This is a question for the total gearheads among us. I have a small chest freezer. It doesn't have exposed coils. Instead, the warm part of the cooling circuit is under the metal casing (typical for chest freezers). You have to leave a couple of inches of airspace around the perimeter of it, and it will get slightly warm to the touch when it runs. I'd like to improve its efficiency. I measured it, estimated annual KWH is in line with mid-range currently available chest freezers. I can't insulate around it, obviously. I don't think I could add insulation to the inside walls in any practical way. But it's painted white. White paint has low emissivity (ability to radiate heat). I know that emissivity matters for windows, and for attics (radiant barrier). And for wood stoves for that matter, which is one of the reasons why you want to keep the stove nicely blacked up and not let surface rust accumulate. In theory, the freezer surface would emit (and absorb) heat more efficiently if it were black. Absorb, I'm not too worried about, for what I think are good reasons (the insulation behind the metal is pretty good). Far as I can tell there is zero internet chatter about this, Energystar doesn't take color into account, and so on. People will buy black freezers for appearance but not for energy savings. So it appears to be a totally loony concept except in theory. I'm going to do a decent pre-post analysis on this, using my Kill-a-watt. But before I paint my freezer black, anybody have anything quantitative to say about whether or not it should make much difference for energy use?
Hi Chogan2, No. The outside is insulated from the inside. Painting the inside black could help theorectically. Its coupled to the cooling coils. Although the improvement would probably be small. If you can feel heat on any of the exterior portion of the refrigerators, those areas should be made black.
Aside from the issue of colour, would another layer of paint insulate the metal even more? What about stripping the paint right off the area that radiates? Is there any way to increase the airflow around the freezer?
Since your goal is improvement of efficiency... Depending on the age of the freezer, and whether it has automatic defrosting, a potentially large efficiency improvement can be the modification of the defrost circuit. Particularly in older refrigerators, the defrost heaters consume a lot of energy: Energy Saving Refrigerator Upgrade - cheap electronic mod saves you $$BIG Might be worth looking into.
You could try to determine the main radiating area of the case and paint *half* of it black, and then try to feel/measure any differences between the two areas. If black helps, finish the paint job. . _H*
I like Hobbit's suggestion - determine where the case rejects the heat and just paint that area black. The cooling coils are only located in one area.
I think this is a solution in search of a problem. A way better use of your time would be to wire a themostatically controlled little fan to force air over the condenser. Also adding 1" of styrofoam on the top will help way more than any paint,, although you have to watch for condensaton between the rigid foam and the freezer case if you are in a humid environment. I add foam insulation to the outside of all my Propane fridges and it lowers the burn cycle considerably. Icarus
A better use of the money might be getting a remote reading temperature sensor. Finding where the heat, or loss of cooling is occurring is more valuable info. A much bigger effect from a poor seal or just one area of the fridge would make the purchase worthwhile and avoid a useless paint job with lots of chemical exposure where your food is being stored. A big side benefit is that the temp sensor can be used for window seals, ducting, and other appliances.
Now why did you have to go and do that? I was going to suggest the very same thing. I've got a small chest type freezer like the OP describes and while the lid is not noticeably cool, I can tell a big difference in the lid surface temp (colder) if I set something on top of it, then remove it a few hours later. I've got some left over 1.5" (R7.5) and 2" (R10) Foamular extruded polystyrene that would probably do the trick. Forcing air over the condenser whenever the compressor is cycling might improve the efficiency some if one connected it to the control circuit for the compressor. However, this prompts another thought: the highest temperature region in the freezer might be around the compressor housing itself. The compressor housing in the ledge/step on the bottom side of the freezer. One could possibly gain a little efficiency by cutting polystyrene insulation for the top/side of this ledge. EDIT: One needs to be certain that there are no heat exchange surfaces on the area to be insulated (ledge/step). I can see where the evaporator coils are inside of my freezer (along the walls.)
The small chest freezers tend to be manual defrost. Being a chest freezer, the cold air generally stays put when one opens the lid, so the need for defrosts is very infrequent. It has been a year since I defrosted mine, and it ran a year and a half before that. The only time it was defrosted was for a move, not because it needed a defrost.
I agree that one should only paint the panels that are used to radiate heat away. You wouldn't want to paint the lid black or any other passive surface, because then it would gain heat from the room slightly more quickly than it would otherwise.
Fridges and freezers, to be most efficient, really should come in two parts. If only the condensing unit could be located a few feet away from the insulated cold space...or even outside. Having a heat source (the condensor) inside a cold space (the fridge) inside a warm space (your house) inside a cold space (outside) doesn't sound quite rational somehow. :twitch:
Hi Hyo...., I saw a TV show about the RMI headquarters. They had modified their fridge this way. They said in the winter the coolant flowed automatically by itself, and the fridge kept things cold without the motor running , most of the time.
You could stick the body of the fridge outside, but in many climates, you'd need to make the insulation in the door a bit less effective, just to let enough house heat in to the fridge to keep the food from freezing. Way back when milk was delivered by truck each morning, people had to retrieve it from the milk box before it froze. edit: Hi donee.
I learned years ago,, living with Kerosene and Propane fridges built in the '30s that keeping them cold was a real challenge. The simplest thing we could do was to throw a wool blanket or quilt over the fridge on a hot day,, especially over the door gasket! Worked great,,, adding rigid foam on the outside of the cabinets has the same effect only more so! I just wish that manufactures would get 'really' energy smart and move the compressors and the condensers away from the 'cold boxes'. At the very least put them on top! It would be great if in the consumer market we could by fridges and freezers with the condensers and compressors remote from the cabinets,,, like a commercial walk in. There is no reason you can't except it comes with an install cost,,, a professional purge and charge. There is also no reason in that scenario that the cabinets couldn't be built with R-100 so that the duty cycle would be about nothing per day! Icarus EDIT,, the previous posts by Hyo-and Donnee came while I was writing,, sorry for the duplication of info!
Thank you all for your responses. After I read these responses I did more research, and my idea is in fact loony. Yes, the freezer does seem to cool via radiation not convection. The entire outside (other than top and bottom) gets 20 to 30 degrees F warmer than the ambient air when the compressor runs. But where I went wrong is that it's the emissivity in infrared that matters, not in visible light, and sources say that white and black paint have roughly the same emissivity in infrared. There are threads on the internet about the cooling effects of painting your car engine black, and that's pretty much the conclusion there. Doesn't help. So I'm just wrong on the facts. I may try insulating the outside top of the box. I found a diagram of one, and the evaporator coils run around the inside walls of the box in just the same way that the condenser coils run around the outside. So I can't insulate the inside of the box. I think I pretty much have to live with it as is.
Pop rivet aluminium electronics heat sinks all over the back of the case. Remove the paint first and use heat sink grease to assist heat conduction.
Hmm. Are the magnetic letters all over my fridge acting as insulation in the wrong place, or increasing the cooling area?
