Test results - Power savings from timer on fridge

[phleas]

GE 1999 Vintage Side-by Side 25 ft3 Fridge turned off at night for 6 hrs

2/18/2011 Data: KillaWatt Measurement kWh = 14.0 over 168 hrs = 0.083 kwh/h

No Timer
11/20/2010 Data: KillaWatt Measurement kWh = 17.5 over 175 hrs = 0.100 kwh/h

Conditions in home were similar in both cases (i.e, 68F).

Peak temp in fridge w/timer= 42F. Normal peak is 39F without timer. No trips to the ER for food poisoning.

Timer giving ~ 17% Savings.

[Daox]

I moved your post into its own thread to give it its own attention. The results are very nice! Much better than my ice testing was showing.

[Ryland]

How does this compare to raising the temp of the thermostat by 3 degrees? you would get the same affect of a max temp of 42F but would not have the same food spoil risk if say, you put a bunch of warm food in right before bed.
Personally I would rather have my food last a few days longer and pay another $1 per month.

Anyone ever seen anymore studies on this? I mean the concept is great, simple and easy to do but I do feel some of the concern that Ryland mentioned as well.

It would be interesting to see some more studies if they are there out there somewhere.

[RobertSmalls]

If the proposed mechanism by which this saves energy is by reducing the number of on/off cycles of the fridge, I would recommend adding thermal mass to the thermocouple that controls the fridge. However, on account of the wider swing, you'd need to lower the set temperature slightly to keep food just as long.

Another way to decrease the number of cycles is to run the fridge on a timer that can be set to power the fridge for, say, the first 30 minutes of every 2hr period, though that has drawbacks as well.

There is a saying: "That which is measured, improves." When you monitor your fuel economy or fridge power consumption, you think about it more often. Perhaps you're more likely to be quick about door opening and closing, and maybe less likely to throw a hot plate of food in there. Maybe your diet shifted as well; who knows.

There is another possibility: What is the idle power consumption of your fridge when it's just doing nothing? Mine's nil, but sometimes it does a 20W "high idle", accompanied by a low rumble from the compressor.

[phleas]

My fridge and freeze compartments are set at "1" with "1" being the warmest on a scale of "1-9." So raising the thermostat above 42F is really out of the question on this 1999 Fridge. I will comment that the 42F is measured at the top most section of the refrigerator. If measured at the bottom, where the cool air stays, the temp is right at 38-39F. So if you have food that might spoil in a few days (e.g. milk), store it at the bottom. This applies as well to the stuff you want to keep longest in your freezer. Keep the doors closed and the cool air will stay inside a very long time.

I do keep the both compartments fairly full of thermal mass (i.e. reused 2L bottles full of water, reused gallon milk jugs full of water). These do act as flywheels to moderate temperature swings.

I try to plan meals so that the left overs get consumed within 2 days after preparation. This means little chance of spoilage.

FYI: My fridge has a standby power consumption of 3W.

[johnlvs2run]

Originally Posted by phleas

2/18/2011 = 0.083 kwh/h

No Timer 11/20/2010 = 0.100 kwh/h

My fridge was using the same as yours, an average of 100 watts per hour (.100 kwh)

It ran about 1/3 of the time when not being used, and more than 2/3 of the time being used.
Every time the door was opened, the cold air fell out, and it was very annoying.

I converted a chest freezer to a fridge, with a temperature control, which resulted in a very quiet operation! The fridge conversion runs only 6 minutes an hour, and uses only 8.4 watts (.008 kwh) round the clock.

[Piwoslaw]

I've decided to try this with my fridge. I put a Kill-a-Watt on it yesterday and in a week I'll put it on a timer.

A few weeks ago I put a bit of thermal mass inside (three 2-liter bottles, one 1.5-liter, and one 4-liter jug), so that should help.

[johnlvs2run]

A timer doesn't work, because the temperature in the fridge quickly goes too high and spoils the food.

The temperature in my upright fridge would only go down to 39 degrees, then up to 43 within 6 minutes when it cycled back on. Without being on, it probably would have been up to 55 to 60 degrees in an hour, without the door being opened. I'd check before getting a timer, by turning off the fhe fridge and seeing what the temperature is in 6 hours. If the fridge stays at 42 for six hours then I'm impressed, but you're still not saving that much energy.

With the freezer-fridge conversion, I can set any temperature range that I want. What I do is set the low for 37 degrees, and 41 for the high. So it turns off at 37 (or 38 depending on the season) and it keeps going down to 33 because the sides are still cold, so the range is really 33 to 41, much colder than the fridge was, and it's using only 1/12th of the energy, an average of 8 watts. The chest fridge is better insulated, and when the door is opened, the cold air stays inside.

[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,
• Week 2: 3.700 kWh over 168 hours.

The first averages out to 540.7 Wh per day (24h), the second 528.6 Wh per day, which is 97.8% of the first. Not much at first glance, but I noticed that the timer itself uses a constant 1W, so the second figure should actually be 3.700-0.168=3.532 kWh/week for the fridge only (without timer), giving a daily average of 504.6 Wh, which is 93.3% of the first week's average.

So, by turning the refrigerator off for 6h at night it uses 6.7% less energy, but since the timer is drawing 1W the improvement is only 2.2%. Finding a timer with lower draw, or manually unplugging the fridge, would be better energywise.

Either way this not much in my case, since our fridge is already very efficient. In fact, its superior insulation means that it gains much less heat during those 6 hours than most other refrigerators. The 6.7% theoretical (2.2% practical) gain could probably be doubled if the fridge was turned off during the day, but in our case there is almost always someone at home, so it is not an option for us. But killing it whenever no-one is home is a good idea, since this is also when the house's thermostat is set to 1°C cooler, further reducing the fridge's heat gain. Maybe the refrigerator's power supply could be somehow tied to the t-stat's settings? Something like "Turn fridge off 1-2h after going into lower temperature mode, turn fridge on 1h before going into higher temp mode".

Unfortunately, "coasting" your fridge doesn't work during the summer months, since the house temperature is 2°-10°C higher then. But then, heating season here is 8 months long

Anyway, I'm continuing the test, the timer is off and will be back on a week from now.