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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.
=~ s,(.*),<sarcasm>$1</sarcasm>,g if any_point_you_wish();
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.
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).
"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.
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!
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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.)
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.
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