Agent Utility Suite (x402)

HVAC coil load and air mixing

hvac_coil_load

Read-onlyIdempotent

Answers "What is the cooling coil load for 10,000 CFM from 80/67 °F to 55/54 °F?", "What leaves a coil that removes 270 MBH sensible and 60 MBH latent?" and "What is the mixed air with 20% outdoor air?" for AHU and RTU selection, coil schedules and design checks. Give the airflow and either the entering and leaving air (any two properties each) to get the sensible, latent and total loads, tons, sensible heat ratio, condensate rate and both full state points; or one state plus the loads to solve the other (cooling or heating). The entering air can be mixed from outdoor and return air states with an outdoor air % or airflow; or, given the mixed air, the outdoor air % is back-calculated. Standard-air equations (Qs = 1.08·CFM·ΔT, Ql = 4840·CFM·ΔW, Qt = 4.5·CFM·Δh as a cross-check), ASHRAE psychrometrics at the site elevation, IP (CFM, MBH) or SI (L/s, kW). Flags impossible (supersaturated) results. Every result includes steps with the equations and numbers. You are only charged when a result is returned: invalid input (400) and upstream failures (4xx/5xx) are not settled. Costs $0.002 USDC per call via x402. Paid per call with x402 inside MCP (see the server instructions).

Input Schema

Name	Required	Description	Default
`via`	No	Optional: the tool whose next_calls suggested this call (filled in for you).
`mode`	No	When solving a state from loads: cooling (default) removes heat, heating adds it. Detected automatically when both states are given.
`units`	No	"IP" (°F, CFM, in, BTU) or "SI" (°C, L/s, mm, kW). Default IP. Applies to inputs and results.	IP
`airflow`	Yes	Total airflow through the coil: CFM (IP) or L/s (SI).
`leaving`	No	Air leaving the coil: two properties, like `entering`.
`entering`	No	Air entering the coil: exactly two of dry_bulb, wet_bulb, dew_point, relative_humidity (%), humidity_ratio (lb/lb or g/kg), enthalpy (BTU/lb or kJ/kg), grains (gr/lb), in `units`. With outdoor_air and return_air but no outdoor air amount, it is the mixed air and the outdoor air % is back-calculated.
`elevation`	No	Site elevation, ft (IP) or m (SI); sets the atmospheric pressure. Default 0 (sea level).
`return_air`	No	Return air (two properties, like `entering`).
`latent_load`	No	Coil latent load, MBH or kW (default 0 when only sensible_load is given).
`outdoor_air`	No	Outdoor air (two properties, like `entering`), mixed with return_air ahead of the coil.
`sensible_load`	No	Coil sensible load, MBH (IP) or kW (SI): with one state, solves the other.
`outdoor_airflow`	No	Outdoor airflow, CFM or L/s (instead of outdoor_air_percent).
`outdoor_air_percent`	No	Outdoor air share of the total airflow, %.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 12, 2026

addedInput schema / properties / via

Added value: +{
+  "description": "Optional: the tool whose next_calls suggested this call (filled in for you).",
+  "maxLength": 64,
+  "type": "string"
+}

AddedOct 6, 2026

TDQS

A4.5/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnly/idempotent/non-destructive, and the description adds substantial extra behavior: it flags impossible supersaturated results, returns `steps` with equations, applies ASHRAE psychrometrics at site elevation, and details the x402 billing semantics including when charges do and do not apply.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Informative and front-loaded with example questions, but the billing/elevation/units detail in the back half is dense and somewhat overlong for a description intended for tool selection.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex 13-param tool with nested state objects and no output schema, the description covers inputs, outputs (loads, tons, SHR, condensate, state points, steps), error behavior, units and billing—everything an agent needs to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3, but the description adds value by explaining the two-property state rule, the mixed-air back-calculation of outdoor air %, and the cooling/heating mode behavior beyond what field descriptions state.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb+resource (cooling coil load / air mixing) and opens with three concrete example questions that map directly to the tool's function, making its scope unambiguous and distinguishing it from hvac_psychrometrics and hvac_duct_size.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly states the required inputs ('Give the airflow and either the entering and leaving air...') and gives context for AHU/RTU selection, coil schedules and design checks. It doesn't explicitly say when to prefer hvac_psychrometrics alone, but the usage context is strong.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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