Test results - Power savings from timer on fridge

[johnlvs2run]

I had expected there to be more of a difference in energy use with using a timer.
The small difference is surprising.

However my main concern with using a timer in such a manner with the fridge is the potentially wider range of temperatures.
Did you happen to note at least the high and low temperatures in the fridge?

I think to maintain temperatures in the fridge, the timer should be run at least once per hour.
This way you could have more control of the temperature swings in the fridge.
Of course the temperature swings in that case would be larger than normal but that might be okay.

In fact, with my freezer to fridge conversion, there is an exponential drop in temperature with time.
For example, from memory, 1 degree might take 3 minutes, then 3 more degrees the next 3 minutes,
then the switch goes off and the fridge continues cooling another 5 degrees.
For example, from 42 (high) to 38 (off), then continues to 33 after off.

So the greater savings of energy is to have wider swings less often, but that might not be as good for the food.

[johnlvs2run]

Here is my summary of how to convert a chest freezer to a fridge.

Here is a temperature control for a much lower price than the one on my blog.

[Piwoslaw]

No, I have no idea what the temperature variations are in the fridge, neither with or without timer. Maybe the small thermometer for projects like this should be moved up on the to-get list?

EDIT (2011-03-15): I got a small indoor/outdoor digital thermometer with min/max yesterday Last night the temperature inside the refrigerator was between 3.9°C and 4.9°C (39°F-41°F) without a timer. I'll keep an eye on it for the next few nights, then put the timer back on.

[Piwoslaw]

Originally Posted by Piwoslaw

OK, first batch of results:
I monitored for two weeks, the first was without a timer, the second was with a timer set to turn the fridge off between midnight and 6am. Here is the raw data:

• Week 1: 3.758 kWh over 166.8 hours (no timer),
• Week 2: 3.700 kWh over 168 hours (with timer).

OK, another two weeks of data:

• Week 3: 3.864 kWh over 167 hours (no timer),
• Week 4: 4.204 kWh over 170.2 hours (with timer).

These numbers are higher than during the first two weeks: With no timer the average this time was 555.3 Wh per day (earlier 540.7 Wh/24h), with timer 592.8 Wh per day (earlier 528.6 Wh/24h).

I think that the reason that both are higher than two weeks earlier is that it's warmer outside, so the indoor temperature is also slightly higher (takes longer to cool down, plus I was forced to up the house's thermostat from 17.5°C to 17.75°C because everyone at home is sick). Also, the week with the timer is even higher since there was more shopping and cooking (more stuff stored in fridge), and a small party (even more stuff in fridge).

As for temperature variations: The digital thermometer I got recorded for the last 2 days of week 3 and all of week 4. Here are the min-max temps:
Without timer: Fridge 3.9°-5.9°C (39°-43°F), kitchen 16.7°-18.7°C (62°-66°F)
With timer: Fridge 3.5°-7.1°C (38°-45°F), kitchen 16.5°-19.8°C (62°-68°F)
The raised t-stat temperature plus extra cooking during week 4 raised the kitchen's max temperature by over 1°C, which also had an effect on the refrigerator's energy usage.

I'll stop this test for now, but will try again next winter. Hopefully then I'll have the test going for much longer.

[Piwoslaw]

A moment ago I put the fridge on a kill-a-watt and timer to repeat the test. Hopefully the results of the extra insulation I added to the fridge a few months ago will show up.

[Daox]

Is your house's ambient temperature the same as before? I've notice that makes a huge difference in my refrigerator's energy usage.

[Piwoslaw]

I've reprogrammed the thermostat, so the kitchen's max temp may be slightly lower. I have no idea what the average temp is, as I don't have any means of calculating it.
Anyhow, it'll be interesting

[Piwoslaw]

Results are in from the last 4 weeks. Last winter the test was also 4 weeks, but with the timer being taken off or on for 1 week at a time. This year I did it for 2 weeks at a time (because I forgot after the first week).

• Weeks 1-2: 8.097 kWh over 334.2h (timer turns fridge off 0-6am)
• Weeks 3-4: 8.429 kWh over 333.5h (no timer)

Recalculating that, and adding the min/max temps inside the fridge and in the kitchen:

• Timer: 581.5 Wh per 24h, temps: 2.6°/6.7°C and 17.2°/20.9°C
• No timer: 606.5 Wh per 24h, temps: 2.3°/4.4°C and 16.1°/19.4°C

Comparing to last year's test:

1. Turning the refrigerator off for 6 hours at night gave the same 4-5% savings.
2. The energy usage is slightly higher than last year, even though I insuated the back of the fridge. This may be because:
   • Judging by the min and max temps, the temperature inside the fridge was ~1°C lower, but the kitchen temperature was higher than last year.
   • The Wife was home this whole month, so there was more cooking and fridge-opening happening.
   • The fridge is a year older... Not sure how much of a difference this makes for the refrigerator's workings, but it's definately making more noises (hisses, crackling, etc.).

I'll try to continue this test for another 2-4 weeks.

[Piwoslaw]

I've finished this test and summed up the results from 2011 and 2012, a total of 12 weeks.

Date	Hours	Wh used	Timer	Wh/24h	Fridge temp min/max °C	Kitchen temp min/max °C
24.02-03.03.2011	166.8	3758	off	540.7	?/?	?/?
03.03-10.03.2011	168.0	3700	on	528.6	?/?	?/?
10.03-17.03.2011	167.0	3864	off	555.3	3.9/5.9	16.7/18.7
17.03-24.03.2011	170.2	4204	on	592.8	3.5/7.1	16.5/19.8
02.02-16.02.2012	334.2	8097	on	581.5	2.6/6.7	17.2/20.9
16.02-01.03.2012	333.5	8429	off	606.6	2.3/4.4	16.1/19.4
01.03-15.03.2012	337.9	8024	on	569.9	2.3/6.4	16.0/20.4
15.03-29.03.2012	331.1	8285	off	600.5	2.1/6.5	16.0/18.8

Comments:

1. The last week (17.03-24.03) of the 2011 test (timer on) saw lots of cooking, so the kitchen was slightly warmer and the refrigerator had more use. This noticeably increased energy consumption.
2. The last two weeks (15.03-29.03) of the 2012 test (timer off) saw lower average kitchen temperatures. The weather was warm enough to keep the central heating from turning on more often than once every 1-2 days, so the house's average temperature was about 0.5°C lower than during the previous weeks. Notice how the kitchen's minimum temps get lower toward the end of the test.
3. The timer itself uses a continuous 1W. It was removed during the 2011 "timer-off" tests, but left on during all 2012 tests.
4. The three situations above skew the results in favor of the "timer-off" tests.
5. The fridge's temps most likely maxed out when the door was open, not towards the end of the 6 hour off time when the timer was on. The thermometer's sensor was in the back, between water bottles, but when the door was open for a longer time, then warmer air had time to get deeper in.
6. During the "timer-on" tests in 2012 I noticed that around 6:30am the refrigerator's compressor was not yet on, even though the timer turned the power back on around 6:00. The temperature inside the fridge was ~5.8°C. On one hand, this would suggest that at night it takes the fridge more than 6 hours to gain enough heat to turn on. On the other, during the day, or during the "timer-off" tests, I never noticed an inside temp as high as 5.8°C - the compressor usually turns on just below 5°C. This leads me to believe that our refrigerator has some sort of safety feature that keeps it from turning on within 30-60 minutes after power is restored.
7. I noticed that the refrigerator's min/max were ~1.5°C lower in 2012 than in 2011. Maybe someone changed its settings?
8. Comparing results between 2011 and 2012 showed an increase in daily power usage: It went from 572.0 to 603.6 Wh (+5.5%) with the timer off, and from 560.9 to 575.7 Wh (+2.6%) with the timer on. I was expecting a decrease from the extra insulation I added to back of the fridge, but I guess this was offset by the lowered temperature.

Summing up all of the raw results:

• Timer on (fridge off from midnight to 6am): Total of 24025 Wh consumed over 1010.3 hours gives 570.7 Wh/24h.
• Timer off (fridge on 24h per day): 24336 Wh consumed over 998.4 hours gives 585.0 Wh/24h (+2.5% more than timer on).

If the 2011 "timer-off" results are increased by the amount of power that the timer would have used (see comment #3), then we get:

• Timer on: 24025 Wh, 1010.3 h, 570.7 Wh/24.
• Timer off: 24670 Wh, 998.4 h, 593.0 Wh/24h (+3.9%).

If all of the tests which used the timer are reduced by the amount of power that it would have used, then we get:

• Timer on: 23015 Wh, 1010.3 h, 546.7 Wh/24.
• Timer off: 23672 Wh, 998.4 h, 569.0 Wh/24h (+4.1%).

[Daox]

Great info Piwoslaw. Too bad there wasn't a more definitive answer. I was really hoping your extra insulation work would have shown better results.