Sunday, July 24, 2016

superinsulating my refrigerator freezer

INDEX to the series
I've spent the better part of the day adding more insulation to the freezer compartment of my refrigerator. It may seem ugly but some experiments are ugly. (click any picture to enlarge)

I am doing this to 1) save energy, 2) have the freezer stay cold longer when I keep it off during my peak period and 3) prolong the appliance life since it won't hopefully be working as hard (as often).

My fridge is a major user of energy. It is older and not as well insulated as those available today. Mine uses only about 150 watts but it runs about one third of the time, 24/7 if I let it. I am intentionally keeping it off during my peak time with a plug-in timer. I've calculated that it currently uses about 412kWh per year (before today). Please see

I've used "superinsulating" in the title in the sense of being on top of or superior to what was there before. Not in the sense of some new technologically advanced stuff. In fact, I am using quite ordinary materials.

The best insulator is a vacuum but we can't economically use vacuum as an insulator for a large appliance like a refrigerator. The result would be heavy and expensive, making a suitable vacuum container to surround the cold space. That would not be practical.

The next best insulator is air that does not move around (convect). Foam is a very inexpensive and lightweight material which traps air and keeps it from moving around. The more foam thickness, the better the insulation.

That's what the manufacturer uses - foam. An 18 cu foot refrigerator like mine in a showroom today is larger by a couple of inches. This is how they have made refrigerators more efficient - thicker insulation. Compressor technology has not changed all that much. The controls might have improved efficiency slightly but the best control improvement I can provide is to keep the fridge from coming on during my peak time. That is a feature not available on today's refrigerators, even the most expensive models.

So I have added insulation on the outside. Adding on the inside would make the space smaller of course but would accomplish the same thing. If I open the door of a current fridge the space on the inside is about the same as mine (18 cu.ft.) but the wall is noticeably thicker and the overall size is larger.

I decided to add insulation on the outside and to check the effect on my old fridge. I can get a new 18 cu ft fridge for $800-2500 and probably have wonderful new features that I don't need except for the increased insulation thickness. I have now added extra wall thickness around the critical freezer section of my refrigerator for about C$20.

I will have to replace mine eventually of course but why NOW when I can do this fine experiment? I have tried to apply the insulation in a workmanlike manner that will be solid for at least a year or two, possibly longer.

For the top and sides, I have used found material, clean and intact surplus styrofoam packaging material that conveniently was in 2" thick block form about a foot square each. I would have used nearly a full 4'x8' sheet if I'd had to buy (Styrofoam SM sheet cost in Canada about C$35).

It might have been easier in some ways to cut from a full sheet but the price was right and the reuse aspect was a plus.

More surplus styrofoam in the form of trays I found at the local recycling depot probably recently carried a large appliance like a microwave oven. They were just slightly smaller than the door and the back of the freezer section.

I filled the trays with a layer of rock wool (Roxul) that I had on hand for the house. I had to split the rock wool down to about 1.5 inch thickness to fit into the trays. The trays filled with rock wool were then attached to the front of the door and the back of the freezer.

The outside is covered with a reflective bubble wrap like material which was really the only thing I bought specifically for this project. A roll of Reflectix Staple Tab Insulation 16"x25'/0.41mx7.6m) cost about $20. I used virtually the whole roll.

Plus lots and lots of packing tape (probably close to a full roll), a few strips of wood and about 10 wood screws to hold the wood to the metal skin of the fridge in a few key spots.

This is not meant to be a complete how to description but rather an overview of what and how I did it. If you would like to know more, please comment below.

I hope to have some preliminary results in a couple of days.

Thank you for your interest.
George Plhak,
Lion's Head, Ontario, Canada

INDEX to the series


Randal Son said...

Well, what did you find out?

George Plhak said...

part 2:

part 3:

Please see the index.

Harry Verdairchee said...

Thanks George, I am a hobby frugalist and appreciate your sharing.. about to insulate my old worktop freezer, for EXACTLY the same reasons.
Last year during a holiday I put it on a timer VERY low temp, timed to off peak, plus short boosts ..

Mojave Mike said...

Hello George, I live in the Mojave Desert. We use an evaporative cooler in the summer and ours is located rooftop. Temperatures up there can exceed 50°C. I used an online heat transfer calculator to determine that we were wasting 10-17 MILLION Btu/hr. I added 2" of styrofoam and a metal shell to protect it from 110km/hr winds. The new calculation determined that we were saving 90% of those losses. On a hot, dry day we have exceeded 28°C temperature drop. Previously the best we had achieved was 17°C.

Mojave Mike

Mojave Mike said...

Hi George, Mojave Mike here. I am a retired mechanical engineer, so I was already familiar with heat transfer. The manual calculations are pages long, so I was thrilled to find this calculator, which is pretty comprehensive for the different types of heat transfer.

By measuring the internal, and external temperatures of the device, along with the ambient temperature, say arbitrarily 2 feet away from the device, you can calculate how much heat is being lost or transferred. It would simplify the calculation if you could assume or make sure the air temperature is homogeneous (use a fan to keep it mixed). Some measurements must be done to account for the pump and such underneath the lower compartment. Probably the best thing you could do would be to enclose the condenser and draw air up from the bottom, then exhaust it to the exterior (summer). This warmed air can be delivered to the living space in cooler months to reduce heating requirements. I would enjoy having a conversation if you would like.