Technical stuff...
Collected tips, tricks and resources
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Building fabric Burners Chillers Compressed air Furnaces Heat recovery Lighting Metering, monitoring and targeting Motors and drives Steam Tanks and vats Travel and transport |
There are many more topics we would like to cover in similar ways. If you are an expert on any relevant technical topic we'd like to hear from you |
Small appliance metering
 
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The Brennenstuhl PM230 is a plug-in meter which allows you to assess the consumption of small electrical appliances. As well as showing the instantaneous load, it has an accumulated kWh readout, so that you can measure the average consumption of an appliance that cycles on and off or operates at different load settings. I have just (4 April 2007) ordered one from the Green and Easy On-line shop who sell the UK-pattern device for £19.95 including VAT and delivery, the best price I could find. Please mention this site if you order from them. |
Remote readout of electricity demand
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Alternatively, you can get a real-time display of your overall home or small business electricity
demand by fitting a simple device from
Electrisave. Make your family or colleagues aware of how much they are using and
when - and encourage them to save. Costs £80 in UK and can usually be fitted by the
householder or proprietor without assistance. A clip-on current transformer (1) is
wired to a battery-powered transmitter (2) which sends data to a wireless readout (3).
Now available with additional sensors at £20 a pair, to monitor three-phase supplies. (V.V. 4 April 07) |
LED up the garden path?
A test report from the US Department of Energy shows that LED lamps are less energy-efficient than compact flourescents and that manufacturers' claims for light output don't always stand up to scrutiny. Thanks to John Field of Target Energy Services for drawing this to our attention
Economic thickness of pipe insulation
Thanks to Hannah Paddock for posing the question on our bulletin board about how to calculate the economic thickness of pipe insulation.My advice to her was to get suppliers to provide her with before-and-after calculations of heat loss. I advised checking their sums for reasonableness using common sense (for running hours, boiler efficiency, fuel prices, etc) and a reference book such as Handbook of Energy Data and Calculations (Peter D Osborn, pub. Butterworths 1985) for heat-loss coefficients. If you can't get hold of a textbook then (with caution) try websites such as www.engineeringtoolbox.com/steel-pipes-heat-loss-d_53.html and www.engineeringtoolbox.com/copper-pipe-heat-loss-d_19.html to corroborate their heat-loss assumptions. Hunting around, I did find an on-line pipe insulation calculator but rather annoyingly it does not allow you to specify zero insulation. If it had done, it would have been more useful. I have contacted the author to suggest it. I have since found what looks like a better article at cheresources.com. V.V. 30 October 2006
The rig can even demonstrate the effect of fitting a capacitor. Running the string around a
pulley, as shown in the right-hand diagram, reduces the tension (current) required
to achieve the same deflection (useful power), regardless of the phase angle.
See also our visualisation of alternating
current, voltage and power waveforms.
Training aid for power factor
This is the design of a rig I use for teaching people about power factor. It consists of a long spring-loaded
pointer, pivoted at the left-hand end. The trainee pulls a string to pull the pointer down to a horizontal
position. A spring balance indicates tension in the string.
Tension here represents the current, while deflection represents the useful power delivered.
Trainees observe that the minimum tension is needed when the string is pulled vertically downwards,
as in the left-hand diagram; this is
analogous to the minimum current being required when alternating voltage and current are in phase.
Pulling the string at an angle (centre diagram) simulates what happens when current and voltage get out of phase.
The tension in the string needs to be higher to achieve the same deflection (higher current
to deliver the same useful power).
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It's sometimes said that a full freezer uses less energy - not true. When the door is closed
and the load is at the required temperature,
all the refrigeration circuit is doing is removing heat that leaks into the compartment
through the insulated walls. The freezer could be full or empty - the rate of heat transfer
will be no different. It will only change if the room temperature changes. You can
detect that it must be dubious advice because of what people suggest for filling the space:
bread (high mass and volume); empty ice-cream cartons (low mass, high volume); and crumpled newspaper
(low mass, low volume). The only thing they have in common is they impede air circulation (of
which more later).
Some people say that by keeping the freezer full, you reduce the amount of chilled air that can spill out. Maybe, but door openings account for only 1 - 2% of annual running costs so the effect is small... In fact one kilowatt-hour of electricity would rechill all the air in a 100-litre freezer about a thousand times. Much more important in causing high running costs are the following:
This myth is almost universal and is promulgated by organisations that should know better. So where did it come from? It probably started with the perfectly true observation that a larger freezer uses more power, so it is unwise to buy one that is bigger than you need. Related to this is the idea that the running costs per pound stored are lower for a freezer that is fuller; but this "operational" efficiency has then been confused with thermodynamic efficiency, which is affected by a lot of things, but not by the loading. Conclusion: store as much or as little as you need; but leave room for air to circulate.
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You may be able to save electricity by voltage reduction if your mains supply voltage is significantly above the statutory minimum. The method works particularly well if lighting is a significant part of your load; motors also benefit. |
Compressed air systems
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The US Department of Energy Industrial Technologies Program has a page containing a number of links to free 'tip sheets' on such things as: alternative strategies for low-pressure end uses; storage and control strategies; system maintenance; effect of intake air on compressor performance; minimizing leaks; and other relevant topics. (added 19 March 2006) |
Electrical energy saving exercises
Sequencing fans with VSD
What's the best strategy for part-load operation of a bank of fans with variable-speed drives? Try this simulation. (V.V. 7 Jan 06)True or false?
If you are leaving the room for less than ten minutes, it's cheaper to leave the fluorescent lights on... find out, feeding in your own assumptions about the size and duration of the startup surge. (V.V. 6 Jan 06)Why poor power factor is a problem
If an electrical circuit suffers from poor "power factor", a higher current than necessary will need to be drawn in order to deliver the required power. This can increase power charges, or stress the supply infrastructure: see a simulation of the effect. (V.V. 6 Jan 06)
Own-goal by HE motor manufacturers
I hear that some makers of high-efficiency electric motors have changed the frame design so the terminal boxes are now on top, rather than on the side. A minor change but one which snookers many works engineers wanting to replace existing motors: if the supply cables run from below, they won't reach, and for the larger and most worthwhile replacements, the time and cost of running new cables will knock the idea on the head. Thanks to G.A. and P.P. for this item. (V.V., 7 Dec 2005) [Send a comment by email]
Sankey diagram softwareThe product recommended by one of our readers in October has been upgraded: click here for feedback from the user and news from the supplier.(V.V. 2 Dec 05) |
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Automatic controlsControls can have a part to play saving energy for all users from the largest to the smallest. As well as the well-rehearsed topic of controlling heating lighting and other building services, there are often opportunities in industrial situations as well: see article. (V.V. 20/11/05) |
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