Iran Nezam Mechanical Supervision Exam cheat sheet

Sensible heat equation: Qs = 1.21 × L/s × ΔT (°C) for air at standard conditions, giving watts; in SI, Qs = 1.2 × m³/s × ΔT × 1000/1000 simplified as 1.2 × m³/s × ΔT in kW.

Total coil load = sensible + latent; latent heat Ql = 3.0 × L/s × ΔW (g/kg) in watts, or 3010 × m³/s × ΔW in kW.

Air-side duct sizing continuity: Q = V × A; friction chart design typically targets 0.8–1.2 Pa/m for low-velocity commercial ducts.

Equal friction method: select fan pressure from the longest/index run; balance branches with dampers or resized ducts, not by fan speed alone.

VAV box minimum airflow typically set at 30% of design to satisfy ventilation; verify ASHRAE 62.1 breathing-zone outdoor airflow at minimum.

Chilled water flow: 1 TR ≈ 3.517 kW; flow L/s ≈ kW × 0.239 / ΔT(K) for water (4.19 kJ/kg·K).

Fan laws: flow ∝ N, pressure ∝ N², power ∝ N³; a 10% speed reduction cuts power about 27%.

Pump laws identical to fan laws; system curve intersection defines operating point; check NPSH available vs required for cavitation.

Design outdoor conditions for Iranian cities come from Mabhas 14 tables and ASHRAE climatic design conditions; use 99% heating and 1% cooling dry-bulb.

U-value of composite wall: 1/U = Rsi + Σ(d/k) + Rse; Iranian Mabhas 19 sets maximum U-values by climate zone.

Cooling load components: conduction through envelope, solar through glazing (SHGC × area × peak solar factor), internal gains, infiltration/ventilation, and latent loads.

CLTD/CLF or transfer function methods convert peak external load to hourly cooling load; do not equate peak solar gain with peak load.

Degree-day method: annual energy ≈ (UA × HDD × 24)/1000 kWh for heating, using base temperature 18 °C typically.

Ventilation load from Mabhas 14 minimum outdoor air rates; energy recovery ventilator effectiveness reduces coil load proportionally.

Economizer free cooling permitted when outdoor enthalpy is below return air enthalpy; Iranian code allows air-side economizers in mild seasons.

Boiler efficiency: combustion efficiency from flue CO2 and temperature; seasonal efficiency includes cycling and standby losses.

Fixture unit method (Hunter): assign WSFU per fixture, sum, apply probability curve to get probable flow in L/s or gpm.

Drainage fixture units (DFU) sizing per Mabhas 16 tables; horizontal branch slope 1–2% for pipes ≤100 mm, 1% for larger.

Stack sizing limited by capacity table; wet vent length restrictions and vent stack sizing per Mabhas 16.

Trap seal depth minimum 50 mm and maximum 100 mm; each fixture requires a trap except where listed.

Water supply pressure: minimum residual 100–150 kPa at furthest fixture; use booster pump or gravity tank where street pressure insufficient.

Domestic hot water: storage capacity typically 40–60 L per person per day for residential; recirculation line needed when runs exceed ~15 m.

Pipe material selection: PVC/UPVC for drainage, PPR/PEX for hot water, galvanized steel where code requires; check pressure ratings at temperature.

Backflow prevention: air gap preferred; RPZ device where continuous pressure exists; test annually per Mabhas 16.

Storage tank sizing: daily demand × storage days (typically 0.5–1 day) plus fire reserve if combined; separate fire volume per Mabhas 3.

Roof tank head available = static height minus friction losses; verify at peak flow with Hazen-Williams or Darcy-Weisbach.

Hazen-Williams: hf = 10.67 × L × Q^1.852 / (C^1.852 × d^4.87) in SI; C ≈ 140 for new plastic, 100 for old steel.

Storm drainage: rational method Q = C × i × A; Iranian intensity-duration curves per Mabhas 16; minimum roof drain size by area.

Sump pump and basement drainage: design for inflow plus safety factor; check pump cycling volume and alarm level.

Water hammer control: surge arrestors, slow-closing valves, and pipe support spacing; velocity limit 1.5–2.5 m/s in supply mains.

Greywater and rainwater reuse requires dual piping with purple marking and backflow protection per Mabhas 16.

Pressure-reducing valve required when static pressure exceeds ~500 kPa; install downstream of meter with strainer.

Automatic sprinkler design density and area per occupancy hazard: light hazard 2.05 mm/min over 140 m² (typical), ordinary hazard higher; per NFPA 13 and Mabhas 3.

Sprinkler spacing: max 4.6 m between heads for light hazard, 12.1 m² per head; 3.7 m for ordinary hazard.

Standpipe and hose system: wet standpipe required in buildings over 4 stories or 15 m height; residual pressure 450 kPa at top outlet.

Fire pump: rated flow at 1.0×, 1.5× flow at ≥65% rated pressure, churn at ≤140% rated pressure per NFPA 20.

Smoke control: stairwell pressurization 25–50 Pa differential; lobby 12.5 Pa; verify with door open force ≤133 N.

Fire dampers required at duct penetrations of fire-rated assemblies; smoke dampers in smoke barriers per Mabhas 3.

Fire extinguisher selection by hazard class A/B/C; travel distance limits per Mabhas 3 and NFPA 10.

Hydrant flow test: measure static, residual, and pitot pressure; compute available flow at 20 psi residual (Q = Qtest × (hres-20)/(hstatic-hres)^0.54).

Natural gas heating value in Iran typically 35–38 MJ/m³ (lower heating value); LPG ~46 MJ/kg or ~93 MJ/m³ vapor.

Combustion air: 1 m³ natural gas requires ~10 m³ air stoichiometrically, with 25–50% excess air typical for boilers.

Gas pipe sizing: use Mabhas 17 tables based on pressure drop method; allowable loss typically 1 mbar for low-pressure residential systems.

Gas pipe material: steel (black) for buried and internal; PE for buried exterior; copper restricted; no plastic above ground indoors.

LPG storage: cylinder separation distances per Mabhas 17; vaporizer sizing based on peak draw and ambient temperature.

Flue and vent: Category I appliances require vertical vent with draft hood; Category IV requires sealed vent with positive pressure.

Gas leak detection: install at high points for natural gas (lighter than air) and low points for LPG (heavier than air).

Combustion efficiency test: measure O2/CO2, flue temperature, and CO; CO must remain below safety thresholds (typically <100 ppm air-free).

Refrigeration cycle: COP = cooling effect / compressor work; Carnot COP = Tc/(Th - Tc) in Kelvin.

Chillers: water-cooled ~0.6–0.7 kW/TR, air-cooled ~0.9–1.1 kW/TR; IPLV values reflect part-load efficiency.

Refrigerant safety: R-410A is A1 but higher pressure; R-32 A2L; R-290 A3; comply with ASHRAE 34 and Mabhas 22.

Cooling tower approach = leaving water temp − wet bulb; design 3–5 K; condenser water 29–35 °C typical.

Compressor types: reciprocating, scroll, screw, centrifugal; centrifugal surge at low flow; use VFD or hot gas bypass.

Evaporator superheat 5–8 K; subcooling 5–10 K; check TXV adjustment and charge.

VRF systems: diversity factor and pipe length limits; oil return and branch joint sizing per manufacturer.

Absorption chillers: COP ~0.7 single-effect, ~1.2 double-effect; driven by steam or hot water.

Mabhas 14: HVAC design - outdoor design conditions, ventilation rates, load calculation methods, duct and pipe design.

Mabhas 16: Sanitary and plumbing - fixture units, pipe sizing, venting, water supply, drainage, storm drainage.

Mabhas 17: Gas systems - pipe sizing, materials, venting, safety distances, LPG storage.

Mabhas 22: Energy efficiency in buildings - envelope U-values, HVAC efficiency, lighting power density, commissioning.

Mabhas 3: Fire protection - sprinklers, standpipes, smoke control, fire dampers.

Mabhas 19: Building insulation - envelope thermal requirements by climate zone.

Mabhas 21: Passive defense and seismic - mechanical equipment anchorage and seismic restraints.

Standards hierarchy: national code overrides project spec where stricter; check latest edition and official amendments.

Supervising engineer duties: review shop drawings, approve materials, inspect installation, witness tests, and issue non-conformance reports.

Stamp and seal: only the registered engineer may seal drawings within their competence; unauthorized practice is a violation.

Conflict of interest: disclose financial interests in contractor or supplier; recuse from approval decisions.

Record keeping: maintain daily logs, RFIs, submittals, test reports, and as-built records for the statutory retention period.

Safety: supervisor must halt work when imminent danger exists and report to the employer and authority.

Confidentiality: protect client information; do not disclose without consent except where required by law.

Continuing competence: maintain knowledge of current codes and standards; sign only work you are competent to perform.

Whistleblowing: report code violations or public safety risks through proper channels; document all actions.

Contract types: lump-sum, unit-price, cost-plus; Iranian conditions of contract (Mabhas 1 and 2) define obligations, variations, and claims.

Payment certificates: measure work completed, apply retention (typically 5–10%), deduct advances, and certify within contract period.

Variation orders: require written instruction, price adjustment per contract rates, and time extension if critical path affected.

Bill of quantities: measure per standard method (e.g., CESMM or Iranian metering instructions); mechanical items measured by length, number, or weight.

Escalation: price adjustment formulas indexed to official statistics; apply only where contract permits.

Delay analysis: use as-planned vs as-built, time impact, or window analysis; concurrent delay rules per contract.

Mechanical quantity takeoff: pipe measured centerline excluding fittings; duct measured by surface area; equipment counted by unit.

Final account: reconcile measured quantities, variations, claims, and retention; issue taking-over and performance certificates.