Engineer Building Facilities cheat sheet

Office cooling load rule of thumb: 1 refrigeration ton per 350–400 sq ft of conditioned area; confirm with a block load before sizing or replacing equipment.

Chiller efficiency: kW/ton = 3.517 ÷ COP. A chiller at 0.60 kW/ton is operating at about COP 5.9; lower kW/ton is better.

Fan and pump affinity laws: flow ∝ speed, head or static pressure ∝ speed², brake horsepower ∝ speed³. Reducing speed 20% cuts power to about 51%.

Air-side economizer may operate when outdoor air enthalpy (or dry-bulb) is below return-air conditions; typical dry-bulb changeover setpoints are 55–65°F.

Cooling tower approach = leaving condenser-water temperature − entering wet-bulb temperature; design approach is commonly 3–7°F, and a rising approach signals fouled fill or poor water distribution.

ASHRAE 34 refrigerant safety groups: R-410A and R-134a are A1; R-123 is B1; ammonia (R-717) is B2L and requires detection plus ventilation for occupied spaces.

Elevators follow ASME A17.1/CSA B44 as adopted by NYC Building Code Chapter 30: annual inspections plus periodic Category 1 and Category 5 tests on five-year cycles.

Three-phase electrical: kVA = √3 × volts × amps ÷ 1,000; kW = kVA × power factor. Single-phase kW = volts × amps × PF ÷ 1,000.

Plumbing trap seal depth is 2–4 in. Where a fixture is used infrequently, provide a trap primer or trap guard to prevent seal evaporation and sewer gas entry.

Span of control: 3–7 direct reports per supervisor is the normal range; wider spans require standardized procedures, fewer exceptions, and experienced staff.

Productive hours per FTE ≈ 2,080 − (vacation + holidays + sick + training) ≈ 1,750–1,850 hours per year; use this figure, not 2,080, for staffing calculations.

Availability = MTBF ÷ (MTBF + MTTR). 99% availability permits about 87.6 hours of unplanned downtime per year; 95% permits about 438 hours.

Turnover rate = separations during the period ÷ average headcount during the period × 100.

OSHA 29 CFR 1910.147 requires lockout/tagout for servicing equipment with hazardous energy; 1910.132 requires a written PPE hazard assessment and training.

OSHA 1910.1200 hazard communication training is required at initial assignment and whenever a new chemical hazard is introduced into the work area.

Backlog in weeks = open work orders ÷ average weekly completion rate. A backlog beyond 4–6 weeks indicates understaffing, poor scheduling, or a parts bottleneck.

Progressive discipline sequence: documented verbal warning → written warning → suspension → termination, applied consistently and with a stated improvement period.

The NYC Construction Codes comprise the Building, Plumbing, Mechanical, Fuel Gas, Energy Conservation, and Fire Codes, plus referenced standards including the NYC Electrical Code.

NYC Building Code high-rise threshold: a building with an occupied floor more than 75 ft above the lowest level of fire department vehicle access.

FISP (Local Law 11): exterior walls and appurtenances of buildings more than six stories must be inspected every five years by a Qualified Exterior Wall Inspector and filed as Safe, SWARMP, or Unsafe.

Local Law 97 carbon caps apply to covered buildings over 25,000 sq ft, with limits for 2024–2029 and stricter limits for 2030–2034; annual reports are filed by May 1.

Local Law 84 benchmarking requires annual ENERGY STAR Portfolio Manager submission for buildings over 25,000 sq ft; Local Law 87 requires an energy audit and retro-commissioning every 10 years over 50,000 sq ft.

NFPA 25: sprinkler gauges and valve positions checked monthly, annual main drain flow and alarm tests, internal pipe inspection every five years, standpipe hydrostatic test every five years.

Portable fire extinguishers: monthly visual check, annual maintenance by a licensed technician, hydrostatic test at 5 years (CO2), 6 years (dry chemical), or 12 years (stored water/foam).

NFPA 110: emergency generators are exercised weekly and load-tested periodically; Level 1 systems typically receive an annual test at ≥30% of nameplate for at least 30 minutes.

Before renovating, NYC DEP requires an asbestos inspection filing (ACP-5, or ACP-7 for small residential); OSHA 29 CFR 1926.1101 governs worker protection during disturbance.

Capital vs expense: spending above the capitalization threshold (often $5,000–$10,000) that extends useful life is capitalized and depreciated; routine repairs are expensed in the year incurred.

Simple payback (years) = initial capital cost ÷ annual net savings. It ignores time value of money, so pair it with NPV or life-cycle cost analysis for major projects.

Life-cycle cost: PV = Σ Ct ÷ (1 + r)^t over the study period, including capital, energy, maintenance, and replacement costs.

Three-way match: purchase order, receiving report, and vendor invoice must agree on quantity and price before accounts payable releases payment.

Retainage typically withholds 5–10% of each progress payment until substantial completion and punch-list closeout.

Liquidated damages are a pre-agreed per-day amount for late completion; they must be a reasonable forecast of owner loss, not a penalty, to be enforceable.

Contract types: lump sum for fully defined scope, unit price for measured quantities, time and materials for unknown scope, guaranteed maximum price for CM-at-risk, IDIQ for recurring indefinite needs.

Deferred maintenance ratio = deferred maintenance backlog ÷ current replacement value; benchmarks treat ratios above roughly 2–5% as escalating capital risk.

Escalation: future cost = current cost × (1 + r)^n. At 3% annually, a $1.00 cost today is about $1.34 in 10 years.

Sensible air heat: Q (Btu/h) = 1.08 × CFM × ΔT (°F).

Latent air heat: Q (Btu/h) = 0.68 × CFM × Δgrains, or 4,840 × CFM × Δlb/lb moisture ratio.

Water heat: Q (Btu/h) = 500 × gpm × ΔT (°F), where 500 = 8.33 lb/gal × 60 min.

1 refrigeration ton = 12,000 Btu/h = 200 Btu/min = 3.517 kW.

Pump brake horsepower = (gpm × head in ft × specific gravity) ÷ (3,960 × pump efficiency).

Fan brake horsepower = (CFM × total pressure in inches w.g.) ÷ (6,356 × fan efficiency).

Duct airflow: CFM = velocity (ft/min) × area (ft²). A 12 in. × 12 in. duct at 1,000 fpm carries 1,000 CFM.

Pressure conversion: 1 psi = 2.31 ft of water column; 1 ft of water = 0.433 psi.

Illuminance by lumen method: E (footcandles) = (lumens per lamp × lamps × coefficient of utilization × light loss factor) ÷ area (ft²).