ASHRAE Certified HVAC Designer (CHD) Overview
These study notes are designed to prepare candidates for the ASHRAE Certified HVAC Designer (CHD) exam. The content is anchored to official ASHRAE handbooks, standards, and codes including the International Mechanical Code (IMC) and International Energy Conservation Code (IECC). Each subject covers key concepts, must-know items, clinical applications (field/design applications), high-yield distinctions, common pitfalls, and review tasks. Candidates should verify specific exam details (format, pass mark, eligibility) with ASHRAE's official certification resources.
For Technical Conquer practice planning, this module is tracked as 100 questions over about 120 minutes with a listed pass mark of 70%. Treat those numbers as practice baselines and verify the current official format before scheduling.
How This Guide Is Organized
The sections below turn the syllabus into studyable subject blocks. Read a subject first, explain the must-know ideas without notes, then use questions, flashcards, and mind maps to test whether the knowledge holds under field-style pressure.
- Load Calculations and Psychrometric Analysis
- Air Distribution and Duct System Design
- Hydronic System Design and Equipment Selection
- HVAC Equipment Performance and Integration
- Building Automation and Control Sequences
- Codes, Standards, and Professional Compliance
Exam Snapshot and Readiness Target
Format: 100 questions, 120 minutes (practice baseline); verify official format with ASHRAE.
Candidate level: Professional engineer or experienced HVAC designer; typically 4+ years of experience.
Readiness target: Demonstrate comprehensive knowledge of HVAC design principles, codes, standards, and system integration.
Most candidates should budget at least 47+ focused study hours, then adjust upward for unfamiliar equipment, code, regulatory, commissioning, controls, or calculation-heavy content.
Load Calculations and Psychrometric Analysis
Syllabus Focus
- Heating and cooling load calculation methods (ASHRAE Fundamentals, ACCA Manual J)
- Psychrometric processes and chart interpretation
- Indoor and outdoor design conditions
- Sensible and latent heat gains
- Infiltration and ventilation loads
Key Notes
- Load calculations must follow ASHRAE Fundamentals or ACCA Manual J for residential/light commercial. Use CLTD/CLF or RTS methods for cooling loads.
- Psychrometric chart: understand dry-bulb, wet-bulb, dew point, relative humidity, humidity ratio, enthalpy, and specific volume.
- Design conditions: ASHRAE Handbook provides 0.4%, 1%, 2% annual percentiles for outdoor conditions; indoor comfort ranges per ASHRAE Standard 55.
- Sensible heat gain includes conduction, solar, internal loads (people, lights, equipment). Latent gain from occupants, infiltration, and processes.
- Ventilation loads: per ASHRAE 62.1 (commercial) or 62.2 (residential), based on occupancy and floor area.
Must Know
- Calculate total cooling load using RTS method: radiant time series for solar and internal gains.
- Determine supply air conditions: use sensible heat ratio (SHR) to find apparatus dew point (ADP) and bypass factor.
- Apply ASHRAE 62.1 ventilation rate procedure: breathing zone outdoor airflow = Rp × Pz + Ra × Az.
- Understand psychrometric processes: sensible heating/cooling, humidification/dehumidification, adiabatic mixing.
Field and Exam Application
- Design a VAV system: calculate zone loads, determine minimum ventilation, and select air handling unit cooling coil.
- Evaluate existing building: measure temperature and humidity, plot on psychrometric chart to diagnose comfort issues.
- Sizing duct heaters: based on sensible load and temperature rise, accounting for heat loss through duct walls.
High-Yield Distinctions
- RTS vs. CLTD/CLF: RTS is more accurate for modern buildings with high thermal mass; CLTD/CLF is simpler but less precise.
- ASHRAE 62.1 vs. 62.2: 62.1 for commercial, 62.2 for residential; different calculation methods and IAQ requirements.
- Sensible vs. latent heat: sensible affects dry-bulb temperature; latent affects humidity; both impact coil sizing.
Common Pitfalls
- Forgetting to include latent loads from infiltration and occupants, leading to undersized dehumidification.
- Using incorrect outdoor design conditions (e.g., using 1% instead of 0.4% for critical applications).
- Misapplying RTS: not accounting for thermal storage in heavy construction, causing over/under sizing.
Review Tasks
- Practice load calculation for a small office using RTS method and compare with CLTD/CLF.
- Plot a psychrometric process: outdoor air mixed with return air, then cooled and dehumidified to supply condition.
- Calculate ventilation airflow for a conference room per ASHRAE 62.1.
Air Distribution and Duct System Design
Syllabus Focus
- Duct design methods (equal friction, static regain, velocity reduction)
- Duct sizing and pressure loss calculations
- Air terminal devices (diffusers, grilles, registers)
- Fan laws and system curves
- Duct construction and leakage testing
Key Notes
- Equal friction method: constant pressure drop per unit length (typically 0.08-0.12 in.wg/100 ft). Static regain: reduces velocity to recover pressure, used for long ducts.
- Duct pressure loss: major losses (friction) per Darcy-Weisbach or ASHRAE friction chart; minor losses (fittings) per loss coefficients.
- Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³. System curve: pressure ∝ flow².
- Air terminal devices: selection based on throw, drop, noise criteria (NC), and coverage area.
- Duct leakage: SMACNA classes (A, B, C); leakage testing per ASHRAE 215 or SMACNA standards.
Must Know
- Size a duct system using equal friction: determine total pressure drop, select fan, and balance branches with dampers.
- Calculate fan total pressure: sum of duct losses, terminal losses, and equipment pressure drops.
- Select diffuser: based on room dimensions, airflow, and acceptable noise level (NC 25-35 typical).
- Understand duct construction: SMACNA standards for rectangular and round ducts, gauge, reinforcement.
Field and Exam Application
- Retrofit existing duct: measure static pressure, compare to fan curve, identify restrictions or undersized ducts.
- Design a duct system for a restaurant kitchen: high exhaust, makeup air, grease duct requirements per IMC.
- Commissioning: perform duct leakage test, verify airflow at terminals using flow hood.
High-Yield Distinctions
- Equal friction vs. static regain: equal friction simpler but may cause imbalance; static regain better for long runs but more complex.
- Fan laws vs. affinity laws: fan laws apply to same fan geometry; affinity laws for geometrically similar fans.
- SMACNA leakage classes: Class A (3% leakage), Class B (6%), Class C (12%); lower class for high-pressure ducts.
Common Pitfalls
- Ignoring fitting losses: using only friction loss underestimates total pressure drop.
- Oversizing ducts: increases cost and space; undersizing increases noise and energy use.
- Not accounting for duct heat gain/loss: especially in unconditioned spaces, affects supply air temperature.
Review Tasks
- Design a simple duct system for a floor plan using equal friction method, including fittings.
- Plot a system curve and select a fan from manufacturer data.
- Calculate pressure drop for a 90° elbow using loss coefficient from ASHRAE Duct Fitting Database.
Hydronic System Design and Equipment Selection
Syllabus Focus
- Hydronic system types (primary-secondary, variable primary, constant flow)
- Pump selection and system curves
- Pipe sizing and pressure drop
- Expansion tanks and air separation
- Chillers, boilers, cooling towers, and heat exchangers
Key Notes
- Primary-secondary systems: decouples production and distribution loops; allows variable flow in secondary while constant in primary.
- Pump head: sum of pipe friction, fittings, equipment pressure drops, and static head (if open loop).
- Pipe sizing: based on velocity (typically 2-4 ft/s for water) and pressure drop (1-4 ft/100 ft).
- Expansion tank: sized for system volume and temperature range; diaphragm tanks pre-charged to system static pressure.
- Chiller types: air-cooled vs. water-cooled; efficiency (kW/ton, EER, IPLV). Boiler types: condensing vs. non-condensing.
Must Know
- Calculate pump head for a closed loop: friction losses only (no static head). For open loop: include static lift.
- Select expansion tank: use ASHRAE formula or manufacturer software; ensure acceptance volume meets expansion.
- Determine chiller capacity: based on building load, diversity factor, and safety factor (typically 10-15%).
- Understand cooling tower approach: difference between leaving water temperature and ambient wet-bulb.
Field and Exam Application
- Design a primary-secondary system for a campus: multiple chillers, variable speed pumps, and building loops.
- Troubleshoot low delta-T syndrome: measure supply/return temperatures, check for bypass or fouling.
- Select a condensing boiler: ensure return water temperature below 140°F for condensing operation.
High-Yield Distinctions
- Primary-secondary vs. variable primary: primary-secondary simpler but less efficient; variable primary saves pump energy but requires careful control.
- Air-cooled vs. water-cooled chillers: air-cooled lower maintenance, higher condensing pressure; water-cooled higher efficiency but requires cooling tower.
- Condensing vs. non-condensing boilers: condensing >90% efficiency but requires low return temperature; non-condensing simpler but less efficient.
Common Pitfalls
- Oversizing pumps: leads to high velocity, noise, and energy waste; use system curve and diversity.
- Neglecting air separation: air in water causes corrosion, noise, and reduced heat transfer; install air separators and vents.
- Incorrect expansion tank sizing: too small causes relief valve opening; too large wastes space and cost.
Review Tasks
- Calculate pump head for a 10-story building closed loop with 500 ft of pipe, fittings, and a chiller with 20 ft pressure drop.
- Size an expansion tank for a system with 1000 gallons of water, 40°F to 200°F range, 50 psig pre-charge.
- Compare energy consumption of air-cooled vs. water-cooled chiller for a given load and climate.
HVAC Equipment Performance and Integration
Syllabus Focus
- Air handling units (AHUs) and rooftop units (RTUs)
- Coils (cooling, heating, DX) and heat pumps
- Fans and fan performance
- Heat recovery systems (energy wheels, heat pipes, run-around loops)
- Equipment selection and part-load performance
Key Notes
- AHU components: mixing box, filters, cooling coil, heating coil, fan, humidifier, dampers. Draw-through vs. blow-through configuration.
- Coil performance: sensible and latent capacity depend on entering air conditions, coil surface temperature, and airflow.
- Fan performance: fan curves show pressure vs. flow; operating point is intersection of fan curve and system curve.
- Heat recovery: sensible (heat pipes, run-around) and total (energy wheels) effectiveness typically 50-80%.
- Part-load performance: chillers and heat pumps have degraded efficiency at low loads; use multiple units or variable speed.
Must Know
- Select AHU coil: use manufacturer software or psychrometric analysis to meet leaving air conditions.
- Calculate fan brake horsepower: BHP = (CFM × TP) / (6356 × fan efficiency).
- Determine heat recovery effectiveness: (T_outdoor_exhaust - T_outdoor_supply) / (T_outdoor_exhaust - T_outdoor_ambient).
- Understand EER, SEER, COP, IPLV: efficiency metrics for different operating conditions.
Field and Exam Application
- Design an AHU with heat recovery for a hospital: ensure minimum outdoor air, recover energy from exhaust.
- Retrofit a constant volume system to VAV: add VFD to fan, install VAV boxes, and reset static pressure.
- Commissioning: verify coil capacity by measuring air and water temperatures and flow rates.
High-Yield Distinctions
- Draw-through vs. blow-through: draw-through has fan after coil (lower fan heat gain); blow-through has fan before coil (better mixing).
- DX vs. chilled water coils: DX direct expansion with refrigerant; chilled water uses water from chiller; DX simpler but less flexible.
- Energy wheel vs. heat pipe: energy wheel transfers both sensible and latent; heat pipe only sensible; wheel requires purge section to avoid cross-contamination.
Common Pitfalls
- Selecting coil with too high face velocity (>500 fpm) causes moisture carryover; use velocity below 500 fpm for cooling coils.
- Ignoring fan heat gain: fan motor heat adds to supply air temperature, especially in draw-through configuration.
- Oversizing heat recovery: payback period may be too long; consider climate and operating hours.
Review Tasks
- Select a cooling coil for an AHU: given entering air 95°F DB/78°F WB, leaving 55°F DB/54°F WB, airflow 10,000 CFM.
- Calculate fan BHP for a system with 20,000 CFM and 4 in.wg total pressure, fan efficiency 75%.
- Compare energy recovery options for a 20,000 CFM exhaust system in a cold climate.
Building Automation and Control Sequences
Syllabus Focus
- Control system architecture (DDC, sensors, actuators, controllers)
- Common control sequences (VAV, chilled water, hot water, DX)
- Setpoint reset strategies (static pressure, supply air temperature, chilled water temperature)
- Optimization and energy management
- Commissioning and troubleshooting controls
Key Notes
- DDC systems: sensors (temperature, humidity, pressure, flow), controllers (PID), actuators (valves, dampers), and network (BACnet, Modbus).
- VAV control: zone temperature controls damper position; static pressure reset based on damper positions (trim and respond).
- Chilled water reset: increase supply temperature at low loads to improve chiller efficiency and reduce reheat.
- Hot water reset: decrease supply temperature at mild conditions to reduce boiler cycling and losses.
- Commissioning: verify sensor accuracy, actuator stroke, control logic, and sequence of operations.
Must Know
- Program a PID loop: proportional band, integral time, derivative time; tune for stable control.
- Implement static pressure reset: maintain lowest damper position at 70-90% open; reduce fan speed.
- Understand economizer cycle: use outdoor air for free cooling when enthalpy is lower than return air.
- Troubleshoot control issues: check sensor readings, actuator feedback, and controller output.
Field and Exam Application
- Design a DDC system for a multi-zone VAV system: specify sensors, controllers, and network topology.
- Optimize chilled water reset: analyze building load profile and chiller performance curves.
- Commission a VAV box: verify airflow calibration, damper operation, and reheat valve response.
High-Yield Distinctions
- Proportional vs. PID control: proportional only has offset; PID eliminates offset but requires tuning.
- Economizer high-limit: dry-bulb vs. enthalpy; enthalpy economizer more efficient in humid climates.
- Trim and respond vs. direct setpoint: trim and respond adjusts setpoint gradually; direct setpoint may cause hunting.
Common Pitfalls
- Improper PID tuning: too aggressive causes oscillation; too slow causes poor response.
- Sensor drift: temperature sensors can drift over time; recalibrate annually.
- Overriding safeties: control sequences should not bypass safety limits (freeze protection, high pressure).
Review Tasks
- Write a sequence of operations for a VAV system with static pressure reset and economizer.
- Tune a PID loop for a hot water valve: simulate step response and adjust gains.
- Design a BACnet network for a building with 10 AHUs and 100 VAV boxes.
Codes, Standards, and Professional Compliance
Syllabus Focus
- ASHRAE standards (62.1, 62.2, 55, 90.1, 189.1)
- International Mechanical Code (IMC) and International Energy Conservation Code (IECC)
- SMACNA and ACCA standards
- Professional ethics and liability
- Permitting and inspection processes
Key Notes
- ASHRAE 62.1: ventilation for acceptable indoor air quality; requires minimum outdoor air per occupancy and area.
- ASHRAE 90.1: energy standard for buildings except low-rise residential; prescriptive and performance paths.
- IMC: governs mechanical systems; includes duct construction, combustion air, refrigeration, and exhaust.
- IECC: energy code; references ASHRAE 90.1 as alternative compliance.
- Professional compliance: designs must meet applicable codes; engineers seal drawings; liability for errors.
Must Know
- Calculate minimum outdoor air per ASHRAE 62.1: breathing zone = Rp × Pz + Ra × Az; zone air distribution effectiveness.
- Determine energy code compliance: use ASHRAE 90.1 Appendix G for performance rating method.
- Apply IMC requirements for combustion air: two openings or mechanical ventilation for gas appliances.
- Understand SMACNA duct construction standards: pressure class, leakage class, and reinforcement.
Field and Exam Application
- Design ventilation for a classroom: 25 people, 1000 sq ft; per 62.1, Rp=5 cfm/person, Ra=0.06 cfm/sq ft.
- Perform energy code compliance for an office building: use ASHRAE 90.1 prescriptive envelope, lighting, HVAC.
- Review a mechanical plan for IMC compliance: check duct sizing, exhaust, and equipment clearances.
High-Yield Distinctions
- ASHRAE 62.1 vs. 62.2: 62.1 for commercial, 62.2 for residential; different calculation methods and IAQ requirements.
- IMC vs. IECC: IMC focuses on safety (combustion, exhaust, refrigeration); IECC focuses on energy efficiency.
- Prescriptive vs. performance path: prescriptive simpler but may be more restrictive; performance allows trade-offs.
Common Pitfalls
- Not accounting for zone air distribution effectiveness: mixing vs. displacement ventilation affects required airflow.
- Ignoring local amendments: many jurisdictions modify IMC and IECC; check local codes.
- Assuming ASHRAE 90.1 is the only energy code: some states have their own energy codes (e.g., California Title 24).
Review Tasks
- Calculate ventilation for a restaurant dining area per ASHRAE 62.1: 100 people, 2000 sq ft.
- Compare energy code compliance using ASHRAE 90.1 prescriptive vs. performance path for a sample building.
- Identify IMC requirements for a commercial kitchen exhaust system: hood type, duct material, fire suppression.
How To Use These Notes With Practice Questions
Do not jump straight from reading to a full mock. Work by subject first: review the key notes, make a short recall sheet from memory, then answer a focused question set. After each miss, decide whether the problem was missing theory, weak code/source recall, poor measurement setup, calculation error, or a field sequence you did not visualize.
Technical Conquer's question bank, flashcards, mind maps, and spaced review tools are most useful after this instruction layer because they reveal which parts of the notes are not yet retrievable.
Final Review Checklist
- Review all ASHRAE Handbook chapters on load calculations, psychrometrics, and system design.
- Practice using psychrometric chart and RTS method for load calculations.
- Understand fan laws, pump curves, and system curves for equipment selection.
- Memorize key ASHRAE standards: 62.1, 62.2, 55, 90.1, and 189.1.
- Familiarize with IMC and IECC requirements for mechanical and energy compliance.
- Review control sequences for VAV, chilled water, and hot water systems.
- Take practice exams under timed conditions to build speed and accuracy.
- Verify exam format, pass mark, and eligibility with ASHRAE official resources.
Official Sources and Further Reading
Use these sources as the final authority for format, eligibility, rules, regulatory limits, and exam updates. Study notes are a preparation layer, not a replacement for official candidate guidance.