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Thread: Watt-Meters??

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    Watt-Meters??

    We have a potential client (large industrial) who is considering moving to LED technology. They do however, want to explore actual delta in kwh and watts to get some kind of confirmation on our estimated savings. Is there a a device we can temporarily install to measure a circuit for a week and then change out the fixtures on that circuit and then re-measure? I've seen watt-meters for residential applications but nothing for commercial.

    Any help is appreciated.

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    Quote Originally Posted by thewiseguy31 View Post
    We have a potential client (large industrial) who is considering moving to LED technology. They do however, want to explore actual delta in kwh and watts to get some kind of confirmation on our estimated savings. Is there a a device we can temporarily install to measure a circuit for a week and then change out the fixtures on that circuit and then re-measure? I've seen watt-meters for residential applications but nothing for commercial.

    Any help is appreciated.
    The first thing you need to ask is whether you really want a watt meter, which could be used at any time to measure the current lighting load on the circuit(s) or a watt-hour meter that you would leave in place for, say, 7 days to find the average usage over both working and non-working days.
    IMHO the watt-hour meter will give you a more useful number. Especially if it also offers the instantaneous watt reading.

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    You have to make sure time is left out of the equation. Either assure simultaneous operation or on 24/7.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by LarryFine View Post
    You have to make sure time is left out of the equation.
    Why would you want to do that? You pay for energy, kWh, don't you?

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    Quote Originally Posted by Besoeker3 View Post
    Why would you want to do that? You pay for energy, kWh, don't you?
    What i mean is, if you're comparing the cost of operation of different load types, you have to make sure the hours of operation are identical.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
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    Quote Originally Posted by GoldDigger View Post
    The first thing you need to ask is whether you really want a watt meter, which could be used at any time to measure the current lighting load on the circuit(s) or a watt-hour meter that you would leave in place for, say, 7 days to find the average usage over both working and non-working days.
    IMHO the watt-hour meter will give you a more useful number. Especially if it also offers the instantaneous watt reading.
    so sounds like a watt hour meeting would be best. Any mfg recommendations?

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    Quote Originally Posted by LarryFine View Post
    What i mean is, if you're comparing the cost of operation of different load types, you have to make sure the hours of operation are identical.
    I agree.

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    Quote Originally Posted by thewiseguy31 View Post
    so sounds like a watt hour meeting would be best. Any mfg recommendations?
    I have used these in the past to perform load analysis on electrical panels in the past. These are tricky to setup the first time, but once you get the hang of it after a few times, you can do it with no problem. Just make sure the panel is de-energized. If you want a true loading on the panel you will need to folow NEC guidelines.

    http://www.dranetz.com/power-quality-analyzers/

    I used the PX-5

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    Quote Originally Posted by LarryFine View Post
    What i mean is, if you're comparing the cost of operation of different load types, you have to make sure the hours of operation are identical.
    Quote Originally Posted by thewiseguy31 View Post
    so sounds like a watt hour meeting would be best. Any mfg recommendations?
    But consider what Larry mentioned. If one load runs for 10 hours, make sure an replacement load is compared for same 10 hours. Otherwise an instantaneous watt reading of each load (presuming a steady load) should tell you one is XX% different than the other regardless of how many hours it may have ran.

    Rather inexpensive "kill-o-watt" meter can tell you instantaneous watts, VA, power factor, etc. May not be extremely accurate, but should be accurate enough to be convincing that a certain item is pretty efficient compared to another item.
    I live for today, I'm just a day behind.

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    190515-1507 EDT

    thewiseguy31:

    I agree with kwired that a Kill-A-Watt EZ (about $30 at Home Depot), and additionally a light meter might be all you need.

    The Kill-A-Watt is limited to nominal 120 V and 15 A. These are relatively accurate and have 0.1 V resolution at 120 V. To demonstrate what you want only requires a wattmeter. You don't need to measure watt-hours.

    You probably only need to demonstrate the difference between two single fixtures. This may be in the capability of the Kill-A-Watt EZ.

    The experiment needs to be structured so the number of fixtures for each type of source covers the same surface area, and at the same light level. One fixture of each type might be sufficient. Then you simply show the differences in power input, and power factor. An LED vs fluorescent might show 50% less power input, and PF of LED might approach 1.

    As an aside you should evaluate the RFI (radio frequency interference) of your LED.

    .

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