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Archive for the ‘Electricity supply’ Category
A few months ago I wrote a blog posting about how tighter regulation of electricity supply voltages could save Australia 15 million tonnes of greenhouse gas a year.
However a comment on that posting suggested that voltage reduction may not result in any useful savings.
Below I report on the results of an experiment we undertook to identify how much power can be saved, if any, by operating equipment at a lower voltage.
We measured a variety of single phase loads at different voltages. A variable transformer was used to vary the voltage. A German made Power Tech plus plug in power meter was used to measure voltage, current, power and power factor at the different loads. Loads experimented with included typical single phase lights, computer equipment and a fan.
The experimental set up is shown above. Below is a graph showing the results of the testing.
This graph clearly shows that for common lighting loads power consumption decreases with decreased voltage
- Incandescent lamp (resistive load)
- T8 fluorescent (inductive load)
- T5 fluorescent (electronic ballast)
The reduction in power consumption with the T5 fluorescent (with an electronic ballast) was unexpected.
The fan, with a single phase (shaded pole?) motor, also used less power with lower voltage, interestingly the power factor improved as voltage was lowered, with the power factor the highest at 220 volts.
The PC computer and monitor both showed lowest power consumption at 230 and 240 volts, but power consumption generally did not decrease with voltage. Power factor improved a little at lower voltages.
This experiment shows that for a variety of loads power consumption is in fact less at lower voltage.
For heating or cooling loads equipment may need to run longer when at lowered voltage to reduce the same amount of heating or cooling, with no net energy savings.
Three phase synchronous motors are unlikely to use any more or less power (a theoretical assertion, we don’t have the equipment to test), having the motors run at 230 volts rather than 240 or 250 volts however is unlikely to cause motor damage due to excess current as the voltage difference is only small.
But with lighting and many single phase motors power consumption drops with lowered voltage.
My back of the envelope calculations still come up with a saving of around 15 million tonnes of greenhouse gas if voltages were closer to the 230 volt standard rather than being at 240 to 250 volts.
If high voltage drops in distribution were a problem additional network infrastructure could be used to deliver a more consistent voltage across the network. 2009 is the year of the “smart grid.” A smart grid could mean multitap transformers that can be changed on the fly to deliver a more consistent 230 volts across the whole electrical network.
T5 fluorescent lighting has been around for a while now, but is not yet widely used in the manufacturing or warehouse sectors. Paul Smith has compared T5s with metal halide, and is interested in how T5s compare in terms of their total environmental impact.
As Paul writes, T5s strike faster, have good colour rendition, and a well designed T5 high bay luminaire, with 4 tubes, can be more efficient than a metal halide lamp, and have less lumen depreciation over its lifetime.
Both metal halide and T5 lamps contain mercury. T5 refers to the diameter of the tube, with T5 tubes being 5/8″ (16mm) in diamater. “Standard” fluorescent tubes are called T8s and are 8/8″ (25mm) in diameter. With a smaller diameter T5s use less glass and mercury than a T8 of comparable brightness.
Having said that, quite a few myths have developed around T5 lamps and as a result many people believe they are the best thing since sliced bread was invented. The luminous efficacy in lumens per watt of good T5 lamps approaches 105 lumens per watt, but this is only slightly better than the best T8 which is near 100 lumens per watt. Large wattage metal halides also have luminious efficiencies approaching 100 lumens per watt. However, like most things, just because a lamp is a T5 doesn’t mean its luminous efficacy is above 100 lumens per watt, there are many T5s on the market with an efficacy of only 80 lumens per watt.
The uptake of T5s has been much greater in the commercial building sector, particularly in offices, than in manufacturing and warehouses. The reason for this I believe is LEED (in Australia Greenstar) and other standards where building designers are seeking maximum efficiency in lighting. These drivers aren’t yet as strong in the manufacturing and warehouse sectors. Certainly in our work we mostly come across T5s in office buildings which are pursuing a high green star rating. And metal halide highbay light fittings are still much cheaper and much more readily available than T5 highbay fittings.
If you are designing a new commercial building it makes economic and environmental sense to use T5 lighting with high efficiency luminaires. The luminaire (light fitting) chosen is important too. The purpose of the luminaire is to direct the light coming out of the tube to where it is needed. Low efficiency luminaires are inefficient at doing this. To get the most out of T5 lighting you also need to be specifying high efficiency luminaires. A big advantage T5 lights have over conventional T8 is their use of an electronic ballast, which extends lamp life, eliminates flicker, and reduces lumen depreciation.
For a commercial building retrofit the use of high efficiency replacement T8 tube in a double fluorescent luminaire and fitting of a specular reflector behind the tube to increase the efficiency of the luminaire enables the removal of one tube and halves energy use of the fitting. This is called delamping (more at our delamping webite). This provides larger energy and cost savings and is less expensive and more reliable than fitting T5 adaptors - devices than enable a T5 tube to be used in a T8 fitting. T5 tubes fitted with T8 adaptors have a lower luminous efficacy than the best T8 tube, so their use is not advised, not withstanding the marketing hype surrounding T5 adaptors.
In new warehouses in my opinion T5 high bay luminaires as described by Paul are far superior to metal halides. Paul outlines several reasons for this. The instant start of T5s is in many case perhaps the biggest advantage. When undertaking energy audits of warehouses I have usually see the high bay lights running all day, even though different sections of the warehouse will often be empty. This is very wasteful. Unfortunately HID lamps, such as metal halide, high pressure sodium, and the less efficient but inexpensive mercury vapour all take a long time to warm up, and therefore its not practical to switch them off in empty spaces. Forklift operators and staff just aren’t prepared to wait 10 or 15 minutes for the lights to warm up to full brightness.
T5 or T8 linear fluorescent lamps don’t have this problem. So they can be controlled by motion or occupancy sensors. In many cases the hours of operation of lights in warehouses could be reduced from 10 to 12 hours a day to less than 4 hours a day with the use of sensors and T5 high bay fittings. Lighting energy costs can easily be halved.
Another metal halide replacement is the induction lamp, which has the advantage of instant start as well, but can in some cases be retrofitted into the existing high bay fittings. Their luminous efficacy is also pretty good, they are easily dimmed (good where daylighting controls are installed), and prices are coming down. Induction lamps also have a very long lamp life, in the order of 50,000 hours (compared with 14,000 hours for a good metal halide and 20,000 hours for a good T5)
LED lighting is rapidly becoming more efficient, and we have tested LED fluorescent tube replacements achieving over 70 lumens per watt - which is a big improvement over the 40 to 50 lumens/watt we were seeing 12 to 18 months ago. If the luminous efficacy of white LED technology continues to improve this quickly, and prices start to drop, then we may find in five years time that LED is better than all other forms of lighting.
In Australia electricity codes stipulate that the supply voltage of mains electricity should be 230 volts (phase to neutral).
For example in Victoria the Essential Services Commission has mandated in the Electricity Supply Code that the voltage of supply should be 230 volts plus 10%, minus 6%. Distribution businesses supplying electricity err on the high side.
Voltage measurements and voltage logging undertake across multiple sites by CarbonetiX show however that phase to neutral voltages are typically in the range of 240 to 250 volts. In fact we regularly see cases where the maximum voltage exceeds the maximum permissible 253 volts.
With the exception of three phase synchronous motors (eg motor typically used to power equipment such as pumps, fans, chillers, industrial machinery etc), the lower the voltage the lower the power consumption. If you remember your high school physics, you’ll know that for a resistive load Power = Volts x Current, and based on Ohms law Volts = Current x Resistance. Put the two togehter and for a resistive load (eg a halogen light bulb) power consumption is proportional to the square of voltage. So a 10% drop in voltage leads to a 19% energy saving! For single phase inductive loads such as fluorescent lighting there is also a power saving when the voltage drops.
The supply of voltage at well over the 230 volt standard means that electricity consumption, and thus greenhouse gas emissions in most buildings across Australia is higher than it would be were the voltage to be kept closer to the 230 volt standard.
I estimate that across the country a 5% electricity and greenhouse gas saving could be achieved if voltages were generally kept in the 225 to 235 volt range rather than the 240 to 250 volt range we typically see. This would translate into a greenhouse gas saving in the order of 15 million tonnes. To put this in context, that’s equivalent to the annual greenhouse gas emissions of Australia’s most climate unfriendly power station - Hazelwood - pictured above.
Distribution businesses may be supplying voltage on the high side to enable them to cope with periods of high demand, when the voltage drops in the distribution network are higher (eg on a hot summer afternoon). However these periods of high demand typically only account for around 50 to 100 of the 8760 hours in a year.
Some organisations are now installing their own voltage reduction devices to compensate for the overly high mains voltage supplied and to thus achieve cost and greenhouse gas savings.
Whilst perhaps politically challenging, there would be much greater benefit to the environment and to consumers if standards were established that kept supply voltages lower and closer to the 230 volt standard.
For example the standard could be ammended to stipulate:
- For 90% of the year the voltage shall be kept at 230 volts plus 4% minus 6%.
- For 10% of the year the voltage shall be allowed to vary between 230 volts plus 10% minus 6%.
Regulation such as this would allow distribution businesses sufficient buffer to take precautionary measures when they think demand may spike (eg based on the weather forecast) whilst still saving significant amounts of greenhouse gas.
I would encourage any organisation keen to see Australia reduce its greenhouse gas emissions take up this important issue of voltage standards with the relevant government organisations. And lets hope that as emissions trading comes in this is recognised as an opportunity for electricity generators and distribution businesses to collaborate together for significant greenhouse gas savings.