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Green Building Bible, Fourth Edition
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Data and monitoring: OWL - energy monitor

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  1.  
    • CommentAuthorbiffvernon
    • CommentTimeSep 25th 2010
     
    Anyone with an OWL checked the calibration accuracy of the display. Mine seemed to be under-reporting by about 6% and I'm told that if I reset the voltage from 230 to, say, 240 that might improve things. Any experience?
    •  
      CommentAuthorDamonHD
    • CommentTimeSep 25th 2010
     
    If you're trying to measure any non-resistive load (eg CFLs, and any newish electronics with a switch-mode or similar power supply) then such a clip-on meter may be badly off, up to 3x over-estimating in some cases (due to a device power factor of as low as 0.3).

    I am told also that even less-obviously tricky appliances such as dishwasher and washing machine can give poor readings.

    I would suggest calibrating by buying (or borrowing) a £10 plug-in power meter from (say) Maplin, which because it can measure phase and voltage is likely accurate to within ~1%, and using that to mentally adjust your Owl readings.

    Do it for (say) washing machine and a CFL in a plug-in lamp.

    Rgds

    Damon
    • CommentAuthorTuna
    • CommentTimeSep 27th 2010
     
    Check your line voltage - the OWL and others assume you get 250volts (from memory), but if that's wrong (and it can be - there's quite a wide allowed deviation in supply voltage) then the measured values will also be wrong. Maplin's infamous power meter costs about 25 quid and allows you to check the consumption of individual appliances. More importantly it is a proper volt meter so it can confirm what your incoming supply is running at.
    • CommentAuthorevan
    • CommentTimeSep 27th 2010 edited
     
    Posted By: DamonHDIf you're trying to measure any non-resistive load (eg CFLs, and any newish electronics with a switch-mode or similar power supply) then such a clip-on meter may be badly off, up to 3x over-estimating in some cases (due to a device power factor of as low as 0.3).


    The power factor on newish electronics is generally pretty good now, as it tends to use a PFC topology, i.e. appears pretty close to a perfect resistive load.
    The bigger problem here is just that the meters have a poor resolution and can't accurately represent low wattage loads, and often mis-calculate the power factor as well.
    If there is any distortion of the mains waveform due to other loads in your house or in the neighbourhood, that can throw the meter off as well.


    I am told also that even less-obviously tricky appliances such as dishwasher and washing machine can give poor readings.


    Washing machines *will* give a poor power factor as they still use phase angle switching. Not quite sure why that's allowed..
    •  
      CommentAuthorDamonHD
    • CommentTimeSep 27th 2010 edited
     
    Hi evan,

    Thanks!

    I see the 80 PLUS pf stuff now, which I was not aware of, but what about mains CFLs/LEDs and other lower-power loads? I've seen pfs of (say) 0.5--0.7 on the devices that I've actually measured. Maybe I need to measure a few newer ones?

    Rgds

    Damon
    • CommentAuthorevan
    • CommentTimeSep 27th 2010 edited
     
    LED drivers should always have a high PF (better than 90%)

    I'm not too sure about the current state of CFL, especially the suspiciously cheap ones! I need to have a look at some dead ones. By and large, if it doesn't have an IC (chip) in the circuit, I wouldn't expect the power factor to be too great, so your measurements may well be correct.
    • CommentAuthorDavipon
    • CommentTimeJan 29th 2011
     
    Have been told there can be an issue with OWLS if used where a PV system has been installed, anyone had similar probs?
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 29th 2011
     
    All the simple clip-on meters will be unable to tell the difference between import and export.

    Rgds

    Damon
    • CommentAuthorJoiner
    • CommentTimeJan 30th 2011 edited
     
    And I thought I was being so good when I bought my 'efergy' thingy from Maplins, assuming, because it cost almost thirty quid, that it would be a better guide to useage than the cheaper one you lot are now saying is the bee's knees. Bugger.:sad:

    If anyone's not familiar with the 'efergy' monitor, the sender clips onto the cable between the incoming junction box and the distribution board and sends the info to the monitor on my desk, which gives a read-out in both cost of useage and kW, with a daily average below that in kWh. It records the history of energy use and currently tells me that I'm using 2.07kW (£0.23) with a daily average of 10.8kW (£1.19). That gives me a predicted bill of £130, which is pretty close (+/- £5) to what it's been at this quarter for the past two years.

    So what "clip on" meters are the problem?

    (Oh, it also tells me that my daily average of kgCO2 has been 10.4)
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 30th 2011
     
    I use a CurrentCost with extra transmitters. All wireless and stores data. Just got to find a nice easy way to view the data without buying some extra third party software that does not seem to do what I want anyway.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 30th 2011
     
    J: any meter that works by clipping on to your mains feed tails cannot tell (a) whether you are importing or exporting if you have microgen on site (b) what actual voltage or phase is which reduces accuracy.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 30th 2011
     
    Yes not sensing the voltage is a problem but the supply voltage is legislated for so can set bounds and at less than 30 quid.

    With a bit of playing about with a volt meter, power meter and too much time those bounds can be set quite low.

    If you have a CC on the AC outlet of the inverter will that still sense just the house current?
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 30th 2011
     
    Since the microgen is usually fed into the house side of the meter, and usually thorough a circuit on the main board, there is often not going to be any single point to sample that indicates gross consumption as you want, though the wires from the microgen, unless there is ever significant self-consumption, might give you a pure-ish generation value. However, as you don't know the sign of any of the other values I think it's still going to be difficult to pick anything out some of the time.

    Actual voltage, waveform shape, powerfactor of loads, etc, can all act against the clamp measurement being accurate.

    I must just bleeding well get on with my own project that I've been sitting on for months now.

    Grrr

    Rgds

    Damon
    • CommentAuthorJoiner
    • CommentTimeJan 30th 2011
     
    As I have no form of exporting going on here and am just a simple soul connected to the grid, how accurate is that efergy thingy then? The literature claims >90%.

    Voltage range (in the sensor): 110V - 400V

    Measuring current: 50mA-95A
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 30th 2011 edited
     
    Unless you have lots of oldish electronics (including cheap CFLs) running, I'd guess its claim is probably OK.

    Rgds

    Damon
    • CommentAuthorJoiner
    • CommentTimeJan 31st 2011
     
    Thanks Damon. You save it from the bin.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 31st 2011
     
    If you can calibrate big loads that may be difficult for it to get right (eg washing machine on spin) with a plug-in meter that may give you a better idea of how good it really is and avoid surprises later. You may be able to borrow such a plug-in meter from your local library for example.

    Rgds

    Damon
    • CommentAuthorJoiner
    • CommentTimeJan 31st 2011
     
    Hardly worth borrowing for ten quid!:bigsmile:
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 31st 2011
     
    Indeed.

    The two make a good combo, eg you can check a single appliance more easily with the plug-in meter. Maplin have several and I did a little review on the ones that I have tried:

    http://www.earth.org.uk/note-on-plug-in-power-meters-for-the-UK-REVIEW.html

    Rgds

    Damon
    • CommentAuthorwookey
    • CommentTimeFeb 1st 2011
     
    But it can be as bad as 70% - it depends what stuff you have and what actual voltage you get (and whether you can be bothered setting the device assumed voltage if it allows that).

    Plug-in meters are much more accurate so long as you get one with high resolution so it can do laptops and phones as well as washing machines and fridges. Some are great, some terrible, in this regard. I know the one Navitron do is good for small loads and the old brennstuhl grey ones are completely hopeless (because I have those two, as well as an efergy)

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