why are black radiators more energy efficient than white radiators?
353023
Radiation caused by temperature is often called "Black-Body Radiation." Perfectly Black Bodies are the best type of objects to absrob heat - as most of us know if you wear a black T-Shirt in the sun, as compared to a white one!\n\nI quote to you a fundamental statement of black-body radiation "The best possible absorber of radiation is also the best possible emitter of radiation."\nThis is because the efficiency of a black body does not depend on whether radiation is being emitted or absorbed.\n\nA black radiator is much more efficient than a white radiator because it can absorb (and therefore radiate) better.
1102710
Probably you would not notice much of a difference. In fact if you used electric heat you wouln't notice any difference at all (at least in the winter). The reason is the amount of electricity an appliance uses is pretty much proportional to the amount of heat it generates. If you really want to save electricity get rid of your oven, refrigerator, toaster, hair dryer, basically any appliance which generates a lot of heat.
125096
No, generally speaking larger laptops use more power, usually because they are more powerful and have larger displays (which takes more electricity).  Smaller laptops tend to be less powerful, less features, and smaller screens, so therefore use less power.\nThis explanation does not apply to battery life as well though, if you are interested in this.  But since you mentioned Energy Star, I'm assuming you are most interested in Energy Conservation, not battery life.  For this, you will be best off with the smallest profile of laptop, the subcompact laptop, if it suites your needs.
970427
The difference is big.  With a water cooled chiller, there is a unit located in the building that acts as the driving force to transfer the heat from the building water loop to a secondary loop (condenser water loop).  The second water loop is then run up to a cooling tower usually located on the roof of a building where the heat is then expelled to the atmosphere.  High efficency with these type of devices.\n\nWith an air cooled chiller, there is no secondary water loop, and the primary water loop from the building runs directly up to the roof.  There, the chiller uses the thermodynamic principles of refrigerants to directly remove the heat to the atmosphere.  There is less equipment with this system, but the efficiency is half that of the water cooled systems.\n\nAlso, air cooled chillers are limited in the total size of the cooling system that they can adaquatly handle, where as water cooled chillers can be much much larger.
290359
The energy of a photon is given by E = h*f where h is planck's constant and f is the frequency.  Since photons travel at the speed of light, c, the wavelength is just:\nlambda = c / f.\n\nThe spectrum of light goes from red to violet, where red has the lowest frequency (longest wavelength) and violet has the highest frequency (shortest wavelength).  This means that violet light has more energy per photon than red light.\n\nIn radiation heat transfer, a black body is an object that absorbs all incoming radiation and reflects none (stars are nearly black).  Also, a black body emits a spectrum of radiation based on its temperature.  A plot of monochromatic emissive power vs. wavelength shows the relative "concentration" of different wavelengths of radiation in the total output.  This plot has a characteristic shape given by Planck's Law of blackbody radiation, and it has a maximum at:\n\nlambda_max * T = 2898 micrometers * K = constant\n\nwhere T is the temperature in Kelvin\n\nThus lambda_max is inversely proportional to Temperature.  This means, as the temperature of the emitting body increases, the wavelength at which more of the energy is radiated at decreases (the frequency increases).\n\nI wish I could show you the loglog plot of monochromatic emissive power vs wavelength in Mills page 453.  It shows how low temperature bodies emit in the infrared and negligibly in the visible range and as the temperature increases, the maximum moves toward the visible range.  The sun, at 5800 K has a nice plateau maximum in the visible range which explains why being able to see light is so useful for us.  Another cool thing to see in the plot is that the curve is steeper on the low wavelength side than it is on the high wavelength side: this means that as you increase the temperature of an object, it will glow red and then white because anything hot enough to have its maximum in the violet range also has a large emissive power for everything colder than violet, so all colors of light will be present.\n\nSince a hotter body radiates at higher frequencies, in a sense violet light is "hotter" than red light.\n\nTake a look at the book (or another heat transfer engineering text).  I can't explain very well with only text.
1123190
Laptops are thin, naturally. And laptops contain ICs which require much energy (the CPU, graphics processor chip, etc) and, being so thin, the heat geenrated by them appears on the outside of the laptop. If on the bottom, your lap is likely to get warm as the laptop heats up. \n\nA cooler pad is a device (which can work in any of several ways) which either dissipates the heat, or provides a way for it dissipate. some are props for lifting the bottom o fthe laptop allowing more air flow and so loweing the heat reaching the bottom of the laptop. \n\nAlternatively, a pad could include a fan to increase the rate of heat removal. \n\nNote that laptops which get hot are getting the energy for the heating from the battery,  and so reducing the battery life. Hot laptops are battery charge eating laptops, and to be avoided by those who need to have a laptop running, away from an energy source, for an extended time. \n\nUnfortunately, it's generally true that the faster a laptop runs (the clock rate claimed for the CPU uses is often a good measure) the more it heats up. This is one of the reasons the Intel Pentium 4 CPUs never reached their planned speeds. They couldn't find a way to keep the power draw, and so the heat emitted, down. They had to change the way they were designing and building their CPUs, and haven't quite caught up with their competitors yet. One of the things they're doing is to build in to the CPU ways to shut down (or slow down) portions of the chip whcih needn't run so fast just now. Not easy to do, really. Other CPU makers (and video processor chip makers as well) are doing similar things with their chips. One of the tricks is lowering the power supply voltage at which the chips work. Years ago, CPU ships reguired 5 volts DC (and some even required some power at 12 volts). Today's CPUs run on a volt or less. It reduces the power required and so the heat generated. \n\nIt's what's called a race condition in other engineering situations.
921578
120W would be brighter, and here is why:\n120W light bulb would have higher temperature (rough argument: dQ/dt= c*m-sigma*T^4, at equalibrium c*m = sigma*T^4 =P =V*I, where c= heat capacity per mass), and by Planck's law of black-body radiation will emitt more visible light than Infra Red light, so it's more efficient in producing visble light for the same energy than 2x 60W light bulbs. Great question.
14382
Many of the items and services offered do result in lower operating costs, such as insulation, thermal pane windows, caulking, weatherstriping. There are fuel savings from modifications to your automobile and driving habits.\nSome items are not true energy savers, such as expensive flourecent light bulbs that replace the incandesant bulbs in regular lamps. They will reduce your electric bill. However, if you compare the price of the bulbs and the life of the bulbs, you will find the financial savings to be about a wash. On a more global scale the energy to produce these bulbs and the raw material is significantly higher.
60139
The colored piece of glass will absorb more light which will heat it up quicker.\n\nLight goes right through clear glass. Very little light/energy is absorbed.
587921
Both CPUs are using clock speeds at different frequencies.  The performance delta between the two processors is going to be due to the internals of the processor.\n\nThe processor may have internal components which need to tell the clock "wait, I'm still working on something" and then let it know when it is finished.  That 'wait' operation takes the same amount of cycles on a faster clock as it does on a slower clock.\n\nSo, the main factors (aside from the outside of heat and cooling) are the number of clock cycles consumed by internal components of the processor.  The more 'streamlined' the internal components of a processor (i.e. the less clock cycles they consume) the faster they perform an operation.\n\nYes, it is possible to have a processor that operates at lower clock speeds and performs just as fast as processors that operate at higher clock speeds, only because they found a way to solve a problem in less steps.
34105
The electromagnetic radiation from electrical devices COULD be used to induce a tiny current in a conductor, and used for some purpose. However, energy efficient devices experience very little leakage of radiation at these frequencies, or else they would violate FCC rules and interfere with a lot of other things. The biggest source of electromagnetic radiation from these devices is probably infrared radiation, or heat, which you could use to heat your home or for other purposes.
1136153
many materials absorb better at the infrared wavelengths than the shorter wavelengths so the absorbed energy is conserved as heat.  There are materials that absorb shorter wavelengths and convert the energy to heat, such as a microwave oven???  Water absorbs at that frequency (1-2 GHz) and the water molecule resonates.  The vibrational energy is re-emitted as heat due to a Stokes shift.\n\nThe shorter wavelengths are more energetic and more capable of depositing energy that might show up as heat but it depends on the absorption of the material itself.
12565
Laser printers are more cost effective, they are typically black only though the more expensive ones have color as well.  \n\nNormal Printers (Inkjet Printers) cost more because they use more ink, they are typically color/black.  The unit is useually cheaper but the ink is what makes the difference.
1133476
The hot summer sun is the predominant source of heat absorbed by cars. This is radiant heat transfer. The amount of heat the car absorbs is proportional to T^4 power (where conduction and convection heat transfer is proportional to T). So if the temperature of the car rises from 100 degrees to 120 degrees the amount of radiant heat transfer is (460+125)^4  - (460+100)^4 times reflectivity and emissivity constants. As you can see that’s a lot of heat! And is precisely why that car is so hot in the sun. So the question now becomes how do you minimize the amount of radiant heat transfer being imparted to the car? The best way would be to get a silver car cover. The shinier the better.  Ideally a mirror. Radiant heat will reflect off the surface and not be absorbed into the car. Short of that the lightest brightest white fabric will work best at reflecting the radiant energy. The object is to reflect radiant heat from the most absorbent surfaces that are darker and attract radiant energy.  I think if I lived in the desert I would have a white car with all white interior. Then you would not need anything at all. Except a wash since the dark dirt will attract heat.\nIf you have ever wondered why office buildings in hot citys are so shiny, now you know. Less radiant heat from the sun less air conditioning! Cheeper to operate!
991673
Well, baseboard electric heat is radiant, and most gas furnaces are convective.  Good radiant heat is probably more comfortable for occupants.  As to the efficiency, the gas is far more efficient as a energy distribution mechanism.  There is no loss from the well to the house, and modern furnaces are very good at cleanly burning the fuel.  The heat is transferred to the air quite efficiently as well.  But, if you are a greener, and you want to lower your 'carbon footprint', go electric in areas where that resource is hydro or nuclear.  \n\nIf it is new construction, get radiant floor heating.  This is even better than baseboard, and can be fueled by electricity or gas.
918889
um. dunno. maybe energy efficiency (everything else seems to be energy efficiency rated these days), safety and increased development cost.
237314
In any machine there is a way to put the energy inside and there is a way to take the energy out.The out put energy need not be the same type of  input energy.\nIn any machine as per conservation of energy the input and out put energies  must be equal.\n But what we speak of efficiency of a machine is the ratio of the useful out put energy to the input energy.\nNaturally this will be less than  the total out put energy. It follows efficiency is less than 100%.\nBut we can try our best to reduce the unused energy (not used for our purpose)to be the minimum possible.\n\nFor example in machines due to friction many energy is being lost as the parts are heated. But with out friction no parts will work. So  some minimum amount of energy has to be wasted (wasted according to us and not according to nature). \nA car rolls down the road because of friction and the same friction reduces efficiency. \nThe efficiency of an incandesant bulb is low because the useful  light energy is low compared to the input electical energy and most of the energy is wasted as heat energy.\nThe florescent bulb has high efficiecy compared to the ordinary bulb because less amount of energy is not used for our purpose.