Basic Engineering Practice
What the exam tests
Basic Engineering Practice is the "everything else" domain: units and dimensional analysis, engineering economics, statistics and uncertainty, codes and standards, project delivery, and professional ethics. Questions are usually short and deceptively simple, so the real skill is disciplined unit tracking.
Concepts to master
- Unit conversions: 1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW. 1 kWh = 3,412 Btu. 1 hp = 2,545 Btu/h = 0.746 kW. 1 psi = 2.31 ft of water. 1 in. w.c. = 0.0361 psi.
- Reference states: gauge vs. absolute pressure (add 14.7 psi), and °F vs. °R (add 459.67) whenever a gas law or Carnot relation is involved.
- Economics: present worth, annual worth, capitalized cost, simple payback, and life-cycle cost. Watch the compounding period and whether the interest rate is nominal or effective.
- Statistics: mean, standard deviation, and propagation of uncertainty in a calculated result.
Common traps
Substituting volumetric flow where mass flow is required without a density correction; treating nominal and actual lumber/duct/pipe dimensions as equal; forgetting that fan and pump power scale with the cube of speed; and dropping a 1.08-type constant where the actual density differs from standard air (0.075 lb/ft³).
Worked example
A chiller is rated 350 kW of cooling. Convert to tons: 350 kW × (3,412 Btu/h per kW) ÷ 12,000 Btu/h per ton = 99.5 tons (or 350 ÷ 3.517 = 99.5 tons).
Rule of thumb: 1 gpm of water with a 1°F temperature change carries 500 Btu/h; 1 cfm of standard air with a 1°F change carries 1.08 Btu/h.