Technical Trade SchoolBAS-300 service-series
BAS-304
Concept reading and source route

BAS-304 Reading Guide

How to use this reading guide

This is the concept-review layer for a 100% online course. Read each module before its lesson, complete the retrieval prompts without looking, then use the linked authoritative sources to verify project-specific editions, requirements, and manufacturer procedures.

Online evidence is not OJL: browser simulations, document cases, and isolated remote equipment build reasoning and documentation skill; supervised field performance is recorded separately.

Module 1

Diagnostic contract, capacity, and energy balance

Why it matters: A physically impossible energy balance is evidence that measurement, units, assumptions, or system boundary is wrong.

Vocabulary and working scope

Complaint; intended state; boundary; load; sensible/latent/total; mass versus volume flow; density; source data; roles; safe tests; restoration.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

An AHU appears to remove more heat from the air than the chilled-water side can absorb.

Calculation: Use approved airside and waterside heat equations with units, density/fluid assumptions, and reasonableness checks.

Retrieval prompts

Module 2

Fans, filters, ducts, and static-pressure profiles

Why it matters: One static reading cannot locate a restriction; compare pressure before and after components under known airflow and fan conditions.

Vocabulary and working scope

Fan curve concepts; system resistance; total/static/velocity awareness; filter/coil/duct/damper restrictions; fan speed/current; proof; leakage; bypass; diversity.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

Duct static is low while fan speed and motor current are high and filter differential pressure is elevated.

Calculation: Calculate pressure differences, percent change, fan affinity estimates, and airflow only from approved pickup/K data.

Retrieval prompts

Module 3

Mixed air, economizers, and psychrometrics

Why it matters: Mixed-air state must lie within the physical mixture of outdoor and return air when measurements and mass balance are valid.

Vocabulary and working scope

OA/RA/MA mass balance; dry-bulb; wet-bulb; RH; humidity ratio; dew point; enthalpy; sensible/latent process; minimum OA; free cooling; low limit.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

Mixed-air temperature plots colder than both outdoor and return air without active cooling upstream.

Calculation: Calculate mixed-air fraction, humidity ratio, dew point, enthalpy comparison, and sensor/mass-balance residual.

Retrieval prompts

Module 4

DX cooling and heat-pump diagnosis

Why it matters: Airside and control evidence can justify refrigeration escalation but cannot establish charge or internal refrigerant condition by assumption.

Vocabulary and working scope

Vapor-compression orientation; compressor; condenser; metering; evaporator; staging; reversing valve; defrost; safeties; airflow dependency; BAS versus licensed evidence.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

Cooling is commanded, compressor status is on, airflow is low, and the evaporator begins to ice.

Calculation: Calculate airside sensible/total capacity from supplied state points and compare stage/run-time expectations.

Retrieval prompts

Module 5

Heating systems and combustion boundary

Why it matters: A BAS enable is not proof of safe ignition, combustion, heat transfer, or airflow.

Vocabulary and working scope

Electric heat; gas-fired; hydronic; enable/proof; stages; modulation; airflow; high limit; freeze; fuel/combustion; simultaneous heat/cool; discharge limits.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

The furnace command is on, the fan proof is intermittent, and high-limit trips recur.

Calculation: Calculate expected temperature rise or heat transfer from supplied airflow/input data only within stated assumptions.

Retrieval prompts

Module 6

Coils, valves, dampers, and service application

Why it matters: Position is not flow; valve authority, close-off, pressure drop, linkage, system pressure, and coil load determine response.

Vocabulary and working scope

Two/three-way valves; fail position; authority; close-off; rangeability; leakage; pressure drop; coil approach; damper opposed/parallel awareness; actuator torque/linkage; sizing boundary.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

A valve modulates from 20% to 80% with almost no change in flow until near full open.

Calculation: Calculate supplied pressure-drop ratios, valve authority concept, coil ΔT/capacity, and damper pressure effects; full sizing remains BAS-400.

Retrieval prompts

Module 7

Hydronic distribution, pumps, and differential pressure

Why it matters: Pump speed and proof do not establish delivered flow; pressure reference, system path, valve positions, and measurement matter.

Vocabulary and working scope

Two-way/three-way; primary/secondary; variable primary; pumps; speed; proof; DP sensor location; bypass; air; strainers; balancing; minimum flow; terminal diversity.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

Remote coils starve while plant differential pressure appears normal near the pumps.

Calculation: Use supplied pump/flow relationships, DP changes, terminal demand, and Q=flow×ΔT×factor reasonableness.

Retrieval prompts

Module 8

Plant interaction and low-ΔT diagnosis

Why it matters: Low ΔT is a symptom family with many possible mechanisms, not a single valve or plant fault.

Vocabulary and working scope

Chiller/boiler/tower/pump state; load; flow; supply/return temperature; bypass; coil performance; staging; reset; minimums; simultaneous demand; low-ΔT causes.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

Chilled-water flow is high, return temperature is low, and many valves are fully open.

Calculation: Calculate system load, expected versus actual ΔT, flow required for load, and contribution of bypass or ineffective coils.

Retrieval prompts

Module 9

Zone-to-system interactions and cause classification

Why it matters: The loudest complaint location may be a downstream symptom of an upstream system or shared-source limitation.

Vocabulary and working scope

VAV; VVT/hybrid VVT; FCU; heat pump; VRF; rogue zone; simultaneous demand; pressure; ventilation; schedule; envelope; occupancy; upstream/downstream.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

One hybrid-VVT zone repeatedly wins the vote and drives the RTU away from the needs of the other zones.

Calculation: Compare zone demand, vote/priority, airflow, discharge conditions, runtime, and diversity across the same interval.

Retrieval prompts

Module 10

Verification, restoration, referral, and capstone

Why it matters: A defensible HVAC conclusion states what the evidence proves, what it only suggests, what requires another trade, and what remains unknown.

Vocabulary and working scope

Baseline; next safe test; qualified referral; correction authority; stable response; acceptance source; affected modes; collateral impact; overrides; as-left; customer record.

Source-to-result trace

  1. Locate the controlling requirement and establish authority.
  2. Identify the physical and digital boundaries.
  3. Preserve as-found state and timestamps.
  4. Trace the initiating condition through logic, interfaces, equipment, and process response.
  5. Compare expected and actual evidence.
  6. Calculate with units and stated tolerance.
  7. Record action, result, restoration, uncertainty, and owner.

Worked thinking prompt

The BAS correction improves temperature temporarily, but the mechanical restriction and test override remain.

Calculation: Reconcile before/after energy and state-point evidence under comparable conditions and close all temporary states.

Retrieval prompts

Required and deeper reading

Adoption note: Standards, codes, project requirements, owner criteria, manufacturer instructions, and employer safety programs control. Confirm the adopted edition and authority before applying a numeric requirement.