HKIE Professional Assessment - Energy Discipline flashcards

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

Exergy

The maximum useful work obtainable from a system as it reversibly comes to equilibrium with its environment. Unlike energy, exergy is destroyed by irreversibility, so exergy analysis pinpoints where quality of energy is lost.

Capacity factor

Actual energy generated over a period divided by the energy the plant would produce running at rated output continuously. It measures how fully a generating asset is used.

Load factor

Average load divided by peak load over a period. A low value indicates peaky demand, meaning capital-intensive plant is underused and unit costs rise.

Carnot efficiency

The maximum thermal efficiency of any heat engine between a hot reservoir at Th and cold reservoir at Tc, both in kelvin: 1 minus Tc over Th. It is an unattainable upper bound.

Overall heat transfer coefficient

A combined coefficient U for a wall or exchanger, where 1/UA equals the sum of convection and conduction resistances. The largest resistance dominates the design.

NTU effectiveness method

A heat exchanger design method using effectiveness, the ratio of actual to maximum possible heat transfer, and NTU, the number of transfer units. It avoids iterative outlet temperature solving.

Rankine cycle

The steam power cycle of pump, boiler, turbine and condenser. Efficiency improves with higher steam pressure and temperature, lower condenser pressure, reheat and regenerative feedwater heating.

Combined cycle efficiency

A gas turbine exhausting into a heat recovery steam generator that drives a steam turbine. Overall efficiency of 55 to 62 percent exceeds either simple cycle alone.

Turbine heat rate

The thermal energy input in kilojoules per kilowatt-hour of output, equal to 3600 divided by cycle efficiency. A lower heat rate means better plant performance.

Theoretical air for combustion

The stoichiometric air required to fully oxidise a fuel; for a hydrocarbon CxHy, oxygen moles equal x plus y over four per mole of fuel. Practical plant uses excess air above this.

Betz limit

The maximum fraction of wind kinetic energy a turbine can extract, 16 over 27 or about 0.593. Real turbines achieve power coefficients of 0.35 to 0.45.

Performance ratio of PV

Actual PV energy yield divided by the yield expected at standard test conditions. Values of 0.75 to 0.85 account for temperature, soiling, inverter and wiring losses.

PV temperature coefficient

The fractional change in module power per kelvin above 25 degrees Celsius, typically minus 0.3 to minus 0.45 percent per kelvin. Hot modules therefore produce less than rated output.

Feed-in tariff

A guaranteed payment per kilowatt-hour for renewable generation exported or generated over a fixed contract term. Hong Kong operates technology and capacity banded rates under CLP and HK Electric schemes.

IPMVP Option C

A measurement and verification approach that uses whole-facility metered energy, with a regression baseline adjusted for weather and activity, to determine savings from a retrofit programme.

Simple payback period

Capital cost divided by annual energy cost saving, expressed in years. It ignores the time value of money and any savings beyond the payback period.

Affinity laws

For a centrifugal fan or pump, flow varies with speed, head with speed squared, and shaft power with speed cubed. Halving speed cuts power to about one eighth.

Load duration curve

A plot of load against the hours per year it is equalled or exceeded. It shows how much time peak plant runs and helps size generation and demand-side measures.

Chiller kW per RT

Cooling power input in kilowatts per refrigeration ton of cooling delivered, related to COP by 3.517 divided by COP. Water-cooled chillers typically reach 0.55 to 0.65.

Low delta-T syndrome

A condition where chilled water returns too warm, giving a small supply-to-return difference. Flow must rise, pumping energy increases and more chillers are forced on.

Power factor correction

Adding capacitors to raise power factor toward unity, reducing kVA demand, cable losses and utility penalties. Capacitor kVAr equals kW times the tangent difference of the two angles.

Demand-controlled ventilation

Modulating outdoor air intake using CO2 or occupancy sensors instead of a fixed design rate. It saves fan and cooling energy where occupancy varies through the day.

Levelised cost of energy

Total discounted lifetime cost divided by discounted lifetime energy output, giving a cost per kilowatt-hour. It excludes system integration and flexibility costs of variable generation.

Scope 2 emissions

Indirect greenhouse gas emissions from purchased electricity, heat, steam or cooling, calculated by multiplying consumption by a grid emission factor. Reported location-based or market-based.

Marginal abatement cost curve

A ranking of measures by cost per tonne of carbon dioxide equivalent abated, with negative-cost measures on the left. It guides which measures to implement first.

Fuel clause adjustment

A tariff component that passes through changes in fuel cost to customers, adjusted periodically. It separates fuel price risk from the basic charge for capacity and network.

Retro-commissioning

A systematic process of testing and tuning existing building systems to meet current operating needs. It typically delivers 5 to 15 percent energy savings at low capital cost.

Lockout tagout

A hazardous energy control procedure isolating and locking all energy sources before maintenance, with isolation verified by test rather than assumed from a drawing.

Environmental permit

An approval required under the Environmental Impact Assessment Ordinance before constructing or operating designated projects, setting binding conditions on emissions, noise and ecology.

HKIE Code of Conduct

The professional obligations of HKIE members: integrity, competence within one's field, priority of public safety, and written disclosure of conflicts of interest.

Continuing professional development

Documented ongoing learning required to maintain professional registration, covering technical and non-technical subjects and recorded against a minimum annual hours requirement.

Signing and sealing work

Certifying personal technical responsibility for a design or report. A member should sign only work personally supervised or reviewed and should record the basis of judgement.