CH:
There are different techniques for measuring and calculating energy use and energy
efficiency, and we will look at some of them today.
CH….
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CH:
But we will also look at when to measure vs calculate and how they are applied.
Kevin, why do we measure energy and what is it used for?
Hand over to KH ….
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KH: Some ideas are so simple and so cheap that we can just use trial and error to see if we get
the benefit we think will happen.
However, for many improvement suggestions we need to introduce a bit more rigour especially
where:
• to implement the idea will cost time and or money and we need to be careful to get the best
outcome
• there are ideas which are competing for funding or effort, or something similar and so we
need to make a choice
• we need to be able to demonstrate that the idea has worked and that we have gained a
benefit
• we’re not sure what/where the problem is and so where to put our effort.
In these cases we need to be able to analyse and compare the ideas. To do this we need relevant
information to help us make these decisions and to demonstrate the benefits. The best way to
do this is through the use of appropriate numbers.
If we can measure the current energy use in different parts of the process, we can work out
which parts use the most energy.
If we measure energy use, we can also measure the energy saved by implementing the idea and
so we have hard data to argue our case and demonstrate that the benefits have been achieved.
Or we might want to compare our energy use to what other people are doing and this might
help us know whether to proceed. This is typically called a benchmark and provides data for
similar businesses based on location, type of business, size and so on. For example, hotels can
use the ‘Earthcheck’ benchmark figures for ‘energy use per guest per night’.
KH ….
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KH:
Measurement is usually about reading gauges or meters. These gauges/meters may
already be installed or you may need to have them installed.
Typically for an energy improvement initiative, a largish number of temporary gauges
allowing us to both read and record energy use will be installed and we usually call this
data logging. This is to give us the information we need to analyse and improve our
energy efficiency.
Having done this we may install some permanent meters to aid ongoing energy
efficiency
Hand over to CH ….
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CH: So once we’ve done some measurements, why do we need to use calculations?
Hand over to KH ….
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KH:
While measuring is good, sometimes it is not practical to measure everything.
For example we might calculate when:
• measuring equipment is not installed and to install it may be expensive/take time
• the wiring/plumbing system is such that to identify or meter individual items would
be extremely difficult
• we’re not sure what parts of the process will benefit most from installing measuring
equipment
In these situations we may need to estimate energy use through calculation, either to
work out where we want to install the meters, or instead of installing meters.
And we can apply calculations in much the same ways we used measurements – to work
out which parts of a process use the most energy and to quantify the energy saved by
implementing an idea.
Often the initial calculations need not be completely accurate (just estimates) to help us
find the areas needing attention or as ballpark figures that we can use for comparison.
Another application is if we want to compare the energy we have used with the
‘theoretical energy use’. Put simply this is what we would have used in an ideal world
where none of the energy was wasted.
And we calculate this from some data about the materials we are using, the amount
consumed/produced, the context and so on.
KH ….
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KH:
We might also want to manipulate data that we have collected – from measurements,
energy bills or audits.
So we might calculate in order to:
• compare things that aren’t the same
• convert the data to make it more meaningful
• estimate the big picture from local data
• estimate the local picture from broader data
• model scenarios – test out ideas using different figures for production, costs, energy
use etc.
CH:
We will come back to modelling a bit later.
Chris, you use a combination of measuring and calculation in your audit process, can you
explain the types of calculations you might use?
CH - Hand over to Chris….
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Chris…
If you just look at one power bill you might find you’ve used 150 000 kWh. What does
this mean?
By itself, it means very little, just an amount of consumption.
So there are different ways of making the data more meaningful.
Typically you would collect 24 months data from bills and this allows you to see trends
as well as have a better picture of total energy use.
The amount of energy use will depend on
• whether it is summer or winter
• is the plant producing or shut down
• And what part of the value chain the data covers
These and many other questions may need to be answered in order to turn this data into
meaningful information.
Chris…
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Chris…
The first question we should answer is: ‘What part of the value chain does it cover?”
If it covers all of the value chain at a given site, we might do some calculation to make
sense of it.
If it covers the manufacturing plant, then it might be useful to divide this amount by the
volume of material produced over this period. We would measure volume of production
in terms of number of units, litres, tonnes or metres. This is usually obvious from day to
day operations.
This then gives us kWh/unit of production. We can now compare this ratio over time.
If the energy use is only for the production process, then this ratio should be fairly
steady. If it goes up and down with the weather, then it shows you have heating and
cooling costs included and so on.
If the energy use is only for an office, or similar facility, then it might be more
appropriate to express this as a ratio of kWh to hours worked or something similar.
Typically if we can express the energy use as a ratio to some measure of work effort then
it will be more useful.
Chris…
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Chris:
Typically when we start analysing energy efficiency we only have data applying to the entire site or
business, or at least to large chunks it. One of the first things we may wish to do is to try and estimate how
much of the total energy usage we can attribute to each area. We’ll restrict this discussion to electricity
just to make it less confusing. The same principles can be applied to other energy sources.
Count and multiply
The simplest way of doing this is to simply walk through each area, count the number of energy using
devices and then multiply by the rating of each item. This works well for things like lights, computers and
plant and equipment where you have the specifications or the rating plate. Let’s look at some examples.
Lights
You walk through a work area and county 315 light globes/fittings, each globe or fitting is 100W (you’ll
know the wattage from the globes you buy to replace them).
So, this area consumes 315 x 100 = 31 500 W or 31.5kW
This area has the lights on for 9 hours per day, 5 days per week and so uses 9 x 31.5 = 283.5 kWh/day or
283.5 x 5 = 1417.5 kWh/week.
Motors and appliances
All electric motors and appliances have a rating plate. These may not always be obvious, but they do have
one. As with the light globes, if we multiply the rated kilowatts by the hours it is turned on we will get
kWh.
Adding all of these up for an area will lead to the total kWh for motors and appliances in the area.
Summing it up
If we add up all of these kWh numbers for an area we will get an estimate of the total energy use for that
area.
If we repeat this for all areas covered by the bill, and add the values for each area, we should get a total
something like the value on the bill. It may vary a bit. If it varies too much, ask questions and find out why.
This information will quickly show which areas use the most energy and so where efforts to reduce energy
use will be most effective.
CH: thanks Chris – you’ve touched on some different sources of data for these calculations, and we one
of our energy efficiency videos looks at this in more detail - available from sustainabiltyskills.net.au at the
energy efficiency videos page.
CH…
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CH:
We mentioned modelling before and this is another use of calculations. We have a video
clip where Phillip the operations manager from Marquis Bathroom products is talking
about how they used modelling when deciding about solar energy…
CH: Kevin, how would you use calculations in modelling?
KH:
Modelling is about using maths to work out the possible impacts of a change before we
actually make the change.
Replacing old with new may be a great energy saver. This needs to be balanced against
the cost of the replacement and a business case made. Sometimes the savings are
sufficient to justify the change. But how do you know without buying, installing and
testing it out?
KH ….
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KH:
So for example if we currently have two, 22 kW compressors running 24 hours per day,
five days per week, we can calculate that they will be consuming 2 x 22 x 24 x 5 =5280
kWh per week.
KH…
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KH:
If we now add one 5 kW compressor which runs 8 hours per day while the 22 kW
compressors now only run 16 hours per day, we can model our new energy use for the
compressors:
2 x 22 x 16 x 5 = 3520
5 x 8 x 5 = 200
Total energy use = 3520 + 200 = 3720 kWh
KH…
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KH:
So with a quick calculation you can see a saving of 1560 kWh/week.
This is quite a simple example of modelling, but we could use the same approach for a
more complex modelling and may choose to set it up in a spread sheet so we can easily
do ‘what if’ scenarios.
As Phillip was talking about in the video clip – they factored in some ‘what ifs’ about
energy price increases and additional equipment they might need in the future. So theirs
were much more complex calculations - they looked at the capacity of their current
electricity supply, their current and future energy needs, projected costs and production
rates and so on.
Hand over to CH…
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CH:
So measuring and calculating are both key aspects of quantifying energy efficiency and
are often complementary.
While measurements can be very accurate they are not always possible or necessary and
calculating an approximate figure is often sufficient for comparisons and identifying
problem areas for further investigation.
And using calculations to model different scenarios is useful to predict the energy
savings and the costs of achieving them
CH….
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