Readind/understanding energy usage labels.

Re: Readind/understanding energy usage labels.

Arkansasoffgrid wrote: »

Ex. A fridg. label states 365kwh yearly. Is that stating 1000 watts used daily x 365 days, or 1000 watts used every hr "1000w x 24hrs x 365days" ? Just started my off grid load list and needed clarification first. Did my first test using the kill-a-watt meter and only seeing .01kwh for a 13watt cfl after 1 hr.

Watch your units... Watts and kWatts are "rates" (like gallons per hour). Watt*Hours and kWH are "amounts" (like gallons pumped).

Anyway, a refrigerator in a warm room (90F?), not opened very often and not making ice will use 365 kWatt*Hours per year.. .Or:

• 365 kWH per year * 1/365 days per year = 1 kWH per day = 1,000 Watt*Hours per day

The "average load" will be:

• 1,000 WH per day * 1/24 hours per day = 41.7 Watt average load

If you assume the refrigerator motor is running ~1/3 of the time (20 minutes per your), then the average running load would be:

• 41.7 watts * 3 duty cycle = 125 Watts when compressor is running

Frost Free freezers and refrigerators have a heater inside to melt frost off the evaporator (typically runs ~1 hour every 12 hours). That is usually around a 500-600 watt load.

And the starting current for a typical compressor is around 5x running load:

• 125 watts * 5 starting current = ~625 VA starting load

Typically, an Energy Star refrigerator will need around 1,200-1,500 watt AC inverter (and large enough battery bank) to start reliably and run a few other loads (lights, laptop computer, etc.) at the same time.

-Bill