Just how bad a small 'frige is

BB.

Re: Just how bad a small 'frige is

One thing to be aware of with Sun Frost--Their advertising tends to push 0.48 kWH per day, which is very low, for their R16 fridge. However that is at 70F.

When comparing to Energy Star Numbers--Last time I looked up the ratings, those tests appear to be equivalent to the 90F testing numbers for Sun Frost (0.7 kWH per day or ~46% more power). Still, not bad, especially if you want a DC powered appliance. But the high costs of Sun Frost, and others, will usually cover the extra costs of an inverter, more panels, and a bigger battery bank.

So, compare and contrast in an apples to apples comparison.

-Bill

Dusty

Re: Just how bad a small 'frige is

I converted a Kenmore 10 cubic foot chest freezer using an external Johnson Controls thermostat a few years ago (for homebrew fermentation).

Using the Kill-a-watt meter, with the chest freezer set to 35 degrees, here are the stats (sorry, I don't have a surge meter):

122 running watts elapsed over 141 hours (5.875 days) came to 1.3 KWh, or 221.28 Wh per day. Much better than my side-by-side that measured 2766Wh per day.

With utility power @ 11 cents/Kwh, the chest freezer-now-refrigerator uses $0.74 per month, while the old non-energy star side-by-side used $9.26 per month.

Cariboocoot

Re: Just how bad a small 'frige is

Hmm. That's about the same as my upright 16 cubic foot standard (non energy star) 'frige.

That side-by-side was a nightmare, eh?

Dusty

Re: Just how bad a small 'frige is

Yes, that side-by-side was an energy hog. Thanks to the Kill-a-watt meter, I now use it for a dry goods storage locker. It's even lighted! :roll:

I really like that when I open the chest freezer/fridge, I lose very little cold air. However, I'm a bit surprised that you're getting similar results with a standard fridge. That's great!

I can live with $0.74 a month operating cost. My other chest freezer is the same brand and size Kenmore (10 cubic feet), and used as a freezer it's costing $3.52 a month to operate. The 14 cubic foot Kenmore chest freezer costs even less--$2.95 per month.

ywhic

Re: Just how bad a small 'frige is

So from what I'm gathering a 1000 watt pure sine inverter would work for most fridges??

I may forgo buying the Xantrex SW 2000 and just end up with a Cotek ST-1000.. its hardwire and has a xfer switch built in..

waynefromnscanada

Re: Just how bad a small 'frige is

ywhic wrote: »

So from what I'm gathering a 1000 watt pure sine inverter would work for most fridges??

As long as the inverter has good surge capacity, it should work. I did however purchase a "Pure Sine" 1500 watt inverter a couple of years ago at a major automotive/hardware chain, only to find it was pretty much useless at starting anything with an induction motor. Had no surge capacity at all. Yes, I returned it the next day.
Found it rather shocking, as cheaper MSW inverters would start those same and bigger motors.

BB.

Re: Just how bad a small 'frige is

Around 1,500 watt inverter is the minimum our host recommends to run a refrigerator and a few lights.

But, like Wayne says--there are a lot of different inverters out there and a lot of different loads. Your choice is to take a shot and (try to) return those that don't work. Or work with a retailer/installer that has lots of experience with the products they sell.

-Bill

Cariboocoot

Re: Just how bad a small 'frige is

waynefromnscanada wrote: »

As long as the inverter has good surge capacity, it should work. I did however purchase a "Pure Sine" 1500 watt inverter a couple of years ago at a major automotive/hardware chain, only to find it was pretty much useless at starting anything with an induction motor. Had no surge capacity at all. Yes, I returned it the next day.
Found it rather shocking, as cheaper MSW inverters would start those same and bigger motors.

I think I know that store.
A few years back I tested just about every model they had trying to find one that would run a refrigerator. None of them could. Most of them didn't live up to their rated Watt capacity either. No telling what they'd be like today, as the models offered now are not the same nor are they likely made by the same manufacturer. The difference between a "retail brand" and real brand.

ywhic

Re: Just how bad a small 'frige is

I had red 4-5 X the running watts to start a fridge usually.. This Cotek/Samlex is rated at 1150 watts for 3 minutes.. 1000w continuous and 2000w surge..

They make a ST-1500 Cotek (1725w for 3 minutes and 3000w surge) as well with the Xfer switch in it.. but at that point I'll be at the same $$ as the SA-2000K-24.. so then that won't make as much sense in my $ book..

Trying to get one for the normal stuff at this point and NOT the A/C maybe..

waynefromnscanada

Re: Just how bad a small 'frige is

Cariboocoot wrote: »

I think I know that store.
A few years back I tested just about every model they had trying to find one that would run a refrigerator. None of them could. Most of them didn't live up to their rated Watt capacity either. No telling what they'd be like today, as the models offered now are not the same nor are they likely made by the same manufacturer. The difference between a "retail brand" and real brand.

Haha You know the store alright
And yes, that's pretty much what I found. Buying "retail brand" is too often buying a pig in a bag, sight unseen as far as performance is concerned. A shame really, taking advantage of unsuspecting, trusting customers.

TheBackRoads

Re: Just how bad a small 'frige is

I just wanted to post another fridge. I think it is 4CuFt... GE small fridge. Now I turned it to max cold (for a different test) and had it running for half a day or so (it was cycling on and off). The below is after it reached its ~25 deg F average. 27 hours and 1.6KWH in 70-85 degree air.

KWH

Hours

Temp (probe inside, in middle - other reading ambient temp)

Some Specs

TheBackRoads

Re: Just how bad a small 'frige is

I should also note, it was not opened during this time and had 1 small bottle of water inside (never froze).

waynefromnscanada

Re: Just how bad a small 'frige is

TheBackRoads wrote: »

4CuFt... GE small fridge. Now I turned it to max cold (for a different test) and had it running for half a day or so (it was cycling on and off). The below is after it reached its ~25 deg F average. 27 hours and 1.6KWH in 70-85 degree air.

In my opinion it's nothing short of criminal that ANY manufacturer would offer for sale a 4 cu ft fridge capable of sucking back over 1.4 Kwh / day!
There's just no excuse! My 8 cu ft freezer converted to fridge, and running cold enough to freeze milk, uses 0.28 Kwh in the same time period!
That works out roughly to 350 watt hours per cu ft/day for the little 4 cu ft fridge, against less than 35 watt hours per cu ft/day for the 8 cu ft converter freezer, meaning the small one consume roughly 10 times the energy per cu ft, of the converted freezer. And this is with the converted freezer being opened and used as usual throughout the day! Criminal in my opinion!

Cariboocoot

Re: Just how bad a small 'frige is

Not a big fan of regulation myself but ...
We have fuel mileage standards for cars.
If governments were serious about energy conservation/pollution ...

BB.

Re: Just how bad a small 'frige is

Cariboocoot wrote: »

Not a big fan of regulation myself but ...
We have fuel mileage standards for cars.
If governments were serious about energy conservation/pollution ...

...And then people buy larger cars/motors/pickups/vans and drive more miles...

...Sound perplexing? This situation is the result of a trend newly quantified by MIT economist Christopher Knittel: Because automobiles are bigger and more powerful than they were three decades ago, major innovations in fuel efficiency have only produced minor gains in gas mileage.

Specifically, between 1980 and 2006, the average gas mileage of vehicles sold in the United States increased by slightly more than 15 percent — a relatively modest improvement. But during that time, Knittel has found, the average curb weight of those vehicles increased 26 percent, while their horsepower rose 107 percent. All factors being equal, fuel economy actually increased by 60 percent between 1980 and 2006, as Knittel shows in a new research paper, “Automobiles on Steroids,” just published in the American Economic Review (download PDF).

Thus if Americans today were driving cars of the same size and power that were typical in 1980, the country’s fleet of autos would have jumped from an average of about 23 miles per gallon (mpg) to roughly 37 mpg, well above the current average of around 27 mpg. Instead, Knittel says, “Most of that technological progress has gone into [compensating for] weight and horsepower.”
...
That said, Knittel is skeptical that CAFE standards by themselves will have the impact a new gas tax would. Such mileage regulations, he says, “end up reducing the cost of driving. If you force people to buy more fuel-efficient cars through CAFE standards, you actually get what’s called ‘rebound,’ and they drive more than they would have.” A gas tax, he believes, would create demand for more fuel-efficient cars without as much rebound, the phenomenon through which greater efficiency leads to potentially greater consumption.

-Bill "there aught to be a law" B.

dhsola

Re: Just how bad a small 'frige is

Interesting article about refrigerators old and new, Energy Star program, CEE Tier rating and some good comments below the article. Lots of links.

http://www.greenbuildingadvisor.com/blogs/dept/musings/choosing-energy-efficient-refrigerator

waynefromnscanada

Re: Just how bad a small 'frige is

dhsola wrote: »

Interesting article about refrigerators old and new, Energy Star program, CEE Tier rating and some good comments below the article. Lots of links.

http://www.greenbuildingadvisor.com/blogs/dept/musings/choosing-energy-efficient-refrigerator

A great read! Thanks for sharing. Re the "card board" insulation mentioned in the old "Monitor Top", I've discovered that in several of the earlier fridges, including a propane fridge I helped my Uncle rebuild. We replaced the cardboard with foam insulation in that one by the way.
The early folks really were a LOT more energy aware than those who came later. Unfortunately, in my opinion, most alive today in North America believe it their God given right to consume and waste energy like there is no tomorrow. Then they sit back and complain about their electric bill, wondering why it's so high.

dhsola

Re: Just how bad a small 'frige is

Saw an old advertisement for the Monitor-Top fridge on ebay today. In the ad, they touted low "current" consumption. It's certainly worth noting these refrigerators are still operating today, 80 years later, cardboard insulation and all. And they're still being bought and sold, refurbished or not! (I wonder how many of those avocado green, '70's vintage fridges are being restored )?

Too bad about the Energy Star program being all but useless. Seems to be a recurring problem with govt entities these days. Fortunately, we have CEE (Consortium for Energy Efficiency) and SEHA (Super Efficient Home Appliance Initiative) and their Tier program. CEE

I hope we begin seeing more fridges with three inch thick walls (compressors that last 80 years would be nice too). Still, putting a heater on a refrigerator is about the dumbest thing they did. My old manual defrost fridge runs at least 100w less than the auto-defrost-heater fridge. It might be interesting to look into building your own fridge. I've seen instructions/suggestions here and there on the internet.

ggunn

Re: Just how bad a small 'frige is

waynefromnscanada wrote: »

Unfortunately, in my opinion, most alive today in North America believe it their God given right to consume and waste energy like there is no tomorrow.

That there's a self fulfilling prophesy for ya'!

waynefromnscanada

Re: Just how bad a small 'frige is

Or a statement of fact about the attitude of a modern and spoiled society. lol

pabloesguapo

Re: Just how bad a small 'frige is

OK, help me with my math. Looking at an energy star fridge at Lowes today. 5.3 amps @ 120v. How many watts? (Amps x volts = watts, right?)

Trying to figure how many amp hrs this thing would eat from my battery bank. Late. Tired...

Photowhit

Re: Just how bad a small 'frige is

pabloesguapo wrote: »

OK, help me with my math. Looking at an energy star fridge at Lowes today. 5.3 amps @ 120v. How many watts? (Amps x volts = watts, right?) Right! 5.3 x 120 = 636 watts

So it uses 636 Watts while running...
...The trick is you want to know how many "amp hours" it will use, since it runs off a thermostat it doesn't run all the time, so you can trust the ratings, knowing that they are based on a specific ambient temperature (not sure what that is) and adjust to your situation, if it's going to be in the cool basement, maybe less, if it's going to be in the un air conditioned garage likely more, if you live in south texas and it's 90-100+ degrees all the time around the fridge, lots more!

waynefromnscanada

Re: Just how bad a small 'frige is

It can get complicated. Multiplying the AC amps by the AC volts will give you the "VA", which, if the motor (compressor) has a poor Power Factor rating, will be higher than the actual wattage consumed (and paid for if you're on grid power). The good thing is that most Energy Star fridges and freezers how have excellent PF, so the VA will be very close to the actual wattage. It's the Watt Hours consumed that really matters, but operating a device with poor PF can be stressful to inverters, as it can APPEAR as a much greater load than it actually is, because the Amps drawn, are not in phase with the supplied voltage.
A Kill_A_Watt can show you the PF; Voltage; amps; as well as the actual wattage consumed.
As an example, running my induction motor powered water pump, with no back pressure, to water my garden: The motor is 1/4 Hp and rated 5 amps @ 115 volts. That would lead one at first glance, to expect a consumption of 575 watts. In reality the Kill-A-Watt shows 165 Watts, which surprised me that it was that low. It does of course go up when back pressure and thus load is added to the motor. The PF however was poor and the VA was showing over 400 on the K-A-W meter. As an experiment, I tried connecting Motor Run capacitors across the motor for PF correction and found that roughly 98 MFD brought the PF in line, reducing the VA from over 400 all the way down to 168, which should be much easier on the inverter.

vtmaps

Re: Just how bad a small 'frige is

The nameplate amps may also include the heater used in the defrost cycle or the heater in the gasket (to prevent sweating). You may be able to turn these heaters off... Does the fridge have an 'eco mode'?

--vtMaps

pabloesguapo

Re: Just how bad a small 'frige is

Photowhit wrote: »

So it uses 636 Watts while running...
...The trick is you want to know how many "amp hours" it will use, since it runs off a thermostat it doesn't run all the time, so you can trust the ratings, knowing that they are based on a specific ambient temperature...!

Why would i spend over $1000 on a brand new refridgerator and then put it in a garage?

It'll be in the kitchen, so let's assume a constant temperature of 70°F. Let's also assume 5.3amps is an average, after wefactorin start up, not running all the time, defrost,etc. Let's use it as a worst case scenario. So, 5.3 amps times 24hrs in a day equals 127.2 amp hours drawn from my batteries?

BB.

Re: Just how bad a small 'frige is

Don't even go there with that math. :roll:

First that is 5.3 amps at 120 VAC:

• 120 VAC * 5.3 amps * 24 hours per day = 15,264 VA per day (or worse case 15 kWH per day)

If you have a 12 VDC battery bank, that would be:

• 15,264 VA / 12 volts = 1,272 AH @ 12 volts per day

The reality is much different.

Lets assume you have a large fridge that uses around 500 kWH per year (check the yellow tag on the fridge):

• 500 kWH per year / 365 days per year = 1.4 kWH per day = 1,400 Watt*Hours per day
• 1,400 WH per 24 hours / 24 hours per day = 58 watt average load (not 600+ watt average load)

If you where using a 12 volt battery bank and a 85% efficient AC inverter:

• 58 watts * 1/0.85 inverter eff * 1/12 volt battery bank = 5.7 amps @ 12 volts average load
• 5.7 amps * 24 hours per day = 137AH @ 12 volts per day

Note, the fridge still takes >600 VA to run (compressor + heaters typically). And will draw >1,000 VA to start (note that Watts=VA*Power_Factor).

The Inverter needs to support "VA", the battery bank needs to support "Watts" and Watt*Hours.

The peak power (and peak VA) of the fridge is important, but overall system design also needs to look at average power used. Sort of comparing fuel mileage with a car that is doing jack rabbit starts, up hill, pulling a trailer, vs the average MPG per tank of fuel. Size the engine for maximum loads, size the tank for average fuel mileage.

Also remember that Amps needs to know the voltage you are working with. 12 volt current will be ~10x the 120 volt name plate current for that fridge (power=volts*amps, 1/10 the voltage, 10x the current for the same power).

So--First thing, look at the yellow hang tag for the kWH per year, then get a Kill-a-Watt type power meter and measure the load(s). Come back here and lets talk math and supporting hardware.

-Bill

Cariboocoot

Re: Just how bad a small 'frige is

pabloesguapo wrote: »

Why would i spend over $1000 on a brand new refridgerator and then put it in a garage?

It'll be in the kitchen, so let's assume a constant temperature of 70°F. Let's also assume 5.3amps is an average, after wefactorin start up, not running all the time, defrost,etc. Let's use it as a worst case scenario. So, 5.3 amps times 24hrs in a day equals 127.2 amp hours drawn from my batteries?

5.3 Amps is likely a maximum draw. Any standard refrigerator that pulls 636 running is a piece of junk. Most use less than 200 Watts during normal cycling; the higher Wattage would be for occasional defrost (heating element on).

What is typical for a medium size refrigerator is around 1200 Watt hours per day. On a 12 Volt system this is roughly 100 Amp hours, not including conversion losses and inverter power. On a 24 Volt system it is 1/2 that.

Your math contains a major flaw, btw: the 5.3 Amp draw of the refrigerator is at 120 VAC. When you shift to DC there will be a considerable Amperage change. For 12 VDC is roughly a factor of 10, for 24 about 5. So 5.3 Amps on the AC side becomes 53 Amps @ 12 VDC which would be 1272 Amp hours from the batteries. Aren't you glad that isn't right?

pabloesguapo

Re: Just how bad a small 'frige is

Thanks for the math lesson, guys. Complicated, but I'm beginning to see a different picture. I think...

I'm definitely going to buy a kill o watt. Saw 'em on amazon for $20-something.

So, that "typical" medium sized fridge... I'm running a 48v system. If 1200 watt hrs ÷ 12 volts = 100 AH. So, 1200 watt hrs ÷48v = 25AH?

BB.

Re: Just how bad a small 'frige is

Yep (ignoring losses).

Note that 100 AH @ 12 volts of batteries will weight/cost about the same as 25 AH @ 48 volt battery bank.

Then you want 1-3 days of storage and 50% maximum discharge (for long battery life):

100 AH * 2 days of storage * 1/0.50 maximum discharge = 400 AH @ 12 volts

But you have an 85% efficient inverter:

400 AH * 1/0.85 inverter eff = 471 AH @ 12 volts

So, that 1,200 WH / 100 AH @ 12 volts turns very quickly into a 471 AH @ 12 volt battery bank (or 118 AH @ 48 volt battery bank).

Next there is the whole solar panel / backup generator set of calculations based on battery size and amount of sun.

-Bill

Cariboocoot

Re: Just how bad a small 'frige is

Ah, but the upside is the 48 Volt system is every-so-slightly more efficient than 12 Volt.
And most inverters will run around 90% efficiency these days.

So the 1200 Watts hours is 1333 on the DC side, plus the 480 Watt hours of the inverter being always on (20 Watts per hour) = 1813 Watt hours. Divide by 48 Volts and you get roughly 38 Amp hours per day to run the 'frige.

Some caveats: the refrigerator's actual use will vary from day to day due to changes in ambient temperature and how often the door is opened; the current draw from the batteries is not fixed because of the Peukart Effect (more current as the battery goes down in Voltage - calculating it at system nominal gives an advantage as that should be the minimum Voltage seen); panels recharging during the day should take some of the load entirely, further reducing the battery draw (except on days when there is insufficient sunshine).

That's the reason for the fudge factors; adjust the numbers the right way and you get enough margin for error to make it work all the time.