Refrigerator KW consumption daily / weekly

[O C Diver]

I'm considering getting a new refrigerator for the boat. Currently looking at apartment refrigerators. As with many boat items, wanted to get some power consumption numbers. According to the government , one of the units I'm looking at should consume around .8 KW per day. While I plan to measure mine for 3 weeks next month while going North, I figured some of you solar power live aboards might have some real numbers already.

What I'm looking for are actual usage numbers versus theoretical calculations. If you could give me real numbers per day or a week and whether your in the tropics or the arctic, I would be very appreciative.

Thanks!

Ted

 

[twistedtree]

I'm considering getting a new refrigerator for the boat. Currently looking at apartment refrigerators. As with many boat items, wanted to get some power consumption numbers. According to the government , one of the units I'm looking at should consume around .8 KW per day. While I plan to measure mine for 3 weeks next month while going North, I figured some of you solar power live aboards might have some real numbers already.



What I'm looking for are actual usage numbers versus theoretical calculations. If you could give me real numbers per day or a week and whether your in the tropics or the arctic, I would be very appreciative.



Thanks!



Ted

I have compared the energy star consumption figures with real, measured consumption over several weeks on several different fridges and freezers. The energy star numbers are dead nuts on. So I would definitely use them to compare appliances, size batteries, etc.

The only caution would be that the energy star numbers assume some usage pattern. With an always on appliance like a fridge, it doesn't matter. But for something used intermittently, the numbers are valid for comparing products, but might differ from your actual monthly consumption because of different usage.

 

[Ski in NC]

I have an under counter bar fridge, it draws about 1.7A at 120Vac. I'd figure the larger apt size fridge would run about 3-4A. I run mine off the inverter and I can see the AC panel ammeter from my helm position. Just a gut feel is it runs about 50% of the time. And that depends a lot on how many times the door is opened. Open the door once and the thing seems to run for about a half hour to chill it back down. We keep drinks in a cooler so fridge is generally only opened for prep'ing meals. Assuming some loss at inverter, figure it draws 20A at 12Vdc. So using 50% run time, that is 240AH per day for mine. 3A would be 425AH, 4A would be around 560AH.

Not sure what to make of the 0.8kW per day?? Must mean 0.8kWhr per day?? That's way lower than mine which comes out to like 2.8kWhr per day. Maybe I am doing something wrong with the numbers.. Or my fridge is a real power hog..

 

[FoxtrotCharlie]

Watching

 

[DavidM]

I believe that the Energy Star values are reasonable for very light use, ie opening infrequently and never filling it with warm beer. But it all depends on how you use it. If you put a case of warm beer in every day it will use much, much more.

0.8 kWHrs daily is very little for a 120V refrigerator. To power it from an inverter would only take 800/12/.9 = 74 AHs. That is about what a marine Danfoss compressor system would require with normal opening and closing and a little warm food put in occasionally. My Novakool 2.5 cu ft fridge uses about that much.

So because it is an Energy Star appliance (good for a 120V system) the real world numbers are probably somewhere between 74 and Ski's 240 AHs. Low to mid 100s would be my guess.

David

 

[FF]

BEWARE , the gov figures only include energy for cooling.

Many house units have heater wiring to dry the very thin insulation and to defrost the door seals.

Look for a schematic on line to see how many amps these draw.

Thank K street for the fact the gov information is useless.

If you have the room a Sunfrost 12v or 120v is made for minimum electric use.

Sun Frost: Energy Efficient Refrigerators, Freezers, and Sustainable ...

www.sunfrost.com/


Sun Frost: worlds most energy efficient refrigerators and sustainable living products. Including composters, solar vaccine refrigerators and composting toilets.‎Refrigerators and Freezers · ‎Models · ‎Specifications and Retail Price ...

 

[O C Diver]

I have an under counter bar fridge, it draws about 1.7A at 120Vac. I'd figure the larger apt size fridge would run about 3-4A. I run mine off the inverter and I can see the AC panel ammeter from my helm position. Just a gut feel is it runs about 50% of the time. And that depends a lot on how many times the door is opened. Open the door once and the thing seems to run for about a half hour to chill it back down. We keep drinks in a cooler so fridge is generally only opened for prep'ing meals. Assuming some loss at inverter, figure it draws 20A at 12Vdc. So using 50% run time, that is 240AH per day for mine. 3A would be 425AH, 4A would be around 560AH.

Not sure what to make of the 0.8kW per day?? Must mean 0.8kWhr per day?? That's way lower than mine which comes out to like 2.8kWhr per day. Maybe I am doing something wrong with the numbers.. Or my fridge is a real power hog..

Appreciate the effort!

A KW is a measure of energy irrespective of time. Your power company sends you a bill for how many KW your house or shop consumed last month.

In your example, your fridge draws 1.7 amps at 120vac. So it consumes 204 watts per hour (volts x amps), or .204 KW per hour. Since you think it has normally a 50% duty cycle, that would be .104 KW per hour. In a 24 hour period it should consume 2.5 KW (2.496 kW).

Depending on the age of the unit (insulation and compressor efficiency ), those numbers could be close. In reality, there is a lot of the night when you don't open the door, add warm beer to be cooled, and the ambient room temperature is less. So, your real consumption numbers could be quite a bit less.

This is why I'm looking for people who have track actual consumption with a battery monitor or watts meter. If you're interested in knowing what yours is, there a simple devices that go between the appliance and the outlet to monitor consumption over time. Without looking, I think they're less than $20.

Ted

 

[fryedaze]

We have a T80 Tundra frig/freezer. It draws 7.5 dc amps. The duty cycle is 30 min an hr. That's about 1.1kwhr a day. We also have a Dometic CF110. Its performance is about the same. I believe they both have the same Danfoss DB50 compressor.

 

[boathealer]

Looking for some of this info myself in the near future.

From: https://reductionrevolution.com.au/...er-consumption-can-the-star-rating-be-trusted

"We found that our fridge used 0.607 kilowatt-hours in a 24 hour period, which equates to around 221 kWh per year. The Power Meter showed that the fridge was drawing power for 6 hours and 10 minutes over that 24 hour period, or 25% duty, which is very energy efficient (a typical duty cycle for fridges is around 30%, or 8 hours per 24-hour period). This is an office fridge so it's almost empty most of the time. We have also made sure there's at least a 10cm gap around all sides to allow air to move around the unit.
------
I did the same test with my fridge at home and found that it uses about 1 kWh per day, which is typical for small units under 250 litres capacity."

This is all in an air-conditioned house/office, mind you, not a 90deg tropical boat environment.

This was also an interesting site: http://michaelbluejay.com/electricity/refrigerators.html

 

[O C Diver]

BEWARE , the gov figures only include energy for cooling.

Many house units have heater wiring to dry the very thin insulation and to defrost the door seals.

Look for a schematic on line to see how many amps these draw.

Thank K street for the fact the gov information is useless.

In the most recent rule making for energy star and tier efficiency, power consumption for defrost is no longer exempted. Within comparable models, the defrost feature could add from 5 to 20% additional power consumption depending on how the frost free is achieved. As a side note, accumulated frost and ice inside the freezer and around the coils reduces efficiency also. So unless you are going to regularly defrost a non frost free unit, the difference may be extremely small.

Ted

 

[Ski in NC]

Ted- you have your units a bit mixed up. kW is a measure of power, kWh is a measure of energy.

My fridge running at 1.7A at 120 is consuming 204W, or 0.204kW of power.

If it runs one hour, it has used 0.204kWh. Run 24hrs at 50% duty cycle, that's 12h x 0.204kW = 2.45kWh. kWh is energy, or power used over a period of time.

I might be overestimating the run time. Seems that 50% might be high.

 

[O C Diver]

If you have the room a Sunfrost 12v or 120v is made for minimum electric use.

Sun Frost: Energy Efficient Refrigerators, Freezers, and Sustainable ...

www.sunfrost.com/


Sun Frost: worlds most energy efficient refrigerators and sustainable living products. Including composters, solar vaccine refrigerators and composting toilets.‎Refrigerators and Freezers · ‎Models · ‎Specifications and Retail Price ...

Have followed Sunfrost for years and am really impressed with their efficiency. Their closest unit to my needs is about 20% larger and consumes half the enery. Unfortunately it costs almost $2,000 more. The good news is that if it costs me $0.50 per KW, I could break even in 27 years if I bought the Sunfrost and it and I lasted that long.

Ted

 

[O C Diver]

Ted- you have your units a bit mixed up. kW is a measure of power, kWh is a measure of energy.

My fridge running at 1.7A at 120 is consuming 204W, or 0.204kW of power.

If it runs one hour, it has used 0.204kWh. Run 24hrs at 50% duty cycle, that's 12h x 0.204kW = 2.45kWh. kWh is energy, or power used over a period of time.

I might be overestimating the run time. Seems that 50% might be high.

Oh well, the terms were wrong, but the math was correct.

Ted

 

[catalinajack]

I'm considering getting a new refrigerator for the boat. Currently looking at apartment refrigerators. As with many boat items, wanted to get some power consumption numbers. According to the government , one of the units I'm looking at should consume around .8 KW per day. While I plan to measure mine for 3 weeks next month while going North, I figured some of you solar power live aboards might have some real numbers already.

What I'm looking for are actual usage numbers versus theoretical calculations. If you could give me real numbers per day or a week and whether your in the tropics or the arctic, I would be very appreciative.

Thanks!

Ted

Beware of household units if they are to live in an enclosure. When we bought our Defever four years ago it cam with two household units side-by-side in a cabinet separated by a plywood wall. They worked but I determined to trash when, one day, I slid one unit out of the cenclosure to check on what was behind it and discovered both sides of the fridge almost to hot to touch. Turns out that the heat dissipation was from coils embedded in the sides, a highly inefficient situation in that the heat was being trapped. Note the the enclosure was vented on both sides.

I replaced them with Vitrifigo refer only units and am a very happy customer. Right now the refers are set at minimum cooling and the temp measures at a consistent 33 degrees. I attribute that to winter temps that reduce the bulkhead temp at the back of the enclosure. Last summer, at peak temps, I did not have to go to max cooling.

My units are hard-wired 12-volt only. My thinking is why use 120 so the fridge can then invert back to 12 volts. Plus, that fridge inverter is just something else that can fail.

 

[Comodave]

Even if it takes a bit more power to have self defrosting it would be worth it to me. I hate defrosting the fridge every week or so when we are on the boat long term.

 

[boathealer]

Even if it takes a bit more power to have self defrosting it would be worth it to me. I hate defrosting the fridge every week or so when we are on the boat long term.

Not only that, when you defrost it, you are letting ALL the cold out, and considerable power is needed to bring it back down to cold. Probably as much as the defroster would have taken anyway......

 

[Comodave]

And defrosting is a PITA...

 

[Simi 60]

.

If you have the room a Sunfrost 12v or 120v is made for minimum electric use.

Sun Frost: Energy Efficient Refrigerators, Freezers, and Sustainable ...

Energy Efficient Refrigerators, Freezers, and Sustainable Living Products - Sun Frost


Sun Frost: worlds most energy efficient refrigerators and sustainable living products. Including composters, solar vaccine refrigerators and composting toilets.‎Refrigerators and Freezers · ‎Models · ‎Specifications and Retail Price ...

Don't know how much extra they cost there but here the price difference between normal house fridge and super efficient is easily 4x or more

That price difference pays for another 1000 amps of batteries for us so sticking with easily obtainable household, even if it uses a bit more juice is an easy choice.

 

[Roamer Blue]

get a "Kill-a-watt" meter to measure the energy use of your 120 ac devices.

It can also let you zone in the generator with the Hertz scale.

2 different ones on Amazon, $21-$28.

Get into the schematic and add your own switch to the door edge and defrosting circuits, so you can put the fridge on electron rationing as needed?

RB

 

[HiDHo]

Ted, we replaced our Nevercold with a apartment size refrig/frzer thats about 5 cuft and 2 cuft freezer from Summitappliance.com, a NY state company as I recall. When I called the company to size a dedicated inverter they gave me 1.2 run amps, 4 start amps but had no figure on defrost amps. Priced at less than half the cost of a NC.
Cold beer, frozen ice cream and no defrosting and quiet running. We have owned it for 5 years 2 as full time live aboards with no problems at all. The one we ordered at the time was a direct replacement size wise for the Nevercold.

 

[Insequent]

I have used a kill-a-watt and also an equivalent DC device to measure 24 hour consumption of various electrical items on board. This was done in late summer in Brisbane, latitude 27.46°S. So I guess similar to Fort Pierce which is 27.44°N

I had 2 Norcold units which were 120VAC or 12VDC. Both use less energy when operating on 12VDC, and the consumption below is all 12VDC. The holding temps/consumption are when nothing new was added into the unit, but some drink or food may have been removed.

My main galley fridge is a Norcold DE0061R. It used 80Ah/day, which is fairly reasonable for an old unit. The freezer door was likely only opened once and the fridge door maybe half a dozen times.

The pilothouse had a Norcold DE 400C. A much smaller size, and only used for drinks. It consumed 156AH/day, just cooling (small freezer tray only) with only being opened once. So the 400C was immediately removed and sold!

In place of the Norcold 400C I put an Engel (30 litre) fridge/freezer unit that I bought in 1980 and use for camping trips. It used 56Ah holding at +0.5°C, or 102Ah holding at -3.8°C. And it is too old to have the really efficient Danfoss compressor!

I also have a Dometic CF 110. It has more than 3 times the volume capacity of the Engel, but is more efficient with the Danfoss compressor. Holding at +3°C used 21Ah. Holding at -5°C used 62AH. And holding at -10°C used 131Ah.

Of course pull-down to the hold temperatures did use significantly amounts of energy as duty cycle was then 100% for quite a while. The Dometic CF 110 used 252Ah over 24hours to pull-down from ambient to -5°C and hold there. It was about 25% full at the time. But since the pull-down occurs either at the dock or underway it is not that important. The steady-state holding mode is what matters overnight at anchor.

 

[twistedtree]

I believe that the Energy Star values are reasonable for very light use, ie opening infrequently and never filling it with warm beer. But it all depends on how you use it. If you put a case of warm beer in every day it will use much, much more.

0.8 kWHrs daily is very little for a 120V refrigerator. To power it from an inverter would only take 800/12/.9 = 74 AHs. That is about what a marine Danfoss compressor system would require with normal opening and closing and a little warm food put in occasionally. My Novakool 2.5 cu ft fridge uses about that much.

So because it is an Energy Star appliance (good for a 120V system) the real world numbers are probably somewhere between 74 and Ski's 240 AHs. Low to mid 100s would be my guess.

David

I measured the energy consumption for our sub-zero which are generally believed to be power pigs. I collected data a couple of times, always over at least a week of normal operation, in use every day in whatever is "normal" for us. I don't drink a case of beer per day, but we are in and out without much consideration other than wanting something that's inside.

The daily consumption was 930 Wh, or 0.930 kWh. The EnergyStar figure is 1.2kWh, so it's actually performing better than expected.

The second test was a chest freezer. By nature you are not in and out of it all the time, and we definitely were not. I don't have the figures at hand, but it came out within spitting distance of the EPA number as well.

Granted it's a sample size of two, but it's two our of two.

To FF's point about not including the defrost cycle, our fridge does have a heater defrost cycle that runs every few days, so that's included in our numbers.

If you look at the EPA figures, you can find significant differences between products. There is less difference than a few years ago, but it can still be significant. For example, on our new build std equipment includes an extra two drawer freezer. The EPS power draw on it sucks. We substituted dual chest freezers for significantly more cold storage with less overall power draw.

It pays to shop power consumption, especially on a boat.

 

[O C Diver]

Beware of household units if they are to live in an enclosure. When we bought our Defever four years ago it cam with two household units side-by-side in a cabinet separated by a plywood wall. They worked but I determined to trash when, one day, I slid one unit out of the cenclosure to check on what was behind it and discovered both sides of the fridge almost to hot to touch. Turns out that the heat dissipation was from coils embedded in the sides, a highly inefficient situation in that the heat was being trapped. Note the the enclosure was vented on both sides.

I replaced them with Vitrifigo refer only units and am a very happy customer. Right now the refers are set at minimum cooling and the temp measures at a consistent 33 degrees. I attribute that to winter temps that reduce the bulkhead temp at the back of the enclosure. Last summer, at peak temps, I did not have to go to max cooling.

My units are hard-wired 12-volt only. My thinking is why use 120 so the fridge can then invert back to 12 volts. Plus, that fridge inverter is just something else that can fail.

Yes, I was aware of some units embedding there coils in the side panels. The enclosure that the fridge goes into will have a couple of inches on both sides. Planning to direct airflow up from the bottom with a pair of small fans tied to the compressor. The compartment is vented at the top for good thermal syphoning.

Ted

 

[O C Diver]

Even if it takes a bit more power to have self defrosting it would be worth it to me. I hate defrosting the fridge every week or so when we are on the boat long term.

+1

I have a bad freezer door seal that can't be replaced. Sick and tired of defrosting at least twice a month.

Ted

 

[O C Diver]

Ted, we replaced our Nevercold with a apartment size refrig/frzer thats about 5 cuft and 2 cuft freezer from Summitappliance.com, a NY state company as I recall. When I called the company to size a dedicated inverter they gave me 1.2 run amps, 4 start amps but had no figure on defrost amps. Priced at less than half the cost of a NC.
Cold beer, frozen ice cream and no defrosting and quiet running. We have owned it for 5 years 2 as full time live aboards with no problems at all. The one we ordered at the time was a direct replacement size wise for the Nevercold.

Good information! Lots of choices out there. Currently looking at a Magic Chef for around $435 delivered to the Home Depot of my choice. Still looking though, and will check out Summit.

Ted

 

[kchace]

My back of the napkin power consumption for our de0061 Fridge is about 75ah per 24 hours which lines up with what others are saying.

 

[O C Diver]

I have used a kill-a-watt and also an equivalent DC device to measure 24 hour consumption of various electrical items on board. This was done in late summer in Brisbane, latitude 27.46°S. So I guess similar to Fort Pierce which is 27.44°N

My main galley fridge is a Norcold DE0061R. It used 80Ah/day, which is fairly reasonable for an old unit. The freezer door was likely only opened once and the fridge door maybe half a dozen times.

Thanks Brian! Think that's what's currently in my boat.

Ted

 

[Bay Pelican]

Made the following comparison using a Kill-o-Watt meter and various conversion formulas:

Old Sub-Zero undercounter refrigerator and undercounter freezer, approximately 440 amp hours per day. Replaced with Isotherm refrigerator and Isotherm freezer. The isotherm units were slightly smaller (10%) but are both AC and DC. When on AC they recorded 140 amp hours per day. This is consistent with what I see on DC using a connected ammeter.

At anchor the difference in the power usage was important to me as I like to reduce generator usage.

 

[O C Diver]

Made the following comparison using a Kill-o-Watt meter and various conversion formulas:

Old Sub-Zero undercounter refrigerator and undercounter freezer, approximately 440 amp hours per day. Replaced with Isotherm refrigerator and Isotherm freezer. The isotherm units were slightly smaller (10%) but are both AC and DC. When on AC they recorded 140 amp hours per day. This is consistent with what I see on DC using a connected ammeter.

At anchor the difference in the power usage was important to me as I like to reduce generator usage.

That's quite an improvement for 2 units going from 5.5 KWh to 1.6 KWh per day.

Ted

 

[hjorgan]

Interesting. This weekend I was servicing the genny and started paying attention to the gauges. Genny cranked and running at idle. 0ish KW. Refrigerator running.
Added the battery charger. Maybe 1 KW. Add the AC (this shocked me no pun) the needle popped then settled at 4KW. Thought it would be more. Turned the thermostat way down, she's blowing cold. No waver. So add the microwave. NOW we bust 11KW. Next hit the biggie -- electric stove eye -- hit 20 KW instantly. So what I learned is that my little 3.5 Nextgen can easily handle my average loads. That's good news!