specific heat at average humidity ratio, and reports latent load as the reconciled balance. Water removal is based on dry-air mass flow times humidity-ratio reduction.
Hydronic and saturated-steam calculations#
Hydronic load and flow#
ventilatepro calc hydronic-load --gpm 120 --delta-t 10ventilatepro calc hydronic-flow --load 600000 --delta-t 10Defaults are water at 8.33 lb/gal and 1.0 Btu/lb·°F. Supply project-specific density and specific heat for glycol or other fluids.
Saturated steam#
ventilatepro calc steam --pressure 15 --pressure-units psig --load 1000000 --jsonPressure may be psig, psia, kPa, or MPa. Results include saturation temperature, saturated-liquid and saturated-vapor specific volumes, h_f, h_fg, h_g, quality, mixture enthalpy, and optional required steam mass flow. Gauge pressure uses 14.6959488 psi atmosphere.
Fan, pump, duct, and heat-exchanger tools#
Fan input power#
ventilatepro calc fan-power --cfm 20000 --static-pressure 4 --fan-efficiency 0.68 --motor-efficiency 0.92Pump input power#
ventilatepro calc pump-power --gpm 500 --head 60 --pump-efficiency 0.75 --motor-efficiency 0.90Duct geometry#
ventilatepro calc duct-size --cfm 2400 --velocity 1200 --aspect-ratio 2Log-mean temperature difference#
ventilatepro calc lmtd --hot-in 200 --hot-out 150 --cold-in 80 --cold-out 120 --arrangement counterflowEfficiencies are decimal fractions from 0 to 1. Duct results are geometric starting points and do not replace friction-rate, noise, fitting-loss, leakage, or constructability checks. LMTD validates both terminal temperature differences and rejects temperature cross.
The same calculations for AI agents#
The local MCP server exposes explicit tools with typed arguments and structured results. These tools remain offline and unauthenticated even when the project-management tools require a VentilatePro token.
| MCP tool | Purpose |
|---|---|
vp_list_hvac_calculations | Discover the local calculation catalog. |
vp_calculate_psychrometrics | Resolve a complete IP or SI moist-air state. |
vp_calculate_sensible_load | Conventional sensible air load. |
vp_calculate_total_load | Conventional total air load from enthalpy. |
vp_calculate_air_process | Altitude-adjusted PsychroLib air-process balance. |
vp_calculate_hydronic | Load from GPM or GPM from load. |
vp_calculate_steam | IAPWS saturated properties and steam rate. |
vp_calculate_fan_power, vp_calculate_pump_power | Shaft and input power. |
vp_calculate_duct_size, vp_calculate_lmtd | Distribution geometry and heat-exchanger temperature difference. |
References, accuracy, and limits#
- Psychrometric calculations use PsychroLib 2.5.0 in its selected IP or SI unit system. PsychroLib documents its equations and coefficients as implementations of ASHRAE Handbook—Fundamentals psychrometric relationships.
- Steam properties use the IAPWS-IF97 formulation through CoolProp 8.0.0's IF97 backend. Saturation requests are limited to the water triple-point and critical pressures.
- The CLI serializes every result with its calculation name, values, units or input basis, formulas where applicable, and sign convention. Hard validation failures return a non-zero exit code.
- Downloaded VentilatePro charts sample saturation at 0.25°F and other property families at 0.5°F, solve enthalpy/saturation intersections numerically, clip curves to the physically valid region, and preserve vector paths in the PDF.
- These tools are engineering calculation aids. Verify final design values, safety factors, code requirements, equipment selections, fluid properties, and manufacturer data for the project.
Downloaded psychrometric charts#
Browser psychrometric charts preserve vector paths in PDF exports. Keep the station pressure, unit system, and source inputs with the report. The altitude worked example explains how pressure changes humidity ratio and specific volume.
Machine-readable documentation#
AI crawlers and retrieval systems can discover the concise documentation index at /llms.txt and the full Markdown corpus at /llms-full.txt. Both endpoints are public, indexable, linked from every documentation page, and included in robots.txt.