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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.
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.
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If you were blocking sigs, you wouldn't have to read this.
Because outside air contains all sorts of things that you don't want in your data center: humidity, contamination (dust, pollen), etc. While you could get rid of dust with filters (that would need frequent replacing), there's no simple answer for humidity.
!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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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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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=
"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.
To me it looks like this:
The wheel allows air to pass through it, but is very conductive - it quickly changes temperature to match the ambient temperature. As it is rotating, a section heats up when it is exposed to the inside air, then cools when it is exposed to the outside air. This in turn cools the inside while heating the outside. The air itself doesn't actually mix.
Of course, this could be completely wrong, but that's what it appears like.
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.)
That works only if the humidity and dust are taken care of. Humidification isn't too hard, but de-humidification takes nearly as much energy as air conditioning.
A heat exchanger doesn't take much power at all to run, quite probably than a filter + humidity control (keep in mind, a filter costs power because the blower has to work against it's resistance).
Actually, it is. Not only are all humidification plants natural growing ground for fungi - which, if you think about it, is a really bad thing since all the spores will be blown straight to the building - but it actually takes a lot of water to humidify large quantities of air.
A heat exchanger of the type described (which, BTW, doesn't work by mixing air, it works by using the mass of the wheel as a heat battery and moving it between the two airstreams) indeed requires very little power to run; just enough to keep the wheel turning against friction losses. Here in Finland we use the same system for, ironically enough, to cut down heating costs. I once saw the ventilation plant for a large school building; the wheel was just a meter in diameter and moved a hundred rotations or so a minute.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.
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.
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.
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