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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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If you were blocking sigs, you wouldn't have to read this.
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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!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.
That happens a lot when you don't read TFA:
"This system has all the benefits of Airside Economizing, without the exposures of airside economizing like contamination and humidity control."
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=
He may well have read TFA. The article and your post only mention 'Airside Economizing' which mixes the two air flows. Heat exchangers don't necessarily do that, and have been around for a very long time. Even the old VW bug used a system that didn't mix. All this system does different is use a wheel, adding a moving part to a very common method of stripping waste heat from plant exhaust.
The article specifically omits comparing it to other heat exchanger systems. They give an example data center, but don't tell us what the data center did before.
Most telling is the quote: "Heat wheels have been used for many years in industrial air conditioning, but never in data centers." Other than asking "really?" and "why not?", since data centers are industrial use, the question is why aren't they comparing like with like here? There were plenty of things like this when I was dealing with 'super-insulated' building construction in the 80s.
This article is really just the manufacturer's PR release regurgitated, and is properly tagged 'slashvertisement' here. Data center managers should definitely know about heat exchanger technology, but get a better source.
Looks like the proposal is to use rotary regenerative air heaters (often known as Ljungstrom(tm) heaters in the power plant biz) for a low-temperature application.
I once gave a presentation to senior management on a situation with the air heaters at our plant; I had to practice saying "Ljungstrom re-gen-er-a-tive heater" for two weeks before I could do it without stumbling!
sPh
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).
The computer room Lieberts commonly used in data centers actually cool, then re-heat when the temperature is within range, but the humidity is too high.
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.
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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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)
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
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