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  • Appliance load calculations

    I'm refining my load calculations to determine our final configuration, the worksheet that I'm using asks for Volts, Watts, and Summer / Winter operating hours per day/days per week. Since this is a new build I don't have many of the items purchased to put a Kill A Watt on to get real wold readings.

    I could use some guidance on calculating things like a refrigerator from the spec's provided:
    Electrical Specifications

    • Voltage Rating: 120V 60Hz
    • Amps @ 120 Volts: 6
    • Minimum Circuit Required (Amps): 15A
    • Connected Load (kW Rating) @ 120V: 0.72
    • Power Supply Connection Location: Right Rear Bottom
    • Annual Energy (kWH): 363
    First question is to calculate the watts is that: 120V X 6 AMPS = 720 watt...seems high. Or should I be using the "Connected Load (kW Rating) @ 120V: 0.72" so 120 x 0.72= 86.4 watts?

    Second question is for hours per day. Since a refrigerator is plugged in all the time is it "running" 24 hours per day using the above wattage or should we just be taking a swag at the hours the compressor is kicked in? Not sure what that would be but this will be a fill time home with 2-3 people at home. No excessive eaters/open door refrigerator staring going on....

    Thanks as always for the help!

  • #2
    The connected load of that frig is 720 watts or 0.72kW. But the annual energy usage is 363kWh which calculates to about 1kWh a day for every day of the year.

    To be safe I would use that 1kWh x 1.5 or 1.5kWh a day to make sure you have some extra capacity in your system for those days (like the summer time or opening the door more often) that you use more than 1kWh

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    • #3
      Thanks SunEagle, I kept looking at that 363kWh # and thinking just divide it by 365... sometimes you just need to see it in writing...

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      • #4
        The fridge's cooling unit does not operate 24/7. It cycles on/off in response to the difference between the set temp. and the ambient temp. of its surroundings.

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        • #5
          When you look at an appliance annual usage is pretty much a fairy-tale made up by the Employment Prevention Agency. Good example is Est MPG. When was the last time your vehicle ever had that good of a MPG?

          Smart money takes the yearly number, multiply by 1.4, then divide by 365.

          Daily Kwh = Yearly x 1.4 / 365. If you have kids use 1.6.

          Where this does not work is with HVAC.
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            When you look at an appliance annual usage is pretty much a fairy-tale made up by the Employment Prevention Agency. Good example is Est MPG. When was the last time your vehicle ever had that good of a MPG?

            Smart money takes the yearly number, multiply by 1.4, then divide by 365.

            Daily Kwh = Yearly x 1.4 / 365. If you have kids use 1.6.

            Where this does not work is with HVAC.
            FWIW, I've pretty much always done better than the EPA mileage est., by ~ 10% or so around town. More on the interstate. Seems easy to do if I don't drive like it's a race.

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            • #7
              Originally posted by J.P.M. View Post

              FWIW, I've pretty much always done better than the EPA mileage est., by ~ 10% or so around town. More on the interstate. Seems easy to do if I don't drive like it's a race.
              Yeah I got lead in my feet.

              MSEE, PE

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              • #8
                Originally posted by Sunking View Post
                Yeah I got lead in my feet.
                Not a knock. Pay your money, take your choice.

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                • #9
                  Originally posted by J.P.M. View Post
                  Not a knock. Pay your money, take your choice.
                  I know it is not a knock. I do not make rabbit starts and stops. While cruising my Radar and Laser detector go fast as conditions safely allow. I can afford the extra gas and hate wasted time behind a wheel. Hell that is why I once owned a plane for trips.
                  MSEE, PE

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                  • #10
                    Originally posted by Sunking View Post
                    I know it is not a knock. I do not make rabbit starts and stops. While cruising my Radar and Laser detector go fast as conditions safely allow. I can afford the extra gas and hate wasted time behind a wheel. Hell that is why I once owned a plane for trips.
                    One of my mentors was a naval aviator in WWII & Korea. Now deceased. R.I.P. He treated every start/stop like a carrier takeoff/landing. His gas mileage and brakes suffered, not to mention wear/tear, but what a ride.

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                    • #11
                      Important to economy is driving to minimize use of the brakes. Every time you use the brakes, you are throwing away
                      gasoline. Process here is immediately get up to speed, the inertial energy is the SAME whether you do it in 8 sec or 25.
                      Then COAST to the next stop sign, the original inertial energy is RECOVERED to overcoming rolling friction. The poke
                      who very slowly builds up speed and puts on the brake at the last second, burns up the inertial energy in the brakes, so
                      he must supply ADDITIONAL energy (gasoline) to overcome rolling friction.

                      Some describe a carrier landing as a controlled crash. Bruce Roe

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                      • #12
                        Originally posted by J.P.M. View Post

                        One of my mentors was a naval aviator in WWII & Korea. Now deceased. R.I.P. He treated every start/stop like a carrier takeoff/landing. His gas mileage and brakes suffered, not to mention wear/tear, but what a ride.
                        While in the Navy I got catapulted off a carrier. My Mother was seriously injured while I was out at sea and was not expected to live so I got a hardship pass and express ride home. They shot me off the deck of the USS Lexington and took me to San Diego on a Grumman C2 Greyhound. Hard to describe the feeling. Pilot powers up to full power, the plane shakes and vibrates violently, the sound is deafening, and then you are plastered into the seat when the catapult sling shots you off the deck. Only other thing that comes close to that is a roller coaster I rode a few years ago that uses linear magnetic motor to launch you 0 to 70 in a second before you go straight up 200 feet or so. If I recall correctly around 5g's and 5g's is as thrilling as 0g's in a plane or sky diving.

                        Ever jump out of a plane? If not you have missed one heck of a rush.

                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by Sunking View Post
                          While in the Navy I got catapulted off a carrier. My Mother was seriously injured while I was out at sea and was not expected to live so I got a hardship pass and express ride home. They shot me off the deck of the USS Lexington and took me to San Diego on a Grumman C2 Greyhound. Hard to describe the feeling. Pilot powers up to full power, the plane shakes and vibrates violently, the sound is deafening, and then you are plastered into the seat when the catapult sling shots you off the deck. Only other thing that comes close to that is a roller coaster I rode a few years ago that uses linear magnetic motor to launch you 0 to 70 in a second before you go straight up 200 feet or so. If I recall correctly around 5g's and 5g's is as thrilling as 0g's in a plane or sky diving.

                          Ever jump out of a plane? If not you have missed one heck of a rush.
                          Another of my mentors was a Naval Reserve officer. After yachting with the navy in the early/mid '40's in the Pacific, and as a PHD.M.E., he spent non teaching summers in the late 40's-50's working on steam catapult design. Very interesting stuff if you're into steam power.

                          I've never jumped out of a plane, but back in the glory days I fell several thousand feet from barstools a few feet at a time. Does that count ?

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                          • #14
                            Originally posted by J.P.M. View Post
                            Another of my mentors was a Naval Reserve officer. After yachting with the navy in the early/mid '40's in the Pacific, and as a PHD.M.E., he spent non teaching summers in the late 40's-50's working on steam catapult design. Very interesting stuff if you're into steam power.
                            Well the USN still uses steam power on catapults. I do recall hearing the next line of carriers catapults will use linear motors like a roller coasters and monorails use. Basically same principle a Rail Gun uses. Heck the USN either has or is installing a Rail Gun on a ship or two. Quite a few videos on You Tube of the USN testing Rail Guns if you care to watch a few. Amazing the destructive power of kinetic energy. Another one is called Rod of God missiles. Can destroy a small city with no explosives like a meteorite. All it needs is velocity and mass of depleted uranium.

                            Originally posted by J.P.M. View Post
                            I've never jumped out of a plane, but back in the glory days I fell several thousand feet from barstools a few feet at a time. Does that count ?
                            Yes sir. Been there done that when I was young and dumb. You just described every sailor on shore leave. My biggest challenge like most sailors on leave have to figure out how to divide their money between alcohol and hookers.

                            Last edited by Sunking; 05-18-2017, 12:19 PM.
                            MSEE, PE

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                            • #15
                              It's not the fall that's dangerous, it's the sudden stop at the end.
                              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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