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Thread: Electricity Cost Calculation

  1. #1
    DIY Senior Member LOTW's Avatar
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    Default Electricity Cost Calculation

    We have a strange situation. We own a rental duplex. Each unit has separate meters and pays its own electricity and other utilities. The duplex has a detached duplex garage, with one tenant having one stall and the other tenant having two stalls. When the duplex and garage were built about 15 years ago (before we owned them) all the garage's electical wiring was apparently connected to one of the duplex units. The tenant in this unit is now concerned that he has to pay for the other tenant's operation of the garage door opener, interior garage light, etc. I told him that any cost to him would be miniscule. How could I calculate what the actual cost to him is? Any thoughts?

  2. #2
    In the trades Dana's Avatar
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    You could kill all the other breakers in his panel, turn all the lights on, and have some kid open & close the garage door as much as he can for an hour and measure it on the meter or something. :-)

    Or you can install only high-efficiency lighting and put an occupancy-sensor switch on it. The biggest cost to him would be if someone left the lights on, since the motor is probably less than 200 watts, and only runs a minute or two per day. 200 watts is 0.2 kw, 2 minutes is 0.033 hours, so...

    0.2 kilowatts x 0.033 hours is 0.007 kwh/day x 365= 2.5kwh/year

    A couple of 40 watt lights is 0.08 kilowatts, but if you left them on for a whole day (24 hours), that's about 1.9 kwh per DAY.

    With an occupancy sensor or timer switch that can't happen, and odds are it would add up to less than 1 hour per day, so it would be at most the power rating of the lights, x 365 days/year.

    Or you could just comp him a 6-pack once or twice a year for being such a good sport. ;-)

    If he insists on the penny-accounting, look up the specs for the actual power draw of the garage door opener, measure how many seconds it take to both open and close it, take a reasonable stab on the average daily open/close, and add it up for a year in hours x kilowatts. Do a similar estimate on garage light use & power. It's not nothing, but it's probably less that the value of the time it takes to calculate it.

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    Plumber jimbo's Avatar
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    I don't know what kind of laws you have up there. Around here, if the one tenant complained to the landlord that someone else's usage was on his meter, you the landlord would be in deep kim chi. Also, the regulations of the public utilities commission in many places would not allow you to "estimate" the usage and charge the tenants accordingly. SO, the city would force you to separate the uses , or pay both bills yourself and simply increase the rent by an appropriate amount guestimated, and the rent contract would say "electricity included".

    Now, the usage in question is probably minimal....dollars per month, but not tens of dollars, probably, unless one guy is using a lot of lights, power tools, etc. SO, to keep peace in the family, you could make the guy who gets the bill an offer he can't refuse. Give him a Starbucks card, or whatever!!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    There are some plug-in devices (similar to a surge suppressor) that measure the power consumption of the items plugged into it. I think they also allow you to insert the local cost per Kw, and then you can just read out the actual cost of the stuff, or at least a good estimate. This only works on stuff with a plug that can be plugged into the device, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member johan4551's Avatar
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    Default Electricity Cost Calculation

    Hello everyone
    LOTW I have an idea which you can apply and may be helping you in calculating electricity bill. Try to switch off all the electrical appliances of your home and monitor the reading of your tenant meter and ask your tenant to switch off all the appliances and then open and close your garage door so that you can get the reading of electrical unit consume by that door. In this way you can calculate the reading.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    The label on the opener will have a (max) current draw. Time how long it takes to open. Do the same for closing (they may not be the same). Estimate how many times a day it typically happens...take that and using your electrical rate, figure out an approximation.

    But, if you use one of the devices I mentioned, and input your local rates, it will read out what the cost total is. It should be fairly accurate.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Jack of all trades DonL's Avatar
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    This meter will let you enter your rate per killowatt, and store the usage, even if the power fails.

    You could just read it ever month.

    But as Jim said. the device has to plug into it, and running threw it.

    But they work very well.

    http://www.amazon.com/P3-Internation.../dp/B000RGF29Q


    DonL
    Theory only works perfect in a vacuum.

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    DIY Senior Member LOTW's Avatar
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    After rigorous calculations it has been determined that the cost of the electricity is precisely equal to the cost of one case of Newcastle Nut Brown Ale minus the six bottles I was required to sample.

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    DIY Senior Member BobL43's Avatar
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    I've got one of those devices, the older one that does not store the readings and loses it in a power failure; but even the one I have is indeed a very nice tool the Kill A what (spelled wrong here of course) for anybody that thinks they pay a lot for electricity, I think I'll make them feel better by posting a copy of my electric bill here. We have LIPA here on Long Island, NY, and we pay through the nose.
    I am definitely not a pro plumber, but I am a pro crastinator

  10. #10
    Jack of all trades DonL's Avatar
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    The new one is worth the price, It is only a few dollars more, now.

    It would be nice if it had back lighting on the display, but it works very well and calculates the cost for you.

    And LOTW, that is nice, sounds like you found a solution, that benefits all.


    Have a great Day


    DonL
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  11. #11
    DIY Senior Member BobL43's Avatar
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    I like your new Avatar Don!
    I am definitely not a pro plumber, but I am a pro crastinator

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