Help with equipment to monitor 220 individal appliance energy usage

[digitalincome]

Hello - I'm new to this forum having searched for electrical engeneer experts forum - and could use some advice on equipment. I'm looking for the most accurate device to measure the use of an individual appliance that uses 220v - specifically - a walk-in freezer i recently purchased.

Problem - I rent space from a motel owner and after he agreed to allow installatin of a walk-in freezer - later had a fit when seeing the size of a typical 7.5' x 6' x 8' walk-in and said it would use too much electricity after i already purchased the used unit and had partally assembled. After some discussion - agreed to let it remain as long as i paid for the additional energy consumption. So - i need an accurate way to determine it's usage both to make sure I pay for what it uses, and also to make sure that i don't get stuck paying for energy use increases and higher bills that are a result of others rooms, etc and not a attributed to the walk-in freezer.

Solution? A device that would record the HW usage of the freezer accuratly - and I pay him what consumers energy charges. i've read another post about something called "kill a watt" - but in reviews and engeneer said it was junk, others said inaccurate, others complained about defective - etc - so going right to those that would know.

I don't need to monitor the entire complex electric usage - just an individual appliance - a devise that i could mount near the freezer - and display/calculate monthly usage so the property owner and i can agree.

Thank you for taking the time to read my question - and thanks in advance for any help you could provide

 

[OperaHouse]

If used with 12V inverters I've heard that the power supply will burn out. That wouldn't be a problem with normal line power. While not super accurate it will be sufficient to get a reasonable billing charge. I've found anything with a digital reading is more believable. There are used typical electric meters available on ebay. The box to mount it on will probably cost more.

 

[jraef]

The Kill-A-Watt is not necessarily junk, but it is optimized to do a good job recording complex power supply energy use because of what are called harmonic waveforms. These would be found in things like computer power supplies, TVs, Steros, high intensity discharge lighting ballasts etc. etc., things that most momeowners are interested in monitoring. So because of this, the accuracy on other types of loads is somewhat compromised and less than advertised; they claim 0.2% accuracy, but on inductive loads they tend to be 3-5% accurate (for the geeks among us I heard it was because they are looking at distortion power factor but not displacement power factor).

A freezer is going to have an AC motor for the compressor and fan(s); so expect the lower accuracy. What does that mean? It means if your utility cahrges 10 cents per kWH, and the meter is off by 3%, you could be paying 10.3 cents per kWh or the landlord might only be getting 9.97 cencts. Either way at the end of the month you are probably talking less than $5 (assuming about 50kWh/day).

There is another more expensive unit called "The Energy Detective", abbreviated as TED, that is supposedly better and can provide a remote wireless interface, but parts of it may need to be installed on the circuit in the breaker panel, so should be done by an electrician. It's a clamp-on device so it's not permanent from that standpoint, but working on your own circuit panel is not likely covered by your landlord's insurance policy!.

http://www.theenergydetective.com/

But neither are qualified as "revenue metering" anyway, which by the way requires special permits in many areas. So if you both agree to abide by the readings of the Kill-A-Watt or TED unit, keep it among yourselves. Bringing it up later in a courtroom could land you both in hot water with the utility.


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[ScottyUK]

Would the utility actually care? They are paid based on their revenue meter, and as long as that was not disturbed or interfered with then what interest would they have in any sub-metering arrangement within the customer's installation, regardless of whether it used revenue-class metering or some Chinese toy?


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Hi Scotty. The utility doesn't care about the accuracy of the added meters although other government agencies may. The issue with the utility is the terms of service which probably prohibit reselling of electricity.
I am involved in exactly that situation now. A property owner subdivided a parcel in such a way that the subdivided property was supplied with electricity from the original owners meter. That was in violation of his terms of service.
I am waiting to hear from the expensive lawyer as to how this will progress.
PS the only worry the utility has in this issue is whether they may be complicit in that they should have been aware of the situation some years ago and did not take timely action. Everyone is trying to cover their ASSets.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

digitalincome; Most electrical supply houses sell regular kilowatt-hour meters. They look just like the utility meter. I'd use one of those wired in permanently with the walk-in box.

There are many on the web:

http://www.ezmeter.com/yosemite.php

http://www.metersusa.com/Watt-Hour-Meters/index.htm

Google "watthour submetering"

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Our little utility used to buy reconditioned, recalibrated meters for $8 each in quantity.
Hialeah Meters in Florida as I remember.
Avoid the dial type meters. Look for the cyclometer type. They have a readout like an old style auto odometer. Much easier to read.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FreddyZ]

"Avoid the dial type meters. Look for the cyclometer type. They have a readout like an old style auto odometer. Much easier to read. " - is it really that difficult to pick the smaller of two numbers that each needle lies between, as when reading a multi-dial meter? Wow.

 

[waross]

I bow to your years of experience reading dial meters.
However without those years of experience it is a little challenging to pick the correct number when the needle lies right over a number. Often what looks like one number may actually be one less number. Untrained, unexperienced people reading a dial type meter may cause more arguments than it solves. It is particularly challenging when one of the dials is a bit out of register and passes the number a few degrees early. Been there, done that.


Bill
--------------------
"Why not the best?"
Jimmy Carter