Past Paper Answers SOLA5057 Flashcards
Compare the simple payback period with discounted
payback period.
Qualitatively explain the difference
SPP - used for low capital and immediate substantial savings
Discounting - useful when comparing projects with different cost profile (i.e. coal plant, high fuel cost, wind farm, high capital cost). The amount of money in the future is converted to present day value. Money in future is worth less than today money .
Briefly describe incandescent, fluorescent, compact fluorescent, high intensity discharge, and low pressure sodium lamps and discuss their luminous efficacy.
Incandescent - inert gas inside frosted glass. Tungsten filament heated with electricity, CRI 100, CCTs 2600-3000, 15lm/Watt
Halogen Lamps - (a type of incandescent, downlights, need a log 40W each, very inefficient) 20lm/W
Fluorescent - sealed glass tube, small amount of mecury and low pressure inert gas. fluorescing coating on glass tramsforms UV energy to light. 70-90lm/W CRIs 80 CCTs 2900-7000. cheaper than CFLs, more light, last longer
Compact fluorescent - small diameter fluroescent, folded for compactness. 70lm/W last about 10 000 hours
High intensity discharge - produce light by striking electrical arc across tungsten electrodes inside glass tube filled with gas and metals. High temp high pressure
Low pressure sodium lamps - up to 180 lm/W highest efficacy of common lighting
operate like fluorescent lamp, CRI is 0
Discuss FOUR energy saving methods that can be used to increase industrial furnace efficiency and/or reduce greenhouse gas emissions.
- Rescheduling
schedule so furnace is operating only at full load or shut down. At least reduce energy consumption whilst holding, use furnace with low thermal mass - Regular maintenance of furnace
correct fit and operation of dampers, sealing any gaps, charge feed and removal mechanisms, burners, air-fuel ratios, oil-line heaters, and cleaning of fans, pumps and fillers - Controls
Automatic controls will change furnace conditions to
suit the load and so reduce energy use and increase furnace lifetime. - Insulation
Not only increases energy efficiency but improves safety by protecting from high
internal temperatures.
or
one from: heat transfer, heat gen, heat containment and heat recovery
What is Combined Cycle Generation, what are some of its advantages, and how can it result in reduced GHG emissions?
After gasses have been used to drive a turbine, they are used to heat water to steam, which then drives a steam turbine.
CCG have efficiencies around 55-60%
more efficient = less GHG emissions
Briefly describe the three different approaches to increase transport efficiency.
- Reducing aerodynamic and rolling drag
better shape
lighter
lower RR tyres (inflated correctly) - Switching to EVs and hybrid rather than ICE
ICE run at 15-30% efficiency
EVs run at 75-95% efficiency - CVT (continuous variable transmission) or manual transmissions are generally more efficient than automatic
Briefly outline how the efficiency of a compressed air system can be improved at the point of end-use.
air must be supplied at correct pressure range
air must be clean of particulates etc. These can cause blockages and increased energy consumption.
Air lubrication: air will often contain atomised lubricant
needed for downstream machinery. Lack of lubricant
causes increased friction in tools which leads to wear and energy losses.
Air dryness: excess moisture will condense out and may
block pipes
Briefly outline how the efficiency of a compressed air system can be improved in the distribution network.
inadequate pipe sizing and layout, which can cause pressure losses. Want short, straight, wide pipes to reduce pressure loss
condensation and the methods used to remove it
filters, which can become obstructed
prevent leakages
removal of condensation, used sloped pipes, dessicants
Briefly outline how the efficiency of a compressed air system can be improved at the compressor
Correctly match compressor to the task.
compress air in steps and
cool before each subsequent stage
Cogged belts and VSD’s can improve the drive system efficiency.
The compressor generates a lot of waste heat. It is also noisy and therefore usually well insulated, could use a heat exchanger
Briefly describe 5 different barriers to energy efficiency.
- Lack of understanding of benefits
- Lack of available info
- Captial costs (cheaper to not be efficient in short term)
- lack of policy incentives
- laziness, time priority
Briefly describe 5 different market based policy mechanism that could be used to encourage more efficient usage of energy or energy production with lower carbon emissions than fossil fuels. Give a brief example for each mechanism.
- Subsidies (STC, RE Target)
- taxes (Carbon tax and ETS)
- levies (North Syd Council)
- licence conditions (equiptment licence EQPL)
- buyback tarrifs - solar PV feed in tarrifs
What is meant by taking an ‘entire systems approach’ when optimising an electric motor system? Why is it important?
ESA = more savings because multiple components all with individual losses that multiply and compound, as the system progresses
1kw of energy saved at pipe = 2.4 kW of energy saved at motor
What is a variable speed drive? For a pumping system explain why variable speed drives are a more efficient way to control flow than mechanical throttling with a valve. Draw a Pressure vs Flow rate and a Power vs Flow rate graph to help explain your answer.
for very large flow machines, particularly screw type compressors. They are efficient because they match well the compressor output to the air demand
Briefly explain what power factor is, what causes it, and why it causes energy losses
ratio of the real power and the apparent power
Power factor near 1 will reduce the reactive power in the circuit and most of the power in the circuit will be real power. This will also reduce power lines losses.
