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Old 08-31-2010, 10:54 PM   #1 (permalink)
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Ecomodding my fridge

Ever since I read this article:

DIY, Super-Efficient Fridge Uses .1 kWh a Day | EcoRenovator.org

I've realised my 1KWh/day fridge is much less efficient than it should be. Unfortunately, the above super-efficient setup wouldn't work for me. I would need to find room for a second chest freezer for frozen foods.

The converted chest fridge is set to ~5°C, while I set mine to 1°C to keep wasted food to a minimum. His fridge in my house in the summer would use 0.2KWh/day due to the difference between our ambient and set temperatures. Add in a standalone freezer, and I'd be looking at around 0.6KWh/day. So my fridge/freezer isn't as hopeless as it appears. I need to find a 40% reduction in energy consumption to match his performance, not the 90% reduction that it looks like at first glance.

Door opening losses supposedly account for 7% of heat loss from a typical fridge, so switching from an upright to a chest fridge seems like a poor compromise between efficiency and convenience. I tried some window shrink wrap as a curtain to keep cold air in on the lowest shelf, but it's far too lightweight, crinkly, and annoying. It blows around every time you open the door. I bought a clear vinyl shower curtain at the dollar store, and I've hung it up to outgas and unwrinkle itself. Hopefully, it'll be ready to install next week.

The greatest room for improvement is insulation. Some folks say you can't insulate a fridge. But you can insulate the sides and top of any upright fridge, which accounts for half of its surface area. I currently have a sheet of 2" thick polystyrene insulation on top of my freezer. A thermal probe between the insulation and freezer confirms that it's holding heat in better now.

The back of my fridge has no vents or coils, and is cool to the touch. It sounds like insulating that is fair game, too.

I can't have bare insulation in the kitchen. Fiberglass presents a health concern, exposed polystyrene is a fire hazard in a room with so many ignition sources, and cotton would get filthy. I'd have to build a cabinet to mostly enclose the fridge, probably out of thin plywood. It would have to be built very precisely to keep air from infiltrating between the insulation and the fridge.

I suspected that since the compressor and condenser are on the bottom, heat enters through the bottom of the fridge compartment. A probe below the vegetables drawer under a kitchen towel reads 17°C (versus 10°C elsewhere in the fridge), and confirms that I need more insulation there.

I'd like to replace the fruit and vegetables drawers with fiberglass batting, but I'm not sure if it's okay to keep fiberglass in the fridge. Cotton batting (or corrugated kitchen towels) would be ideal, if only it was locally available and affordable. I've got an old wool blanket in there for now (the same one as my A/C seat cover is made from), but what if I spill some milk or beef juice in the fridge?

I'm open to suggestions. How can I keep insulation in the fridge clean? Does the insulation cabinet sound easy enough to build? Any thoughts on what to do with the door of the fridge?

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Old 09-01-2010, 04:27 AM   #2 (permalink)
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If you are using styrofoam, you'd want to use epoxy resin with fiberglass, which is not a health hazard unless you get to allergy levels. A sheet of Arborite or other countertop laminate is probably easier to get a good finish with, though. Coroplast would be easy, funky, and let you use thumb tacks instead of 'fridge magnets. Inside, the same material recommendations apply. A nice bead of caulking will make up for very casual joinry.

Or, how about gutting a bigger fridge, and slipping the shell over yours? Find your condenser, and its air supply, which should be left unobstructed, but it sounds like they may all be on the bottom, so you can do the back as well.
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Old 09-01-2010, 05:30 AM   #3 (permalink)
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There was an article in Home Power magazine many years ago (late '90's?) about insulating the fridge and building a cabinet arount it. IIRC it was good for a 5%-10% energy reduction.

I can understand not wanting bare, toxic insulation in the kitchen, but what about cork? I read that it's a good insulator, has a nice look, and you can use thumbtacks, as BicycleBob suggested. Just remember that metal thumbtacks are like little heat bridges...

The door can also have a piece of insulation glued to it, but make sure you have enough clearance to open it. I wonder how much heat is lost (gained) through the magnetic skirt around the door's perimeter, and how one would go about improving on that.

If you insulate the back of the fridge, then remember to leave room for free airflow from the compressor.

If there is enough space between the bottom of the fridge and the condenser/compressor you can add insulation there. Maybe a 5mm piece of styrofoam with aluminum foil on one side? Or just alu foil if there isn't enough room.

I've read about keeping large empty containers in the refrigerator to reduce the volume of air that escapes each time the door is opened. If they are filled with water, then the increased thermal mass helps keep the temperature low during a power outage.
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Old 09-01-2010, 05:50 AM   #4 (permalink)
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Except on the hinge side, it is easy to add insulation all around the door seal. Fuzzy mating surfaces may be optimum, but hard to clean. Hard-coated foam parts can be progressively glued in place to give virtually zero air space where the insulation parts. You can also use door weatherstripping material, and a mechanical door latch. Along the hinge edge, you can extend the hinges, or use flexible insulation.
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Old 09-01-2010, 05:55 AM   #5 (permalink)
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Quote:
Originally Posted by Piwoslaw View Post
I've read about keeping large empty containers in the refrigerator to reduce the volume of air that escapes each time the door is opened. If they are filled with water, then the increased thermal mass helps keep the temperature low during a power outage.
On a similar vein, my wife stuffs the freezer with bread after the shopping. Thermal mass helps keep down open door losses. Although the freezer is mostly closed and it has drawers. So the theory is sound only it would apply to fridges more.

Re: the fridge compressor. It produces a lot of heat down there and it has to have a negative effect on fridge temps. Perhaps installing reflective insulation above that would reduce heat rising into the underside of the fridge?

ollie
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Old 09-01-2010, 10:25 AM   #6 (permalink)
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In my old house I had some styrofoam board behind the fridge. I don't think it's that much of a fire hazard. It's not readily ignitable like gasoline.

For the cotton insulation, can you placed it in a larger freezer bag to keep it clean?

I saw a solar decathlon show a couple years ago and the competitors were really worried about door opening time. They made a list of what they wanted to get out of the fridge, then quickly opened it, grabbed the food, and slammed the door. I don't get that crazy, but I do try to minimize door open time.

My current fridge has the coil under it towards the rear by the compressor. A small fan draws air through a vent in the toe kick, blows it over the coil, then exhausts it back out the front. I'm sure this is not optimum as the cooler intake air is mixing with the warm exhaust air. There must be a better way to do this. This is an energy star fridge, though. If your fridge is designed like this, you should be able to add insulation to the sides, back and top without affecting its operation.
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Old 09-01-2010, 11:05 AM   #7 (permalink)
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Quote:
Originally Posted by Patrick View Post
My current fridge has the coil under it towards the rear by the compressor. A small fan draws air through a vent in the toe kick, blows it over the coil, then exhausts it back out the front. I'm sure this is not optimum as the cooler intake air is mixing with the warm exhaust air. There must be a better way to do this.
My Mom's refrigerator is also like that. When I stand in front of it, I can feel the warm breeze on my toes. I seems like the whole fridge is bathed in rising warm air. I imagine that when the door is open, cold air drops out while warm air from underneath climbs inside. No wonder her fridge is on more often than off.
So how about adding a duct to lead the warm air far away from the fridge (or maybe behind/above it)? That way the temperature of the whole area may drop by 1-2 degrees.

The design with condensers (=hottest part) placed underneath is not efficient. The "old fashioned" ice boxes with large coils on the back wall were much better. Granted, they used more energy, but this was because of poor insulation. The large surface area of the coils was much more efficient at transfering heat, and the placement allowed the natural convection of airflow, so no energy hogging fan was needed.

My superefficient refrigerator uses only 0.7kWh/day, and it has rear placed coils. Even when it's been on for 15 minutes those coils are barely warm. I wonder if having the freezer below the fridge helps or hurts efficiency?
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Old 09-01-2010, 01:53 PM   #8 (permalink)
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How about putting your fridge on a timer. Recalling all of my hurricane training, I remember that a fridge can remain without power for about three days without spoiling the food inside with quick access to what you need.

I would suggest setting up a timer that would shut off power to the fridge after a certain time, like after dinner and kick on again before breakfast or later depending on when you first use it in the morning.

It may just save you a couple cycles a day or more depending on your fridge.
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Old 09-01-2010, 07:02 PM   #9 (permalink)
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I think the prettiest option is to have it match the walls or cabinets in the kitchen.

Cork has many nice properties, but I was thinking of adding four inches of insulation to each side of the fridge, at which point cork becomes cost-prohibitive. I'm leaning towards fiberglass batting, as it has the most thermal resistance for the dollar. Can I buy cellulose batting locally?

@Ollie: adding loaves of thermal mass helps reduce door opening losses by reducing the volume of air that can escape during each door opening event. Adding thermal mass doesn't affect the amount of energy that escapes when the door opens: empty water jugs should work just as well as full.

But full water jugs would reduce the number of times during the day it cycles on and off, which could save a little power. Also, the water jugs can be set outside to freeze in the winter, and brought into the fridge to thaw.

Piwoslaw, you have an interesting fridge. I wonder, how much insulation does it have? My fridge's sidewalls including the steel outer and plastic inner shells are 4cm for the fridge, 5.5cm for the freezer.

Another thing I noticed is when my fridge turns on, it draws 680W / 6A, and the voltage at the KaW drops from 121V to 117V. Am I losing an additional 3% through iČR losses between my breaker box and the outlet in the kitchen? The house dates to 1929, and I have no idea how old the wiring is.
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Old 09-01-2010, 07:59 PM   #10 (permalink)
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Quote:
Originally Posted by RobertSmalls View Post
Can I buy cellulose batting locally?
AFAIK they don't make cellulose batting. Its all loose blown.

Rigid foam would be more expensive, but would give you a higher R-value per inch.

I'm quite interested to see how this turns out.

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