Mester i ventilasjonsteknikkfaget common mistakes
Mester i ventilasjonsteknikkfaget · Understand the traps and how to avoid them.
Calculating supply and exhaust air volumes from a stated room airflow requirement without correcting for the density difference between the two air states, then presenting the unbalanced result as the fan duty.
Candidates learn volumetric flow as the primary quantity and treat m³/h as a conserved property, forgetting that mass balance is what must close and that volume flow changes with temperature and pressure through the system.
What to do instead
Always set up the balance in kg/s (or kg/h) first, convert to volume flow at the fan's actual inlet state using the local density, and state the reference state (temperature, pressure, humidity) next to every volume flow in the answer. Add a one-line check that Σm_supply = Σm_exhaust + transfer.
Sizing duct dimensions from a chosen velocity only, without verifying that the resulting pressure drop and the system's total pressure demand are achievable by the selected fan at its operating point.
Velocity-based sizing is the first method taught and gives a quick, plausible-looking number; candidates stop there because the fan curve and system curve intersection feels like a later, separate exercise.
What to do instead
After sizing, sum pressure losses for the index run (straight duct, fittings, terminal units, filters, heat exchanger, dampers), plot or compare against the fan curve, and explicitly state the operating point and any margin. Show the index run identification - the longest/highest-resistance path, not simply the longest duct.
Treating a balanced-pressure ventilation concept as automatically satisfying indoor climate requirements, without checking whether the required air change rate or per-person outdoor air supply is actually met in each zone.
The pressure regime (positive, negative, balanced) is visually intuitive and easy to reason about, so candidates equate 'correct pressure relationship' with 'correct design' and skip the quantitative ventilation rate check.
What to do instead
For each zone, calculate the required outdoor air volume (per person, per m², or per air change) and compare with the designed supply; then verify the pressure direction follows from the supply/exhaust difference. Present both checks in a small table so neither is omitted.
Commissioning answers that describe adjusting dampers until airflow 'looks right' or matches a rough hand-held reading, without documenting measurement method, instrument calibration status, and tolerances against the design value.
Commissioning is experienced on site as a practical, iterative activity, and candidates describe it in the same informal language rather than translating it into documented, verifiable steps.
What to do instead
Structure the answer as: measurement points and method (traverse, hood, orifice), instrument and calibration requirement, acceptance tolerance against design flow, sequence (main branch before terminals), and the record produced. Name the specific proportional balancing principle - the index terminal is left fully open and others are throttled relative to it.
Omitting the pre-startup safety checks - rotation direction, belt tension, filter installation, damper position, duct cleanliness, and interlock with heating coil - and jumping straight to running the fan.
Candidates focus on the airflow result and treat mechanical and safety checks as site tacit knowledge that does not need to be written in an exam answer.
What to do instead
Keep a fixed pre-start checklist in memory and write it out in order: electrical isolation removed and rotation verified by bump test, free-running impeller, filters fitted and differential pressure zeroed, dampers and fire dampers open, frost protection and heater interlock proven, then start. Mention that the heating coil interlock and frost thermostat must be proven before the fan runs at low outdoor temperature.
Describing drift and maintenance only in general terms ('regular service and filter change') without linking measured indicators to specific actions and intervals.
Operations content is often learned as a list of tasks rather than as a condition-monitoring regime, so candidates produce generic maintenance prose that earns little credit.
What to do instead
Tie each indicator to a threshold and an action: filter differential pressure rise triggers change, belt condition and tension checked at set intervals, fan and motor vibration trend, bearing temperature, damper and actuator function test, and a periodic airflow re-measurement compared with the commissioning record. State that the comparison baseline is the commissioning protocol.
Citing a regulation or standard by name or number without stating what it actually requires in the case at hand, or citing a superseded edition.
Candidates memorize document titles under time pressure and use the citation as a substitute for the substantive requirement; edition years are easy to overlook.
What to do instead
For every reference, write one sentence of substance: what the provision requires, to whom it applies, and how it applies to the scenario. Verify the current edition before the exam and note that Norwegian building regulation requirements are given as functional performance requirements, with the standard or guide used as documentation of fulfilment - not as the legal text itself.
Answering a documentation question with a list of document names (shop drawings, O&M manual, test protocol) without saying what each must contain or who is responsible for producing and handing it over.
Documentation is perceived as administrative box-ticking, so candidates list titles instead of describing content and responsibility allocation between contractor, designer, and client.
What to do instead
For each document, state content, author, timing, and recipient. Emphasize that as-built documentation and the commissioning protocol with recorded measured values are what the operator will later use as the baseline, and that incomplete handover documentation is a defect regardless of how well the plant performs.
Calculating life-cycle cost or profitability by summing investment and energy cost only, ignoring the discount rate, the analysis period, and the residual value or replacement cost of components with shorter life than the system.
Simple payback is the familiar calculation and candidates present it as if it were life-cycle cost, missing the time value of money and the differing lifetimes of fans, filters, and control equipment.
What to do instead
State the method explicitly: analysis period, real discount rate, energy price escalation assumption, and which components are replaced within the period. Present net present value and note that a low simple payback can still hide a poor life-cycle result if the analysis period is short or the discount rate is high. Show the formula used.
Treating an HVAC tender or contract question as purely technical, ignoring allocation of responsibility, interface boundaries, and change-order handling between disciplines.
Candidates prepare for the technical domains and treat management and economics as a soft add-on, so they answer with technical scope instead of contractual scope.
What to do instead
For any project-management scenario, first draw the interface boundary: who supplies, installs, connects, tests, and documents each item, and where the responsibility line sits between ventilation, electrical, and building automation. Then address change handling - written notification, consequence for time and cost, and approval before execution.