Electricity accuracy meter thread: Update... [long post!]

[Alan]

Beware, long post....

After the pointers on Friday (thread title "How accurate are domestic electricity meters typically") I did a load of testing over the weekend. This became an excuse to buy a clamp ammeter! (Do we all need excuses to buy new tools??!)

Clamp meter confirmed 0 amp draw when everything is off, and electricity meter also didn't move so good start. Plug-in kwh meter revealed that the 500w heater in the garage got through about 7kwh in a 24 hour period. Obviously this would be more in colder weather. Clamp meter showed that 3 computers and associated equipment drew about 2 amps, therefore about 12kwh in 24 hour period. Clamp meter showed that fish tank also draws about 2 amps and gets through about 12kwh in 24 hour period.

Suddenly it's not hard to see where the 30+ kwh per day is going, before I even switch on the kettle! So, focus is now off the meter and on to reducing running load.

Garage: The 500w heater has a built-in 5 degree thermostat (minimum setting) to keep the garage above freezing. In the past there were 2 of these (and lower bills), maybe both helped maintain the temperature better (and used less power overall?) than the one that's there now. Dunno. Changes: I've re-instated 2nd heater and used timers to fire up both heaters during the E7 period, and one at a time intermittently during the "peak" period. So far E7 usage has gone up by about 3kwh/day but too early to tell if peak rate has come down by much.

Computers:

3 running 24/7 will soon reduce to 2. Jobs are: workstation, surveillance (security camera motion detection) and backup PC (Solaris box with DLT tape drive hung from it, backing up other 2). Tape drive will move to one of the other machines so backup PC can go. Workstation is used regulally all day every day and waiting to boot is not really an option so this will continue to run 24/7, as will security camera PC.

Fish tank: This draws more power than I expected it to, and has been pretty much unchanged in 5 years running. However, I will break down each component's load over the next few days and see what can be left off or run in E7 period instead. Some life-critical tank equipment is fed from a big UPS, and my testing so far has shown this is pretty inefficient. Will get figures soon but this may be due for replacement next.

So, any ideas how to further reduce power usage? I need to work out if E7 is actually saving me anything. If not then I'll switch. Power supplier switch on the cards also as Virgin Energy are not the best deal any more acording to

Also, any suggestions on how to reduce the garage running costs? I just need to prevent things in there from freezing without introducing moisture - so free standing gas heating is out. No mains gas there either. Maybe use a more powerful [blower] heater but on a more accurate thermostat set to 1 degree so it only runs when really needed? I have a plug-in digital thermostat unit and 2x 3kw wall mounted air-curtain type heaters in there also for heating when I use the garage as a workshop - maybe I could utilise this lot?

Any ideas gratefully received!

Alan.

[Christian McArdle]

Fit insulation in the garage. Even 50mm of cheap polystyrene sheet glued to the walls and a bit of draughtproofing of the door would make a huge difference.

Investigate power saving options on the PCs. Make sure hard disks and monitors turn themselves off. Ensure that the operating system HALTs the processor during idle phases. Investigate "suspend" and "hibernate" modes that your processor/OS supports. Run your motherboard utility program, as this may have a fan control mode that can cut energy usage (and noise). My desktop PC is very happy to hibernate to disk and boots up in about 10-15 seconds with all my programs already running. It crashes on normal "Suspend", though.

Christian.

[Richard Sterry]

[snip]

In order for something in the garage to freeze, the temperature will have to fall below zero for quite some time, so there should be no need to have a thermostat which operates much above freezing - it's not as if the heat has to permeate roof spaces, header tanks etc. which is a factor when fitting a frost stat inside the house. I inherited a small electric panel radiator similar to the Dimplex ones, (about 1kW I think), and with the thermostat right on minimum it does the job very nicely, without wasting heat when there is no danger of freezing. It rarely seems to operate, so didn't cost me a fortune in juice.

I have recently had to have the garage roof re-decked and weatherproofed, so I got the contractors to stick 80mm thick Kingspan on the top before the waterproof membrane. This insulation was mostly intended to stop the garage getting oppressively hot in summer, but I have noticed that as a bonus it has also made the temperature much more stable in colder weather as it holds the heat better. This should save on the juice, too. If you don't want to mess about with the outside of the roof, you could consider insulating the inside, having due regard for ventilation of the timbers and so forth.

FTR my garage is a detached one, with flat roof, about 5m x 5.5m, and with single-leaf walls.

HTH

Rick

[Alan]

Christian,

I forgot to mention the [large*] garage is well insulated, about 100mm in all walls and 150mm in roof also, all fibre-glass type. It keeps heat pretty well, and stays cool in the summer also.

• Garage is a 28' x 13' wooden building, with pitched roof. Walls have 100mm vertical timbers at about 400mm spacing, so I filled each space with insulation before lining inside with plywood. Outside has plywood then shiplap so no draughts. Roof is similar, but timbers run along the length with insulation between them and then lined with plywood on the inside. Heavy-duty felt tiles over plywood roof. Garage was my main project of 2002, it's a great result!

Alan.

[Dave Liquorice]

Ouch. Do you *need* to keep the whole garage above freezing? The only things that I can think of that object to being frozen are some paints etc. Tools don't mind but you may have to take precautions against condensation but that doesn't mean you have to keep things above 0C, just ventilated and above the dew point.

Insulation and draft proofing for the whole garage will make a big difference. Small tools/paint could be kept in a cupboard with vents top and bottom and small light bulb(*) in the base to keep it "warm" and create convection for ventilation.

Surely when mains is available the UPS just passes that on, taking just a little power for it's circuitary and battery charging. Without mains (rare?) it'll be on battery and effeciency won't be that good but who cares if it keeps your fish alive...

See previous post generally speaking if you are using around 22% of your total daily power consumption in the off peak period you will be breaking even, anything more is "profit".

Power prices seem to be in flux again. Just had a letter from PowerGen detailing their *3rd* increase this year. The last one made me switch the main account, this one may well make me switch the other two. They are very low useage so a penny or two per unit doesn't make a great deal of difference to the final bill. Mind you one is E7, winter is coming and electricity is used for space heating...

(*) "Adjusted on test" to see what is enough to keep condensation at bay. 100W would be more than enough, may be 40W (1 unit/day).

[Ian Stirling]

Is it a "True RMS" meter? If not, then it may be significantly inaccurate on computers and some other loads.

[Peter Parry]

If the garage heating is mainly to try to prevent things rusting consider using a dehumidifier rather than a heater. The small heat gain from it is effectively free and as long as you chose a model designed for low temperatures the results are better than a heater at lower cost.

[Alan]

I'm beginning to wonder the same thing myself! The cost of electricity probably outweighs any paints etc written off by freezing over a winter! I may just run the heaters for a short while each night to minimize damp, otherwise just leave as-is.

In an ideal world, yes, but this is an ex-industry double-conversion UPS which converts AC to DC and then generates the output AC from the batteries / DC side. Good for keeping the output sinewave constant at all times (and a decent sinewave at that), but not good for efficiency. It probably dates from late 80's / early 90's. A modern smaller UPS without double conversion may be the way to go. Will measure loss on this tonight.

Will do, thanks.

[Pete C]

Hi,

A digital thermostat would be a lot better than the themostat in the heater, especially if the latter is on 14h/day in fairly mild weather.

If it's just to keep the frost off paints etc then a tube heater in a cupboard would be much more economical than heating the whole garage.

BTW why is a separate PC needed for the security camera?

cheers, Pete.

[dms1.go-plus.net]

A lot of plugs and as you have found out soon adds up!

Depending on size I would try a timer and have various on/off periods for filters etc. Water is often over saturated with air.

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[Alan]

Don't know, will check...

[Alan]

Mainly because it needs an "always on" machine, the motion detection software seems to hammer the CPU to 100% permenantly, and I don't have a spare PCI slot for the quad input video card in the "workstation" PC at the moment. Also the video cables all terminate in the loft, where the security PC resides...

Alan.

[usenet]

If it was really pushing 500 watts into the fish tank continuously the water would boil eventually surely! It makes no difference if that's light, or pumps, or whatever, it all ends up as heat. While not all of it will end up in the water a lot of it will and, as I said, I would have thought that a continuous 500 watts going into the water would make it pretty warm.

I'd check that those two amps *really* represent 500 watts, it may well be that the load is very reactive (motors for example) and that spending a lot of effort on reducing it is a waste of time.

Then again I've just realised that you have a UPS in the equation here don't you and it may simply be that much of the 500 watts is disappearing into heat losses in that.