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"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.
how about dropping the ac - dc - ac - dc to one AC - DC part?
I always assumed computers use DC because AC would fry the chips or not flow correctly. Am I mistaken?
There are seemingly not many fans of the DC powered data center on /.
Every little bit helps and point of load DC-DC converters are quite efficient, thus do not generate much heat. Additionally, since the back-up power for a data center is based on batteries... well, you can do the math on that. Generators are a different issue, but even they don't have to be AC, though probably more efficient if they are.
Every reduction in heat generation improved energy efficiency. Likewise, running on DC would reduce energy consumption by some measure. 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."
It will take many small steps to achieve big results. DC power is but one of them.
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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();
I RTFA, and I still don't get it, why is it better than outside air in, exhaust air out?
You just got troll'd!
!news. Many (most?) well designed AC systems employ heat exchangers.
What's the diff between a rotating and a conventional heat exchanger? Efficiency? Cost? Of course TFA doesn't mention any of it.
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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();
how about dropping the ac - dc - ac - dc to one AC - DC part?
The Offline UPS has a possibility of not kicking in soon enough.
If your data centre guarantees four nines uptime to clients...
Seems to me that a better solution would be to simply draw in outside air at -4 to +30 and add it to the room and exhaust the 31 to 37 dgree air to the outside directly. It seems to me that this would be more efficient and require less hardware to perform. All you would really need to do is open and close a hole in the ceiling and have an inlet to let the cool outside air in. This would be even more efficient with less airflow... The building I work in employs this very tactic for cooling in the summer (factory type setting). The total cooling capacity is remarkably high, and the total cost is $0 (completely passive cooling. In the winter we close the vents and turn on the heat).
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Why not just say that data centers are using heat exchangers and outside air to cool their computer rooms.
All the stupid wheel is is a heat exchanger like any other. Many types of heat exchangers allow the inclusion of outside air, though I would think it would be better to keep your computer room air closed from the outside if it is possible.
Sometimes the best solution is to stop wasting time looking for an easy solution.
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).
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Laptop power supplies are separate from the laptops. All you need is access to the appropriate DC feed and a correctly sized adaptor. "appropriate DC feed" is often 12V, and usually one of only a few standard voltages.
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Not until superconductors are workable. Even in the short runs between servers, DC tends to have higher losses. You're better off spending money on higher efficiency power supplies.
http://event.on24.com/event/95/75/4/rt/1/documents/player_docanchr_1/wp63_fr.pdf
Not a typewriter
This looks exactly like an Enthalpy Wheel, which transfers some of the moisture as well as heat between the exhaust and intake streams.
I am actually quite shocked these things have NOT been used for data center ventilation before. The bigger the ventilation job, the more these things make sense.
Only thing I can think of, though, is that data centers probably don't have high ventilation requirements... machines don't need a constant supply of fresh air for breathing, so a lot of it can be cooled and recycled.
But if all they're doing is transferring heat (and not humidity as well) then there are better options available.
=Smidge=
You are quite correct but the point is that using DC powered equipment still has more advantages than AC powered equipment, especially in that 24/7 environment. The 48 volt setting is also due to the fact that your POTS line was powered by it. There are safety factors and equipment requirements from long ago that help determine such parameters. The DC power to the phone is ages old, and ensured that your phone worked even when your power was out. Early technology required this, reliability helped ensure it's lasting existence.
Still, the point remains. If AC power had become more efficient or economical, they would have abandoned DC power for main/central equipment... they didn't.
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"A data center in the Netherlands using this approach only has to use chillers 11 days a year."
Umm.. yeah... the netherlands is generally a cold place. Not really saying much if the listener knows a little something about geography and weather.
Energy Recovery Ventilation Systems...
Been around for years at least 15 or better that I know of. I used to work
for a company that built these units.
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I would suggest you review the information in the paper you linked regarding HV DC distribution. They show it to be significantly (for the values that pass for sig. in this case) more efficient than conventional AC power distribution, and help simplify the PSU design. In addition, I do believe that use of higher voltages would, for computer PSUs, at least, allow for more efficient DC-DC designs, a fact not accounted for in the paper. (Unless I messed something, they only considered the removal of the PFC component of the PSU.)
HV DC is a rather clear winner. The only reason AC is better than DC in this environment is because it's at an inherently higher voltage. Obviously 48V DC is going to have significantly higher ohmic losses because it's going to have to carry twice the current to deliver the same power, while still needing to going trough a DC-DC anyway. I frankly can't imagine why 48V was seriously proposed.
As an aside, I do believe that, for a given voltage and power (rms values for AC) DC has exactly the same ohmic losses as AC. (Less, if you count the skin effect.) The only reason AC won the "War of Currents" is because it could be distributed at high voltages and stopped down at its destination. (FWIW, I think that DC would have lower losses than AC in the ultra high voltage transmission lines, as corona discharge actually dominates losses at that point, and is largely a function of peak voltage, though I've not done any research specific to this topic.)
I looked at this as part of a course on datacentre design I took this year, there is a fairly major difficulty - the size of the wheel needed to get effective results can be taller than the datacentre itself.
You would think that the obvious solution to that is to mount it horizontally, but that doesn't work as the temperature differences alongside the weight of the wheel causes it to warp.
Without knowing the square footage of datacentre and the heat they are dealing with it's impossible to say whether it's a viable solution. Similarly it's damn difficult to retro-fit to en existing building.
"Mistaken" is not the right word. The question itself makes no sense.
In my day, we called it "opening a window".
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.
I sure am glad someone brought this up.
I don't know how many headaches I have had to deal with because someone thinks a $50 ups at office max is the same thing as the Double-conversion ups that cost quite a bit more. Ad to that someone who thinks a rinky dink 5500 Wat portable generator can keep the computers up and running during a power failure and we have some serious problems with brownouts and so on.
Most laptop power bricks put out 20V
Your question is a little ambiguous because any voltage that isn't constant (DC) can be called an AC signal. There's nothing special about the sinusoidal voltage you get from a wall socket, it's just not much use to a computer. Digital systems are supposed to act like boolean logic, so ideally there are only two voltage levels (0V and 5V, say) allowed in the circuit. They do have AC (time-varying) signals -- a clock, inputs, and outputs. Transistors in the circuit are switched on and off in response to the clock and inputs to produce the outputs. When a transistor turns on, it connects part of the circuit to either 0V or 5V, so you need a stable source of those voltages. That's why digital circuits need DC power supplies.
In analog circuits, it's a slightly different story. Electronic devices like transistors don't work the same way at all voltage levels (I'm greatly simplifying transistors here). So if you want to make, say, an audio amplifier, you want the transistors in the circuit to act in a controlled way (e.g. not like switches). To do this, you "bias" the transistors by adding DC voltages to your AC signals within the circuit, which means you need a DC supply. Once you have one or two of those, it's easy to derive other DC voltages from them, so you often don't need any more. That's why you need DC in analog circuits.
There are many circuits that only use AC power or work on AC signals without needing extra power. The former are things like light bulbs or motors where you only care about absorbing power or can use sinusoidal electromagnetic fields. The latter are things like simple filters or signal splitters, which don't add anything to the signal (but might take something away).
Hope that answered your question. Feel free to ask more if you like.
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The passive wheels (which are motor driven) have been around at least 15, perhaps 20 years. The general idea of heat/cool recovery is ancient. We did it when I designed HVAC 35+ years ago.
The great advantage of AC over DC was the ease of voltage conversion. Nowadays, DC to DC conversion is almost as easy (though except at small currents, it's still done by converting to AC and then back to DC. The DC->AC stage is what has been improved). But of course there's an absolutely enormous AC infrastructure, and generally no compelling reason to switch to DC.
Running a data center on DC... OK, you get AC in. You convert to DC to your UPS unit. You convert back to AC, then back to DC, then to AC (inside the switching power supplies) then to various DC voltages. If you run on DC, you still get AC in. You convert to DC. You skip the chopper and don't convert back to AC. Then you leave out the front end rectifier on all your power supplies (meaning you need a whole bunch of custom parts!). How much energy do you save? Compared to managing to turn off your HVAC compressor by doing efficient heat exchange with outside air, not much. Which isn't to say it hasn't been considered; there's even been Slashdot articles about it.
"there's no simple answer for humidity."
Move somewhere where the climate is drier and cooler.
The outside air here currently has a dewpoint of -6c and the temperature is -2C
Are these people stupid?
Heat wheels, free cooling, ground loop heat pumps, these are all technologies that have been around for 50 years, and have been mainstream for just as long.
I work in the HVAC controls industry, and even the smallest private schools and the like use heat recovery wheels, free cooling, and many use ground loop heat pumps.
Goodness, every packaged rooftop unit manufacturer has done free cooling for decades. They are usually controlled by enthalpy sensors or return air CO2 levels. No fancy computers are required to control them, although our job is to add that functionality.
Of all industries, the IT cooling one seems to be in the dark ages.
And yes I know they haven't been using these technologies, I work around server rooms quite a bit and can't get over how much energy they waste by not economizing.
It's not rocket science and it should be blatantly obvious to the engineers that design the systems.
Actually a switching power supply leaves the power DC.
Switching power supplies are easy to understand, here is the basic idea:
take a bunch of capacitors and charge them in parallel (for a voltage increase) or in series (for a voltage drop) and then discharge them in the opposite configuration.
So if you charge two caps in series at 3V when you discharge them in parallel they will produce 1.5v each.
Think of it in the same way as batteries, in series they voltage is added together. This is why it is called a switching power supply, the caps are switched to charge then to discharge, then back many times per second. A large capacitor on the output side smooths out the voltage to within tolerances.
This is VERY efficient, since switching is very cheap in terms of power used, and capacitors lose very little energy charging and discharging.
Have a handy link to read more: wikipedia
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Stick to what you know Slashdot....
next you will tell us that some brilliant guy came up with the revolutionary idea of using the earth as a thermal mass and pumping some kind of fluid through it to temper the fluid to either cool it down or heat it up based on the need. look i have said it before just because you own a computer that doesn't make you "technical". Next I'll log onto HPAC and they will have an article about the astonishing discovery of introducing "impurities" into pure silicone and passing electricity through it. They will even reveal its nifty sounding name something like "semi-conductors". Stay tuned folks next week we discover using fluid under extreme pressure to perform some kind of linear motion....
I would suggest you review the information in the paper you linked regarding HV DC distribution. They show it to be significantly (for the values that pass for sig. in this case) more efficient than conventional AC power distribution, and help simplify the PSU design.
But it also says the "high voltage ac" option which appears to the the european 230/400V three phase system is almost as good and that is a system that should be easilly deployable in datacenters worldwide without needing any special kit (PC power supplies have been dual voltage for many years).
They also briefly mention that there is a safety issue with DC distribution at higher voltages. The problem is DC at a given voltage is much more prone to arcing than AC, that means all switches and circuit protection devices would need to be redesigned (and would end up considerablly more expensive) for such a system.
FWIW, I think that DC would have lower losses than AC in the ultra high voltage transmission lines
It does but the cost (both in terms of the capital cost and in terms of the losses while running) mean it is only worth it in special circumstances (very long distance transmission, undersea transmission, transmission between grids that can't be syncronised for political or frequency reasons)
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It converts the power to DC, then to high frequency AC, then runs it through a transformer, then back to DC.
That's a charge pump, not your typical switching power supply. Check your own link.
OK, I'll be the first to say it. Who cares?
Seriously, think beyond the room itself. Computers capable of complete immersion in non-conductive liquids, GPUs offloading CPU processing thereby spreading heat "signatures" around the board even further, we're likely less than five years from a complete revamp in the way we cool computers themselves, thereby quite possibly eliminating this kind of cooling requirement altogether from a Data Center.
That paper was written by the CTO of APC. And yet, APC won't actually manufacture any UPS or surge protection devices that function correctly on the 240V single phase electrical system in North America. Lots of people could change even their small home computer systems, as well as the computer rooms of small businesses (a great many of which do not get any three phase power, and most that do get less than 240V) in the USA. Their competition won't manufacture these products, either. Chicken. Egg. I guess the only business they want are the giant data centers and they don't give a damn about power efficiency in many tens of millions of homes and small businesses.
The North American single phase power system is a dual-voltage system. There are 2 hot "phases" that are 120V relative to neutral/ground of opposing polarity (180 degrees). Between them it's 240V. This is unlike the electrical system in most of Europe, UK, Australia, India, etc., in which single phase power is around 230V relative to neutral/ground. This difference requires a different UPS design if a bypass relay is included (though a continuous online dual conversion type without a bypass relay could convert either electrical system to DC and then convert the DC back to one of the systems without problems). Surge protectors also have an issue because the MOVs between hot and ground (the neutral won't be used) need to be the type for 120V or they won't provide as good protection.
now we need to go OSS in diesel cars
DC at these higher voltages (340V to 500V) is more difficult to work with than the corresponding AC. As a result, the initial installation costs, and some maintenance costs, are higher. For example, a circuit breaker that can safely shut off a short circuit fault current at 120V AC is more limited at DC. The maximum voltage they are rated for in DC is 48V. Breakers for higher AC voltages can do relatively higher DC voltages. But you'll need breakers of a class for well over 1000V AC in order for them to be able to handle 500V DC. It is harder to extinguish an arc in DC because there is no zero crossover times that happen at 100 or 120 times a second for AC.
The higher voltage AC needs to be considered at least as a reference point. Then if the savings the higher voltage DC offers (such as simpler PSUs) can exceed the extra costs involved of HVDC distribution, it could be viable. Otherwise I suggest someone putting in a large data center in North America special order their power at the 416Y/240 service voltage (uncommon, but doable with 3x 240V transformers), and just plug each computer into a 240V circuit (1 hot, 1 neutral, 1 ground) much like already done in Europe (except in North America it will be 60 Hz which is irrelevant to switching mode PSUs).
now we need to go OSS in diesel cars
Most laptop power bricks put out 20V
Really? The two that I have are 19V and 16V.
And every little bit of extra cost adds up... And make no mistake, a DC datacenter costs a LOT.
No they aren't. There's nothing magic about DC that makes it more efficient to convert. Why do so many people seem to think that when the input and output voltages are a bit closer together, it's more efficient? In fact the opposite is closer to accurate.
AC can be converted to DC trivially, with bare minimum losses. The same is true for the inverse. You're not going to possibly see more than 3% efficiency improvements along the whole chain, and yet, you'll need a huge investment to convert to all-DC.
Here we go... The cure for your ignorance: http://www.apcmedia.com/salestools/SADE-5TNRLG_R5_EN.pdf Enjoy.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
It's 48 volts because 50 volts and above you need an electrician's license to work with it, and the people who originally started using the standard (phone companies, I believe) didn't want to pay union rates for an electrician.
My blog. Good stuff (when I remember to update it). Read it.
Generally an emergency is not the time for messing around trying to work out laptop power supply compatibility (and any servicing you do during a power outage is likely to be emergency related).
Your service engineer, normally from a random vendor, arrives from outside. He has never seen your system before. You give him a power interface he understands and has used before. That means AC.
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The repulsion and attraction between current carriers in high voltage DC transmission systems is a non-trivial engineering issue. It is a non-issue in high voltage AC transmission systems.
DC has some inherited disadvantages too. First of all the choice was made long before SMPS were invented. DC currents really dont work well with transformers.
Another disadvantage is that DC is polarized, leading to all kind of problems including electrolises.
DC poses a greater health risk.
110Vac or even 230Vac isnt peak voltage, you would need that voltage to replace it. so 48Vdc would require 4,5 times the current, and including losses. That is forgetting the fact that SMPS operate at peak voltages, so let's say 320Vdc
Transport Lines running at 300KVac, require a transformer to lower the voltage, think of the DC-DC convertor you would need to use.
A data center in the Netherlands using this approach only has to use chillers 11 days a year.
This came as a shock to the hard working serial chillers.
Carbon based humanoid in training.
It's 48 volts because 50 volts and above you need an electrician's license to work with it...
No, we're talking about DC where anything below 120V is considered to be ELV. The phone companies trained their own installers they didn't need to hire electrical contractors.
Besides 48V dates back to the days of telegraph long before the NEC was even thought of.
The use of -48V is based on a compromise between state of the art batteries at the time and the distance that the signals needed to travel.
My dad, a tool and die maker, worked in a building that was build in the 40-50's. It had something that worked on the same principle. There was this long duct shaft that went up the east wall, across the room, and down the west wall. Where the ducts reached the floor there were huge fans, two at each entrance. In the morning the east fans would run. In the evening the west fans would run. During the winter they would change the direction the fans pushed air.
Having to work for a living is the root of all evil.
That has to be the most bizarre explanation of switching power supply technology I have ever seen!
Did you even read the wiki page? It's actually not bad.
A common practice to to connect 120/240 rated PSUs as a 208V single-phase load on a 208Y/120 system (phase to phase connection). Just be sure to use sockets and plugs with an adequate voltage rating, and two-pole circuit breakers. Everything you need is available off-the-shelf at the electric supply wholesaler, and any competent electrician can install the circuits. There's no good reason to run anything using more than 1kW from a 120V circuit.
TFS says that "the heat wheel briefly mixes the outside air and exhaust air to create an air-to-air heat exchanger". That is not at all how it works, but is rather a side effect of the gap required to rotate the cylinder. The unit works by heating and cooling strips of metal instead of compressed gases as in a "chiller."
Currently hooked on AMP
DC Power for data centers is a good technology, but if you are suggesting 48VDC you must own copper futures! Most of the data center scale systems proposed today are 600VDC (nominally), as you can easily get to 6MW on a single bus. 48VDC would only give you 300kW, assuming your runs were very short. (Bus size based on a 4-wire, 5,000A bus duct with two phase busses per pole.)
This difference requires a different UPS design if a bypass relay is included
Afaict in most of europe there is no gaurantee which wire is live and which wire is neutral so a UPS designed for european use would have to be able to tolerate either side of it's input being live, given this I would not expect there to be a problem running it on american 240V
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Which wire is hot is well defined for three-pin plugs (assuming of course that the plug and socket are wired correctly).
Many plugs for low power however have just two wires in the free-socket end of the power cord (usually an "8" connector) and these of course cannot be relied upon.
why is this better than a standard air-to-air intercooler? Seems like it would be worse because this still mixes the air somewhat.
My car has an air-to-air intercooler that doesn't mix the air streams but very effectively exchanges the heat. All you really need is a fan to keep the air moving and you're done, no silly wheels or compressors involved.
Which wire is hot is well defined for three-pin plugs
That may be true for some types but it is not true in the general case. German plugs use side clips for earth and are not polarised. Italian plugs use three pins in a straight line and again aren't polarised. French plugs are polarised but from what I can gather the french aren't very carefull about which way round they wire them.
So any UPS sold for use accross europe will have to be able to tolerate the incoming live and neutral either way arround. Given that I would be very surprised if it did not also tolerate the american 240V system.
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This both true and not true.
The "Euro" plug that is now standard in the EU (except for UK) is polarized and will only mate in one orientation.
It will still be some time however before these are used everywhere. There are still a lot of legacy three-pin or two pin sockets around and most of these are not polarized.
Of course if a plug or socket is miswired, there is no way to get around that. Most Euro cables for appliances are molded and do not require the customer to wire it. Socket wiring is down to the professionalism of the installer.
The "Euro" plug that is now standard in the EU (except for UK) is polarized and will only mate in one orientation.
If you mean a CEE 7/7 plug which is as far as I can tell the most common earthed plug in europe nowadays it is polarised when used with a french socket but unpolarised when used with a german socket.
If you mean some other plug type please specify exactly which plug type you mean (link to a picture if needed).
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That they're opening the window and letting the heat out?
Maybe attaching a fan to help move the air?
Brilliant!
WTF? Over?