This situation got me wondering about power consumption of refrigerators as opposed to the badged numbers (fire safety electrical ratings). The most convenient way to measure actual consumption of power while you use it is with a $30 meter called "Kill-a-Watt".
Dying bought-new-and-never-moved 2003 Energy Star kitchen full-sized self-defrosting refrigerator with top-freezer: 125W with compressor running (almost all of the time).
GF's boss offered us a 1980's upright refrigerator with self-defrost: 115W for an hour from warm. Next to that was a late-1950's manual defrost rounded-top kitchen refrigerator with built-in ice box: 105W for an hour from warm (hooray, vintage R-12!)
Found on curb across the street: Haier HSB01 cube dorm refer. Cleaned, plugged in, worked great at about 110W. Unbeatable for price, power consumption high for volume cooled, good for temporary use when kitchen refrigerator is too full or too far. FS: http://portland.craigslist.org/mlt/app/2613985118.html
Found on Craigslist by a Columbia river marina: 2003 model Norcold DE-441 medium sized refer pulled from a boat. What's interesting is that it runs on 120/60Hz as well as 12/24DC and uses 45W peak with a duty cycle dependent on ventilation/outside temp/openings. Casual observation suggests that it can run on 300W/H per day if left shut. Retail is about $1250, but used for $100 seemed fair. Web search resulted in mean criticism of "Nevercold" brand refers, but I suspect that the users didn't allow enough ventilation for the coils and pump to remove the interior heat. Norcold specifies them with 100 square inches of overhead and another 100 square inches of below venting for passive or 50 & 50 inches square with a stout 24v fan.
There are refrigerators that have peak power consumption of about 30W and 4" insulation available. Expect to pay over $1000 for a 12/24v DC model, but if you are off-grid, it's worth the money for energy not needed to be generated.
The big surprise was the Dometic ammonia refrigerator in the trailer. Connected to 120v from the house, it's using 195W. From an inverter, this would drain your batteries flat fast. To its' credit, the freezer compartment is +13F with 80 degree ambient. Use propane with ammonia refers for best off-grid results. A 5 gallon tank of propane will last weeks and provide very cold beverages. When there is extra space in the freezer, I put extra blocks of "blue ice" inside to freeze and take up air space. Same strategy in the refrigerator but with jugs of drinkable water.
I'd like to know what kind of power consumption a Peltier device cooler like "Kool-a-tron" has in warm weather. I have read that they have some difficulty cooling more than -40 degrees F below ambient.
It's interesting that much larger capacity household refrigerators have similar power consumption (between 110-150 Watts) to vehicle mounted Dometic when using grid power ("shore power" to boaters). Household models may not hold up to boating or road travel, but they cost so much less that breaking (under warranty?) is okay if you need the refrigerated space.
Update on the Dometic 120v/Propane refer in the trailer:
ReplyDelete40.6hrs logged used 5.7KW/Hrs. I've opened it briefly about 3 times in 2 days. When I checked instantaneous Watts, it was 4.6W, with the freezer at +8 degrees F. This is better than the initial 195W showing, but 140W average over some hours is almost 3x the peak consumption of the compressor-driven Norcold (which is only occasionally running the compressor).
I stand by my conclusion that for off-grid use, get a compressor-based DC refrigerator/freezer for use with solar/batteries, and use propane to run any ammonia refrigerator capable of using it. When in-town, plug in, charge batteries, and save propane. In an RV lot, you have paid for the power, so use it.
pdxr13
Still eating frozen food from the kitchen refrigerator with failed big refer section. This is why people pay $500 and love appliance stores who come out with the new box/take the old box on the same day.
ReplyDeleteAt 138 hours, the Dometic ammonia absorbtion refrigerator on 120v used 18KW/Hours. I think I've opened it about once a day.
ReplyDeleteIt's been pretty mild and overcast the past 4 days, and that affects the duty cycle somewhat. This might be the cause of the somewhat-dropping average consumption down to 130W/Hours.
Kill-a-watt moved to the Norcold on the back porch. It's packed with food in both the refrigerator and freezer and gets opened a few times a day.
Norcold TEK II Dual Electric Refrigerator DE/EV-441:
ReplyDelete17hrs overnight, 61 degrees F. ambient temp, used 340W.
That's 20W per hour. Since the motor will draw 45W full-on, starting warm, this is Duty Cycle of 47%. (Motor drives compressor 47% of the time). Temp dial is set at half-way between "on" and "coldest".
A 150W solar panel with MPPT controller and a cheap Group27 deep cycle battery would run this refrigerator. Higher summer temps bring more solar power, lower winter temps come along with poorer sun (less power, or none for days). That could be about $250 for a panel, $200 for a controller, $69 for a new battery, misc. brackets/covers and hook up wire. DMM already owned.
Would this make economic sense to go solar without some kind of dot-gov subsidy? Not if the grid stays up, forever. If I needed to keep a life-critical medicine cool no-matter-what, it would be a no-brainer to spend this much money on assuring life.
It might make sense in an RV or a remote cabin (can't afford $90K to run power from the road), because it's compared to running a generator daily or humping in propane tanks (to run a propane refrigerator).
Last power update on the Norcold:
ReplyDelete4.65 KW/H used over 285 hours of regular kitchen use.
That's 16.31W per hour. Frost was getting about a half-inch thick and needed defrosting.
There was a little rust and bubbling paint around the door frame to scrub off and re-prime. That's what I get for a 9 year old unit.
11 November update:
ReplyDeleteNorcold running at "1" (just above "Off"), not freezing milk any more. 389 hours (16.2 days) with moderate Portland weather (days in the 50's and low 60's F., night to +34F (brrrrr!) consumed 4.48 KW/Hrs= 11.51 Watts/hr.
At PGE 12 cents / KW/hr, this will cost less than $2 for a month. Next year power bill ought to go down (KW/Hrs, not price) a little when compared to the old refrigerator/freezer.
The refrigerator is on a stand at standing height and 2 feet out from the wall, so it's got lots more ventilation than any kind of cabinet mounting. Next project will be to mock up a cardboard cabinet simulator to restrict air movement and monitor cooling/power consumption effects.