The meaning of Energy Star Ratings

May 10th, 2018

This section is a regular feature of our newsletters.  It is intended to be unbiased, general Industry comment dealing in objective facts.

What do Star Ratings mean?   They have been used in the US since the 1970s and in Australia since the 1980s.   There used to be a 6 star system, which was based on a fixed amount of energy improvement per star, but now we have a 10 star system, with a cumulative % improvement per star.

When I see, say, a 4 star, versus a 7 star, refrigerator for example, how can I tell that whether the extra price is worth it? When I look at the estimated annual energy consumption on the typical ERL (Energy Ratings Label), such as below, how meaningful is it?

Source: Wikipedia

As always, the devil is in the detail.

Let’s start by putting the energy use of the commonest appliances into perspective.  The following chart shows the aggregate Australian use of energy for various appliances.

It is in PJ (petajoules), peta being 10 to the power 15.  One joule is 1 watt for a second.

1 Petajoule is equal to 278 Gigawatt hours, which is the heat content of 43,000 tonnes of black coal or 29 million litres of petrol.  Total annual Australian Energy consumption is about 6,000 PJ.

Source: ESS and Energy Ratings Label Review Report

Pool equipment would appear on the chart above at about 16 Peta Joules (PJ).  Bearing in mind that only one in 6 houses has a pool and that all houses have (multiple) refrigerators, pools are far and away the largest, single energy consuming ‘appliance’ in most pool-owning homes.

Star Ratings

A single star means that the appliance is a 20% improvement upon a standard test appliance that happened to be in common use at the time the star test was agreed.  Under the present rating system it is a sliding scale with each star another 20% improvement over the previous star.

So, one star wins you a 20% improvement over the ‘test appliance’.  Two stars gets you 36%.  Three stars get you 49%, four stars 59% and 5 stars 67%.  From there, the going gets tougher.  The difference between a 9 star and a 10 star is only 2% of the original consumption.  So clearly, the more stars the better, but once you get to about 5 stars, further improvement is significantly small.

The other part of the ERL or Energy Ratings Label, is the energy consumption estimate.   Here, you really have to read the small print as you can find some very optimistic estimates.  For example, a clothes drier estimated to use 104 kWh per annum was tested for 2 hours a week running at 25 degrees air temperature at 50% humidity.  This bears very little resemblance to a real world situation of 4 kids and the drier running many hours a day in a humid environment.  The real world consumption of the drier in the example, could be 10-20 times what it is on the label.

The estimate for a refrigerator is likely to more accurate as it does not depends as much on the number of times you use it, since it is on all the time, but it really depends on where it is located, how well it is ventilated, what temperature it is set to, how much food is kept in it and how often you open the door.

In the case of pool pumps, which currently have a voluntary labelling system, there is an emerging standard with star ratings and energy use estimates that is in much the same category as the clothes drier.  It all depends on how the pump is used.  The standard test for a pool pump was set up about 50 years ago and is against a theoretical filter that bears little resemblance to modern filters.

The real energy measure of any pump in any application, is how well it is matched against the load.   In pools, this depends upon the type, size and cleanliness of the filter and what is in it, the skimmer, how many leaves are in it, the nature, size and shape of the plumbing, the chlorinator, heaters and other equipment in the circuit, the equipment location and many other things.  Applying an over-simplified test of a pump against a standard filter is something of a nonsense, as it does not represent the real world.

What is actually required in most control systems, pools included, is an adaptive system that senses what is going on and responds to it.  Your automatic car does this. You change the power level by pressing the accelerator and the car changes gear to match the load, depending on how you are driving, how much weight it is carrying and what sort of hill it is climbing.  You would not drive a car in top gear at full throttle all the time, which is exactly what a single speed pump in a pool does.

Likewise, you would not select a single, lower gear and a single accelerator setting for 6 months of driving, which is effectively what the so-called variable speed pumps in pools do.  Such pumps are not really variable speed, they are ‘settable’ speed.  You need systems that vary gears and speed when needed to match conditions.

Still, star labels are an important guide, especially for stand-alone devices such as refrigerators, air-conditioners, televisions and washing machines and driers as long as you read the small print on the amount of energy consumed.

If you have a 5 star appliance, getting one more star wins a further 7% in efficiency.  At 7 stars, the next one wins 4%. Is it worth it?   It depends on how much energy the appliance uses.  You should not assume that the annual energy consumption guide on the ERL Label is correct.  Thinks about what you are going to do with the appliance.  In the case of the drier,whose ERL consumption is estimated on the basis of weekly use, but the reality is multiple day uses, that drier will consume Megawatt hours rather than the indicated ~100kWh.  In this case, you should absolutely get a higher star rated drier.  Also, maybe a lot bigger one.  If a large drier takes twice the load, it may not run at quite half the aggregate time, but it should be more efficient than the small drier.  You need to do the calculation using whatever data is available.

As for refrigerators, it’s probably worth getting into the mid-star range.  One kWh costs about 30 cents on average, and so, if your fridge uses an extra 100 kWh p.a., that’s $30. You will likely have the fridge for 20 years and there is $600.  The annual energy usage guide on the label should be read carefully and can then be used as a basis for comparison.  However, where the appliance is deeply embedded in a system, such as a pool pump, the issue is system performance and not component performance.  Look at the overall result and see how well it really works.  A sensor based system with adaptive control will outperform any multi-star pump in virtually every situation, even if the pump itself has few or no stars.


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