IRHACE Certified HVAC Engineer (IRHACE) Overview
These study notes are designed to prepare candidates for the IRHACE Certified HVAC Engineer exam. They cover the six core subjects identified by Technical Conquer, anchored to official sources including ASHRAE Handbooks, International Mechanical Code (IMC), International Energy Conservation Code (IECC), ACCA standards, EECA energy management scheme, and IRHACE guidelines. Candidates should verify all specific exam rules, pass marks, and eligibility with IRHACE directly.
For Technical Conquer practice planning, this module is tracked as 100 questions over about 180 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.
- Psychrometrics and Thermodynamic Process Analysis
- Air Distribution and Ventilation System Design
- Hydronic Systems and Heat Transfer Equipment
- Refrigeration Cycles and AS/NZS 5149 Compliance
- Building Management Systems and Control Logic
- Energy Efficiency and NZBC Clause H1 Compliance
Exam Snapshot and Readiness Target
Format: 100 questions, 180 minutes, pass mark 70% (practice baseline; verify with IRHACE)
Candidate level: Engineer-level professional certification
Readiness target: Demonstrate comprehensive knowledge of HVAC/R engineering principles, codes, and standards applicable in New Zealand.
Most candidates should budget at least 42+ focused study hours, then adjust upward for unfamiliar equipment, code, regulatory, commissioning, controls, or calculation-heavy content.
Psychrometrics and Thermodynamic Process Analysis
Syllabus Focus
- Psychrometric chart interpretation
- Sensible and latent heat processes
- Air mixing, cooling, heating, humidification, dehumidification
- Thermodynamic cycles and property relations
Key Notes
- Psychrometric chart: dry-bulb, wet-bulb, dew-point, relative humidity, humidity ratio, enthalpy, specific volume.
- Sensible heat ratio (SHR) determines slope of process line; used for coil selection and zone control.
- Cooling and dehumidification: air passes below dew point; condensate removal; bypass factor affects leaving conditions.
- Adiabatic humidification: evaporative cooling; enthalpy constant; wet-bulb temperature decreases.
- Heating and humidification: often requires steam or spray; ensure no condensation in ducts.
- Thermodynamic processes: isothermal, isentropic, polytropic; apply first and second laws to HVAC cycles.
- ASHRAE Handbook Fundamentals provides standard psychrometric data and equations.
Must Know
- Plot and read all points on psychrometric chart accurately.
- Calculate mixed air conditions using weighted average of dry-bulb and humidity ratio.
- Determine coil load: Q = m_dot * (h_in - h_out) for cooling; include latent component.
- Apply ASHRAE comfort zones (summer/winter) for design conditions.
Field and Exam Application
- Design air handling unit (AHU) cooling coil to achieve specified supply air conditions.
- Troubleshoot insufficient dehumidification: check coil temperature, airflow, bypass factor.
- Optimize economizer operation using enthalpy comparison vs. dry-bulb.
High-Yield Distinctions
- Sensible vs. latent heat: sensible changes dry-bulb; latent changes humidity ratio.
- Bypass factor vs. contact factor: bypass factor = (T_leaving - T_coil) / (T_entering - T_coil).
- Adiabatic vs. isothermal: adiabatic has no heat transfer; isothermal constant temperature.
- Enthalpy is total heat; wet-bulb approximates adiabatic saturation temperature.
Common Pitfalls
- Confusing relative humidity with humidity ratio; RH is temperature-dependent.
- Forgetting to account for fan heat gain in supply air temperature.
- Using incorrect altitude correction for psychrometric properties.
- Assuming constant enthalpy during cooling without dehumidification.
Review Tasks
- Practice plotting processes on psychrometric chart for typical summer and winter design days.
- Calculate mixed air temperature and humidity for given return and outdoor conditions.
- Solve for coil leaving conditions given entering conditions and SHR.
Air Distribution and Ventilation System Design
Syllabus Focus
- Duct design methods (equal friction, static regain, velocity reduction)
- Ventilation rates per ASHRAE 62.1 and IMC
- Air distribution effectiveness and comfort
- Fans and duct system pressure losses
Key Notes
- ASHRAE 62.1: ventilation rate procedure (VRP) uses breathing zone outdoor airflow; IMC adopts similar.
- Duct design: equal friction maintains constant pressure drop per length; static regain reduces velocity to recover pressure.
- Total pressure loss = friction loss + dynamic losses (fittings, dampers, terminals).
- Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³; affinity laws for variable speed.
- Air distribution: throw, drop, and spread of diffusers; ADPI (Air Diffusion Performance Index) for comfort.
- Duct leakage testing: SMACNA standards; pressure class determines allowable leakage.
- IMC Chapter 6: duct construction, insulation, and clearance requirements.
Must Know
- Calculate ventilation airflow using VRP: V_ot = R_p * P_z + R_a * A_z.
- Select duct size using friction chart or ductulator; typical friction rate 0.1 in.wg/100 ft.
- Determine fan total static pressure: sum of duct losses, coil, filter, damper, and terminal losses.
- Apply diversity factor for ventilation when zones have intermittent occupancy.
Field and Exam Application
- Design duct system for a small office building using equal friction method.
- Troubleshoot insufficient airflow at terminal: check damper position, duct blockage, fan speed.
- Commission VAV system: verify minimum ventilation at design and part load.
High-Yield Distinctions
- Equal friction vs. static regain: equal friction simpler; static regain yields more uniform static pressure.
- Ventilation rate procedure vs. IAQ procedure: VRP prescriptive; IAQ requires contaminant modeling.
- Constant volume vs. VAV: constant volume simpler but less efficient; VAV saves fan energy.
- Duct pressure class: low (≤2 in.wg), medium (2-6), high (>6); affects leakage and construction.
Common Pitfalls
- Oversizing ducts increases cost and may cause low velocity; undersizing increases noise and pressure drop.
- Ignoring duct heat gain/loss in unconditioned spaces.
- Using same friction rate for all duct sections without considering fitting losses.
- Neglecting to balance system; dampers should be used for fine-tuning, not major adjustments.
Review Tasks
- Design a simple duct layout for a 5-zone system; calculate trunk and branch sizes.
- Compute ventilation airflow for a classroom using ASHRAE 62.1 VRP.
- Select a fan from catalog given required flow and static pressure.
Hydronic Systems and Heat Transfer Equipment
Syllabus Focus
- Hydronic system components (pumps, pipes, valves, expansion tanks)
- Heat exchangers: shell-and-tube, plate, finned-tube
- Pump curves and system curves
- Pipe sizing and pressure drop
Key Notes
- Hydronic system types: open vs. closed; primary-secondary; variable primary flow.
- Pump curve: head vs. flow; system curve: pressure drop vs. flow; operating point at intersection.
- Cavitation: NPSH available must exceed NPSH required; check at pump suction.
- Expansion tank: accepts water volume change; diaphragm tank pre-charge set to system static pressure.
- Heat exchanger: LMTD method; fouling factor reduces performance; counterflow most efficient.
- Pipe sizing: velocity limits (4-8 ft/s for water); pressure drop per 100 ft (typically 2-4 ft/100 ft).
- Valves: balancing valves for flow control; control valves (2-way vs. 3-way) for temperature control.
Must Know
- Calculate system pressure drop and select pump head.
- Size expansion tank: V_tank = (V_sys * (v2/v1 - 1)) / (1 - P1/P2).
- Determine heat exchanger area: Q = U * A * LMTD.
- Apply diversity to pump flow for multiple coils.
Field and Exam Application
- Design primary-secondary loop for a chiller plant with multiple chillers.
- Troubleshoot low delta-T syndrome: check for bypass, fouling, or oversized pumps.
- Commission variable primary flow system: verify minimum flow through chiller.
High-Yield Distinctions
- Closed loop vs. open loop: closed has no evaporation; open (cooling tower) has evaporation and makeup.
- Primary-secondary vs. variable primary: primary-secondary decouples production and distribution; variable primary simpler but requires chiller minimum flow.
- 2-way vs. 3-way valves: 2-way modulates flow; 3-way diverts flow; 2-way saves pump energy.
- Counterflow vs. parallel flow: counterflow has higher LMTD and efficiency.
Common Pitfalls
- Oversizing pump leads to high velocity, noise, and valve wear; undersizing causes insufficient flow.
- Ignoring pipe insulation for hot water systems increases heat loss.
- Forgetting to include control valve pressure drop in system curve.
- Not providing air vents at high points; air binding reduces flow.
Review Tasks
- Plot pump and system curves; determine operating point and required pump power.
- Size a plate heat exchanger for a given duty.
- Calculate expansion tank volume for a 1000-gallon system with 40°F to 200°F range.
Refrigeration Cycles and AS/NZS 5149 Compliance
Syllabus Focus
- Vapor-compression refrigeration cycle
- Refrigerants: types, ODP, GWP, phaseout schedules
- AS/NZS 5149: safety, installation, leakage detection
- Superheat, subcooling, and system performance
Key Notes
- Vapor-compression cycle: compressor, condenser, expansion device, evaporator; P-h diagram analysis.
- Coefficient of Performance (COP) = Q_evap / W_comp; higher COP means better efficiency.
- Superheat: temperature above saturation at evaporator outlet; typically 5-15°F; ensures no liquid slugging.
- Subcooling: temperature below saturation at condenser outlet; typically 10-20°F; improves efficiency.
- Refrigerant types: CFCs (phased out), HCFCs (phasing out), HFCs (high GWP), HFOs (low GWP).
- AS/NZS 5149: classification by toxicity (A/B) and flammability (1/2/3); charge limits based on occupancy.
- Leak detection: fixed or portable sensors; annual leak checks for systems > 5 kg charge.
Must Know
- Read P-h diagram: locate cycle points, determine enthalpy differences for COP and capacity.
- Calculate superheat and subcooling from pressure and temperature measurements.
- Apply AS/NZS 5149 charge limits for given refrigerant class and room size.
- Identify refrigerant phaseout dates: R-22 (2020), R-404A (2025), R-410A (2025-2030).
Field and Exam Application
- Diagnose low superheat: possible overfeeding or low load; high superheat: underfeeding or low charge.
- Perform leak test per AS/NZS 5149: pressure test with nitrogen, then vacuum.
- Select expansion valve: TXV based on capacity and refrigerant; ensure proper bulb placement.
High-Yield Distinctions
- Superheat vs. subcooling: superheat indicates evaporator performance; subcooling indicates condenser performance.
- TXV vs. capillary tube: TXV maintains constant superheat; capillary tube fixed orifice, simpler but less efficient.
- R-134a vs. R-1234yf: R-134a GWP 1430; R-1234yf GWP 4, mildly flammable (A2L).
- AS/NZS 5149 vs. ASHRAE 15: similar but AS/NZS 5149 is New Zealand/Australia specific.
Common Pitfalls
- Confusing superheat with subcooling; measure at correct locations.
- Overcharging system: high subcooling, high head pressure, possible liquid slugging.
- Undercharging: low subcooling, low superheat (if TXV starving), low capacity.
- Ignoring refrigerant safety: use proper PPE, recovery equipment, and ventilation.
Review Tasks
- Plot a refrigeration cycle on P-h diagram for R-134a; calculate COP and mass flow.
- Determine required charge limit for an R-410A system in a machinery room per AS/NZS 5149.
- Calculate superheat and subcooling from given pressure and temperature readings.
Building Management Systems and Control Logic
Syllabus Focus
- Direct Digital Control (DDC) architecture
- Control loops: PID, on/off, floating
- Sensors and actuators
- BACnet and communication protocols
Key Notes
- DDC: sensors → controller → actuators; controllers can be standalone or networked.
- PID control: proportional (P) reduces error; integral (I) eliminates offset; derivative (D) anticipates change.
- On/off control: simple, but causes cycling; differential gap prevents short cycling.
- Floating control: three-point (open/close/stop) for actuators; no feedback position.
- BACnet: ASHRAE standard 135; common protocol for BMS interoperability; supports MS/TP, BACnet/IP.
- Sensors: temperature (RTD, thermistor), humidity (capacitive), pressure (piezoresistive), flow (paddle, ultrasonic).
- Actuators: electric (modulating or floating) or pneumatic; fail-safe position (normally open/closed).
Must Know
- Tune a PID loop: set P first to reduce oscillation, then I to eliminate offset, D if needed.
- Design sequence of operation for AHU: heating, cooling, economizer, fan start/stop.
- Select sensor type based on accuracy, range, and environment.
- Configure BACnet points: AI, AO, BI, BO; ensure proper object mapping.
Field and Exam Application
- Commission a VAV box: verify airflow sensor calibration, damper actuator stroke, and reheat valve operation.
- Troubleshoot temperature offset: check sensor location, calibration, and PID tuning.
- Integrate chiller plant with BMS using BACnet; monitor setpoints, alarms, and energy data.
High-Yield Distinctions
- Proportional vs. integral: proportional alone leaves offset; integral eliminates offset but can cause overshoot.
- BACnet MS/TP vs. BACnet/IP: MS/TP uses RS-485, slower but simpler; IP uses Ethernet, faster.
- Analog vs. digital sensors: analog outputs continuous signal; digital outputs discrete (e.g., pulse).
- Open loop vs. closed loop: open loop no feedback; closed loop uses sensor feedback to adjust output.
Common Pitfalls
- Improper PID tuning: too high P causes oscillation; too low I causes slow response.
- Sensor drift: recalibrate annually; use calibration offsets in software.
- Network communication issues: check termination resistors, baud rate, and device addresses.
- Forgetting fail-safe positions: actuators should fail to safe position on power loss.
Review Tasks
- Write a sequence of operation for a single-zone AHU with economizer.
- Tune a PID loop for a heating valve; describe steps to adjust P and I.
- Configure a BACnet MS/TP network with three controllers; assign addresses and baud rate.
Energy Efficiency and NZBC Clause H1 Compliance
Syllabus Focus
- NZBC Clause H1: energy efficiency requirements for buildings
- Building envelope: insulation, glazing, thermal bridging
- HVAC system efficiency: minimum COP, EER, IPLV
- Energy modeling and compliance paths
Key Notes
- NZBC Clause H1: three compliance paths - Schedule Method, Calculation Method, Modelling Method.
- Schedule Method: prescriptive R-values for walls, roof, floor, glazing; based on climate zone.
- Calculation Method: building performance index (BPI) must not exceed reference building.
- Modelling Method: use energy simulation software (e.g., EnergyPlus, IES VE) to demonstrate compliance.
- HVAC minimum efficiency: AS/NZS 3823 for heat pumps; NZBC Acceptable Solution H1/AS1 references.
- Thermal bridging: reduce through insulation continuity; use thermally broken frames.
- Air leakage: building envelope airtightness; blower door test for compliance.
Must Know
- Determine climate zone (1-6) per NZBC; apply corresponding R-values.
- Calculate BPI: total energy use per floor area; compare to reference.
- Select HVAC equipment meeting minimum COP/EER per AS/NZS 3823.
- Identify thermal bridge details: slab edge, window frames, balcony penetrations.
Field and Exam Application
- Perform energy audit: identify major energy uses (HVAC, lighting, plug loads); recommend upgrades.
- Design high-performance envelope: specify insulation levels, triple glazing, and airtightness.
- Model a small office building using NZBC Modelling Method; compare design vs. reference.
High-Yield Distinctions
- Schedule vs. Calculation vs. Modelling: Schedule simplest but least flexible; Modelling most accurate.
- R-value vs. U-value: R is resistance; U is conductance (U=1/R).
- COP vs. EER: COP for heating; EER for cooling; both at rated conditions.
- IPLV (Integrated Part Load Value) accounts for part-load efficiency; more realistic than full-load EER.
Common Pitfalls
- Ignoring thermal bridging: can reduce effective R-value by 30% or more.
- Using incorrect climate zone for location; check NZBC maps.
- Oversizing HVAC equipment: leads to short cycling and poor part-load efficiency.
- Neglecting air leakage: infiltration increases heating/cooling load significantly.
Review Tasks
- Calculate required R-values for a house in Climate Zone 3 using Schedule Method.
- Compute BPI for a simple building and compare to reference.
- Select a heat pump that meets minimum COP for heating per AS/NZS 3823.
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 six subjects systematically; focus on weak areas identified during practice.
- Practice psychrometric chart reading and P-h diagram analysis until fluent.
- Memorize key code references: ASHRAE 62.1, IMC, NZBC H1, AS/NZS 5149.
- Understand control logic sequences and PID tuning principles.
- Be able to calculate ventilation rates, duct sizes, pump head, and expansion tank volume.
- Know refrigerant phaseout dates and safety classifications.
- For energy efficiency, be comfortable with NZBC compliance paths and HVAC minimum efficiencies.
- Verify all exam-specific details (pass mark, format, eligibility) with IRHACE directly.
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.