Effects of Room Temperature

seligman

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Mar 25, 2007
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I would like to know how room temperatures affect the temperatures of a PC. I realize that it's related, but there's a lot I don't understand.

Years ago, I knew a guy in the refrigeration business. He always pointed out the misconception held by many that "fans cool the air". His remark was that fans cool people, not air.

So how does this concept transfer to electronics when you have heat sinks involved? What if the temperature of a heat sink was identical to the room temperature? Would a fan be useless in this situation? Likewise, does the effectiveness of a fan (or fans) depend on the presence of cooler air?

You're probably wondering why I'm asking these questions. My house doesn't have air conditioning. When I look at my PC temperatures, I sometimes have to remind myself what month of the year it is and how hot the room is. As long as my room temperature is warm/hot, is there only so much I can achieve by upgrading the fans?
 

rammedstein

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Jun 5, 2006
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air being blown through a fan will always exhibit a chill factor, even if it is at the same temperature as the thing it is being blown on, this is because it will pick up any of the excess energy on the outside of the object as it passes by, even if it is only a small amount. a good way to prove the point is by getting a thermometer, leave it in a room until the temp stabilizes and then record the temp, do the same again with a fan running facing it, the temp should be lower due to the chill factor. The main purpose of a fan on a heat sink is not to cool it, but to stop it heating up in the first place, therefore if room temp rises, the heatsink will be hotter if the room temp is hotter.
 

Wembley

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Jul 4, 2007
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"Chill factor" for a device only applies if there is either a temperature difference or there is moisture involved. If the temperature of the heat sink is the same as that of the air then no cooling happens. If the air is hotter (you run your CPU in an oven for one mad example) then the heat sink will actually absorb heat and make the CPU even hotter.

The effect of room temperature on cooling is that the rate of transfer of heat (ie. cooling) is proportional to the temperature difference between the two devices. In the situation of a fan, the fan makes sure that as the air is heated it is then blown away and replaced by cooler air ensuring the maximum temperature difference (hot heat sink, cool air) rather than the hot air staying in place and the rate of heat transfer away from the heatsink slowing.

Now to room temperature. Basically the hotter the room the less the temperature difference between the air and the heatsink and therefore the less the total cooling. Be aware that insufficient movement of air through a case can heat the airjust as much as a warm house before it even gets to the CPU/heatsink to begin cooling at that point.
 
Chill factor was a phrase coined to reflex the effects on an animate object, ie humans. It relates to velocity vs Humidity. in cold weather increased velocity results in an increased rate of cooling which is componded by the rate of moisure evaporation, This rate of evaporation increases as humidty decrease. Only on anamite objects, and liquids, will the temperature drop be low ambient. For Liquids (ie water) this is due to water molecules going from a liquid state to a gas This takes energy away from the remaining water. For solid objects, very very few molecules go from a solid straight to a gas.

Graysky - Very good. I pretty much confirmed your results. The increase being greater than a 1::1 ratio on the CPU is componded in that this also applies to Hard drives and Graphics card. A 1 C increase, means that the Air intake across the heat sink is > 1C ( Note I mounted a Thermistor about 1 1/2" bhind the HSF sothat I could Monitor Air temp that was beening blown across the CPE ( Right now my ambient is 25C, air at the HSF is 29C)