Egypt Engineering Consultant Mechanical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Sensible heat ratio

The ratio of sensible cooling load to total cooling load, SHR = Qs/(Qs + Ql). It determines the apparatus dew point required to meet room conditions and whether reheat or a dedicated outdoor air unit is needed.

Coil bypass factor

The fraction of air that passes the coil without contacting its surface, BF = (h_out − h_ADP)/(h_in − h_ADP). Lower bypass means more rows or lower chilled-water temperature and a closer approach to saturation.

Carnot refrigeration COP

The maximum COP between two temperatures, COP = T_evap/(T_cond − T_evap) with absolute temperatures in kelvin. Real cycles achieve roughly 50-70 % of this value depending on compressor and heat exchanger effectiveness.

VRF diversity factor

The ratio of total indoor unit capacity to outdoor unit capacity, typically 0.7-0.9. It reflects that not all indoor units run at full load simultaneously and must respect manufacturer connection limits.

Fixture unit

A dimensionless measure of the probable load a plumbing fixture places on the water supply or drainage system. Fixture units are summed and converted to design flow using Hunter curves or code tables.

Trap water seal

The depth of water in a trap, normally 50-75 mm, that blocks sewer gas. Venting must limit pressure fluctuation across the seal to about ±250 Pa to prevent blow-out or siphonage.

Sprinkler design density

The water flow rate in mm/min applied over the design area for a given hazard class. Light hazard is about 2.25 mm/min, ordinary 5.0 mm/min, and extra hazard up to 12.5 mm/min.

Jockey pump setting

A small pump that maintains system pressure and starts about 10 psi above the main fire pump start pressure, stopping below it. It prevents the main pump from cycling on minor leaks.

Dittus-Boelter equation

A convection correlation, Nu = 0.023 Re^0.8 Pr^n, with n = 0.4 for heating and 0.3 for cooling. It applies to fully developed turbulent flow in smooth tubes with Re above 10,000.

Pump affinity laws

For a geometrically similar pump, flow varies with speed, head with speed squared, and power with speed cubed. They allow predicting performance at a new speed or impeller diameter from a known point.

Overall heat transfer coefficient

The combined conductance U across a wall, where 1/UA is the sum of convection film and conduction resistances in series. It is used with q = UA·LMTD for heat exchanger and envelope calculations.

Log mean temperature difference

The effective temperature driving force in a heat exchanger, LMTD = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2). It is used with a correction factor F for multipass and cross-flow arrangements.

Isentropic compressor efficiency

The ratio of ideal isentropic work to actual work, η_s = (h2s − h1)/(h2 − h1). It captures internal losses and is used to find the real discharge temperature and power.

Generator derating

Reduction of a generator's rated output for ambient temperature above 40 °C, altitude above 1000 m, and power factor below 0.8. Manufacturers publish derating curves used during sizing.

Chiller kW per ton

The input power in kW required per ton of refrigeration. A value of 0.55 kW/ton equals COP 6.4; lower values indicate higher efficiency and drive operating cost comparisons.

Combined cycle efficiency

The overall efficiency of a gas turbine whose exhaust heat generates steam for a bottoming steam turbine. Modern combined cycles reach 55-62 %, well above simple cycle values of 35-40 %.

Boiler indirect efficiency

Efficiency found by subtracting all losses, including dry flue gas, moisture, unburned carbon and radiation, from 100 %. It identifies where heat is lost and guides improvement measures.

Fan power equation

Shaft power in kW equals air flow in m³/s multiplied by total pressure in Pa, divided by 1000 and by fan efficiency. Motor input power adds belt and motor losses.

BACnet device instance

A unique integer identifying each device on a BACnet internetwork. Duplicate instances cause communication conflicts, so the controls contractor must maintain a device instance register.

Voltage drop limit

Branch circuits are usually limited to 3 % voltage drop and the total from origin to load to 5 %. Cable size is increased when the calculated drop exceeds these limits.

Power factor correction

Capacitor kVAr equals active power times the difference of tangents of the initial and target power factor angles. Correction reduces current, losses and utility penalty charges.

PID control output

The controller output is Kp·e + Ki∫e dt + Kd·de/dt, where e is the error between setpoint and measured value. Tuning balances response speed against overshoot and oscillation.

Star-delta starting

A motor starting method that connects windings in star for run-up then delta for normal operation. It reduces starting current and torque to about one third of direct-on-line values.

Egyptian Fire Law 308

Law 308 of 1955 and its executive regulations form the basis of fire protection requirements in Egypt. The Egyptian Fire Code supplements it with detailed occupancy, egress and system rules.

FIDIC claim notice period

Under the FIDIC 2017 Red Book, a contractor must give notice of a claim within 28 days of becoming aware of the event, or the claim is time-barred.

Order of precedence clause

A contract clause ranking documents to resolve conflicts, typically agreement, conditions, specifications, drawings and bill of quantities. It determines which document governs when documents disagree.

Earned value cost index

CPI equals earned value divided by actual cost. A value below 1.0 means cost overrun; forecast at completion equals budget at completion divided by CPI when performance continues.

AACE estimate class

A classification of estimate accuracy by project definition. Class 5 is −30 %/+50 %, Class 3 is −20 %/+30 %, and Class 1 is −10 %/+15 % at full definition.

Contingency versus management reserve

Contingency covers identified risks and is part of the project budget. Management reserve covers unknown-unknowns, sits outside the budget, and requires sponsor approval to release.

Hierarchy of controls

The order of risk control: eliminate, substitute, engineering controls, administrative controls, then personal protective equipment. PPE is the last line of defence, not a substitute for design controls.

Confined space entry testing

Before entry, test oxygen (19.5-23.5 %), flammable gas below 10 % of the lower explosive limit, and toxic gases. Continuous monitoring, an attendant and a rescue plan are required.

Standard of care

The degree of skill and care of a reasonably competent engineer in similar circumstances. Breach of that standard, causing loss, establishes negligence; it is not a guarantee of perfect results.