Slashdot Mirror
"Heat Wheel" Could Lower Data Center Power Bills
miller60 writes "An air conditioning technology called the 'heat wheel' is getting a test drive in data centers, and early adopters cite impressive reductions in their power bills. The heat wheel — also known as a rotary heat exchanger or Kyoto Cooling — is a refinement of cooling systems using outside air. Rather than introducing exterior air directly into the server room (the air economization we discussed recently), the heat wheel briefly mixes the outside air and exhaust air to create an air-to-air heat exchanger. A data center in the Netherlands using this approach only has to use chillers 11 days a year." The article points out that the heat wheel is not new, but it hasn't been applied to data centers until recently.
That's pretty normal in "teleco" equipment. 48V is standard for exchanges etc, and many server manufacturers provide it. It definitely helps for some circumstances and makes battery backup easier (generators, however, are disadvantaged since they need to be on the other side of your rectifier)
You always end up with a fair amount of invertors for all sorts of stupid things that you have to get AC for (e.g. service engineers laptop power supplies). You also end up with lots of big copper cables and / or buzz bars. That gets quite expensive. I've seen whole buildings kitted out for that, but it needs real pre-planning.
=~ s,(.*),<sarcasm>$1</sarcasm>,g if any_point_you_wish();
How does this thing really work? It seems to me to be carrying the heat round on the wheel from one air mass to the other rather than mixing the air? If you RTFA it seems to imply that the first mix and then unmix the air. That would be worth of a patent...
(moderate: -1 troll - suggests Reading TFA anon-comments: Ewe muzt be newzor here)
=~ s,(.*),<sarcasm>$1</sarcasm>,g if any_point_you_wish();
There is a reason that telephone exchanges are run on -48VDC, and it's not some fscked up reason like "oh, that's how they ran the first switches in England, and we never got around to changing."
Ah, I know that one, or at least half of it. The reason for the negative voltage is electrolysis. A positive voltage would result in a migration of metal from wires exposed to the environment (telephone poles) to earth. Negative voltage makes the infrastructure last longer.
As for the magnitude being 48 Volts (actual spec. usually 36-72 volts) it most likely has to do with the maximum voltage drop between the central office and the terminal (phone).
It's easier to control opening and closing of transistors and diodes and other components associated with digital signals that will be present in any IC circuit with DC.
If AC was used, you would have to put the ability to control the signals and such into each and every circuit which would cause an excessive requirement for materials and components as well way more heat if it was even possible. This is why the power supply breaks this down and give DC in the various voltages where it is needed. Using DC also allows you to create a base signal that is increased or decreased in order to have a desired effect on a component that simply would be possible with an on off switch like AC.
My explanation probably sounds strange and I could be completely off on a few of the generalities that I purposely attempted to keep general. When dealing with computers and ICs, you really need to look at the operations more like a radio station broadcasting then switches turning on and off. It is the words in the broadcast (the peaks and valleys of the radio waves) that turn other gates on and off and allow the computational happiness to happen. The communication built into a digital circuit is a lot like a broadcast with a timer to declare a signal length for on and off when the base wave is changed. AC is just the most available source of power so it is commonly used.
As for 12 volt systems like in cars, the voltage is really too low to be useful for long. The drain from a 450 Wat power supply on a 12 volt system would be something like 37-38 amps which means a lot of heat will be generated when delivering the power where in a 120 volt AC system, it is something like 3-4 amps which doesn't generate as much heat or require as big of lines. Now I know a 450 won't be pulling 450 but it gives an idea of the requirements and hopefully helps answer your question/statement.
A heat wheel is an odd way to cool a data center; it requires fairly low outside air temperatures to work. We've had better luck with indirect evaprative coolers pre-cooling the hot-aisle return air and discharging to the space. Unless your wet-bulb temperature is below 60F, you will still need some compressor cooling, but since wet bulb temperature is never higher than dry bulb you get much better range and efficiency.