From Nick Pine (via usenet): Article 63609 of misc.consumers.frugal-living: From: nick@ufo.ee.vill.edu (Nick Pine) Newsgroups: alt.energy.renewable,sci.engr.heat-vent-ac Subject: Re: Refrigerator -keep it full? Date: 2 May 1997 08:26:06 -0400 Organization: Villanova University Mark A. Yedinak wrote: >Polar wrote: >> I'd always heard that refrigerators should be kept full to >> work at maximum efficiency. If the door is closed, full or empty won't make much difference. If the door is opened once in a while, empty seems better, because the greater the surface area inside the refrigerator (eg the more stuff inside) the more heat will transfer to those cold surfaces from warm room air that circulates around them when the door is open. This is known as "Newton's law of cooling," invented by Isaac Newton, who also brought us gravity and calculus :-) >> An engineer friend has just debunked this theory as follows: >> >> He says the basis for the "theory" was that keeping refrig. >> full decreased the volume of air which might escape when door opened. >> The warm air entering, would then have to be cooled. It seems to me that as long as the door is open, room air circulates through the fridge, all the while warming the contents, if any. It's not like a single slug of room air replaces a single slug of refrigerator air, and then airflow stops. A 6' tall fridge might have 16.6x2ft^2sqrt(6'(70F-40F)) = 500 cubic feet per minute of air flowing through it when the door is open. If the door is open for 10 seconds, 80 ft^3 of air might flow through the fridge. Suppose an EMPTY 3' cubical fridge contains 27 ft^3 of space and 54 ft^2 of wall area, and it's 30 F inside and the door is open 10 seconds, allowing 70 F room air to circulate through the fridge. Suppose when the door closes, all the air in the fridge is 70 F and it needs to be cooled to 30 F again. Since 1 Btu can cool about 55 ft^3 of air 1 F, cooling that mass of air requires 27(70F-30F)/55 = 19.6 Btu (0.006 kWh.) But while the door was open, the circulating air heated the 54 ft^2 of interior surface (slightly) with a thermal conductance of about 1.5 Btu/h-F-ft^2, by about 10/3600(70-30)54x1.5 = 9 Btu. So opening the door added about 29 Btu to the empty fridge. Now suppose we FILL the fridge with 216 2 liter soda bottles (each about 12" tall x 4" diameter, with about 1.2 ft^2 of surface area) in 3 layers of 72 bottles, in a nice regular array, with air free to circulate around them, and open the door for 10 seconds. When the door closes, we now only have to cool 27 ft^3 - 216x2/28.32 = 11.75 ft^3 of air, which requires only 8.5 Btu, but while the door was open, we heated 54 + 216x1.2 = 313 ft^2 of surface by 10/3600(70-30)313x1.5 = 52 Btu, adding a total of about 60 Btu to the fridge, twice as much heat. (And perhaps more importantly, we also condensed a lot more water vapor onto that greater surface, at 1000 Btu/lb. The vegetables inside may also have cooled themselves by evaporating more water, which dripped out through the bottom of the fridge and evaporated into the room.) >> ...the energy expended to cool the water bottles, or whatever, is much >>greater than than which would be expended to cool the air entering a >>near-empty frig. True, but that's like comparing apples and oranges, or non-recurring and recurring costs, and it's related to that old myth that setback thermostats don't save money. We only need to spend the energy to cool the thermal mass of the water once, not every time the door is opened. >Your engineer friend is incorrect. The reason a refridgerator runs more >efficiently when full than when empty... Does it? It might, if the compressor cycles less. But years ago (ca 1930), when people cared more about energy efficiency (and today, in Sunfrosts), refrigerators used to have "heat accumulators," thermal mass on the outside of the fridge, attached to the hot coils on the back, to allow them to stay warm even when the compressor was not running, so they could more efficiently transfer heat to the room on a full time vs a part time basis, keeping the hot coils cooler (while making hot water?) I guess empty fridges tend to cycle more often, ie work more in this way. >is because the refridgerator itself is not required to work as much. A full fridge has to work harder at first to cool the contents, but after that, things are about the same. That initial cost is a lot less than the recurring cost, over a few days or more. >When an empty refridgerator is opened and then shut again, the warmer air >which entered needs to be cooled again. The only thing which will be able >to do this is the fridge itself. Agreed, but the objects the warm air warmed while the fridge was open also need to be cooled (and dried) again. The fewer things inside, the less of that cooling is required. >...when the fridge is full, those items take longer to warm, therefore they >stay cool even after the fridge has been opened and closed. These items now >help in cooling the air around them. Agreed, but that doesn't seem relevant to this kind of energy consumption (vs. "thermal mass refrigerators" powered by outdoor coolth, eg in Earthships.) >So, try to keep the fridge full. It will run more efficiently because it >will need to run less. So, try to keep the fridge empty. It will run more efficiently because it will need to run less. Nick It's a snap to save energy in this country. As soon as more people become involved in the basic math of heat transfer and get a gut-level, as well as intellectual, grasp on how a house works, solution after solution will appear. Tom Smith

Thanks for 'figuring out' what I meant. I have so many details swimming around in my head about this house remodel that sometimes I think I'm brain dead! :-) Of course I meant wattage, not voltage. I wonder if I should re-post the question. The 2 hoods I'm looking at have the following lighting. 2- 40 watt incandescent bulbs in the front (reviewers said the light was quite good, but I was skeptical because they aren't halogens). 2- 20 watt halogen bulbs in the front (someone also mentioned about this lighting being good) Our ceilings are only 8 feet high, so the hood will probably be 28-30" above the cooktop. captsmethwick.....do you like your Broan hood? Do you have the model # by any chance? I was just wondering how quiet it is on the lower settings. I don't mind if it's loud on the highest setting because I don't plan to use that for long periods of time. But one of our options is Broan, so I just wondered. Thank you both for your answers!

I've only been using LED downlights for about 9 months, but my oldest lamps, BR40s made by Lighting Science (both their Definity brand at 3000k and the Home Depot Ecosmart at 2700k) are going strong. Our au pair never turns out the lights, even on a bright sunny day, so these have been on for at least 16 hours a day (full blast for 8 or more hours a day, dimmed at night). Almost as old are two Phillips Airflux BR30s in 2700k and 5000k, and a Lighting Science Definity BR30 (GP30) at 4000k. The reason I went with LED in the first place because (1) we were going through halogens left-and-right (lights left on all day), (2) LEDs are dimmable, and (3) the halogens left on all day really warmed up the kitchen and family room. Right now I'm experimenting with Feit/Utlitech 22-watt (1350 lumen) BR40s in the basement. The previous owner had installed 65watt Br30s in the 6-inch cans, it was like a dungeon down there. As each bulb burns out, I'm replacing it with LEDS (also, the au pair never turns out the lights in the basement). They are WAY bright and dim well, but I've only had them for a month. One thing I have learned is that I definitely prefer 3000k over 2700k (2700k is too dingy), and 4000k over 5000k (5000k is too blue, and 4000k seems to be just right). So far, only Lighting Science seems to make bulbs in those colors. I did try a CREE CR6 (it didn't fit my cans), but I was unimpressed with the brightness and color.

normel, you are correct. There is no GFCI. All pumps are hard wired. The neutral he used was on one of the 120V circuits. Absolutely true. Bus driver, click the link below for a Scotchlok. One of the worst inventions ever created. Handy, yes. But the source of more issues and problems than you can ever imagine. I don't care if they are legal or not. Any competent technician would never, ever use them. I frequent this site every day. I love the information it gives. I am not a licensed electrician. I do have a very good idea of what is going on when it comes to electricity, but I am by no means an expert. That's why I ask a lot of questions that many here answer intelligently and willingly. I NEVER offer advice to anyone that I am not 100% positive I am sure is safe and compliant. Even then I will qualify that with a remark to wait for a licensed electrician to chime in. Bus driver, over time, I have come to accept your sarcastic and condescending remarks as just being you. I actually find humor in many of them. But it really does seem like you feel slighted that a DIY is taking money out of your pocket by doing something himself. But you do make valuable contributions to this site and you definitely seem to know your business. For that, all of us "non-pros" are grateful. I have an engineering, physics, and mathematics education. I have taught automotive computer systems to techs for years. (try working with CAN/LAN automotive systems for a while) So while I haven't earned the right to have a piece of paper that says I'm an electrician, (I'm not even close) I do have a good basic knowledge. I love some of your complicated circuits you build...they are fascinating. I don't know the NEC. I don't know why you guys do some of the things you do. I want to know these things. You and others provide that thirst for knowledge and it's greatly appreciated. However, if you feel I am a hazard to this site, I will most definitely bow out gracefully. But quite honestly, I don't believe I have ever offered advice to anyone in a hazardous way. Ever. I usually just ask questions that many of you pros are willing to answer. Brickeyee, normel, and many others...your input is invaluable. Thank you. Here is a link that might be useful: Scotchlok